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Ima li primjera skupine mikroorganizama koja kontinuirano obuhvaća dvije ili više klasifikacija vrsta?

Ima li primjera skupine mikroorganizama koja kontinuirano obuhvaća dvije ili više klasifikacija vrsta?



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Postoje li primjeri grupe mikroorganizmi gdje su označene dvije različite, utvrđene vrste i te dvije skupine zadovoljavaju sve aspekte definicije vrste (možda se ne mogu međusobno razmnožavati?), ali se ispostavilo da postoji kontinuirana distribucija pojava ove skupine tako da mogu reproducirati "lokalno" s obližnjim članovima?

Nedostaje mi sofisticiranost u biologiji da bih znao najbolje moguće riječi koje bih ovdje koristio pa su neke smjernice dobrodošle, a budući da koncept klasifikacije vrsta postoji mnogo dulje od sekvenciranja i analize genoma, sama tema se oslanja na koncepte iz nekoliko različitih stoljeća.

Stoga sam nacrtao jednostavan dijagram s 1-D pojednostavljenim "spektrom" genetske razlike, dok bi, naravno, vjerojatno bio višedimenzionalan.


Simbiotski odnos između organizama | Mikrobiologija

Sljedeće točke naglašavaju sedam glavnih tipova simbiotske veze koja postoji između organizama. Vrste su: 1. Mutualizam 2. Parazitizam 3. Amensalizam 4. Natjecanje 5. Predacija 6. Protokooperacija 7. Komensalizam.

1. Mutualizam:

Mutualizam opisuje odnos u kojem oba povezana partnera izvlače neku korist, često bitnu, od zajedničkog života.

Tablica 33.1 je pokušaj da se sažete glavne vrste uzajamnih asocijacija od kojih su neke trivijalne i od znanstvenog interesa, ali druge kao što su asocijacija rizobium-mahunarke, mikorize, koralj-mikrobna asocijacija, asocijacija biljojeda i mikroba i lišajevi su vrlo važni, ili nezamjenjiv, kako za lokalni ekosustav tako i u svjetskim razmjerima.

Udruga Rhizobium-Legume:

Najvažnija i najbolje proučavana mutualistička povezanost mikroorganizama i biljaka je nedvojbeno ona između Rhizobium spp. i razne mahunarke.

Mycorrhizae (Sing. Mycorrhiza):

Mikorize predstavljaju uzajamnu simbiozu između korijenskog sustava viših biljaka i hifa gljiva. Frank, koji je prvi primijetio postojanje takve karakteristične asocijacije u korijenima Cupulifereae 1885., skovao je izraz ‘mycorrhiza’. Tijekom posljednjih 20 godina temeljni radovi koje su provele stotine istraživača iz različitih zemalja pokazali su da je ova povezanost temeljna i univerzalna.

Među različitim simbiotičkim vezama između mikroorganizama u tlu i korijena biljaka, mikorize su najraširenije jer se javljaju na više od 90% vaskularnih biljaka.

Međutim, Kumar i Mahadevan (1984.) proučavali su veliki broj mikoriznih asocijacija i otkrili da su pod velikim utjecajem otrovnih tvari koje su, kada su prisutne, u osnovi koncentrirane u korijenu biljaka. Takve tvari mogu biti alkaloidi, fenoli, terpenoidi, tani, stilbeni itd.

Mikoriza je povoljna jer:

(i) Gljiva dobiva hranjive tvari preko korijena biljke. Šećeri koji nastaju u lišću kreću se niz stabljiku kao saharoza. Sama saharoza se nikada ne nakuplja u gljivi, ona se pretvara u izomere kao što je ‘trehaloza’ što rezultira niskom koncentracijom šećera,

(ii) gljivične hife djeluju poput masivnog sustava korijenskih dlačica, hvataju minerale iz tla i opskrbljuju ih biljci, i

(iii) Zbog ove povezanosti, biljni partner, osim nutritivnih prednosti, razvija otpornost na sušu, toleranciju na pH i temperaturne ekstreme, te veću otpornost na patogene zbog ‘fitoaleksina’ koje oslobađa gljiva.

Mikorize se općenito dijele na dvije vrste, iako neki prepoznaju treći tip koji je manje-više kombinacija prva dva. Dvije glavne vrste nazivaju se Ectomycorrhizae i Endomycorrhizae, dok se treći, međutim, naziva Ectendomycorrhizae.

Ektomikoriza (ektotrofna mikoriza):

Ektomikoriza (slika 33.2) česta je na mnogim šumskim stablima, posebice borovima, bukvi i brezi koji imaju veliku gospodarsku vrijednost. Gljivične hife tvore ovojnicu preko vanjske strane korijena koja se općenito naziva ‘plašt od hifa’. Iz ovog plašta hifna mreža nazvana hartignet proteže se u prvih nekoliko slojeva korteksa ili rijetko dublje, a zatim doseže endodermu.

U zaraženom korijenu potiskuje se stvaranje korijenske dlake, a morfologija korijena se mijenja ponovnim stvaranjem kratkih grana s tupim vrhovima i ograničenim rastom. Uobičajeni ektomikorizni rodovi su Basidiomycetes, posebno Agaricales kao što su Amanita, Tricholoma, Russula, Lactarious, Suillus, Leccinum i Cortinarius’, a zabilježeni su i neki Ascomycetes kao što su tartufi.

Gljive ectomycorrhizae luče različite tvari koje potiču rast kao što su auksini, citokinini i giberelinske kiseline. Ipak, oni proizvode neke antimikrobne tvari koje štite biljku domaćina od patogena iz tla.

Gljive dobivaju svoj ugljik iz domaćina u obliku glukoze, fruktoze ili saharoze koja se na kraju pretvara u manitol, trehalozu i glikogen. Poznato je da ove mikorize stimuliraju rast biljaka i unos hranjivih tvari u tlima niske do umjerene plodnosti.

Ektomikoriza (ektotrofna mikoriza):

Mikorize u kojima hife gljiva prodiru u stanice korijena bez stvaranja bilo kakvog vanjskog omotača, plašta hifa, nazivaju se endotrofne mikorize. Obično neki dio invazivnih gljivičnih hifa leži izvana kao labava masa hifa, ali ne tvore plašt.

Prepoznate su tri vrste endomikorize:

(i) Vasikularna arbuskularna (VA),

(i) vezikularno-arbuskularne (VA) mikorize:

Vezikularno-arbuskularne (VA) mikorize (slika 33.3) predstavljaju asocijacije između gljiva, uglavnom pripadnika Zygomycetes, i velikog broja kritosjemenjača kao što su stabla tropskih šuma, gotovo sve poljoprivredne kulture (osim riže na rizovitim poljima) i većinu bilje i trave tropskih i umjerenih prirodnih ekosustava.

Gljive koje tvore VA mycorrhizae ograničene su na samo jednu obitelj, Endogonaceae, Zygomycetes s dva roda, Endogone i Glomus, tvoreći asocijacije s velikim brojem udaljenih biljaka. VA mikorize su posebno važne zbog svoje raširenosti i povezanosti s poljoprivrednim kulturama.

Kod VA mikorize hife gljiva razvijaju neke posebne organe, zvane vezikule i arbuskule, unutar kortikalnih stanica korijena. Vezikule su debelih stijenki, sfernog do ovalnog oblika, nošene su na vrhu hifa ili u međustaničnim prostorima ili u kortikalnim stanicama korijena. Ove vezikule su organi za pohranu hrane gljiva.

Međutim, arbuskule su poput četkice, dihotomno razgranate (opsežno) haustorije razvijene unutar kortikalnih stanica. Iako su zemljopisno široko rasprostranjene, VA mikorize nisu uobičajene na područjima koja su stalno poplavljena (Keeley, 1980.).

Važnost VA mikorize je u učincima koje imaju na ishranu biljaka, posebno na nepokretne elemente kao što je fosfor. Vanjske hife uvelike povećavaju volumen tla i prenose fosfor u korijenje. Biljke su jako zaražene VA mikoriznim gljivama u tlima s nedostatkom fosfora, a mikorize su slabo razvijene kada je opskrba fosforom odgovarajuća.

Stoga je to samoregulirajući sustav, koji povećava unos fosfora kada je ovog elementa manjkava. Fosfor koji se tako apsorbira pretvara se u polifosfatne granule u hifama i prenosi u arbuskule za konačni prijenos do biljke domaćina. Gianinazzi i sur. (1979) su pokazali da se prijenos polifosfata događa u prisutnosti kisele fosfataze tijekom životnog vijeka ili scene arbuscule.

