ch25

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Chapter 25

PROKARYOTES:

DOMAINS

DOMAINS BACTERIA AND A

BACTERIA AND ARCHAEA

RCHAEA

All organisms are classified in three Domains, the highest taxon: Eukaryotes, Bacteria and Archaea.

here are t!o

here are t!o "ranches of prokaryote e#olution: Archaea and Bacteria $Eu"acteria%."ranches of prokaryote e#olution: Archaea and Bacteria $Eu"acteria%.

he Domain Bacteria includes the "acteria and the cyano"acteria, !hich !ere kno!n as "luegreen

algae.

he Archaea li#e in extreme en#ironments such as hot pools, acidic ha"

he Archaea li#e in extreme en#ironments such as hot pools, acidic ha" itats and anoxic en#ironments.

itats and anoxic en#ironments.

&rokaryotes are e#ery!here. &rokaryotes are e#ery!here.

hey ha#e a tremendous impact on life

hey ha#e a tremendous impact on life on Earth.on Earth. '.5 "illion years ago ((((( prokaryotic type cells. '.5 "illion years ago ((((( prokaryotic type cells.

).5 "illion years ago ((((( eukaryotic cells called acritarchs. ).5 "illion years ago ((((( eukaryotic cells called acritarchs.

STRUCTURE OF THE PORKARYOTIC CELL

&rokaryote Characteristics

•

&rokaryote cells are smaller than those of eukaryotes* they usually are "et!een ).+ and +.5 m.

-ycoplasmas are a"out +.2 m.

•

Almost all ha#e !alls that gi#e them one

Almost all ha#e !alls that gi#e them one of three "asic forms: rods $"acilli%, spheres $cocci% or

of three "asic forms: rods $"acilli%, spheres $cocci% or

coils $spirilla%.

•

Cyano"acteria ha#e mucilage sheaths to hold doens of cells together.

•

Cyano"acteria can produce specialied cells called

heterocystsheterocysts

and

ak!etesak!etes

..

•

hey lack mem"rane "ound organelles.

•

heir chromosomes are circular D/A molecules lacking protein and are located in an

heir chromosomes are circular D/A molecules lacking protein and are located in an area

area

called the

!"c#eo$!"c#eo$

..

•

0E1 lack split genes $no introns%.

•

&rokaryotes ha#e ri"osomes called +3 ri"osomes.

•

hey di#ide "y "inary fission.

•

hey lack mitosis and meiosis.

•

4ccasionally undergo genetic recom"ination through conugation $exchange of D/A% "y

means of pili $sing. pilus%.

•

hey often ha#e slimy capsules and

hey often ha#e slimy capsules and a flagellum, !hich allo!s limited motility.

a flagellum, !hich allo!s limited motility.

•

-any are colonial forming filaments "ut the cells remain independe

-any are colonial forming filaments "ut the cells remain independe nt !ithout any cytoplasmic

nt !ithout any cytoplasmic

connections.

•

/utrition is "y the a"sorption of food in soluti

/utrition is "y the a"sorption of food in solution through their cell !all and plasma mem"rane*

on through their cell !all and plasma mem"rane*

some o"tain energy through chemical reactions in#ol#ing inorganic su"stances $e.g. 0

22

3 or

3

22

+

''2(2(

thiosulfate ion% and others are photosynthetic.

CELL %ALL

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Eu"acteria: peptidogly

Eu"acteria: peptidoglycan !ith can !ith muramic acid cell muramic acid cell !all.!all. &ra'()ost*e ce##s

&ra'()ost*e ce##s

•

• hick !all, )5 6 7+nmlayer of hick !all, )5 6 7+nmlayer of peptidoglypeptidoglycan.can. •

• &eptidoglycan is a polysaccharide made &eptidoglycan is a polysaccharide made of /(acetylgucosamine and /(acetylmuramic acid.of /(acetylgucosamine and /(acetylmuramic acid. •

• he molecules peptide "ridges form crosslinks and the !all "ecomes one giant molecule.he molecules peptide "ridges form crosslinks and the !all "ecomes one giant molecule.

