,ACCESS Test Bank for Brock Biology of Microorganisms 16th EditionMadig
c c c c c c c c c c
an
CHAPTER
The Microbial World
c c
1
Summary
Chapterc1cintroducescthecstudycofcmicrobiologycforcstudents,cmostcofcwhomcwillcha
vechadclittlecorcnocexposurectocthecsubject.cConsequently,cyouchavecacgoodcopportun
ityctocprovidecancoverviewcofcmicrobiologycthatcdemonstratescthecimportantcrolescm
icroorganismsc(orcmicrobes)cplaycinchumancactivitiescandcincthececologycofcthecentir
ecbiosphere.cThecabilitycofcmicroorganismsctocexistcindependentlycincnaturecascfree-
livingccellscwithinclargercmicrobialccommunitiesc(Figurec1.1)cconferscenormouscada
ptivecadvantagescoverccellscofcmacroorganisms,cwhichcarecincapablecofcancindepend
entcexistence.
1.1 | Microorganisms, Tiny Titans of the Earth
c c c c c c
Describectocstudentscwayscincwhichcmicrobiologycservescascbothcacbasiccandcancappliedcbiolo
gicalcscience.cFromcacbasiccperspective,cthecstudycofcmicroorganismscinclaboratorycculturecha
scbeencthecprimarycmeanscbycwhichcthecfundamentalcgeneticcandcbiochemicalcpropertiescofcli
vingccellschavecbeencrevealed.cFromcancappliedcperspective,cmicroorganismscdirectlycaffectcth
ecqualitycofchumanclifecincbothcdetrimentalcandcbeneficialcways.cAlthoughcmicroorganismscar
ectheccausativecagentscofcsomecofcthecmostcimportantchuman,canimal,candcplantcdiseases,ctheyc
arecalsocusedcforcthecindustrialcproductioncofcantibiotics,cpharmaceuticals,candcfoods.cMicrob
escarecalsocincreasinglycbeingcusedcforcbeneficialcpurposescascdiversecascbioremediationcofcpo
llutedcsites,cgenectherapiescforcgeneticcdiseases,candcthecproductioncofcbiofuels.cMicrobiology
ciscthereforecacsciencecofcfar-
reachingcscope,cwithcapplicationscthatcaffectcthecqualitycofchumanclifecincacvarietycofcwaysc(Fi
gurec1.2).
Youcshouldcalsocemphasizectocstudentscthecimportancecofcmicroorganismscincthecemergen
cecandcmaintenancecofchighercformscofclife.cFromcthecproductioncofcmolecularcoxygenc(bycc
yanobacteria)ctocthecbiogeochemicalccyclingcofckeycelements,csuchcasccarbon,cnitrogen,candc
sulfur,cmicroorganismscplaycacmajorcrolecincsustainingcallclifeconcthecplanet.cPointcoutcincyou
rccoursecintroductioncthatcforcallcthecreasonscsummarizedcincthiscsection,cmicrobiologyciscthec
foundationcofcallcbiologicalcsciences.
1.2 | Structure and Activities of Microbial Cells
c c c c c c
Becausecmicroorganismscgenerallycexistcascfree-
livingccells,citciscimportantctocdiscussctheccharacteristicscofccellscincgeneral.cEmphasizecthatcallccellsce
xhibitcacnonrandomcorganizationcwithcacsemipermeablecmembranecboundarycthatcencompassescancint
ernalcsystemcthatciscnotcincequilibriumcwithcitscenvironment.cPointcoutcthatcprokaryoticccellsc(i.e.,callc
BacteriacandcArchaea)cdocnotccontaincmembrane-
bound,cinternalcorganellescasctraditionallycdescribedcforceukaryoticccellsc(thecEukarya;cFigurec1.4).cI
ncparticular,cthecorganizationcofcprokaryoticcDNAcascacsinglecchromosomecincan
Copyrightc©c2021cPearsoncEducation,cInc. CHAPTERc1cThecMicrobialcWorld 1
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c c c c c c c c c c
an
arrangementccalledcacnucleoid,cancaggregatedcmasscofcgeneticcmaterialcwithinctheccytoplasm,ciscincstarkc
contrastctoctheccompartmentalized,cmultichromosomalcconfigurationctypicallycfoundcinceukaryotes.cHo
wever,cdespitecthecstructuralcandcmorphologicalcsimilaritiescofcBacteriacandcArchaea,cmakecsurecyourcst
udentscarecawarecearlyconcthatcthesecgroupscofcmicroorganismschavecquitecdistinctcevolutionaryclineage
scandcare,ctherefore,cnotccloselycrelatedconcacgeneticclevel.cThiscconceptciscdiscussedcincmorecdetailcincSe
ctionc1.5.