Osim stimulacije unosa fosfora, mikorizne gljive stimuliraju ukorjenjivanje, rast i preživljavanje transplantata. Lambert i sur. (1979.) proučavali su da VA mikoriza stimulira unos cinka, bakra, sumpora i kalija u biljci, pojačava nodulaciju u mahunarkama, smanjuje trulež uzrokovanu gljivičnim patogenom, te prodiranje korijena i razvoj ličinki nematoda.

(ii) Orhidejska mikoriza:

Orhidejske mikorize (slika 33.4) vrlo se razlikuju od VA mikorize. Ovdje viša biljka privremeno ili trajno parazitira na gljivama, potonje su uglavnom iz roda Rhizoctonia sa savršenim stadijima koji se javljaju kod bazidiomyceta i askomiceta. Sjeme orhideja je sitno (0,3-14 μg), bez značajnih rezervi hrane.

Neke uopće ne uspijevaju klijati osim ako nisu zaražene gljivicom, druge klijaju, ali razvoj ubrzo prestaje osim ako se sadnica ne zarazi gljivom. Hife gljive prodiru u stanice korteksa i formiraju zavojnice unutar kortikalnih stanica. Ove hifalne spirale bogate hranjivim tvarima, koje se općenito nazivaju peletoni, zatim se razgrađuju da bi hrana bila dostupna biljci.

Kako orhideja uvjerava gljivicu da se podvrgne ovoj bizarnoj samožrtvi nije poznato, iako je uloga “phytoalexin orchinol” implicirana. Međutim, degenerirajući peletoni opskrbljuju orhideju ugljikohidratima i vjerojatno vitaminima i hormonima dobivenim saprofitskim djelovanjem gljivica izvan korijena.

Većina orhideja s vremenom postane zelena, pa se povezanost između orhideje i gljive može pomaknuti s parazitizma na uzajamnost. Druge orhideje, npr. Neottia nidus-avis (orhideja ptičjeg gnijezda) ostaju acholorophyllus i parazitiraju na gljivama tijekom svog života.

(iii) Ericaceous mycorrhizae:

Ericaceous mycorrhizae (slika 33.5) povezane su s dvije obitelji, ericaceae i epakridaceae, u kojima gljiva tvori gustu intracelularnu zavojnicu u vanjskim kortikalnim stanicama. Ranije se vjerovalo da je gljiva Phoma sp. ali su kulturološke studije dokazale da se radi o Pezizella ericae (askomicetu).

Ova gljiva ima ogroman kapacitet mineralizacije i apsorpcije organskog dušika, pa uvelike potiče unos dušika i rast biljaka čak i na neplodnom tresetnom tlu. Englander i Hull (1980) su predložili Clavaria spp. kao mikorizna gljiva Rhidodendron spp. i Azalea spp. Međutim, ova mikorizna povezanost rezultira izostankom razvoja korijenskih dlačica, kao i odsutnošću epidermalnih stanica korijena.

Ektendomikoriza (ektendotrofna mikoriza):

Mikorize koje imaju obilježja obje, ekto- i endomikorize, neki su kategorizirani kao ektendomikorize. Gljivični partner uspostavlja plašt od hifa na površini korijena, kao i hifne zavojnice i haustorije unutar invadiranih kortikalnih stanica korijena.

U šumama, asocijacija ‘Conifer-Boletus-Monotropa’ predstavlja dobro proučen primjer ektendomikorize. Monotropa, neklorofilna biljka, obično raste blizu korijena četinjača u šumama.

Sada je dobro utvrđeno da gljiva zvana vrganj tvori zajedničku mikoriznu asocijaciju između crnogorice i Monotropa, iako se priroda povezanosti razlikuje s dvije biljke. Vrganj tvori ektomikorizu s Monotropa i endomikorizu s crnogoricom. Gljiva tvori most između dviju biljaka.

Sintrofija:

Sintrofija (grč. syn = zajedno trofe = hrana) je takav uzajamni odnos između dva različita mikroorganizma koji zajedno razgrađuju neke tvari (i pri tome štede energiju) da se niti jedan ne može razgraditi zasebno.

U većini slučajeva sintrofizma priroda sintrofičke reakcije uključuje H2 plin koji proizvodi jedan partner, a drugi ga troši. Dakle, sintrofija se također naziva prijenosom vodika među vrstama.

Slijedi nekoliko primjera sintrofnih asocijacija:

(i) Fermentacija etanola u acetat i konačna proizvodnja metana (slika 33.6.) je dobar primjer. Bakterija koja oksidira etanol fermentira etanol proizvodeći H2 koji je vrijedan donor elektrona za metanogenezu pa ga stoga koristi metanogen. Kada se obje ove reakcije zbroje, ukupna reakcija je eksergonična (tj. oslobađanje energije).

Zapravo, oksidacija etanola u acetat plus H2 je energetski nepovoljan, reakcija postaje povoljna kada H2 proizvedeni tijekom njega troše se metanogeni. Na taj način oba partnera koriste energiju koja se oslobađa u spregnutoj reakciji sintrofičkog povezivanja.

(ii) Oksidacija maslačne kiseline u octenu kiselinu plus H2 sintrofom koji oksidira masne kiseline Syntrophomonas je još jedan dobar primjer. Syntrophomonas ne raste u čistoj kulturi na maslačnoj kiselini jer je energija oslobođena tijekom oksidacije maslačne kiseline u octenu kiselinu vrlo nepovoljna za bakteriju. Ali, ako se vodik proizveden u reakciji odmah iskoristi od strane sintrofnog partnera (npr. metanogena), Syntrophomonas bujno raste u mješovitoj kulturi s H2 potrošač.

Butirat – + 2H2O → 2 acetat – + H + + 2H2 + Energija (+ 48,2 kJ)

(iii) Syntrophobacter razgrađuje masne kiseline niske molekularne težine (npr. propionsku kiselinu) kako bi proizveo H2 koji, ako se ne konzumira, inhibira rast proizvođača. Kada ovaj vodik odmah potroši Methanospirillum, sintrofni partner, stimulira se stopa rasta i Syntrophobacter i Methanospirillum, tj. korist imaju oba partnera.

Koraljno-mikrobna udruga:

Koralji su vrlo produktivni, a ipak žive u vodama koje su vrlo siromašne hranjivim tvarima, otvoreni ocean može imati neto produktivnost od 50 g cm -2 godine -1 dok koraljni grebeni mogu proizvesti do 2500 g cm -2 godine -1. Razlozi za to još uvijek nisu jasni.

Smatra se da su dinoflagelatni simbionti, vrste Gymnodinium microadriaticum i Amphidinium, sveprisutni u koraljima koji grade grebene i da prenose životinji najmanje 25%, a vjerojatno čak 60 do 70% svog fiksiranog ugljika kao glicerol i glukozu.

Oni također mogu uzeti nitrate iz vode i prenijeti ga do koralja u upotrebljivom obliku alanina. Cijanobakterije su važne na grebenima u fiksiranju dušika, a mogu biti slobodno živuće ili simbiotske.

Bakterijski simbionti koji žive na vanjskoj strani koralja u sloju sluzi također su uključeni u očuvanje i brzo recikliranje fosfora i dušika u koralje. Stoga postoji niz potencijalnih ili stvarnih simbiotskih mikroorganizama koji bi mogli objasniti produktivnost koraljnih grebena.

Osim aspekata produktivnosti, Gymnodinium je također vrlo važan u taloženju skeletnog kalcija kao rezultat fotosinteze.

Dinoflagelati očito moraju ponovno zaraziti svaku generaciju koralja jer se ne prenose tijekom razmnožavanja. Kako to rade, nije poznato jer nikada nisu pronađeni slobodni da žive u okruženju, iako mogu samostalno rasti u kulturi.

Udruga biljojeda i mikroba:

Biljke sadrže oko 30% celuloze (suhe težine), velikog netopivog inertnog polisaharida. Bilo bi od velike koristi svakom biljožderu probaviti kemikaliju, ali, međutim, jedini biljožder koji posjeduje odgovarajući probavni enzim, celulazu, su puževi.

Svi ostali, od kukaca do sisavaca, ne posjeduju ovaj enzim i uspostavljaju uzajamnu povezanost s bakterijama i protozoama koje cijepaju celulozu. Ovi mikroorganizmi općenito zauzimaju jedno od nekoliko mjesta u crijevima, a najnaprednije stanje je ono kod preživača.