For more

For more details about thdetails about the structure e structure of the gram-posiof the gram-positive cell wall see:tive cell wall see: http:88stud

http:88student.cc"cmd.edu8courses8ent.cc"cmd.edu8courses8"io)9)8lecguid"io)9)8lecguide8unit)8prostrue8unit)8prostruct8c!.ct8c!.htmlhtml

&ra'(!e+at*e ce##s &ra'(!e+at*e ce##s

•

• he peptidoglycan layer is thin, he peptidoglycan layer is thin, a"out )+nm.a"out )+nm. •

• A layer of lipopolysaccharide $&3% co#ers the A layer of lipopolysaccharide $&3% co#ers the peptidoglycan layer.peptidoglycan layer. •

• he &3 does not contri"ute to the he &3 does not contri"ute to the strength of the !all "ut is semipermea"le in nature strength of the !all "ut is semipermea"le in nature and pre#entsand pre#ents

large proteins from approaching the cell

large proteins from approaching the cell mem"rane.mem"rane.

•

• &3 is extremely toxic to animals.&3 is extremely toxic to animals.

For more

For more details about thdetails about the structure e structure of the gram-negatof the gram-negative cell wall see:ive cell wall see: http:88stud

http:88student.cc"cmd.edu8courses8ent.cc"cmd.edu8courses8"io)9)8lecguid"io)9)8lecguide8unit)8prostrue8unit)8prostruct8gnc!ct8gnc!.html.html

Archae"acteria: cell !all incorporates other su"stances "ut no

Archae"acteria: cell !all incorporates other su"stances "ut no muramic acid.muramic acid.

FLA&ELLA FLA&ELLA

-any "acteria ha#e flagella -any "acteria ha#e flagella

Cyano"acteria and archaeans lack flagella. Cyano"acteria and archaeans lack flagella. he flagellum is hollo! and is anchored to the

he flagellum is hollo! and is anchored to the cell "y a set of cell "y a set of rings.rings. 4ne ring is attached in or

4ne ring is attached in or near the cell mem"rane and near the cell mem"rane and the other in the peptidoglycan layer.the other in the peptidoglycan layer. ;n gram(negati#e "acteria, a third set of

;n gram(negati#e "acteria, a third set of rings lies near the &3 rings lies near the &3 layer.layer. <lagella are located at one or

<lagella are located at one or "oth ends of the cell $polar "oth ends of the cell $polar flagellation% or o#er the entire surface $peritrichousflagellation% or o#er the entire surface $peritrichous flagellation%.

flagellation%.

hey rotate continuously and permit the

hey rotate continuously and permit the "acterium to s!im rapidly."acterium to s!im rapidly. -otile "acteria appear to sense certain stimuli and s!im to!ard or

-otile "acteria appear to sense certain stimuli and s!im to!ard or a!ay from them.a!ay from them.

CELL DI,ISION AND REPRODUCTION

his circular D/A mole

his circular D/A molecule is usually attached at one cule is usually attached at one point to the plasma mem"rane.point to the plasma mem"rane. he "acterial D/A is sometimes called the

he "acterial D/A is sometimes called the +e!o)hore+e!o)hore..

he chromosome of "acteria contains a"out )8)+++ of the D/A material found in eukaryotes, and has relati#ely he chromosome of "acteria contains a"out )8)+++ of the D/A material found in eukaryotes, and has relati#ely little protein associated !ith it.

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=eplication and translation is similar to

=eplication and translation is similar to eukaryotes.eukaryotes. &lasmids are small circular

&lasmids are small circular D/A moleculeD/A molecules found s found in "acteria.in "acteria.

•

• &lasmids are separate and independent from the chromosome&lasmids are separate and independent from the chromosome •

• &lasmids are capa"le of replication.&lasmids are capa"le of replication. •

• &lasmids ha#e small num"er of genes.&lasmids ha#e small num"er of genes. •

• hese genes are not normally needed for rhese genes are not normally needed for r eproduction or sur#i#al of the "acterium.eproduction or sur#i#al of the "acterium. •

• hese often encode anti"iotic resistance genes, hese often encode anti"iotic resistance genes, and genes encoding unusual meta"olisms.and genes encoding unusual meta"olisms. •

• &lasmids often consist of copies of one or &lasmids often consist of copies of one or at most #ery fe! at most #ery fe! different plasmiddifferent plasmids.s. •

• &lasmids can "e transferred "et!een cells "y conugation.&lasmids can "e transferred "et!een cells "y conugation.

CE D;>;3;4/ CE D;>;3;4/

Bacteria are haploid and they lack meiosis. Bacteria are haploid and they lack meiosis. heir reproduction is "y

heir reproduction is "y -!ary .sso!-!ary .sso!..