Thecabilitycofccellsctocmaintaincacthermodynamiccenergycflowcfarcfromcequilibriumcdefin
escwhatcwecreferctocascaclivingcsystem.cAllclivingcsystemscdisplaycsomecformcofcenzyme-
drivencmetabolismcincwhichcbothcenergy-yieldingc(catabolic)candcenergy-
cconsumingc(anabolic)cbiochemicalcreactionscareccatalyzedcconcurrently.cThesecchemicalctr
ansformationscallowcforcbiosynthesiscofcnewccellcstructurescand,cultimately,ccellcdivisionc(m
icrobialcgrowth).cFigurec1.5cshowsctheccharacteristicscthatcdefineccellularclife,csomecofcwhic
hcarecuniversalc(e.g.,cmetabolismcandcevolution)candcsomecofcwhichcoccurconlycincsomeccell
sc(e.g.,cdifferentiationcandcmotility).
1.3 | Cell Size and Morphology
c c c c
Thecpresentationcincthectextcofcthecsignificancecofcbeingcsmallciscancimportantcconceptcforcstudentsctoc
internalizecasctheycbeginctheircstudycofcmicrobiology.cTablec1.1cshowscthecwidecsizecrangecvariability
cofcbacterialccells,cwhichcrangecfromcacdiametercofcaboutc0.2cµmctocoverc700cµm.cUsecthectwocexampl
escofcunusuallyclargecbacteriacdiscussedcincthiscsectionctocillustratectheccurrentcupperclimitcofcbacterial
ccellcsize:c(1)cthecsurgeonfishcgutcsymbiontcEpulopisciumcfishelsonic(>600cµmcinclength;cFigurec1.6a)
,candc(2)cthecsulfurcchemolithotrophcThiomargaritacnamibiensisc(750cµm;cFigurec1.6b).cThecevolutio
naryc“rationale”cforcthecexistencecofcunusuallyclarge-
celledcbacteriaciscacmysterycwhenconecconsiderscthatcthecmetaboliccratecofcaccellcvariescinverselycwithc
thecsquarecofcitscsize.cAskcyourcstudentscforcideascand/orchypothesescthatcmightcexplaincthecselectivec
advantagecofclargeccellcsizecincthesectwocprokaryotes.
Thecfactcthatcbacteriaccanclivecindependentlycascsingleccellsc(unlikecancindividualccellcofcacmulticel
lularcorganism)csuggestscthatctheycmustcpossesscsomeccapabilitiescthatcprovidecacselectivecadvantagec
overctheircmulticellularccounterpartscthatcensurectheircsurvivalconcthecplanet.cSmallccellschavecmorecsu
rfacecareactocvolumec(i.e.,cachighercsurface-to-
volumecratio),candcthiscalonecconferscmanycofcthecevolutionarycadvantagescofcbeingcsmall,cincludingct
hecfollowing:
● Rapidcnutrientcandcwastectransportcintocandcoutcofctheccellcallowscforcfastercmetaboliccratescandcg
rowthcrates.
● Rapidcgrowthcratescresultcincthecrapidcproductioncofclargecpopulationscofccells.cThesecpopulation
s,cincturn,ccancgreatlycaffectcthecphysiochemicalcconditionscofcancecosystemcwithincacshortctimecp
eriod.