Preživači, kao što su krave i ovce, razvili su jedinstveni četverokomorni ‘želudac’ što ih je pomoglo uspostaviti kao iznimno uspješne biljojede (slika 33.7). Volumen buraga je velik u odnosu na veličinu sisavca (kod krave je 80-100 L) tako da postoji dugo vrijeme otpora na razgradnju celuloze. Biljni materijal se žvače, miješa sa slinom i prenosi u burag.

Burag sadrži vrlo brojne mikroorganizme od kojih je oko 90% sekretora celulaze. To mogu biti 10 4 do 10 5 protozoa, 10 10 -10 11 bakterija i 4 x 10 4 gljivica. Sadržaj buraga se kontinuirano miješa polaganim kontrakcijama stijenke u intervalima od 1-2 minute.

Djelovanje mikroba u rumenu preživača:

Celulaze hidroliziraju celulozu u glukozu, a mikroorganizmi zatim fermentiraju glukozu u razne organske kiseline kao što su octena kiselina (etanoat), maslačna kiselina (butirat) i propionska kiselina (propionat), čime osiguravaju energiju za vlastiti rast (sl. 33.8).

Oko 10 3 dm 3 dnevno CO2 i CH4 nastaju kao otpadni proizvodi koje životinja podriguje. Tako mikroorganizmi prisutni u buragu pretvaraju uglavnom neprobavljiv biljni materijal u ugljične spojeve niske molekularne težine koje mogu iskoristiti biljojedi.

Lišajevi:

Lišajevi su izvanredni po tome što se u prirodnim uvjetima alga-gljivična ili cijanobakterijsko-gljivična zajednica ponaša kao jedan organizam. Gljiva (mikobiont) je obično askomiceta i opisano je oko 20 000 gljiva lišaja što je otprilike 25% svih poznatih gljiva. Poznato je samo oko 30 rodova algi (fotobiont koji se ranije zvao fikobiont) i cijanobakterija (cijanobiont) za koje se zna da tvore lišajeve.

Odnos između dvaju suradnika steljke lišaja još uvijek nije u potpunosti potvrđen, iako su lišajevi bili klasični materijal za proučavanje mikrobne mutualističke simbioze. Fikobiont/cijanobiont opskrbljuje mikobiont ugljikohidratima, a drugi može opskrbljivati ​​minerale prvom.

Nemamo eksperimentalnu potvrdu da mikobiont također opskrbljuje minerale svojim suradnicima, fikobiont bi mogao apsorbirati vlastite minerale iz supstrata. ‘Dobri’ laboratorijski uvjeti uzrokuju raspad povezanosti, dok nepovoljni uvjeti pomažu u njenom održavanju. To ukazuje da udruga vjerojatno omogućuje suradnicima iskorištavanje staništa koje bi bilo neprikladno kada se razdvoje.

Lišajevi se smatraju ‘pionirskim organizmima’ jer se tvrdilo da su važni u povećanju brzine stvaranja tla iz golih stijena. Oni mogu ubrzati fizičko uništavanje stijene skupljanjem i širenjem stene, mogu razgraditi stijenu širokim spektrom kemijskih tvari kao što je ugljični dioksid (djelujući kao H2CO3), razne organske kiseline i kelirajuća sredstva.

Lišajevi mogu akumulirati minerale i dušik koji se na kraju otpuštaju u primitivno tlo kada se talus lišajeva raspadne. Na lišajeve uvelike utječe (čak i ubija) razina SO2 prisutni u atmosferi njihova se brojnost može koristiti kao pokazatelj onečišćenja atmosfere. Oni ili njihovi proizvodi mogu se koristiti kao boje za hranu i indikatori (lakmus).

2. Parazitizam:

Parazitizam predstavlja simbiotsku povezanost dvaju živih organizama i pogodan je za jednog od suradnika (parazit), ali je štetan za drugog (domaćina) u većoj ili manjoj mjeri. Paraziti mogu biti destruktivni ili uravnoteženi. Prvi uništavaju stanice domaćina u kasnijim fazama razvoja, dok drugi ispunjavaju svoje zahtjeve od domaćina na način da se stanice domaćina ne uništavaju već nastavljaju živjeti.

Fakultativni i obvezni paraziti:

Asocijacije bi bilo lako opisati kada bi se organizmi uvijek ponašali na isti način. Nažalost, nemaju. Mnogi mikroorganizmi, na primjer, mogu preživjeti i kao paraziti i kao saprofiti.

Gljiva Ceratocystis ulmi, koja uzrokuje nizozemsku bolest brijesta, ubija stablo, a zatim živi saprofitski na njegovim mrtvim ostacima. Takav organizam koji uglavnom živi kao saprofit, ali rijetko ima naboj parazita, naziva se fakultativnim parazitom.

Nasuprot tome, peronospora, pepelnica itd. rastu samo na živoj protoplazmi biljke domaćina u prirodi. Takav organizam koji u prirodi ne može živjeti drugdje osim na živoj protoplazmi svog domaćina naziva se obvezni parazit (biotrof). Fakultativni i obvezni paraziti često se razlikuju po svom patogenom učinku, tj. po sposobnosti ozljeđivanja domaćina.

Budući da su obligati ograničeni na žive organizme, njihovi učinci na domaćina često su manje ozbiljni, iako domaćin može pokazati manje snažan rast. Nasuprot tome, fakultativni paraziti koji su tek nedavno dobili domaćina, obično su štetniji.

Mikoparazitizam:

Kada jedna gljiva parazitira na drugoj, taj čin se naziva ‘mikoparazitizam’. Ovaj se izraz općenito koristi naizmjenično s ‘hiperparazitizmom’, ‘izravnim parazitizmom’ ili ‘intergljivičnim parazitizmom’. Poticatelj se općenito naziva ‘mikoparazit’ ili ‘hiperparazit’.

Mikoparazitizam je klasificiran u dvije glavne skupine na temelju nutritivnog odnosa parazita i domaćina:

Nekrotrofni (destruktivni) parazit dolazi u kontakt sa svojim domaćinom, izlučuje otrovnu tvar koja ubija stanice domaćina i koristi hranjive tvari koje se oslobađaju. Biotrofni (uravnoteženi) parazit može dobiti svoje hranjive tvari iz živih stanica domaćina, odnos koji inače postoji u prirodi.

Mikroparazitizam je česta pojava i primjeri se mogu naći među svim skupinama gljiva od chytrida do viših bazidiomyceta. Nekoliko primjera je kako slijedi.

Prijavljeno je i tročlano udruženje mikoparazita u kojem je Chytridium parasiticum parazit na Chytridium subercrelatum koji također parazitira na Rhizidium richmondense, drugom chytridu.

Biološka kontrola biljnih bolesti u posljednje je vrijeme postala područje intenzivnog istraživanja s obzirom na opasan utjecaj pesticida i drugih agrokemikalija na ekosustav. Među biološkim agensima značajno mjesto zauzeli su mikoparaziti.

Predloženo je da treba uložiti napore da se istraži biološka kontrola biljnih bolesti putem parazitiranja i grabežljivaca. Stoga mikolozi i biljni patolozi tragaju za novim mikoparazitima jer što ih je veći, veća bi bila šansa da ih iskoriste kao sredstva za biološku kontrolu. Trichoderma je važan primjer.

3. Amensalizam:

Amensalizam (od latinskog znači ne za istim stolom) odnosi se na takvu interakciju u kojoj jedan mikro i shyorganizam oslobađa specifičan spoj koji negativno djeluje na drugi mikroorganizam. To jest, amensalizam je negativna interakcija mikroba i mikroba.

Neki važni primjeri su sljedeći:

(i) Proizvodnja antibiotika od strane mikroorganizma i inhibicija ili ubijanje drugih mikroorganizama osjetljivih na taj antibiotik je najvažniji primjer amensalizma. Koncentracije takvih antibiotika u tlu ili vodi su zasigurno male, iako bi mogla postojati dovoljno velika količina na razini mikrostaništa da inhibira obližnje mikroorganizme.

Antibiotici smanjuju saprofitnu sposobnost preživljavanja patogenih mikroorganizama u tlu. Mutualistički odnos Attini mrava i gljivica promiču bakterije koje proizvode antibiotike (npr. Streptomyces) koje se održavaju u gljivičnim vrtovima (vidi okvir). U ovom slučaju, Streptomyces proizvodi antibiotik koji kontrolira Escovopsis, postojanu parazitsku gljivicu, koja može uništiti gljivični vrt mrava (slika 33.9).