D/A repli

D/A replicates and a trans#erse !all is formed "y

cates and a trans#erse !all is formed "y the ingro!th of the plasma mem"rane and

the ingro!th of the plasma mem"rane and cell !all.

cell !all.

A "acterium may ha#e se#eral

A "acterium may ha#e se#eral circular chromosomes "efore the cell circular chromosomes "efore the cell di#ides.di#ides. E?C0A/@E 4< @E/E;C -AE=;A

E?C0A/@E 4< @E/E;C -AE=;A Tra!s.or'ato!

Tra!s.or'ato!: hen a "acterium dies and falls apart, : hen a "acterium dies and falls apart, its D/A "reaks into short chains containiits D/A "reaks into short chains containing a fe!ng a fe! genes* other "acteria cells a"sor" these small pieces and some may

genes* other "acteria cells a"sor" these small pieces and some may "e inserted into the cells D/A th"e inserted into the cells D/A thusus "ecoming part of the cel

"ecoming part of the cell genome. he foreign gl genome. he foreign genes can no! "e passed to denes can no! "e passed to daughter cells.aughter cells. Tra!s$"cto!

Tra!s$"cto!: a #irus in#ades the "acterium and : a #irus in#ades the "acterium and reproduces. 3mall pieces of the "acterium D/A can "ereproduces. 3mall pieces of the "acterium D/A can "e incorporated into the #irus. hen a #irus attacks a ne! "acterium, the

incorporated into the #irus. hen a #irus attacks a ne! "acterium, the D/A from the first "acterium is releasedD/A from the first "acterium is released and then is incorporated into the D/A of the second "acterium. Bacterium enymes usually destroy the foreign and then is incorporated into the D/A of the second "acterium. Bacterium enymes usually destroy the foreign D/A though.

D/A though. Co!/"+ato!

Co!/"+ato!: ;t occurs !hen t!o : ;t occurs !hen t!o cells of different mating types come together and genetic material iscells of different mating types come together and genetic material is transferred from one cell to the other "y means of a

transferred from one cell to the other "y means of a se0 )#"sse0 )#"s. he pilus is made of . he pilus is made of proteins.proteins. @enetic exchange has ne#er "een found in cyano"acteria.

@enetic exchange has ne#er "een found in cyano"acteria.

METABOLISM

&rokaryotes ha#e alternate methods for

&rokaryotes ha#e alternate methods for many meta"olic processes like photosynthesis, cellular respiration andmany meta"olic processes like photosynthesis, cellular respiration and sources of energy.

sources of energy.

-any "acteria utiliing a fe! simple sugars and essential minerals synthesie all their o!n #itamins, lipids, -any "acteria utiliing a fe! simple sugars and essential minerals synthesie all their o!n #itamins, lipids, amino acids and

amino acids and other macromolecules.other macromolecules. ;n many plant cells, many amino acids

;n many plant cells, many amino acids and lipids are synthesied in plastids, !hich are prokaryote(deri#edand lipids are synthesied in plastids, !hich are prokaryote(deri#ed organelles, and not in the

organelles, and not in the cytosol.cytosol. &04431/0E3;3

&04431/0E3;3

See Mauseth pages 240 and 241 See Mauseth pages 240 and 241 ..

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Cyano"acteria produce car"ohydrates using the C

Cyano"acteria produce car"ohydrates using the C'', Cal#in Cycle, of photosynt, Cal#in Cycle, of photosynthesis. his process is the same ashesis. his process is the same as

the one used "y land plants. his similarity is not surprising "ecause chloroplasts in all pro"a"ility arose from the one used "y land plants. his similarity is not surprising "ecause chloroplasts in all pro"a"ility arose from the endosym"iosis of c

the endosym"iosis of cyano"acteria.yano"acteria.

•

• Cyano"acteria ha#e chlorophyllCyano"acteria ha#e chlorophyll aa as as the photosynthetic pigment "ut lack chlorophyllthe photosynthetic pigment "ut lack chlorophyll bb.. •

• Accessory pigments are phyco"ilin, !hich a"sor"s light most strongly "et!een 2+ and 9+ nm, yello!Accessory pigments are phyco"ilin, !hich a"sor"s light most strongly "et!een 2+ and 9+ nm, yello!

one of the spectrum. one of the spectrum.