● Transportcratescarecacfunctioncofcthecsurfacecareacofctheccytoplasmiccmembranecrelativectoccellcvol
ume.cUsecFigurec1.7ctocmathematicallycdemonstratectocstudentscthatcthecsurfacecareacofcacsphereci
scacfunctioncofcthecsquarecofcthecradius,cwhereascthecvolumecofcacsphereciscacfunctioncofctheccubecofcth
ecradius.cThiscmeanscthatcthecsurface-to-
volumecratiocofcacsphericalccellccancbecexpressedcasc3/r,cwherecrcequalscthecradiuscofctheccell.cTher
efore,caccoccusccellchavingcacsmallercradiuschascmorecsurfacecareacpercvolumecand,cthus,cmoreceffic
ientctransportccapabilities,cthancaccoccusccellchavingcaclargercradius.
● Ratescofcevolutionarycchangecarechighercincsmaller,cfastercgrowingchaploidccellscthancinclarger,
2 INSTRUCTOR'ScMANUALcFORcBROCKcBIOLOGYcOFcMICROORGANISMS,c16e Copyrightc©c2021cPearsoncEducation,cInc.
mynursytest.store
, ACCESS Test Bank for Brock Biology of Microorganisms 16th EditionMadig
c c c c c c c c c c
an
slowercgrowingcdiploidccells.cThiscallowscforcgreatercadaptivecpotentialcthroughcrapidcselectioncf
orcadvantageouscmutationscandccounterselectioncagainstcdeleteriouscmutations.
Thectheoreticalclowerclimitcofcsizecforcaclivingccellcisclikelycnearc0.2cμmcincdiameter.cThisclimitcisc
dictatedcbycthecamountcofcvolumecrequiredctoccontainccellularccomponentscthatcareccrucialcforc
maintainingclife,csuchcasc(1)cthecpresencecofcessentialcgenesconcthecchromosome;c(2)chavingcacs
ufficientcnumbercofcribosomes;candc(3)ccontainingcacminimalcnumbercofcmetabolic,cstructural,ca
ndctransportcproteinscwithinctheccell.cChallengecstudentsctoclistcthesecandcothercmolecularccomp
onentscthatcaccellcwouldchavectoccontainctocmaintainclife.cRemindcstudentscthatcsomeccellscarecp
arasiticcincnature.cInformcthemcthat,cmuchclikecviruses,csuchcmicroorganismscoftenchavecstream
linedcgenomescthatclackcimportantcgenescandcmaycmakecthemcdependentcuponctheirchostscforcgr
owth.cCancsuchcorganismsctrulycbecconsideredcliving?cThiscmightcmakecacgoodcoutsidecprojectcf
orcgroupcdebate,crequiringcstudentsctocviewctheccellcascacthree-
dimensionalcphysicalcstructurecconstrainedcincspacecandctocresearchcacproblemcthatcisccurrentl
ycbeingcdebated.
UsingcFigurec1.8,cpointcoutcthecthreecmajorcmorphologiescofcprokaryoticccellsc(coccus,crod,candcspiril
lum).cInformcyourcstudentscthat,cincsomecspecies,ctheccellscremaincattachedcfollowingccellcdivision,cgi
vingcrisectocdifferentcarrangementscthatcarecoftencgenus-
specific.cForcexample,ccoccusccellscmaycexistcasclongc chainsc(Streptococcus)corcgrapelikecclustersc(St
aphylococcus).cLessccommonccellcmorphologiescalsocexist,csuchcascspirochetes,cappendagedc(buddin
g)cbacteria,candcfilamentouscbacteriac(Figurec1.8).cStressctocstudentscthatcthesecmorphologiescareconlyc
representativecofcthosecfoundcincnature.cOthercunusualcshapeschavecalsocbeencdescribedcincrareccasesc(
e.g.,csquare-candcstar-shapedccells!).
Beforecthecmolecularcera,cmorphologicalcandcphysiologicalcpropertiescwerecusedctocclassifycbacte
rialcspecies.cHowever,cwecnowcknowcthatctheseccriteriacarecpoorcpredictorscofcevolutionarycrelationsh
ips.cForcexample,ccertaincspeciescofcArchaeacmaycappearcidenticalcincsizecandcshapectocspeciescofcBac
teriacundercthecmicroscope,cbutcthesecorganismscarecofcdifferentcphylogeneticcdomainscandcthuscarecn
otccloselycrelatedctoconecanotherconcancevolutionarycbasis.cTheccellcmorphologycofcacparticularcspecie
sciscprimarilycacresultcofcselectivecpressurescincacgivenchabitatcthatcfavoredcacparticularccellcshapecforce
nhancedcreproductivecsuccess.