(ii) Proizvodnja amonijaka od strane neke mikrobne populacije štetna je za druge mikrobne populacije. Amonijak nastaje tijekom razgradnje proteina i aminokiselina. Visoka koncentracija amonijaka inhibira populacije Nitrobacter koje oksidiraju nitrite.

4. Natjecanje:

Za razliku od pozitivnih interakcija mutualizma i sinergizma, natjecanje predstavlja negativan odnos između dviju populacija u kojem su obje populacije štetno pogođene s obzirom na njihov opstanak i rast. U ovom slučaju, mikrobne populacije se natječu za tvar koja je u nedostatku.

Konkurencija rezultira uspostavljanjem dominantne mikrobne populacije i isključenjem populacije neuspješnih konkurenata. Tijekom razgradnje organske tvari povećanje broja i aktivnosti mikroorganizama dovodi do velike potražnje za ograničenom opskrbom kisikom, hranjivim tvarima, prostorom itd.

Mikrobi sa slabom saprofitskom sposobnošću preživljavanja nisu u stanju natjecati se s drugim saprofitima tla za ove zahtjeve i ili propadaju ili postaju mirni stvarajući otporne strukture.

5. Predacija:

Predacija se obično događa kada jedan mikroorganizam, grabežljivac, proguta i probavlja drugi mikroorganizam, plijen, a prvi dobiva prehranu iz drugog. U mikrobnom bratstvu, međutim, razlika između grabežljivca i parazitizma nije oštra.

Interakciju između bakterija Bdellovibrio i drugih malih gram-negativnih bakterija neki smatraju grabežljivcem, a drugi parazitizmom. Bdellovibrio je očito prilično raširen u vodenim staništima i napada druge bakterije, obično gram-negativne, bušenjem rupe u stijenci, ulazeći u bakteriju i uzrokujući lizu s konačnim oslobađanjem mnogih malih bakterija u obliku vibrija.

Glavni mikrobni predatori su protozoe koje mogu progutati bakterije i rjeđe alge i druge protozoe. Ovi sustavi su se intenzivno koristili u modelima i simulacijama odnosa grabežljivac-plijen. U najjednostavnijem obliku populacija protozoa (npr. Tetrahymena) ograničena je svojom bakterijskom hranom (npr. Klebsiella), a broj plijena i grabežljivca pokazuje cikličke oscilacije.

Drugi takav primjer je odnos Didinium-Paramecium (oba protozoa). Didinium lovi paramecijum sve dok populacija kasnijih ne izumre. U nedostatku izvora hrane, populacija Didinium također izumire.

Ako se nekoliko pripadnika populacije Paramecium uspije sakriti i pobjeći od grabežljivaca Didiniuma, tada se populacija Parameciuma oporavlja nakon izumiranja Didiniuma. Dakle, može doći do cikličke oscilacije u populaciji ova dva protozoa.

Predatorske gljive postoje i smatraju se mogućim agensima biokontrole za neke bolesti biljaka uzrokovane mikroorganizmima u tlu. Nematode i protozoe mogu biti zarobljene raznim mrežastim hifama, ljepljivim površinama i omčama. Organizam je tada napadnut hifama i probavlja se.

6. Proto-suradnja (sinergizam):

Protosuradnja (ili sinergizam), poput mutualizma, predstavlja povezanost između dviju mikrobnih populacija u kojoj obje populacije imaju koristi jedna od druge, ali se razlikuje od uzajamnosti po tome što povezanost nije ‘obvezna’.

Obje sinergijske populacije mikroba mogu samostalno preživjeti u svom prirodnom okruženju. Protosuradnja ili sinergizam omogućuje populacijama mikroba da obavljaju metaboličke aktivnosti kao što je sinteza proizvoda koji niti jedna populacija ne bi mogla izvesti sama.

Slijedi nekoliko primjera:

(i) Desulfolvibrio bakterije opskrbljuju H2S i CO2 do Chlorobium bakterija i, zauzvrat, Chlorobium bakterije stvaraju sulfat (SO4 – ) i organski materijal dostupan Desulfovibrio. Stoga mješavina dviju bakterijskih populacija proizvodi mnogo više staničnog materijala nego bilo koja sama (Fie 33.10A).

(ii) Populacije nocardia metaboliziraju cikloheksan što rezultira produktima razgradnje koje koristi populacija Pseudomonas. Vrsta Pseudomonas proizvodi biotin i faktore rasta koji su potrebni za rast Nocardia (slika 33.1 OB).

(iii) Populacije Azotobacter prisutne u tlu fiksiraju atmosferski dušik ako imaju dovoljan izvor organskih spojeva. Druge bakterijske populacije tla kao što je Cellulomonas sposobne su iskoristiti fiksni oblik dušika i osigurati populaciji Azotobacter potrebnih organskih spojeva (slika 33.10C).

7. Komensalizam:

Komensalizam predstavlja odnos između dviju mikrobnih populacija u kojem jedna ima koristi, a druga ostaje nepromijenjena (tj. niti koristi niti šteti). Stoga je komenzalizam jednosmjeran odnos između dviju mikrobnih populacija. To je prilično uobičajeno, često se temelji na fizičkim ili kemijskim modifikacijama staništa, i obično nije ‘obavezno’ za dvije uključene populacije.

Komensalistička povezanost često se uspostavlja kada jedna mikrobna populacija, tijekom svog normalnog rasta i metabolizma, modificira stanište na takav način da druga populacija ima koristi.

Slijedi nekoliko primjera:

(i) Mikrobna populacija koja uzrokuje bolest kada se otvori lezija na površini domaćina, ako stvara ulaz-prolaz za drugu mikrobnu populaciju koja inače ne bi mogla ući i rasti u tkivima domaćina. Radi praktičnosti, Mycobacterium leprae, uzročnik gube, otvara lezije na površini tijela i tako omogućuje drugim patogenima da uspostave sekundarne infekcije.

(ii) Kada fakultativni anaerobi iskorištavaju kisik i snižavaju sadržaj kisika, stvaraju anaerobno stanište koje odgovara rastu obveznih anaeroba jer potonji imaju koristi od metaboličkih aktivnosti fakultativnih anaeroba u takvom staništu.

Naprotiv, fakultativni anaerobi ostaju nepromijenjeni. Pojava obveznih anaeroba u staništima pretežno aerobnog karaktera, poput usne šupljine, ovisi o takvom komenzalnom odnosu.

(iii) Populacija Mycobacterium vaccae, dok raste na propanu, kometabolizira (besplatno oksidira) cikloheksan u cikloheksanon koji zatim koristi druga bakterijska populacija, npr. Pseudomonas (slika 33.11). Potonja populacija stoga ima koristi jer nije u stanju oksidirati cikloheksan u cikloheksanon. Mycobacterium ostaje nepromijenjen jer ne asimilira cikloheksanon.

(iv) Neke populacije mikroba stvaraju komenzalističko stanište detoksikacijom spojeva imobilizacijom. Leptothrix bakterije talože mangan na svojoj površini. Na taj način smanjuju koncentraciju mangana u staništu i tako dopuštaju rast drugih mikrobnih populacija. Ako Leptothrix ne djeluje tako, koncentracija mangana bi bila toksična za druge mikrobne populacije.


MORFOLOGIJA I RAZVOJ JAJA JAJJAJA AMNIOTA

James R. Stewart, u Amniote Origins, 1997

Squamata.–

Prevalencija viviparnosti među gušterima i zmijama potaknula je zanimanje za strukturu placente kod Squamata. Kao rezultat toga, razvoj ekstraembrionalnih membrana poznat je za razne vrste, od kojih je većina živorodna. Glavne značajke obrasca razvoja ne razlikuju se za proučavane vrste jajonosaca.

Razvoj žumanjčane vrećice sastoji se od tri faze karakteristične za druge gmazove. Primarna žumanjčana vrećica je bilaminarna omfalopleura. Trilaminarni omfalopleur nastaje kada se sloj mezoderma proliferira između ektodermalnog i endodermalnog sloja bilaminarne omfalopleure. Nevaskularna trilaminarna omfalopleura se vaskularizira ubrzo nakon toga i formira koriovitelinsku membranu. Transformacija žumanjčane vrećice je progresivna jer se modifikacije povezane sa svakom fazom šire prema van preko mase žumanjka. The concentric growth of the choriovitelline membrane over the surface of the yolk is delimited by a vascular ring, the sinus terminalis.

