Medical Microbiology

ThePhysiologyofMetabolismandGrowthinBacteria 163

BacteriaarecategorizedasthefollowingaccordingtotheirO 2 -related

behavior:

&Facultativeanaerobes.Thesebacteriacanoxidizenutrientsubstrates

bymeansofbothrespirationandfermentation.

&Obligateaerobes.ThesebacteriacanonlyreproduceinthepresenceofO 2.

&Obligateanaerobes.ThesebacteriadieinthepresenceofO 2 .Their

metabolismisadaptedtoalowredoxpotentialandvitalenzymesarein-

hibitedbyO 2.

&Aerotolerantanaerobes.Thesebacteriaoxidizenutrientsubstrateswith-

outusingelementaloxygenalthough,unlikeobligateanaerobes,theycantol-

erateit.

Basicmechanismsofcatabolicmetabolism.Theprincipleofthebiochemical

unityoflifeassertsthatalllifeonearthis,inessence,thesame.Thus,the

catabolicintermediarymetabolismofbacteriais,forthemostpart,equiva-

lenttowhattakesplaceineukaryoticcells.Thereaderisreferredtotextbooks

ofgeneralmicrobiologyforexhaustivetreatmentofthepathwaysofinter-

mediarybacterialmetabolism.

AnabolicReactions....................................

Itisnotpossibletogointoallofthebiosyntheticfeatsofbacteriahere.Suffice

ittosaythattheyare,onthewhole,quiteastounding.Somebacteria(E.coli)

arecapableofsynthesizingallofthecomplexorganicmoleculesthattheyare

comprisedof,fromthesimplestnutrientsinaveryshorttime.Thesecapac-

itiesareutilizedinthefieldofmicrobiologicalengineering.Antibiotics,ami-

noacids,andvitaminsareproducedwiththehelpofbacteria.Somebacteria

areevencapableofusingaliphatichydrocarboncompoundsasanenergy

source.Suchbacteriacan“feed”onparaffinorevenrawpetroleum.Itis

hopedthatthemetaboliccapabilitiesofthesebacteriawillhelpcontrol

theeffectsofoilspillsinsurfacewater.Bacteriahavealsobeenenlistedin

thefightagainsthunger:certainbacteriaandfungiarecultivatedonaliphatic

hydrocarbonsubstrates,whichsupplycarbonandenergy,thenharvestedand

processedintoaproteinpowder(singlecellprotein).Culturingofbacteriain

nutrientmediumsbasedonmethanolisanotherapproachbeingusedtopro-

ducebiomass.

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Kayser, Medical Microbiology © 2005 Thieme