1.4 | An Introduction to Microbial Life
c c c c c
Thiscsectioncofcthecchaptercprovidescancoverviewcofctheckeycfactorscthatcdistinguishccellscofcthecdiffer
entcdomainscofclife,candchowcthesecarecfurthercdistinguishedcfromcacellularcmicrobes—
thecviruses.cFigurec1.9cbeautifullyccomparescthecsizecrelationshipscofcacvarietycofcmicrobialcformscan
dccomponents,cfromcthecuncommonlyclargecbacteriumcEpulopisciumcfishelsonicatcaclengthcofc600cμmc
(seecalsocFigurec1.6)ctocindividualcproteinscatctheclimitcofcresolutioncofcancelectroncmicroscope
(0.2cnm).cMentioncthecfollowingckeycpoints:
● ThecgreatestcdiversitycofcBacteriacandcArchaeachascnevercbeencculturedcinctheclaboratory,candcs
uchcspeciescarecknownconlycbyctheircDNAcsequencescfoundcincenvironmentalcsamples.
● Althoughctheycbothchavecacprokaryoticccellcstructure,cBacteriacandcArchaeacarecnotccloselycr
elated.cOncacmolecularclevel,cArchaeachavecmuchcinccommoncwithctheceukaryotes.
● Thecmetaboliccandcphysiologicalcdiversitycofcmicroorganisms,cespeciallycthecBacteriacand
Archaea,ciscastonishing,cwithcspeciesccapablecofcaerobiccrespiration,canaerobiccrespiration,
Copyrightc©c2021cPearsoncEducation,cInc. CHAPTERc1cThecMicrobialcWorld 3
mynursytest.store
c c c c c c c c c c
an
CHAPTER
The Microbial World
c c
1
Summary
Chapterc1cintroducescthecstudycofcmicrobiologycforcstudents,cmostcofcwhomcwillcha
vechadclittlecorcnocexposurectocthecsubject.cConsequently,cyouchavecacgoodcopportun
ityctocprovidecancoverviewcofcmicrobiologycthatcdemonstratescthecimportantcrolescm
icroorganismsc(orcmicrobes)cplaycinchumancactivitiescandcincthececologycofcthecentir
ecbiosphere.cThecabilitycofcmicroorganismsctocexistcindependentlycincnaturecascfree-
livingccellscwithinclargercmicrobialccommunitiesc(Figurec1.1)cconferscenormouscada
ptivecadvantagescoverccellscofcmacroorganisms,cwhichcarecincapablecofcancindepend
entcexistence.
1.1 | Microorganisms, Tiny Titans of the Earth
c c c c c c
Describectocstudentscwayscincwhichcmicrobiologycservescascbothcacbasiccandcancappliedcbiolo
gicalcscience.cFromcacbasiccperspective,cthecstudycofcmicroorganismscinclaboratorycculturecha
scbeencthecprimarycmeanscbycwhichcthecfundamentalcgeneticcandcbiochemicalcpropertiescofcli
vingccellschavecbeencrevealed.cFromcancappliedcperspective,cmicroorganismscdirectlycaffectcth
ecqualitycofchumanclifecincbothcdetrimentalcandcbeneficialcways.cAlthoughcmicroorganismscar
ectheccausativecagentscofcsomecofcthecmostcimportantchuman,canimal,candcplantcdiseases,ctheyc
arecalsocusedcforcthecindustrialcproductioncofcantibiotics,cpharmaceuticals,candcfoods.cMicrob
escarecalsocincreasinglycbeingcusedcforcbeneficialcpurposescascdiversecascbioremediationcofcpo
llutedcsites,cgenectherapiescforcgeneticcdiseases,candcthecproductioncofcbiofuels.cMicrobiology
ciscthereforecacsciencecofcfar-
reachingcscope,cwithcapplicationscthatcaffectcthecqualitycofchumanclifecincacvarietycofcwaysc(Fi
gurec1.2).