In contrast to all other Reptilia, the course of mesodermal growth in advance of the choriovitelline membrane deviates from the bilaminar omphalopleure and extends into the yolk ( Stewart, 1993 ). This intravitelline mesoderm most commonly forms a sheet that is several cell layers thick and which continues to grow to ultimately form a continuous membrane within the yolk across the entire abembryonic pole. These cells undergo a morphogenetic process similar to that of the mesoderm of the choriovitelline membrane and an extraembryonic coelom, the yolk cleft, is formed. The yolk cleft is lined by splanchnopleure. The outer compartment of yolk that is separated from the yolk mass by this process is termed the isolated yolk mass ( Fig. 3 ). The isolated yolk mass is lined internally by splanchnopleure and externally by the bilaminar omphalopleure. The pattern of growth of the extraembryonic mesoderm has an important effect on the early distribution of blood vessels at the abembryonic pole of the egg. Blood vessels that subsequently form in the abembryonic region of the yolk sac do so in association with intravitelline cells, whereas the bilaminar omphalopleure remains intact and nonvascular at the abembryonic pole. The formation of an isolated yolk mass has been documented in all species of Squamata that have been studied ( Stewart, 1993 ). The subsequent development of this structure following its formation varies among species, but this structural variation has not been linked to specific functional characteristics ( Stewart, 1993 ).

Figure 3 . Extraembryonic membranes of Squamata, based on Elgaria multicarinata ( Stewart, 1985 ).

Development of the region of the yolk sac that transforms into a choriovitelline membrane is similar to other Reptilia. The mesodermal layer separates and an extraembryonic coelom lined externally by somatopleure and internally by splanchnopleure is formed. The vitelline vessels remain associated with the yolk sac splanchnopleure following disruption of the choriovitelline membrane.

The few studies of amniogenesis among squamates are reviewed by Fisk and Tribe (1949) . The most detailed work is on several species of Chamaeleo that are unusual compared to other reptiles in that amniogenesis proceeds concentrically and early in development. The composition and development of the amniochorion for the few species of snakes and lizards that have been described is similar to that of Sphenodon ( Fisk and Tribe, 1949 ).

The allantois of squamates expands to fill the extraembryonic coelom and its outer membrane fuses with the chorion ( Fig. 3 ). Growth of the allantois toward the abembryonic pole of the egg is dependent on the fate of the isolated yolk mass ( Stewart, 1993 ). In some species, the allantois expands as the isolated yolk mass regresses and eventually surrounds the entire yolk mass. In other species, the allantois extends into the yolk cleft.


Notes on Microorganisms | Biologija

In this article we have compiled various notes on microorganisms. After reading this article we will have a basic idea about:- 1. Meaning of Microorganisms 2. Origin of Microorganisms 3. Distribution 4. Nature 5. Nutrition 6. Classification 7. Reproduction 8. Importance of the Study.

  1. Notes on the Meaning of Microorganisms
  2. Notes on the Origin of Microorganisms
  3. Notes on the Distribution of Microorganisms
  4. Notes on the Nature of Microorganisms
  5. Notes on the Nutrition of Microorganisms
  6. Notes on the Classification of Microorganisms
  7. Notes on the Reproduction of Microorganisms
  8. Notes on the Importance of the Study of Microorganisms

Note # 1. Meaning of Microorganisms:

Microorganisms are microscopic forms of life, include bacteria, fungi, algae, protozoa, and the infectious agents at the borderline of life that are called viruses which are not cellular organisms. They are also known as microbes. The term microbe is taken from the French and means a microscopic organism or microorganism, being usually applied to the pathogenic forms.

Again the term germ, in popular usage, refers to any microorganism but especially to one of the pathogenic or disease-producing bacteria. Hence the terms microbe and germ are probably synonymous with bacterium (pi. bacteria). A microorganism that harms its host is also called a pathogen. Microorganisms differ widely in form and life cycle.

Some are single-celled, but others are multicellular. Some of them have no well-organized nucleus, but others do. Some of the microorganisms are predominantly plant-like, others are animal-like, again others share characteristics common to both plants and animals. They grow rapidly and reproduce at an unusually high rate, within 24 hours some of them com­plete almost 100 generations.

Microorganisms have pattern of metabolic processes like that of higher plants and animals. Regardless of the complexity of structure of a microorganism, the cell is the basic structural unit of life. All living cells are funda­mentally similar.

Microorganisms may or may not contain chlorophyll and can use inorganic or organic carbon as the source of carbon. Some have the unique ability of utilizing either radiant or chemical energy and may be autophytes or heterophytes.

Again some are able to utilize atmospheric nitrogen for the synthesis of proteins and other complex organic nitrogenous compounds. Some microorganisms synthesize all their vitamins, while others need to be furnished with vitamins.

Microorganisms play an important and often dominant role in all fields of human endeavour like industry, agriculture, problems connected with food, shelter and clothing, and in the conser­vation of human health and combating diseases.

Note # 2. Origin of Microorganisms:

Microorganisms originate from the earth’s surface and are dispersed in nature through various agencies like air, water, rain, insects and various other media. They occur nearly everywhere in nature where they find food, moisture, and a temperature suitable for their growth and multiplication.

Some are found in the bottom of the ocean and others miles away on the mountain heights, thereby can stand wide range of temperature conditions. Microorganisms occur in water (fresh and marine), stagnant and/or free flowing.

Since they thrive under conditions suitable for human survival, it is inevitable that we live among a multitude of microorganisms. They infest the air we breathe and the food we eat.

Note # 3. Distribution of Microorganisms:

Microorganisms inhabit on our body surfaces, in our alimentary tract, in our mouth, nose and all other body orifices. Fortunately most microorganisms are harmless to us and we have means of resisting invasion by those that are potentially harmful.

The microbial population in our environment is both large and complex. For example, a single sneeze may disperse approximately from 10,000 to 100,000 bacteria. One gram of faces may contain millions of bacteria. Our environment—air, soil, water—likewise consists of a menagerie of bacteria and other microbes.

Soil micro­organisms include many species of bacteria, fungi, algae, protozoa and viruses. A study of the microorganisms in these habitats requires specialized knowledge of the specific microbes present.

The bacterial population of the soil exceeds the population of all other groups of microorganisms in both number and variety. Several billions of bacteria per gram of soil have been reported by direct count method.

Note # 4. Nature of Microorganisms:

All microorganisms of the aquatic environment have patterns of seasonal growth which again are controlled by the nature of water— fresh or marine and stagnant or free flowing. As such it is extremely difficult to enlist the nature of aquatic microorganisms.

Still a very broad idea is given in the following manner:

i. Fresh water planktonic microorganisms include primarily the producer orga­nisms (photosynthetic algae) —green and blue-green algae, diatoms, pigmented bacteria, etc.

Whereas, marine planktonic ones are: diatoms, blue-green algae, dinoflagellates, chlamydomonads species of the genera Pseudomonas, Vibrio, Flavobac- terium, and Achromobacter which give protection against lethal portion of solar radiation protozoa—species of Foraminifera and Radiolaria, and many flagellated and ciliated species.

The characteristic colour of the Red Sea is associated with heavy blooms of a blue-green alga, Oscillatoria erythraea. The chytrid Rhizophidium, small animals and viruses parasitize on planktonic algae causing profound effect on the algal population.

ii. In the benthos epilithic forms include many diatoms (e.g., species of the genera Synedra, Meridion, Licmorphora) species of Chamaesiphon, Rivularia, Chaetophora, Cladophora, Sphacelaria and many microscopic Rhodophytes. Some produce mucilage in which filaments are embedded whilst others precipitate Calcium carbonate around themselves and build up nodular growths.

Again some small algal cells are attached amongst the coating of bacteria on both fresh water and marine sand grains— epiplasmmic flora—the majority belong to the Bacillariophyta, though some of Cyanophyta and Chlorophyta. Besides this, small Crustacea bear epizooic algal populations.

iii. Both pigmented and nonpigmented bacteria including species of Pseudomonas, Chromobacterium, Achromobacter, Flavobacterium and Micrococcus are very common in less polluted water. Bacteria washed into water are mainly species of Bacillus (aerobic) and Clostridium (anaerobic).

