Microbial respiration

M. Sc., Microbiology Study Material (Semester-I, General Microbiology)
Department of Microbiology, School of Bioscience,
Periyar University, Salem.

1. MICROBIAL RESPIRATION
Dr. R. BALAGURUNATHAN
Professor & Head
Dept. of Microbiology
Periyar University
Periyar PalkalaiNagar
Salem –636 011.

2. Microbial Metabolism
A.Basic Concepts of Metabolism
B.GlycolyticPathways
C.Fermentation
D.Respiration
E.Photosynthesis
F.Chemolithotrophy

3. Basic Concepts
•Definitions
–Metabolism:Theprocessesofcatabolism
andanabolism
–Catabolism:Theprocessesbywhicha
livingorganismobtainsitsenergyand
rawmaterialsfromnutrients
–Anabolism:Theprocessesbywhich
energyandrawmaterialsareusedto
buildmacromolecules andcellular
structures(biosynthesis)

4. Basic Concepts
ReductionandOxidation
–Anatombecomesmorereduced
whenitundergoesachemical
reactioninwhichit
•Gainselectrons
•Bybondingtoalesselectronegative
atom
•Andoftenthisoccurswhentheatom
becomesbondedtoahydrogen

5. Basic Concepts
ReductionandOxidation
-Anatombecomesmoreoxidized
whenitundergoesachemical
reactioninwhichit
•Loseselectrons
•Bybondingtoamoreelectronegative
atom
•Andoftenthisoccurswhentheatom
becomesbondedtoanoxygen

6. Basic Concepts
ReductionandOxidation
Inmetabolicpathways,weareoftenconcerned
withtheoxidationorreductionofcarbon.
Reducedformsofcarbon(e.g.hydrocarbons,
methane,fats,carbohydrates,alcohols)carrya
greatdealofpotentialchemicalenergystoredin
theirbonds.
Oxidizedformsofcarbon(e.g.ketones,
aldehydes,carboxylicacids,carbondioxide)carry
verylittlepotentialchemicalenergyintheir
bonds.

7. Basic Concepts
ReductionandOxidation
Reductionandoxidationalwaysoccur
together.Inareduction-oxidationreaction
(redoxreaction),onesubstancegetsreduced,
andanothersubstancegetsoxidized.The
thingthatgetsoxidizediscalledtheelectron
donor,andthethingthatgetsreducedis
calledtheelectronacceptor.

8. Basic Concepts
EnzymaticPathwaysforMetabolism
–Metabolicreactionstakeplaceinastep-wise
fashioninwhichtheatomsoftherawmaterials
arerearranged,oftenoneatatime,untilthe
formationofthefinalproducttakesplace.
–Eachsteprequiresitsownenzyme.
–Thesequenceofenzymatically-catalyzedstepsfrom
astartingrawmaterialtofinalendproductsis
calledanenzymaticpathway(ormetabolic
pathway)

9. Basic Concepts
CofactorsforRedoxReactions
–Enzymesthatcatalyzeredoxreactionstypically
requireacofactorto“shuttle”electronsfromone
partofthemetabolicpathwaytoanotherpart.
–Therearetwomainredoxcofactors:NADand
FAD.Theseare(relatively)smallorganicmolecules
inwhichpartofthestructurecaneitherbe
reduced(e.g.,acceptapairofelectrons)or
oxidized(e.g.,donateapairofelectrons).

10. Basic Concepts
Cofactors for RedoxReactions
NAD
(oxidized)+H
+
+PairofelectronsNADH
(reduced)
FAD
(oxidized)+H
+
+PairofelectronsFADH
(reduced)
NADandFADarepresentonlyinsmall(catalytic)
amounts–theycannotserveasthefinalelectron
acceptor,butmustberegenerated(reoxidized)in
orderformetabolismtocontinue.

11. Basic Concepts
ATP:A“currencyofenergy”formanycellularreactions
–ATPstandsforadenosinetriphosphate.Itisa
nucleotidewiththreephosphategroupslinkedina
smallchain.
–Thelastphosphateinthechaincanberemovedby
hydrolysis(theATPbecomesADP,oradenosine
diphosphate).
Thisreactionisenergeticallyfavorable:ithasaDG°'of
about–7.5kcal/mol
ATP+H
2O®ADP+Phosphate+Energy(7.5kcal/mol)

12. Respiration
•Featuresofrespiratorypathways
–PyruvicacidisoxidizedcompletelytoCO
2.
–Thefinalelectronacceptorisusuallyaninorganic
substance.
–NADHisoxidizedtoformNAD:Essentialfor
continuedoperationoftheglycolyticpathways.
–O
2mayormaynotberequired.
•Aerobicrespiration:O
2isthefinale
-
acceptor.
•Anaerobicrespiration:Ansubstance,usually
inorganic,otherthanO
2istheacceptor(egnitrate,
nitrite,sulfate)
–AlotofadditionalATParemade(upto36per
glucosemolecule).