Youcshouldcalsocemphasizectocstudentscthecimportancecofcmicroorganismscincthecemergen
cecandcmaintenancecofchighercformscofclife.cFromcthecproductioncofcmolecularcoxygenc(bycc
yanobacteria)ctocthecbiogeochemicalccyclingcofckeycelements,csuchcasccarbon,cnitrogen,candc
sulfur,cmicroorganismscplaycacmajorcrolecincsustainingcallclifeconcthecplanet.cPointcoutcincyou
rccoursecintroductioncthatcforcallcthecreasonscsummarizedcincthiscsection,cmicrobiologyciscthec
foundationcofcallcbiologicalcsciences.
1.2 | Structure and Activities of Microbial Cells
c c c c c c
Becausecmicroorganismscgenerallycexistcascfree-
livingccells,citciscimportantctocdiscussctheccharacteristicscofccellscincgeneral.cEmphasizecthatcallccellsce
xhibitcacnonrandomcorganizationcwithcacsemipermeablecmembranecboundarycthatcencompassescancint
ernalcsystemcthatciscnotcincequilibriumcwithcitscenvironment.cPointcoutcthatcprokaryoticccellsc(i.e.,callc
BacteriacandcArchaea)cdocnotccontaincmembrane-
bound,cinternalcorganellescasctraditionallycdescribedcforceukaryoticccellsc(thecEukarya;cFigurec1.4).cI
ncparticular,cthecorganizationcofcprokaryoticcDNAcascacsinglecchromosomecincan
Copyrightc©c2021cPearsoncEducation,cInc. CHAPTERc1cThecMicrobialcWorld 1
mynursytest.store
,ACCESS Test Bank for Brock Biology of Microorganisms 16th EditionMadig
c c c c c c c c c c
an
arrangementccalledcacnucleoid,cancaggregatedcmasscofcgeneticcmaterialcwithinctheccytoplasm,ciscincstarkc
contrastctoctheccompartmentalized,cmultichromosomalcconfigurationctypicallycfoundcinceukaryotes.cHo
wever,cdespitecthecstructuralcandcmorphologicalcsimilaritiescofcBacteriacandcArchaea,cmakecsurecyourcst
udentscarecawarecearlyconcthatcthesecgroupscofcmicroorganismschavecquitecdistinctcevolutionaryclineage
scandcare,ctherefore,cnotccloselycrelatedconcacgeneticclevel.cThiscconceptciscdiscussedcincmorecdetailcincSe
ctionc1.5.
Thecabilitycofccellsctocmaintaincacthermodynamiccenergycflowcfarcfromcequilibriumcdefin
escwhatcwecreferctocascaclivingcsystem.cAllclivingcsystemscdisplaycsomecformcofcenzyme-
drivencmetabolismcincwhichcbothcenergy-yieldingc(catabolic)candcenergy-
cconsumingc(anabolic)cbiochemicalcreactionscareccatalyzedcconcurrently.cThesecchemicalctr
ansformationscallowcforcbiosynthesiscofcnewccellcstructurescand,cultimately,ccellcdivisionc(m
icrobialcgrowth).cFigurec1.5cshowsctheccharacteristicscthatcdefineccellularclife,csomecofcwhic
hcarecuniversalc(e.g.,cmetabolismcandcevolution)candcsomecofcwhichcoccurconlycincsomeccell
sc(e.g.,cdifferentiationcandcmotility).