In water polluted with animal or human excreta some of the common bacteria are: Escherichia coli, Streptococcus faecalis, Proteus vulgaris, Clostridium perfringens, Salmonella typhi and Vibrio cholerae. Where oxygen is available, a wide range of aquatic fungi is available of which chytrids are most important.

Some more common ones are the species of Mycosphaerella, Ceriosporopsis, Saprolegnia, Monoblepharis. Where oxygen is scarce, species of Clathrosphaerina and Helicodendron may be present. Aquatic protozoa are common in both fresh are salt waters. Planktonic protozoa (ciliates, flagellates, and the Heliozoa) and grazing species of other animals fluctuate with the nature of phytoplankon.

Pollution of Natural Waters:

The increasing use of fertilizers and disposal of wastes in streams are resulting in rapidly increasing in nutrient content in many natural water bodies. Enormous algal crops result, followed by their decay giving massive pollution of water. Similar problems of excessive algal growth arise in industrial plants, e.g., in power station cooling towers, and ponds.

The degree of pollution of both fresh and marine waters can be determined by studying the algal growth. Benthic algae are very sensitive indicators. In the extremely polluted zones only algae such as: Oscillatoria chlorina, and Spirulina jenneri occur and in the slightly less polluted zones the diatoms Nitzschia palea and Gamphonema parvulum appear.

The recent growth in number of nuclear power stations, from which large amount of excess heat has to be dissipated, is giving cause for concern over ‘heat pollution’ of rivers and estuaries. It causes direct danger to fish and microorganisms, thereby may disrupt the food chain.

Note # 5. Nutrition of Microorganisms:

Microorganisms are autotrophs and heterotrophs mesophiles, thermnphiles, and psychrophiles aerobes and anaerobes cellulose digesters and sulfur oxidizers nitrogen fixers and protein digesters and other kinds of bacteria in soil which are yet to be discovered.

Large number of actinomycetes, as many as millions per gram, is present in dry warm soils. The most predominant genera of this group are Nocardia, Streptomyces, and Micromonospora which are responsible for the characteristic musty or earthy odour of a freshly ploughed field. They are capable of degrading many complex organic substances and consequently play an important role in building soil fertility.

Fungi are most abundant near the soil surface where an aerobic condition is likely to prevail. They exist in both the mycelial and spore stage. It is difficult to estimate their numbers. Fungi are active in decomposing the major constituents of plant tissues, namely, cellulose, lignin, and pectin. The physical structure of soil is improved by the accumulation of fungal mycelium within it.

The population of algae in soil is generally smaller than that of either bacteria or fungi. The major types present are the green algae and diatoms. Their photosynthetic nature accounts for their predominance on the surface and just below the surface layer of soil. On barren and eroded lands algae may initiate the accumulation of organic matter because of their ability to carry out photosynthesis and other metabolic acti­vities.

The blue-green algae are known to grow on the surfaces of freshly exposed rocks where the accumulation of their cells results in simultaneous deposition of organic matter. This establishes a nutrient base that will support bacterial species. The growth and activities of the initial algae and bacteria pave the way for the growth of other bacteria and fungi.

The mineral nutrients of the rock are slowly dissolved by acids resulting from microbial metabolism. This process continues with a gradual accumu­lation of organic matter and dissolved minerals until a condition results that supports growth of lichens, then mosses, then higher plants. The blue-green algae play a key role in the transformation of rock to soil, a first step in rock-plant succession.

Most soil protozoa are flagellates or arnoebas. Their number per gram of soil ranges from a few hundred to several hundred thousand in moist soils rich in organic matter. Their mode of nutrition involves ingestion of bacteria with some selectivity. Hence protozoa is one of the factors in maintaining equilibrium of microorganisms in soil.

Plant and animal viruses, as well as bacterial viruses (bacteriophages) gain entry into soil microbial population through plant and animal wastes.

In general, some microorganisms survive utilizing solar energy, others use various chemical substances as their fuel, again others have special mechanism of livelihood. As such, microorganisms may behave either as autophytes, as saprophytes, as parasites, or as symbionts.

Microorganisms bring about in nature many changes some desirable (beneficial) and others undesirable (harmful) to us. The diversity of their activities ranges from the enhancement of soil fertility by decomposing dead organic matter, transforma­tion and deposition of minerals in the soil, formation of coal, production of various useful substances, causing diseases of humans and animals and plants to reducing soil fertility and various other activities.

Note # 6. Classification of Microorganisms:

The subject of microbial classification has a long history. One of the first systems was proposed in 1773, and many more appeared since then. Until the eighteenth century, the living organisms were classified into two Kingdoms: plant and animal. Since there are organisms which are typically neither plants nor animals, naturally they do not fall into either plant or the animal Kingdom.

Hence it was proposed that new kingdoms be established to include these organisms. In 1866 E. H. Haeckel, a German zoologist suggested that a third kingdom, Protista, be formed to include those unicellular microorganisms that are typically neither plants nor animals.

These organisms, the protists, include bacteria, algae, fungi and protozoa. Since viruses are not cellular organisms, hence they were not included with the protists.

He referred bacteria to as lower protists and called algae, fungi and protozoa higher protists. But Haeckel’s concept of Kingdom Protista failed to put forward criteria that could be used to distinguish a bacterium from a yeast or certain microscopic algae. Late in the 1940s with the help of powerful magnification provided by electron microscopy it was possible to make more definitive observation of internal cell structure.

It was dis­covered that in some cell, particularly in bacteria, the nuclear substance was not enclosed by a nuclear membrane. Whereas, in other cells, for example typical algae and fungi, the nucleus was enclosed in a membrane. This discovery enabled to sepa­rate one group of protists (bacteria) without membrane bound nucleus from all the others (algae, fungi, protozoa) which possess membrane bound nucleus.

These two cell types have been designated as: procaryotic and eucaryotic and organisms of each cell type are called procaryotes and eucaryotes respectively. Hence bacteria are procaryotic organisms and eucaryotic organisms include algae, fungi and protozoa.

A comprehensive system of classification, designated as five-Kingdom system, was proposed by R. H. Whittaker (1969). This system of classification is based on three levels of cellular organization which evolved to accommodate three principal modes of nutrition: photosynthesis, absorption, and ingestion. The procaryotes are included in the Kingdom Monera, they lack the ingestive mode of nutrition.

Unicellular eucaryotic microorganisms are placed in the Kingdom Protista, all nutritional types are represented here. It includes microalgae whose mode of nutrition is photosynthetic and protozoa with ingestive mode of nutrition.

The multicellular and multinucleate eucaryotic organisms are found in the Kingdoms Plantae (multicellular green plants and higher algae), Animalia (multicellular animals), and Fungi (higher fungi). The diversified modes of nutrition lead to a more diversified cellular organization of the five kingdoms: Monera (bacteria and cyanobacteria), Protista (microalgae and protozoa) and Fungi (yeasts and molds).

The scheme of classification is pre­sented below:

AA. Multicellular organisms

B. Higher algae and green plants.. Plantae

Bergey’s Manual of Determinative Bacteriology in 8th edition (1974) has recogni­zed the Kingdom Monera, but has called it Kingdom Procaryotae because of the procaryotic nature of the cells. This Kindgom is divided into two divisions: the blue- green algae or cyanobacteria (some microbiologists consider the blue-green algae as bacteria) and bacteria (procaryotic organisms other than blue-green algae).

In 1984 the scope of Bergey’s Manual was greatly broadened by bringing together various other information concerning bacterial classification and identification.

It was published under a new name—Bergey’s Manual of Systematic Bacteriology in which all bacteria were placed in the Kingdom procaryotae which has been divided into 4 divisions as follows:

Procaryotes with a complex cell wall structure -Gram-negative bacteria

Procaryotes with a cell wall structure characteristic of Gram-positive bacteria.

Procaryotes that lack a cell wall.

Procaryotes with characteristics of an earlier phylogenetic origin than above Divisions.

The study of cell organization by the electron microscope and by advanced bio­chemical techniques has revealed fundamental resemblances and differences between various microorganisms and offers a sound basis for their division into major groups (i.e. procaryotes and eucaryotes, and viruses) and for their farther subdivision.

L. E. Hawker and A. H. Linton (1978) included under the Kingdom Protista the so-called microorganisms (both procaryotic and eucaryotic) having relatively lowly differentiated body and subdivided it in the following manner.

