Microbial metabolism

This PPT intends to explore the basic understanding of the metabolism in general and bacterial metabolism in particular.

1. Microbial Metabolism
by
N. Sannigrahi, Associate Professor,
Deptt. Of Botany,
Nistarini College, Purulia (W.B) India

2. Hundredsofreactionssimultaneouslytakeplaceinaliving
cell,inawell-organizedandintegratedmanner.Theentire
spectrumofchemicalreactions,occurringinthelivingsystem,
iscollectivelyreferredtoasmetabolism.Ametabolicpathway
(ormetabolicmap)constitutesaseriesofenzymaticreactions
toproducespecificproducts.Thetermmetaboliteisappliedto
asubstrateoranintermediateoraproductinthemetabolic
reactions.
Thedegradativeprocessesconcernedwiththebreakdownof
complexmoleculestosimplerones,withaconcomitant
releaseofenergy.Thebiosyntheticreactionsinvolvingthe
formationofcomplexmoleculesfromsimpleprecursors.A
cleardemarcationbetweencatabolismandanabolismisrather
difficult,sincethereareseveralintermediatescommontoboth
theprocesses.

3. 1.Conversionofcomplexmoleculesintotheirbuilding
blocks:
Polysaccharidesarebrokendowntomonosaccharide’s,lipids
tofreefattyacidsandglycerol,andproteinstoaminoacids.
2.Formationofsimpleintermediates:
Thebuildingblocksproducedinstage(1)aredegradedto
simpleintermediatessuchaspyruvateandacetylCoA.These
intermediatesarenotreadilyidentifiableascarbohydrates,
lipidsorproteins.Asmallquantityofenergy(asATP)is
capturedinstage2.
3.FinaloxidationofacetylCoA:
AcetylCoAiscompletelyoxidizedtoCO
2,liberatingNADH
andFADH
2thatfinallygetoxidizedtoreleaselargequantity
ofenergy(asATP).

4. Krebscycle(orCitricacidcycle/TCAcycle)isthecommon
metabolicpathwayinvolvedinthefinaloxidationofall
energy-richmolecules.Thispathwayacceptsthecarbon
compounds(pyruvate,Succinateetc.)derivedfrom
carbohydrates,lipidsorproteins.
ANABOLISM:Forthesynthesisofalargevarietyof
complexmolecules,thestartingmaterialsarerelativelyfew.
Theseincludepyruvate,acetylCoAandtheintermediatesof
citricacidcycle.Besidestheavailabilityofprecursors,the
anabolicreactionsaredependentonthesupplyofenergy(as
ATPorGTP)andreducingequivalents(asNADPH+H
+
).
Theanabolicandcatabolicpathwaysarenotreversibleand
operateindependently.Assuch,themetabolicpathwaysoccur
inspecificcellularlocations(mitochondria,microsomesetc.)
andarecontrolledbydifferentregulatorysignals.

7. Carbohydrate,theprimarysourceofenergyofmostmicro-
organismsespeciallyglucose,asimplesugar,
Polysaccharideslikestarch,glycogen,cellulose,lignin,
hemicellulosesetcbreakdownbyenzymestoformglucose,
GlucoseisbrokendownbyredoxreactionstoformCo2,H20
andATP.
Mostofthemicroorganismsbreaksdownglucoseanaerobic
allybyfermentation,
Cellularrespirationinaerobicprocesstakesplaceby
Glycolysis,Krebscycle/TCAcycle/citricacidcycle,Electron
transportChain.
Alltheprocessesarecatalyzedbyenzymesandotherfactors
liketemperature.pH,etc.

9. Glucose after break down to form 2 mols pyruvic acid by two
stages-Preparatory phase and pay off or energy conserving
phase
Overall reactions:
Glucose+ 2 NAD+ +2ADP +2ip=2 Pyruvic acid+
2ATP+2NADH +2H,
From 2NADH, 6 mol's of ATPs are produced, the total ATPs
becomes 6+2=8,
It is also called EMP pathway or Embdeon-Mayerhoof Parnas
pathway,
Other pathway of the oxidation of glucose is PPP ( Hexose
Monophosphate Shunt) or Entner-Doudoroff(ED) pathway.

12. ManybacterialikeBacillussubtilis,E.coli,Enterococcus
faecalisetcperformthisprocess,
Productionofintermediatepentosefornucleicacidsynthesis,
productionofcertainaminoacidsetc,
OneATPmoleculesforeachglucosemoleculeoxidizedand
producesNADPHcoenzymes,
Glucose6phosphateisoxidizedtoRibulose5phosphatein
theoxidationphase,inthenon-oxidativephase,thepentose
phosphateisrecycledtoformglucose6phosphate,
PPPactsupontheneedofthecell.Iftherequirementofthe
reducingpowerismorethanitproceedstheformationof
NADPHbutifpentoseisrequired,itfunctioninthedirection
ofpentose.Ifthecellrequiresinstantenergy,thePPPstops
andglycolysisandTCAproceed.