13. Respiration
Stages of Respiration
–Preliminary reactions and the Krebs cycle
(TCA or Citric Acid Cycle)
–Respiratory electron transport

14. Respiration in Bacteria

15. Metabolism –An overview

16. GlycolyticPathways
•Featuresofglycolyticpathways
–Partialoxidationofglucosetoform
pyruvicacid
–AsmallamountofATPismade
–AsmallamountofNADisreducedto
NADH

17. GlycolyticPathways
Major glycolyticpathways found in different
bacteria:
–Embden-Meyerhoff-Parnaspathway
•“Classic” glycolysis
•Found in almost all organisms
–Hexosemonophosphate pathway
•Also found in most organisms
•Responsible for synthesis of pentose sugars used in
nucleotide synthesis
–Entner-Doudoroffpathway
•Found in Pseudomonasand related genera
–Phosphoketolasepathway
•Found in Bifidobacteriumand Leuconostoc

18. Overview of Cell Metabolism

19. –After Sugars are made or obtained, they
are the major energy source of life.
–Breakdown of sugar (catabolism) different
ways:
•Aerobic respiration
•Anaerobic respiration
•Fermentation
Energy Generating Patterns

20. Aerobic respiration
–Most efficient way to extract energy from
glucose.
–Process: Glycolysis
KrebCycle
Electron transport chain
–Glycolysis: Several glycolyticpathways
–The most common one:
glucose-----> pyruvicacid + 2 NADH + 2ATP

21. General Outline of Aerobic Respiration
Glycolysis
Krebs Cycle
Electron Transport System
Transition Reaction

22. General Outline
Glucose
PyruvicAcid
Glycolysis
Oxygen
Aerobic
No Oxygen
Anaerobic
Transition Reaction
Krebs Cycle
ETS
36 ATP
Fermentation

23. Glycolysis Steps –A fuel
molecule is energized,
using ATP.
1 3
1
Glucose
Step
2
3
4
Glucose-6-phosphate
Fructose-6-phosphate
Glyceraldehyde-3-phosphate
(G3P)
Step A six-carbon
intermediate splits into
two three-carbon
intermediates.
4
Step A redox
reaction generates
NADH.
5
5
1,3-Diphosphoglyceric acid
(2 molecules)
6
Steps –ATP
and pyruvic acid
are produced.
69 3-Phosphoglyceric acid
(2 molecules)
7
2-Phosphoglyceric acid
(2 molecules)
8
2-Phosphoglyceric acid
(2 molecules)
9
(2 molecules
per glucose molecule)
Pyruvic acid
Fructose-1,6-diphosphate
Energy In: 2 ATP
Energy Out: 4 ATP
NET 2 ATP

24. How GlycolysisWorks
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25. Krebs Cycle

26. Electron Transport Chain
•Groups of redoxproteins
–On inner mitochondrial membrane
–Binding sites for NADH and FADH
2
•On matrix side of membrane
•Electrons transferred to redoxproteins
•NADH reoxidizedto NAD
+
•FADH
2reoxidizedto FAD

27. ETC

28. Generation of a proton-motive force(1)

29. Generation of a proton-motive force(2)

30. Mechanism of ATPase

31. Electron Transport System and ATP Synthesis
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32. Anaerobic respiration
–Finalelectronacceptor:neverbeO2
Sulfatereducer:finalelectronacceptoris
sodiumsulfate(Na
2SO
4)
Methanereducer:finalelectronacceptoris
CO
2
Nitratereducer:finalelectronacceptoris
sodiumnitrate(NaNO
3)
O
2/H
2Ocouplingisthemostoxidizing,more
energyinaerobicrespiration.
Therefore,anaerobicislessenergyefficient.

33. Fermentation (F)
Glycosis:
Glucose ----->2 Pyruvate(P.A)+ 2ATP + 2NADH
Fermentation pathways
a. Homolacticacid F.
P.A -----> Lactic Acid
eg. Streptococci, Lactobacilli
b. Alcoholic F.
P.A -----> Ethyl alcohol
eg. yeast

34. Fermentation –An overview

35. Alcoholic fermentation

36. c. Mixed acid fermentation
P.A -----> lactic acid
acetic acid
H2 + CO2
succinicacid
ethyl alcohol
eg. E.coliand some Enterobacter
d. Butylene-glycol F.
P.A -----> 2,3, butyleneglycol
eg. Pseudomonas
e. Propionicacid F.
P.A -----> 2 propionicacid
eg. Propionibacterium

