z z z z z z z z
Prescott’szMicrobiology,z12/e
1 The Evolution of Microorganisms and Microbiology
z z z z z z
CHAPTER OVERVIEW z
Thiszchapterzintroduceszthezfieldzofzmicrobiologyzandzdiscusseszthezimportancezofzmicroorganismsznotzonly
zaszcausativezagentszofzdiseasezbutzalsozaszimportantzcontributorsztozfoodzproduction,zantibioticzmanufactur
e,zvaccinezdevelopment,zandzenvironmentalzmanagement.zItzpresentszazbriefzhistoryzofzthezsciencezofzmicro
biologyzandzanzoverviewzofzthezmicrobialzworld.zThezoriginzofzlife,zRNAzworldzhypothesis,zandzmicrobialze
volutionziszputzinzthezcontextzofzmicrobialzphylogenies.
LEARNING OUTCOMES z
Afterzreadingzthiszchapter,zstudentszshouldzbezablezto:
• defineztheztermzmicrobiology
• explainzCarlzWoese’szcontributionszinzestablishingzthezthree-
domainzsystemzforzclassifyingzcellularzlife
• determineztheztypezofzmicrobez(bacterium,zfungus,zetc.)zwhenzgivenzazdescriptionzofzazmicroorganism
• providezanzexamplezofzthezimportanceztozhumanszofzeachzofzthezmajorztypeszofzmicrobes
• explainzthezRNAzworldzhypothesiszandzthezevidencezthatzsupportszit
• designzazsetzofzexperimentszthatzcouldzbezusedztozplacezaznewlyzdiscoveredzcellularzmicrobezonzazp
hylogeneticztreezbasedzonzsmallzsubunitz(SSU)zrRNAzsequences
• comparezandzcontrastzthezevolutionzofzmitochondriazandzchloroplasts
• evaluatezthezimportancezofzthezcontributionszmadezbyzHooke,zLeewenhoek,zPasteur,zLister,zKoch,z
Beijerinck,zvonzBehring,zKitasato,zMetchnikoff,zandzWinogradskyztozmicrobiology
• outlinezazsetzofzexperimentszthatzmightzbezusedztozdecidezifzazparticularzmicrobeziszthezcausativezagentzof
zazdisease
• predictzthezdifficultieszthatzmightzarisezwhenzusingzKoch’szpostulatesztozdeterminezifzazmicrobezc
auseszazdiseasezuniqueztozhumans
• constructzazconceptzmap,ztable,zorzdrawingzthatzillustrateszthezdiverseznaturezofzmicrobiologyzandzh
owzitzhaszimprovedzhumanzconditions
• discusszthezopinionzheldzbyzmanyzmicrobiologistszthatzmicrobiologyziszexperiencingzitszsecondzg
oldenzage
1
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.
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,ACCESS Test Bank for Prescotts Microbiology 12th Edition Willey
z z z z z z z z
Prescott’szMicrobiology,z12/e
GUIDELINES FOR ANSWERING THE COMPREHENSION CHECK QUESTION
z z z z z z
S
Asztheznamezofzthiszsectionzimplies,zthesezquestionszrangezfromzfirst-
orderzretrievalzofzinformationzfromzthezprecedingztextztozapplicationzofzthezcontentztozopen-
endedzquestionszorzscenarios.zAszsuch,zthezanswerszarezeitherzeasilyzobtainedzfromztheztextzorzmayzhavezman
yzdifferentzanswerszthatzcanzbezconsideredzvalid.zForzthiszreason,zwezdoznotzincludezthesezquestionszinzthezins
tructor’szmanual.
GUIDELINES FOR ANSWERING THE MICRO INQUIRY QUESTIONS
z z z z z z
Figurez1.1:zHowzwouldzyouzalterzthiszconceptzmapzsozthatzcellularzorganismszarezdifferentiatedzbyztheirzke
yzfeatures?
Modifyzthiszhierarchicalzconceptzmapzbyzgroupingzorganismszintozthezeukaryoteszthatzcontainzaznucleuszand
zmembrane-
boundzorganellesz(fungizandzprotists)zandzthezprokaryoteszthatzgenerallyzdoznotzcompartmentalizeztheirzinte
rnalzcontentszintozmembrane-boundzorganelles.
Figurez1.3:zHowzmanyzofztheztaxazlistedzinzthezfigurezincludezmicrobes?
Allzofzthem.
Figurez1.5:zWhyzarezthezprobiontszpicturedzaboveznotzconsideredzcellularzlife?
AllzcellszcontainzDNA,zRNA,zandzproteinszandzcanzself-replicate.
Figurez1.9:zWhyzdoeszthezbranchzlengthzindicatezamountzofzevolutionaryzchangezbutznotztheztimezitztookzf
orzthatzchangeztozoccur?
Thezlineszonzazphylogeneticztreezindicatezazmeasurezofzrelatednesszbecauseztheyzrepresentzgeneticzsequencez
divergence.zTheyzareznotzazmeasurezofztimezbecausezitzisznotzknownzhowzmuchztimezwaszneededzforzorganis
msztozdivergezbecausezdivergenceziszinfluencedzbyzmultiplezfactors.
Figurez1.17:zWhyziszthezfourthzpostulateznecessary?
Thezfourthzpostulatezisznecessaryztozcompletezthezloopzofzcausation.zIfzazsuspectedzpathogenzwaszintroducedz
tozazsusceptiblezhostzbutzcouldznotzbezre-
isolatedzfollowingzthezonsetzofzdisease,zthiszmayzimplyzthatzthezorganismzitselfzisznotzthezdirectzcausezofzthezd
iseasezandzwouldzwarrantzazsearchzforzotherzco-zisolatedzorganisms.