•

• And phycoerythrin, !ith maximum a"sorption of light at 55+ nm, "lue one And phycoerythrin, !ith maximum a"sorption of light at 55+ nm, "lue one of the spectrum.of the spectrum. •

• hey posses a &3 ; hey posses a &3 ; and &3 ;; and &3 ;; $photosys$photosystems%.tems%. •

• 4xygen is a 4xygen is a "yproduct of photosynthesis, oxygenic photosynthesis."yproduct of photosynthesis, oxygenic photosynthesis.

&urple and green

&urple and green "acteria do not ha#e "acteria do not ha#e chlorophychlorophyll a, ll a, "ut instead ha#e "acteriochlorophylls."ut instead ha#e "acteriochlorophylls.

•

• BacteriochlorophyBacteriochlorophylls are made lls are made of tetrapyrroles similar to chlorophyll "ut differ in some of the sideof tetrapyrroles similar to chlorophyll "ut differ in some of the side

chains and functional groups. chains and functional groups.

•

• here are carotenoids present that act as accessory pigments.here are carotenoids present that act as accessory pigments. •

• here is only a &3 ; present* &3 ;; is a"sent and electrons cannot "e put "ack onto thehere is only a &3 ; present* &3 ;; is a"sent and electrons cannot "e put "ack onto the

"acteriochlorophy

"acteriochlorophyll. ll. he original ehe original electron comes "ack through lectron comes "ack through a series of carriers, so the electa series of carriers, so the electron flo!ron flo! is cyclic.

is cyclic.

•

• uinone carriers pump electrons from the cytoplasm into the periplasm creating an electrochemicaluinone carriers pump electrons from the cytoplasm into the periplasm creating an electrochemical

gradient that is used to generated A&. his is a chemiosmotic process. gradient that is used to generated A&. his is a chemiosmotic process.

•

• /o oxygen is formed /o oxygen is formed, anoxygenic photosy, anoxygenic photosynthesis.nthesis.

Bacterial photosynthesis is a proton pumping process. Bacterial photosynthesis is a proton pumping process. /;=4@E/ <;?A

/;=4@E/ <;?A;4/;4/ /itrogen is an ess

/itrogen is an essential element for the makential element for the making of proteins.ing of proteins. Atmospheric nitrogen is mostly inert and

Atmospheric nitrogen is mostly inert and cannot "e used directly cannot "e used directly "y most organisms."y most organisms. &lants take it the form

&lants take it the form of ammonia and nitrate.of ammonia and nitrate. /itrogen in org

/itrogen in organic compounds of dead anianic compounds of dead animals and plants is una#mals and plants is una#aila"le to plants and maila"le to plants and must transformed "yust transformed "y decomposers into inorganic

decomposers into inorganic compounds.compounds.

&roteins found in dead plant and animals are "roken do!n

&roteins found in dead plant and animals are "roken do!n "y "acteria and fungi, and oxidied to C4"y "acteria and fungi, and oxidied to C422, 0, 0224 and4 and

/0

/0'' !ith yield of energy. Examples: !ith yield of energy. Examples: •

• =/0=/0₂₂ $4rganic /%  heterotrophic $ammonifying% "acteria F /0 $4rganic /%  heterotrophic $ammonifying% "acteria F /0_'_' $ammonia%  = $ammonia%  = $organic molecules%.$organic molecules%. •

• /0 /0₂₂C0C0₂₂C440  )G 4C440  )G 4₂₂ F 2C4 F 2C4₂₂  0  0₂₂4  /04  /0_'_'  )7 kcal  )7 kcal

;n soils /0

;n soils /0'' is rapidly con#erted to /0 is rapidly con#erted to /099 !hen hydrogen ions are plentiful $p0 H .5%. !hen hydrogen ions are plentiful $p0 H .5%.

/0

/0'' and /0 and /099 are a"sor"ed "y plant r are a"sor"ed "y plant roots and incorporate into amino acids and passed through the food chain.oots and incorporate into amino acids and passed through the food chain.

Ntr.cato!: Ntr.cato!:

During nitrification /0

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/itrosomas "acter

/itrosomas "acteria use ammonia as their sole souia use ammonia as their sole source of energyrce of energy..

•

• /0 /0₉₉  4  4₂₂ F 0/4 F 0/4₂₂  )G 0  )G 0₂₂ F /4 F /4₂₂)()(  90  90  )5 kcal  )5 kcal

/itro"acter uses th

/itro"acter uses the energy left in nitre energy left in nitrite "y oxidiing it tite "y oxidiing it to nitrate.o nitrate.