1.3 | Cell Size and Morphology
c c c c
Thecpresentationcincthectextcofcthecsignificancecofcbeingcsmallciscancimportantcconceptcforcstudentsctoc
internalizecasctheycbeginctheircstudycofcmicrobiology.cTablec1.1cshowscthecwidecsizecrangecvariability
cofcbacterialccells,cwhichcrangecfromcacdiametercofcaboutc0.2cµmctocoverc700cµm.cUsecthectwocexampl
escofcunusuallyclargecbacteriacdiscussedcincthiscsectionctocillustratectheccurrentcupperclimitcofcbacterial
ccellcsize:c(1)cthecsurgeonfishcgutcsymbiontcEpulopisciumcfishelsonic(>600cµmcinclength;cFigurec1.6a)
,candc(2)cthecsulfurcchemolithotrophcThiomargaritacnamibiensisc(750cµm;cFigurec1.6b).cThecevolutio
naryc“rationale”cforcthecexistencecofcunusuallyclarge-
celledcbacteriaciscacmysterycwhenconecconsiderscthatcthecmetaboliccratecofcaccellcvariescinverselycwithc
thecsquarecofcitscsize.cAskcyourcstudentscforcideascand/orchypothesescthatcmightcexplaincthecselectivec
advantagecofclargeccellcsizecincthesectwocprokaryotes.
Thecfactcthatcbacteriaccanclivecindependentlycascsingleccellsc(unlikecancindividualccellcofcacmulticel
lularcorganism)csuggestscthatctheycmustcpossesscsomeccapabilitiescthatcprovidecacselectivecadvantagec
overctheircmulticellularccounterpartscthatcensurectheircsurvivalconcthecplanet.cSmallccellschavecmorecsu
rfacecareactocvolumec(i.e.,cachighercsurface-to-
volumecratio),candcthiscalonecconferscmanycofcthecevolutionarycadvantagescofcbeingcsmall,cincludingct
hecfollowing:
● Rapidcnutrientcandcwastectransportcintocandcoutcofctheccellcallowscforcfastercmetaboliccratescandcg
rowthcrates.
● Rapidcgrowthcratescresultcincthecrapidcproductioncofclargecpopulationscofccells.cThesecpopulation
s,cincturn,ccancgreatlycaffectcthecphysiochemicalcconditionscofcancecosystemcwithincacshortctimecp
eriod.
● Transportcratescarecacfunctioncofcthecsurfacecareacofctheccytoplasmiccmembranecrelativectoccellcvol
ume.cUsecFigurec1.7ctocmathematicallycdemonstratectocstudentscthatcthecsurfacecareacofcacsphereci
scacfunctioncofcthecsquarecofcthecradius,cwhereascthecvolumecofcacsphereciscacfunctioncofctheccubecofcth
ecradius.cThiscmeanscthatcthecsurface-to-
volumecratiocofcacsphericalccellccancbecexpressedcasc3/r,cwherecrcequalscthecradiuscofctheccell.cTher
efore,caccoccusccellchavingcacsmallercradiuschascmorecsurfacecareacpercvolumecand,cthus,cmoreceffic
ientctransportccapabilities,cthancaccoccusccellchavingcaclargercradius.
● Ratescofcevolutionarycchangecarechighercincsmaller,cfastercgrowingchaploidccellscthancinclarger,
2 INSTRUCTOR'ScMANUALcFORcBROCKcBIOLOGYcOFcMICROORGANISMS,c16e Copyrightc©c2021cPearsoncEducation,cInc.
mynursytest.store
, ACCESS Test Bank for Brock Biology of Microorganisms 16th EditionMadig
c c c c c c c c c c
an
slowercgrowingcdiploidccells.cThiscallowscforcgreatercadaptivecpotentialcthroughcrapidcselectioncf
orcadvantageouscmutationscandccounterselectioncagainstcdeleteriouscmutations.
Thectheoreticalclowerclimitcofcsizecforcaclivingccellcisclikelycnearc0.2cμmcincdiameter.cThisclimitcisc
dictatedcbycthecamountcofcvolumecrequiredctoccontainccellularccomponentscthatcareccrucialcforc
maintainingclife,csuchcasc(1)cthecpresencecofcessentialcgenesconcthecchromosome;c(2)chavingcacs
ufficientcnumbercofcribosomes;candc(3)ccontainingcacminimalcnumbercofcmetabolic,cstructural,ca
ndctransportcproteinscwithinctheccell.cChallengecstudentsctoclistcthesecandcothercmolecularccomp
onentscthatcaccellcwouldchavectoccontainctocmaintainclife.cRemindcstudentscthatcsomeccellscarecp
arasiticcincnature.cInformcthemcthat,cmuchclikecviruses,csuchcmicroorganismscoftenchavecstream
linedcgenomescthatclackcimportantcgenescandcmaycmakecthemcdependentcuponctheirchostscforcgr
owth.cCancsuchcorganismsctrulycbecconsideredcliving?cThiscmightcmakecacgoodcoutsidecprojectcf
orcgroupcdebate,crequiringcstudentsctocviewctheccellcascacthree-
dimensionalcphysicalcstructurecconstrainedcincspacecandctocresearchcacproblemcthatcisccurrentl
ycbeingcdebated.