37. 37
Metabolic strategies
Pathways
involved
Final e-
acceptor
ATP
yield
Aerobic
respiration
Glycolysis,
TCA, ET
O
2 38
Anaerobic
respiration
Glycolysis,
TCA, ET
NO
3
-
, SO
4
-2
,
CO
3
-3
variable
Fermentat
ion
Glycolysis Organic
molecules
2

38. Energy/carbon classes of organisms

39. Comparison of reaction centers of
anoxyphototrophs

40. Photosynthesis
•OverviewofPhotosynthesis
–Light-dependentReactions:
•Lightenergyisharvestedbyphotosyntheticpigmentsand
transferredtospecialreactioncenter(photosystem)
chlorophyllmolecules.
•Thelightenergyisusedtostripelectronsfroman
electrondonor(theelectrondonorgoesfromareducedto
anoxidizedstate).
•Theelectronsareshuttledthroughaseriesofelectron
carriersfromhighenergystatetoalowenergystate.
•Duringthisprocess,ATPisformed.
•Inthecyclicpathwayofelectrontransport,electronsare
returnedtotheelectrontransportchain
•Inthenoncyclicpathway,theelectronsareusedto
reduceNAD(orNADP)toNADH(orNADPH)

41. Photosynthesis
Light-independentReactions:
•ATPandNADH(NADPH)fromthelight-
dependentreactionsareusedtoreduce
CO
2toform organiccarbon
compounds(carbonfixation).
•Thereducedorganiccarbonisusually
convertedintoglucoseorother
carbohydrates.

42. Photosynthesis
Oxygenic photosynthesis
–Found in cyanobacteria (blue-green algae)
and eukaryotic chloroplasts
–Electron donor is H
2O: Oxidized to form O
2
–Two photosystems: PSII and PSI
–Major function is to produce NADPH and
ATP for the carbon fixation pathways

43. Oxygenic photosynthesis

44. Photosynthesis
Anoxygenicphotosynthesis
–Found in:
•Green sulfur bacteria (e.g. Chlorobium)
•Green nonsulfurbacteria (e.g. Chloroflexus)
•Purple sulfur bacteria (e.g. Chromatium)
•Purple nonsulfurbacteria (e.g. Rhodobacter)

45. Photosynthesis
Anoxygenicphotosynthesis (cont.)
b)Electron donors vary:
•H
2S or S
oin the green and purple sulfur bacteria
•H
2or organic compounds in the green and purple
nonsulfurbacteria
c)Only one photosystem
•In green bacteria, the photosystemis similar to PSI
•In purple bacteria, the photosystemis similar to PSII
d)Primary function is ATP production, chiefly via cyclic
photophosphorylation

46. Photosynthetic bacteria
(1) Chlorobium-green sulfur bacteria
Use green pigment chlorophyll
Use H
2S (hydrogen sulfide), S (sulfur), Na
2S
2O
3
(sodium thiosulfate) and H
2 as e-donors.
(2) Chromatium-purple sulfur bacteria
Use purple carotenoidpigment, same e-donors
(3) Rhodospirillum-non sulfur purple bacteria
Use H
2and other organic compounds such as
isopropanoletc, as e-donors.
Reaction: CO
2 + 2H
2A-----> CH
20 + H
20 +2A
•Ais not O

47. Chemolithotrophy
•FeaturesofChemolithotrophy
–Electronsareremovedfromareduced
inorganicelectrondonor
–Theelectronsarepassedthroughamembrane-
boundelectrontransportpathway,often
coupledtothesynthesisofATPandNADH
–Theelectronsareultimatelypassedtoafinal
electronacceptor
–ATPandNADHmaybeusedtoconvertCO
2to
carbohydrate

48. Chemolithotrophy
Examples of electron donors
–Ammonia (NH
4
+
) Nitrite (NO
2
-
)
in Nitrosomonas
–Nitrite (NO
2
-
) Nitrate (NO
3
2-
)
in Nitrobacter
–Hydrogen sulfide (H
2S) Sulfur (S
o)
in Thiobacillusand Beggiatoa
–Sulfur (S
o) Sulfate (SO
4
2-
)
in Thiobacillus
–Hydrogen (H
2) Water (H
2O)
in Alcaligenes

49. Chemolithotrophy
Examples of electron acceptors
–Oxygen(O
2) Water (H
2O)
in many organisms
–Carbon dioxide(CO
2) Methane (CH
4)
in the methanogenicbacteria

50. Chlorophyll a and bacteriochlophylla

51. Chemoautotroph
–SomebacteriauseO
2intheairtooxidize
inorganiccompoundsandproduceATP
(energy).Theenergyisenoughtoconvert
CO
2intoorganicmaterialneededforcell
growth.
–Examples:
Thiobacillus(sulfurS)
Nitrosomonas(ammonia)
Nitrobacter(nitrite)
–Variousgenera(hydrogenetc.)