14. Describesthepathwayofenzymecatalyzedchemical
reactionstocatabolizeglucosetoPyruvicaciddifferentfrom
EMPorPPPpathway,
ProposedbyM.DoudoroffandN.Entnerin1952
Ituses6-phosphogluconatedehydratasdeand2-keto-3
deoxyphosphogluconatealdosetocreatepyruvicacidfrom
glucose,
Ithasnetproductionof1ATP,1NADHand1NADPHfor
eachglucosemoleculeitprocessedthrough,
MostlyGram(-)bacterialikePseudomonas,Azetobacter,
Rhizobium,Agrobacterium,E.Coli,Xanthomonasetcutilize
thispathway,
ItisalsoseeninGram(+)bacterialikeEnterococcousfaecalis
andintheArchaeagroupofprokaryotes,

16. Partoftheaerobiccellularrespiration,
ItisdependentonO2tooxidizethereducedcoenzymesuchas
NADH2andFADH2producedduringthiscycletogenerateNAD+
andFAD+tocarryoutthecycle,
Itlinksthecarbohydrate,Nitrogenandfatmetabolism,
TheAcetylcoAderivedfromglycolysisandacceptedbyOAAto
formthefoundationofthiscycle,
Thevariousacidsinthiscyclearecitrate-isocytrate-alpha
ketoglutarate-SuccinylCoA-Succinate-Fumarate-Malatre--OAA,
Occurinthematrixofmitochondriausinganumberofenzymes,
OneturnofKrebscyclegenerates2CO2,3NADH,1FADH2and1
ATP/GTPmolecule.Asoneglucosemoleculeproduces2Acetyl
CoA,theentiretobemultipliedby2.

18. Thefinalstageofaerobiccellularrespiration,
ETCconsistsofelectroncarrierstotransportelectronsby
oxidizingNADH,FADH2andultimatelytoelectron
acceptors,oxygen,
Duringtheflowofelectronsfromhigherredoxpotentialsto
theoxygenATPmoleculesareformed,
TheETCarecapableofoxidationandreduction,
Threetypesofcarriers-flavoproteinscontainingflavin;
cytochromeswithhemeprostheticgroupandubiquinonesor
CoenzymeQwhicharenon-proteincarriers,
TheETSincludeCytb,CytC1,Cytc,cyta1,andCyta3.The
terminalelectroncarrierisknownasterminaloxidaseand
passeselectrontooxygen.Bacteriashowvariationsintheir
ETCduetodifferentnatureofenergyprovidingsubstrate.

19. Anaerobicrespirationtakesplaceinabsenceofoxygen,
inorganicsubstancesarefinalelectronacceptor,
InPseudomonasandBacillus,Nitrateionsasfinalelectron
acceptorwhileDesulfo-vibriousesulphateionasfinal
electronacceptortoformhydrogensulphide,
FermentationproducediverseproductslikeLacticacid(
Streptococcous),Ethanol(Saccharomyces),Propioniocacid(
Propionbacterium),ButyricacidorButanol(Clostridium)
Succinicacid(E.coli)andFormicacid(Enterobacter)etc.as
perthenatureoftherespiratorysubstrate.
Butwhatevermaybe,theamountofenergyproductionisvery
minimumduetopartialoxidationoftherespiratorysubstrates.
Lipidandproteinsarebrokendownandinterlinkedwith
Krebscycle.

20. Incontrasttoalgaeandhigherplantswhichareoxygenic(i.e.,
theyevolveO
2duringphotosynthesisandhavetwophoto-
systemsthatactintandemorseries,thephotosynthetic
bacteriaareanoxygenic(i.e.,theydonotevolveO
2during
photosynthesisandhavecomparativelysimplephoto
transductionmachinerywithonlyonetypeofphotosystemand
reactioncentre.
PurplebacteriahaveTypeIIReactionCentrewhichpasses
electronsthroughbacteriopheophytin(bacteriochlorophyll
lackingcentralMg
2+
ion)toaquinone.Greensulphurbacteria
haveTypeIReactionCentrethatpasseselectronstoanFe-s
protein.

21. TypeIReactionCentre(TheFe-SReactionCentre):
Ingreensulphurbacteria,P-840constitutesthereactioncentre
oftheonlyonepigmentsystempresent.Contrarytothecyclic
photosyntheticelectrontransportofpurplebacteria,the
photosyntheticelectrontransportingreensulphurbacteria
appearstoinvolvebothcyclicandnon-clyclicroutes
TypeIIReactionCentre(TheBacteriopheophytin–
QuinoneReactionCentre):
Inpurplebacteria,P-870constitutesthereactioncentreofthe
onlyonepigmentsystempresent.WhenP-870(B.Chl.a)
receivesaphotonoflight,itgetexcited(*).Anelectronwith
extraenergyisejectedfromitwhichisimmediately(within
picoseconds)capturedbybacteriopheophytina(B.Pheo).
BymeansofCalvincycleorReductiveCarboxylicacidcycle
orCarbonassimilationbyorganiccompoundsarefollowed.

22. Themicroorganismssynthesizethehighercarbohydrates,
lipids,proteins,nucleotidesinsidetheircellsfromthe
chemicalcompoundsformedbythecatabolicprocessand
absorbedfromtheenvironmentinwhichtheygrow.In
addition,purineandpyrimidinebiosynthesisarealsotaken
intoaccountasapartofthebiosyntheticpathwayduringthis
anabolism.
Microbialmetabolicreactionsareefficientandspeedier,
Duetohighertosurfacevolumeratio,thegreaterabsorption
andefficiency,
Variousorganicandinorganiccompoundsaswellaslightto
generateenergy,
Differentelectrontransportchainsdependingonthesourceof
ele4ctrondonors.

24. ACKNOWLEDGEMENT :
Microbiology & Phycology by Mishra & Das
Microbiology-Pelczar, Chan & krieg
Brock Biology of Microorganisms
A Textbook of Microbiology by Chakraborty,
A textbook of Microbiology by Dubey & Maheswari
Different web pages
Google for free download of images
Disclaimer:
This has been prepared without any financial interests, free for
students.