GUIDELINES FOR ANSWERING THE ACTIVE LEARNING QUESTIONS
z z z z z z
1. Whyzaren’tzviruses,zviroids,zsatellites,zandzprionszincludedzinzthezthree-domainzsystem?
Onlyzcellularzorganismszarezinztaxonomiczsystems,zbecausezonlyztheyzarezdescendedzfromzeachzotherzwithzv
erticalzgeneztransmission.zViruseszdoznotzreproduce,ztheyzarezassembledz(likezmachines).zViroidszandzsatell
iteszarezRNA,znotzorganisms.zPrionszarezproteins,znotzorganisms.
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.
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, ACCESS Test Bank for Prescotts Microbiology 12th Edition Willey
z z z z z z z z
Prescott’szMicrobiology,z12/e
2. Somezindividualszcanzbezinfectedzbyzazpathogenzyetznotzdevelopzdisease.zInzfact,zsomezbecome
chroniczcarrierszofzthezpathogen.zHowzdoeszthiszobservationzaffectzKoch’szpostulates?zHowzmightzthezpos
tulateszbezmodifiedztozaccountzforzthezexistencezofzchroniczcarriers?
Inzthezcarrierzstate,zazhostzcarrieszthezpathogenzwithoutzclinicalzsymptoms.zForzexample,zapproximatelyz20%
zofzcollegezstudentszcarryzStaphylococcuszaureuszinztheirznasalzpassages,zwithznozillzeffects.zHowever,zitzcanz
causezdiseasez(damageztozthezhost)zifztheyzbecomezimmunocompromised.zTheyzcanzalsoztransmitzthezbacteri
aztozothers.zTechnically,zthiszdoesznotzrelateztozKoch’szpostulateszbecauseztheyzarezdesignedztozisolatezthezca
usativezagentzofzazdisease,zandzthezcarrierzstatezisznotzdisease.zKoch’szpostulateszmayzbezmodifiedztozincludez
modernzsequencingztechnologyztozinvestigatezresistancezfromzmicrobialzcommunitieszorzincludezinoculation
ztozanzimmune-
deficientzhostztozassesszdiseasezcausationzinzthezabsencezofzimmunezresistancezmechanisms.zThezbottomzline
ziszthatzwhilezKoch’szpostulateszcertainlyzdoznotzapplyzinzeveryzcasezandztheyzhavezlimitations,ztheyzwerezofzt
remendouszhistoricalzimportancezinzdemonstratingzexperimentallyzthezgermztheoryzofzdisease,zwhichzwaszazt
remendouszadvancezinzmodernzmedicine.
3. Supportzthiszstatement:z“Vaccinationszagainstzvariouszchildhoodzdiseaseszhavezcontributedztoztheze
ntryzofzwomen,zparticularlyzmothers,zintozthezfull-timezworkplace.”
Possiblezanswerszinclude:
-Childrenzspentzlessztimezbeingzsick,zthuszmotherszspendzlessztimezawayzfromzwork.
-
Becausezchildhoodzmortalityzhaszbeenzloweredzandzthuszmorezchildrenzsurviveztozadulthood,zthiszmayzcontri
buteztozfewerzchildrenzonzaverageztozeachzfamily,zthuszlesszchildcarezburdenzonzthezmother.
-
SeveralzsiteszincludingzNationalzOpinionzResearchzCenterz(NORC)zhavezcompiledzstatisticszcomparingzvac
cinationzwithzemploymentzstatistics.
4. Forzmanyzyears,zthezoldestzstromatoliteszwithzcompellingzevidencezofzancientzlifezonzEarthzwerezfoundz
inzWesternzAustralia.zThezmicrobialzcommunitieszthatzbuiltzthezsedimentaryzstructureszwerezdatedzatzrou
ghlyz3.5zbillionzyearszold.zHowever,zinz2016zstromatoliteszinzGreenlandzwerezreportedztozbe
3.7zbillionzyearszold.zInterestingly,zthezcomplexityzandzmorphologyzofzthezGreenlandzstromatolitesziszsimi
larztozthatzofzthosezinzAustralia.zWhyziszitzofzinterestztozdocumentzthezoldestzevidencezofzlifezonzEarth?zWh
atzmightzthiszsuggestzaboutzthezevolutionzofzlifezduringzthezinterveningz200zmillionzyears?zWhatziszthezsign
ificance,zifzany,zofzthezgeographiczdistributionzofzthesezstromatolites?
Thiszanswerziszopinion,zsozvariouszanswerszarezpossible.zDocumentingzthezoldestzevidencezofzlifezonzEarthzpr
ovideszinsightzintozthezoriginszofzlife.zThezsimilaritieszinzmicrobialzcommunitieszsuggestzthatzlifezdiversityzw
aszalreadyzcomplexz3.7zbillionzyearszagozandzthatzthesezmicrobialzcommunitieszwerezevolutionarilyzpreserve
dzoverzthezcoursezofz200zmillionzyears.zWhilezthezsimilarityzbetweenzmicrobialzcommunitieszonzsuchzgeogra
phicallyzdistinctzlocationszcouldzsuggestzthatzmicrobialzlifezdevelopedzsynchronouslyzandzindependently,zitzi
szmorezlikelyzthatzatzonezpointzinzhistoryzthesezdistantzlandmasseszwerezconnectedzorzinzproximity.
3
©zMcGrawzHillzLLC.zAllzrightszreserved.zNozreproductionzorzdistributionzwithoutzthezpriorzwrittenzconsentzofzMcGrawzHillzLLC
.
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