•

• /4 /4₂₂)()(  )G 4  )G 4₂₂ F /4 F /4_'_')()(  energy.  energy.

/itrosomas oxid

/itrosomas oxidies '5 moles of nitrogen ies '5 moles of nitrogen for each mole of C4for each mole of C422 assimilated* /itro"acter oxidies )++ moles of assimilated* /itro"acter oxidies )++ moles of

nitrogen for e#ery mole of C4

nitrogen for e#ery mole of C422 assimilated. assimilated.

/itrates are a"sor"ed "y

/itrates are a"sor"ed "y plants and incorpoplants and incorporated into organrated into organic acids.ic acids. -ost plant species prefer nitrate to ammonium.

-ost plant species prefer nitrate to ammonium. /itrates leach mo

/itrates leach more readily than ammonium and e#enre readily than ammonium and e#entually may end in aIuattually may end in aIuatic ecosystems.ic ecosystems.

3J<J= BACE=;A 3J<J= BACE=;A

3ulfur is rarely a limiting nutrient in the en#ironment and is

3ulfur is rarely a limiting nutrient in the en#ironment and is usually a"sor"ed as 34usually a"sor"ed as 3499(2(2 . .

3ulfate is a"sor"ed "y plants and incorporated into sulfur containing amino acids, !hich are passed do!n the 3ulfate is a"sor"ed "y plants and incorporated into sulfur containing amino acids, !hich are passed do!n the food chain.

food chain.

Decomposition of organisms releases sulfate and hydrogen sulfide Decomposition of organisms releases sulfate and hydrogen sulfide

3ulfate(reducing "acteria release sulfur found in dead organic matter as 0

3ulfate(reducing "acteria release sulfur found in dead organic matter as 0223 and 343 and 3499(2(2..

&urple "acteria found in salt marshes and estuarine mudflats utilie 30

&urple "acteria found in salt marshes and estuarine mudflats utilie 3022 as an oxygen acceptor to reduce C4 as an oxygen acceptor to reduce C422 . . •

•  C4 C4₂₂  ' 0  ' 0₂₂3   03   0₂₂4  sunlight4  sunlight →→ C C__00₎₂₎₂44__  ' 0  ' 0₂₂3434_{9 →}₉→ 0 0  34  34₉₉(2(2

CLASSIFICATION OF PROKARYOTES CLASSIFICATION OF PROKARYOTES

Because prokaryotes are mostly unicellular and lack a #ariety of anatomical and

Because prokaryotes are mostly unicellular and lack a #ariety of anatomical and morphological traits, theirmorphological traits, their classification has "een "ased mostly on

classification has "een "ased mostly on their meta"olism, !all chemistry, their a"ility to carry their meta"olism, !all chemistry, their a"ility to carry onon photosynth

photosynthesis, and sensiti#ity esis, and sensiti#ity to oxygen.to oxygen. /ucleotide seIuen

/ucleotide seIuencing is no! the mocing is no! the most relia"le techniIue usst relia"le techniIue used in phylogenetic aned in phylogenetic analysis.alysis.

•

• )3 ri"osomal =/A is the most )3 ri"osomal =/A is the most commonly seIuenced nucleic acid.commonly seIuenced nucleic acid. •

• =i"osomes are present in =i"osomes are present in all li#ing organisms.all li#ing organisms. •

• =i"osomal gene mutations appear to =i"osomal gene mutations appear to "e almost al!ays lethal. "e almost al!ays lethal. herefore, )3 r=/A is extremelyherefore, )3 r=/A is extremely

conser#ati#e and e#ol#es #ery slo!ly. conser#ati#e and e#ol#es #ery slo!ly.

•

• arge portions of )3 rarge portions of )3 r=/A are identical in organisms that di#erged long time =/A are identical in organisms that di#erged long time ago.ago.

D4-A;/ A=C0AEA D4-A;/ A=C0AEA

he archaeans are distinct meta"olically "ut their structure is #ery similar to that of

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•

• Archaeans lack mem"rane "ound Archaeans lack mem"rane "ound organelles.organelles. •

• hey ha#e a +3 ri"osome they ha#e a +3 ri"osome type.ype. •

• hey ha#e cell !all.hey ha#e cell !all.

hey differ from "acteria in: hey differ from "acteria in:

•

• heir !alls ha#e protein, heir !alls ha#e protein, glycoproteins or polysaccharide, "ut lack true peptidoglycan and therefore,glycoproteins or polysaccharide, "ut lack true peptidoglycan and therefore,

they are immune to most

they are immune to most anti"iotics that interfere !ith "acteria !all synthesis.anti"iotics that interfere !ith "acteria !all synthesis.