UsingcFigurec1.8,cpointcoutcthecthreecmajorcmorphologiescofcprokaryoticccellsc(coccus,crod,candcspiril
lum).cInformcyourcstudentscthat,cincsomecspecies,ctheccellscremaincattachedcfollowingccellcdivision,cgi
vingcrisectocdifferentcarrangementscthatcarecoftencgenus-
specific.cForcexample,ccoccusccellscmaycexistcasclongc chainsc(Streptococcus)corcgrapelikecclustersc(St
aphylococcus).cLessccommonccellcmorphologiescalsocexist,csuchcascspirochetes,cappendagedc(buddin
g)cbacteria,candcfilamentouscbacteriac(Figurec1.8).cStressctocstudentscthatcthesecmorphologiescareconlyc
representativecofcthosecfoundcincnature.cOthercunusualcshapeschavecalsocbeencdescribedcincrareccasesc(
e.g.,csquare-candcstar-shapedccells!).
Beforecthecmolecularcera,cmorphologicalcandcphysiologicalcpropertiescwerecusedctocclassifycbacte
rialcspecies.cHowever,cwecnowcknowcthatctheseccriteriacarecpoorcpredictorscofcevolutionarycrelationsh
ips.cForcexample,ccertaincspeciescofcArchaeacmaycappearcidenticalcincsizecandcshapectocspeciescofcBac
teriacundercthecmicroscope,cbutcthesecorganismscarecofcdifferentcphylogeneticcdomainscandcthuscarecn
otccloselycrelatedctoconecanotherconcancevolutionarycbasis.cTheccellcmorphologycofcacparticularcspecie
sciscprimarilycacresultcofcselectivecpressurescincacgivenchabitatcthatcfavoredcacparticularccellcshapecforce
nhancedcreproductivecsuccess.
1.4 | An Introduction to Microbial Life
c c c c c
Thiscsectioncofcthecchaptercprovidescancoverviewcofctheckeycfactorscthatcdistinguishccellscofcthecdiffer
entcdomainscofclife,candchowcthesecarecfurthercdistinguishedcfromcacellularcmicrobes—
thecviruses.cFigurec1.9cbeautifullyccomparescthecsizecrelationshipscofcacvarietycofcmicrobialcformscan
dccomponents,cfromcthecuncommonlyclargecbacteriumcEpulopisciumcfishelsonicatcaclengthcofc600cμmc
(seecalsocFigurec1.6)ctocindividualcproteinscatctheclimitcofcresolutioncofcancelectroncmicroscope
(0.2cnm).cMentioncthecfollowingckeycpoints:
● ThecgreatestcdiversitycofcBacteriacandcArchaeachascnevercbeencculturedcinctheclaboratory,candcs
uchcspeciescarecknownconlycbyctheircDNAcsequencescfoundcincenvironmentalcsamples.
● Althoughctheycbothchavecacprokaryoticccellcstructure,cBacteriacandcArchaeacarecnotccloselycr
elated.cOncacmolecularclevel,cArchaeachavecmuchcinccommoncwithctheceukaryotes.
● Thecmetaboliccandcphysiologicalcdiversitycofcmicroorganisms,cespeciallycthecBacteriacand
Archaea,ciscastonishing,cwithcspeciesccapablecofcaerobiccrespiration,canaerobiccrespiration,
Copyrightc©c2021cPearsoncEducation,cInc. CHAPTERc1cThecMicrobialcWorld 3
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