A. Organization subcellular Viruses

AA. Thallus unicellulr, multicellular, or plasmodial

B. Nucleoplasm not bounded by a membrane Prokaryota

C. Chlorophyll absent, or if present of type different from that of plants

CC. Chlorophyll present, together with charac­teristic blue-green pigment, pigments not located in discrete plastids

BB. Cells or plasmoclia containing one or more discrete membrane-bounded nuclei

D. Cell(s) of vegetative thallus (with a few exceptions possessing a cell wall(s)

E. Chlorophyll present and located in discrete chloroplasts

DD. Gell(s) of vegetative thallus lacking true cell walls

F. Thallus unicellular, remaining so Protozoa

FF. Thallus unicellular at first, becoming a plasmodium or pseudoplasmodium and even­tually forming a fructification Slime molds

In Bergey’s Manual of Systematic Bacteriology (1984) the Cyanophyta (Blue- green algae) have been placed in volume 3—Bacteria with unusual properties in the Section: Oxygenic Phototrophic Bacteria. They were designated as the Cyanobacteria as they contain chlorophyll, can use light as an energy source, and evolve O2 in a manner similar to that of green plants.

This arrangement has not been accepted by the algologists. According to them, the Cyanophyta (Blue-green algae) have closer affinities with algae than bacteria and as such they should be placed under the group Algae and not under Bacteria.

Note # 7. Reproduction of Microorganisms:

Microorganisms reproduce by the simple method of binary fission. Besides this, there are other methods by which they reproduce.

Note # 8. Importance of the Study of Microorganisms:

Microorganisms though microscopic in size are most interesting life forms which attracted attention of workers through ages. They possess immense potentialities which are continuously being explored for the welfare of human society. Not only that they are most fascinating group of organisms, but also have a very simple life form, easy to handle, and are pliable.

With increase in know ledge of the microbial world, the task of befriending the microbial regime—particularly bacterial has now become an urgent agendum in the struggle for existence of the human beings together with the necessary organisms. Following are some of the essential aspects of human society that have opened up based on the study of microorganisms and have emphasized the importance of their study.


Plant Genetic Engineering Towards the Third Millennium

Future Prospects

A strategy for the search of other Bacillus thuringiensis strains carrying novel δ-endotoxin genes was designed in our laboratory. Introduction of δ-endotoxin genes coding for insecticidal proteins differing in their RWW midgut receptor might both enhance efficiency of control and delay appearing of insect resistance. The introduction into rice of insecticidal genes with different mode of action, such as protease inhibitors or lectins, might also contribute to this purpose.

Since some pests of economical importance for rice in Cuba are not of the chewing type, eg. the stinkbug Oebalus insularis, the Homopteran Togasodes oryzicola, and the mite Steneotarsonemus spinki, the potential of insecticidal molecules different from δ-endotoxins of B. thuringiensis need to be explored.

Besides chitinase, glucanase and PRs genes, other antifungal genes are envisaged to be introduced into rice for ensuring a longer lasting effectiveness of transgenic plants in the field. Among these, genes coding for systemic acquired resistance (SAR) would be of outstanding importance.

The development of expression systems for specific expression of the desired proteins in particular tissues, organs, cell compartments, and plant developmental stages will be necessary to cope with the expectations created around transgenic rice plants.

In particular, it would be very convenient to set up systems capable of diminish the risk of gene escaping through the pollen from transgenic plants to sexually compatible wild or relative rice species, and/or controlling the viability of potential undesired hybrids. These is a technical development specially appropriated when creating transgenic plants carrying genes and could confer competitive advantage if unintentionally bred into natural populations.

Transformation of local rice cultivars with genes targeted to improve the defense of the plant against the main environmental stresses limiting rice yields in Cuba (cold, drought and salinity) would enable biotechnology to help breeders to complement rice breeding for attaining genetic goals not feasible using conventional techniques.

The introduction of genes capable of simplifying the technology for production of hybrid seed or providing rice cultivars with the uniqueness of perpetuating the advantages of hybrids will means a breakthrough for rice production in Cuba.


4. Levels in Biological Theory

Besides the more philosophical debates discussed above, levels of organization also play an important conceptual role in biological research and theory. Interestingly, this growing body of literature on levels in evolutionary biology is almost entirely disconnected from the debates on levels in philosophy of science discussed above.

A prominent example is the issue of levels of selection. In this debate, the hierarchical organization of nature into levels is an important background assumption, as the aim is to find out at which level(s) of the biological hierarchy natural selection is taking place (Griesemer 2000 Okasha 2006). Although Darwin&rsquos original account was focused on evolution at the level of organisms, arguably the conditions for natural selection can be formulated abstractly without referring to any specific kinds of entities, which allows for natural selection to operate at any level where the conditions are satisfied (Griesemer 2000 Lewontin 1970). Since the 1970s, the debate on levels of selection has kept on growing and extending to different areas, though no precise consensus has been reached. Positions range from the gene-centered view, where natural selection is taken to operate almost exclusively at the level of genes (e.g., Dawkins 1976 Williams 1966), to the pluralistic multilevel selection theory, which allows for natural selection to operate on any level of the biological hierarchy where we find the right kind of units (e.g., Sober & Wilson 1998 Wilson & Wilson 2008).

One branch of the levels of selection debate that is particularly interesting from the point of view of levels of organization is the issue of evolutionary transitions. Here the focus is on the emergence of novi levels of organization through evolutionary processes (Buss 1987: ch. 5 Griesemer 2000 Maynard Smith & Szathmáry 1995 Okasha 2006). The background idea is that the complex hierarchical organization of nature that we observe today must itself be a result of evolution, and therefore requires an evolutionary explanation. For example, somehow prokaryotes evolved to eukaryotic cells, single-celled organisms evolved to multicellular organisms, individual animals evolved to colonies, and so on. In their highly influential book, Maynard Smith and Szathmáry (1995) proposed that the characteristic feature of major evolutionary transitions is that entities that were capable of replicating independently before the transitions are only capable of replicating as parts of higher-level wholes after the transitions (see also Buss 1987). For example, after a single-celled organism has evolved into a multicellular organism, the cells of the organism can no longer replicate independently of the organism as a whole. For more on levels of selection and evolutionary transitions, see Okasha (2006) and the entry units and levels of selection.

In these debates, the notion of levels of organization is typically used as a primitive term that is assumed to be clear enough and is therefore left undefined (Griesemer 2005). A notable exception is Okasha (2006), who puts forward a proposal for understanding levels of organization in natural selection, building on earlier work by McShea (2001). The starting point is the part-whole relationship, which is the standard definitive feature of levels of organization, but taken alone is insufficient for defining levels of organization: A big heap of sand is made up of smaller heaps of sands, but does not constitute a higher level of organization. Therefore, Okasha (2006) and McShea (2001) propose two further conditions: The parts that form higher-level wholes must interact with each other, and they must be homologni with organisms in a free-living state. For example, the cells that compose organisms interact with each other and are homologous to free-living unicellular organisms, and therefore constitute a level of organization. On the other hand, candidates such as heaps of sand are ruled out, as they do not significantly interact with each other, nor are they homologous to free-living organisms.

Another context in biology where the nature of levels has received explicit attention is the &ldquohierarchy theory of evolution&rdquo developed by Niles Eldredge and colleagues (Eldredge et al. 2016, Vrba & Eldredge 1984). In this theoretical framework, levels and hierarchies are taken to be fundamentally important ontological features of nature:

Biological evolutionary theory is ontologically committed to the existence of nested hierarchies in nature and attempts to explain natural phenomena as a product of complex dynamics of real hierarchical systems. (Tëmkin & Eldredge 2015: 184)

In the hierarchy theory of evolution, a distinction is made between two types of hierarchies and the corresponding levels (Eldredge 1996 Vrba & Eldredge 1984): The ecological i genealogical hierarchy. In both kinds of hierarchies, higher-level things are formed through specific interactions among lower-level things. In the ecological hierarchy, these interactions are exchanges of matter and energy, such as consuming and gathering resources, and in this hierarchy, we find things such as cells, organisms, avatars and ecosystems. In the genealogical hierarchy, the defining activity through which levels are formed is the transmission of information through replication, and the hierarchy includes things such as cells, organisms, demes and species. Note that cells and organisms appear in both hierarchies, but in the ecological hierarchy they are seen as interactors, whereas in the genealogical hierarchy they are seen as replicators.