•

• -em"ranes !ith unusual lipids that ha#e their fatty acids attached to glycerol !ith ether linkages rather-em"ranes !ith unusual lipids that ha#e their fatty acids attached to glycerol !ith ether linkages rather

than ester linkages. than ester linkages.

•

• 3ome lipids are diglycerols, in !hich each end of 3ome lipids are diglycerols, in !hich each end of the fatty acid is linked to a the fatty acid is linked to a glycerol.glycerol.

Archaea li#e in extreme en#ironments like salt pools, sulfur(rich hot acid pools, and anaero"ic 0

Archaea li#e in extreme en#ironments like salt pools, sulfur(rich hot acid pools, and anaero"ic 0 223(rich3(rich

en#ironments like se!age treatment plants. en#ironments like se!age treatment plants. D4-A;/ BACE=;A

D4-A;/ BACE=;A

Bacteria ha#e a much greater

Bacteria ha#e a much greater di#ersity of meta"olic path!ays than do the archaeans.di#ersity of meta"olic path!ays than do the archaeans. he follo!ing groups are

he follo!ing groups are pro"a"ly polyphyletic.pro"a"ly polyphyletic. &#$!+ -actera

&#$!+ -actera

@liding "acteria lack flagella, and mo#e only !hen in contact !ith a

@liding "acteria lack flagella, and mo#e only !hen in contact !ith a solid surface.solid surface. 3ome consists of long filaments of short disk(like cells.

3ome consists of long filaments of short disk(like cells.

•

• Baggiatoa Baggiatoa oxidies 0 oxidies 0₂₂3 first to 33 first to 3++ then to 34 then to 34₉₉2(2(.. •

• ;t forms mutualistic associations !ith cattails, rice and plants that li#e in stagnant !ater* it recei#es;t forms mutualistic associations !ith cattails, rice and plants that li#e in stagnant !ater* it recei#es

nutrients from the plant !hile protecting its roots for 0 nutrients from the plant !hile protecting its roots for 0223.3. •

• !tophaga!tophaga digests cellulose and chitin. digests cellulose and chitin. •

• Cellulases are part of the cell Cellulases are part of the cell en#elope and are not released.en#elope and are not released. •

• hey are important in hey are important in humus formation and soil ecology.humus formation and soil ecology.

Ntro+e! 'eta-o#1!+ -actera Ntro+e! 'eta-o#1!+ -actera /itrogen(fixing

/itrogen(fixing "acteria con#ert atmos"acteria con#ert atmospheric nitrogen $/pheric nitrogen $/22% to nitrites $/4% to nitrites $/422)()(%, nitrates $/4%, nitrates $/4'')()( % and ammonia % and ammonia

$/0 $/0''%.%.

/itrifying "acter

/itrifying "acteria con#ert /0ia con#ert /0'' to /4 to /422)()( and /4 and /4'')()(..

Denitrifying "acteria con#ert nitrates in the soil to atmospheric nitrogen, / Denitrifying "acteria con#ert nitrates in the soil to atmospheric nitrogen, /2.2.

;n natural ecosystems, a"out )2++ species of "acteria, cyano"acteria and legumes are

;n natural ecosystems, a"out )2++ species of "acteria, cyano"acteria and legumes are in#ol#ed in nitrogenin#ol#ed in nitrogen fixation.

fixation.

•

• "hi#obium "hi#obium is the "acterium genus associated !ith legumes. is the "acterium genus associated !ith legumes. "hi#obium "hi#obium is aero"ic. is aero"ic. •

• $#otobacter $#otobacter and and lostridiumlostridium are free(li#ing aero"ic genera found in are free(li#ing aero"ic genera found in the soil.the soil. •

• hese three genera reIuire -o as hese three genera reIuire -o as an acti#ator.an acti#ator. •

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•

• A"out 9+ kno!n species of cyano"acteria are important nitrogen fixers.A"out 9+ kno!n species of cyano"acteria are important nitrogen fixers. •

• hey are found in terrestrial and aIuatic ha"itats and reIuire hey are found in terrestrial and aIuatic ha"itats and reIuire -o for nitrogen fixation.-o for nitrogen fixation. •

• hey are acti#e o#er a hey are acti#e o#er a !ide range of temperatures, from polar !ide range of temperatures, from polar seas to fresh!ater ponds to hot springs.seas to fresh!ater ponds to hot springs. •

• 4ther plants are also 4ther plants are also in#ol#ed in nitrogen fixation: some epiphytes in tropical in#ol#ed in nitrogen fixation: some epiphytes in tropical forests, epiphyllic algaeforests, epiphyllic algae

and "acteria, and phyco"iont algae in lichens. and "acteria, and phyco"iont algae in lichens.