Dodatne informacije

Pristupni kodovi: Geographic range data for New World snakes are archived at Dryad (http://dx.doi.org/10.5061/dryad.qk300) and nucleotide sequences for all newly acquired Sonorini species are deposited in the Genbank nucleotide database under accession codes KU859402 to KU859865.

Kako citirati ovaj članak: Davis Rabosky, A. R. et al. Coral snakes predict the evolution of mimicry across new world snakes. Nat. komun. 7:11484 doi: 10.1038/ncomms11484 (2016).


Fungi Examples

Fungi are important organisms that are so distinct from plants and animals that they have been allotted their own classifications of life on earth. Fungi are tremendously important to human society and the planet we live on. They provide fundamental products including foods, medicines, and enzymes important to industry. They are also the unsung heroes of nearly all ecosystems, hidden from view but inseparable from the processes that sustain life on the planet.

In 1969 fungi were first officially recognized as a distinct group. And more recently, using DNA sequences and comparisons of cell structure, we have learned that fungi are in fact more closely related to animals than they are to plants. Superficially, they remind us more of plants than animals because they don't move, but scratch the biological surface just a little and that's just about the only thing they have in common.

No one knows for sure how many species of fungi there are on our planet at this point in time, but what is known is that at least 99,000 species of fungi have been described, and new species are described at the rate of approximately 1200 per year.

Fungi come in many different sizes and shapes, and are divided into three main groups depending on the shape.

A unicellular fungus which includes baker's yeast. Yeast can also be found in pharmacies as probiotic which can help prevent diarrhea. There is also yeast that can be damaging to the human body. When present in the mouth, esophagus, bowel and vagina, it can cause yeast infections in people with low immune systems. If it invades the blood yeast can be fatal.

A multicellular fungi and appear as fuzzy growths. Mold can be both harmful and beneficial. For example, mold was used to produce the antibiotic penicillin. Mold is used to produce cheese. Mold commonly contaminates starchy foods and when certain types of this contamination are ingested, it can cause miscarriages, birth defects, and some cancers. Most commonly, mold appears on old bread, and decaying fruit. Mildew is a mold growth that is visible on plants, walls, leather, paper, cloths, and damp areas. It is easy to see that mold is a fungus that can be both helpful and harmful.

A fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or on its food source. It typically consists of a stem, cap and gills. Some are harmful and some are not. Some mushrooms are edible and have successfully been cultivated for human consumption. A mushroom develops from a nodule, or pinhead, less than two millimeters in diameter. Many species of mushrooms seemingly appear overnight, growing or expanding rapidly. In reality all species of mushrooms take several days to form primordial mushroom fruit bodies, though they do expand rapidly by the absorption of fluids.


Rezultati

Table 1 summarizes our results, and Fig. 2 maps them. Details of the statistical fits, along with maximum-likelihood confidence intervals (CIs) of the estimates, are provided in Materijali i metode and Dataset S1. Overall, in the analysis we present here, we predict 21% of species are missing from our sample of approximately 108,000 species. This estimate is similar to estimates produced for all the monocots (17%) and for a combination of the taxonomically revised nonmonocots (13%) (10).

Currently known patterns of flowering plant species richness as a percent of all species (Lijevo) and patterns when corrected for species predicted to be missing from the taxonomic record (Pravo). They are broadly similar differences are noted in the text. Although our results do not take area into account, we plot the results in an equal-area projection to help visualize the sometimes confusing relationship between undiscovered species and region. We excluded gray regions (Saharan Africa and the Arabian Peninsula) from the analysis as a result of low numbers of endemic species. Original TDWG regions are shown in Fig. S1. Fig. S3 shows raw estimates of numbers of missing species in each region.

Forty of 50 regions show a marked reduction over time in the number of species described per taxonomist per 5-y interval. This leads to low ratios of numbers of predicted species over numbers of presently known species (Fig. 1 provides the example for Mexico and Central America, where the ratio is 1.17, meaning we predict an additional 17%, a percentage close to the numbers for all species combined). Our model suggests other regions with floras that are relatively well known. These include some biodiversity hotspots including Cuba, southeastern Brazil, India and Sri Lanka, and much of mainland tropical Asia.

Do our estimates change our understanding of the rankings of global biodiversity? Table 1 shows the percentage distribution of known species, as well as for when we include the predicted numbers of species. For ease, we have also added the change in rank. Arrows indicate the direction of this change.

Fig. 2 maps the current (Fig. 2, Lijevo) and predicted (Fig. 2, Pravo) overall percentages of endemic species around the world. The similarities between panels in Fig. 2, along with the rank change column in Table 1, indicate that existing conservation priorities would not be changed significantly by correcting for missing species (rs = 0.97, P < 0,001). For example, the northern Andes and Atlantic Coast forests of South America, Southern Africa, Australasia, and the islands of tropical Asia will remain major centers of plant endemism, as well as areas under threat.

That said, there are geographic differences between what is currently known and what we predict. The region including Ecuador and Peru houses more than 5% of the species in our sample and is currently ranked as the second richest single area. However, this region is projected to contain 29% of the world's missing species, and by incorporating this datum, we expect this region to overtake the area currently ranked first (Mexico to Panama). Further, we predict that Tanzania and the southern cone of South American countries will become relatively much richer in species when missing species are included.

Additionally, it is of conservation interest to note that South American regions will, on average, increase their ranking by 16% (based on the percentage of total possible moves in rank) and African regions by 10%. In contrast, the tropical mainland Asian regions will fall in rankings on average by 6% and the tropical Asian islands by more than 10%. We note that, although increasing taxonomic knowledge generally implies increasing numbers of known species, there has been at least one exception to the rule. In the Eastern Arc Mountains, better information on species ranges and synonymies caused a downward revision of regional endemic plant species, and necessitated a regrouping of the hotspot region (21). Generally, correcting for missing species, as we do here, will increase the number of species endemic to a region.

Finally, there are other species not endemic to the regions we describe, although, given the rather large ranges of these taxa, it is likely that the pool of unknown species is quite small. Approximately 25% of the species we analyzed occur in two or more of the regions we define, and, as one would expect, such generally widespread species are well known and the rate of taxonomic description is now low (Table 1). Species endemic to oceanic islands also show only slow rates of discovery, perhaps because such places are well explored and have been for a long time (Table 1).


Distribution and abundance

Of the more than 65,000 species, about 30,000 are marine, 5,000 live in fresh water, and 30,000 live on land. In general, oceanic gastropods are most diverse in number of species and in variety of shell structures in tropical waters several hundred species (each represented by a small number of individuals) can be found in a single coral reef habitat. This is in contrast to the Arctic or subarctic coasts, where the few species present are represented by many individuals. A number of deep-sea species are known, and a significant snail fauna is associated with hydrothermal vents. Most marine species have large ranges.

Freshwater snails are common in ponds, streams, marshes, and lakes. Usually only a few species are found at one place, but each species will have a rather wide range. Most species are common and feed on algae or dead plant matter. In a few relatively old river systems and lakes—in particular, Lake Baikal in Siberia, Lake Titicaca in South America, Lake Ohrid on the North Macedonia–Albania border, the Mekong basin in Southeast Asia, and the African Rift lakes—extensive and complex radiations of snails have occurred in recent geologic time, producing a large number of species.

Land snails are marginally, but very successfully, terrestrial. When actively moving, they continuously lose water. During periods when water is unavailable, they retreat into their shells and remain inactive until conditions improve. They hibernate during winter periods, when water is locked into snow or ice, and estivate during periods of summer drought. Land snails have been found above the snow line species of Vitrina crawl on snowbanks in Alpine meadows. Other species inhabit barren deserts where they must remain inactive for years between rains.

Fewer than 10 species live in the same area together across most of North America. On the other hand, in such favourable areas as New Zealand, Jamaica, northeastern India, and the wet forests of Queensland (Australia) 30 to 40 different species can be found together. In some parts of western Europe 20 species can be found together. Only one or two species are found in many desert regions, and they have dramatic feeding specializations.

The local abundance of snails and slugs can be spectacular. Millions of some brackish-water and freshwater species can live on small mud flats. An acre of British farmland may hold 250,000 slugs, and a Panamanian montane forest was estimated to have 7,500,000 land snails per acre. Despite this abundance, snails and slugs often pass unobserved. Land and freshwater species often stay hidden during the day and are active at night. Most marine species as well are nocturnal, and the shells of many of these species are so heavily covered with algae and other encrusting organisms that they may be mistaken for bits of rock.


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