Myco)#as'as Myco)#as'as

-ycoplasmas are the smallest li#ing cells kno!: +.2 6 +.' -ycoplasmas are the smallest li#ing cells kno!: +.2 6 +.' m.m.

•

• hey lack cell !all.hey lack cell !all. •

• >aria"le shape: filamentous, coccoid, and rod(shaped.>aria"le shape: filamentous, coccoid, and rod(shaped. •

• -any are pathogenic to plants and animals.-any are pathogenic to plants and animals.

Cya!o-actera Cya!o-actera

Cyano"acteria #ary in sie from cells of

Cyano"acteria #ary in sie from cells of the sie of typical "acteria to the the sie of typical "acteria to the largest cell of prokaryotes,largest cell of prokaryotes, %scillator!%scillator! princeps

princeps, !hich is + m , !hich is + m in diameter.in diameter.

3ome are unicellular "ut the maority exists in large groups held together "y mucilage, or

3ome are unicellular "ut the maority exists in large groups held together "y mucilage, or attached to surfacesattached to surfaces forming long filaments.

forming long filaments.

heir cell !all is similar of that of

heir cell !all is similar of that of gram(negati#e "acteria and produce mucilage.gram(negati#e "acteria and produce mucilage. Cyano"acteria seem to "e the most closely related to

Cyano"acteria seem to "e the most closely related to the organisms that ga#e rise to the chloroplasts ofthe organisms that ga#e rise to the chloroplasts of eukaryotes.

eukaryotes.

hey all ha#e chlorophyll a and &3

hey all ha#e chlorophyll a and &3 ;;, and produce oxygen.;;, and produce oxygen. Proch#oro)hytes

Proch#oro)hytes are a are a group of cyano"acteria that ha#e "oth chlorophyll a and chlorophyll ", and lackgroup of cyano"acteria that ha#e "oth chlorophyll a and chlorophyll ", and lack phycol"ilin

phycol"ilins.s.

-any are nitrogen fixing, a process that takes place

-any are nitrogen fixing, a process that takes place inin heterocystsheterocysts. ;f there is /0. ;f there is /099 in the en#ironment, in the en#ironment,

heterocysts do not de#elop, "ut if it is lacking, heterocysts de#elop from #egetati#e cells. heterocysts do not de#elop, "ut if it is lacking, heterocysts de#elop from #egetati#e cells. hey may form

hey may form ak!etesak!etes, large thick !all cells deri#ed from #egetati#e cells and , large thick !all cells deri#ed from #egetati#e cells and used to sur#i#e periods ofused to sur#i#e periods of harsh en#ironment.

harsh en#ironment.

-ost species are free li#ing, "ut some

-ost species are free li#ing, "ut some form mutualistic relationshipform mutualistic relationships !ith plants:s !ith plants: $nabaena $nabaena and and $#olla $#olla and and cycad roots*

cycad roots* &ostoc &ostoc and and $nthocero $nthoceross..

3ome can !ithstand #ery harsh periods of en#ironmental change,, like extreme desiccation or #ery

3ome can !ithstand #ery harsh periods of en#ironmental change,, like extreme desiccation or #ery hot pools. ;nhot pools. ;n hot pools, they extract lime from !ater

hot pools, they extract lime from !ater and form rock(like masses.and form rock(like masses.

hey form stromatolites in !arm !aters. 3tromatolites are large column like structures of "acteria encrusted hey form stromatolites in !arm !aters. 3tromatolites are large column like structures of "acteria encrusted !ith CaC4

!ith CaC4''. he most ancient stromatolites are thought to "e '.2 . he most ancient stromatolites are thought to "e '.2 "illion years old."illion years old.

Cyano"acteria gro! in "oth salt and fresh !ater and ar

Cyano"acteria gro! in "oth salt and fresh !ater and ar e capa"le of forming large "looms !hen the conditionse capa"le of forming large "looms !hen the conditions are good.

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