Lecture 6, 2005Physiology cont.Review:Respiration - e- donor can be organic or inorganic Aerobic respiration - O2 is final e- acceptor. Anaerobic respiration - Other final e- acceptor(e.g. NO3 -).Fermentation (today)Fig. 6.24. Catabolism of other organic compoundsTable 6.8. Aerobic respiration in chemoautotrophs.Phenolic respiration same as sugar (Fig. 6.8)..i.e. oxidation of the substrate,reduction of NAD+,oxidation of NADH at the e- transport chain,pumping of protons by the e- transport chain,ATPase used to make ATP as protons flow backinDifferences:Note oxygenase step needed to break ringSee Figure 6.25. andOverheads….Aerobic vs. anaerobic respiration in E. coliThe order of catabolic reactions in a sediment…..FermentationInternally balanced oxidation-reduction reactionRegeneration of NAD+Different from respiration because no e-transport chain.Let’s start with fermentation of sugar (e.g. glucose)Start with glycolysis (same as with resp. of glucose)……First step: Fig. 3.30 then glycolysis….Fate of pyruvate is varied depending onthe organism…Fig. 6.23. Endproducts (primary metabolites)of fermentation reactions in variousmicrobes…Regeneration of NAD+ withoutan e- transport chain…….Fig. 06.22Fig. 6.22Lactic Acid FermentationPYRUVATELacticAcidNADHNAD+Used to make yogurt, sauerkraut and pickles.PYRUVATEAlcoholic Fermentation - 2 step processACETALDEHYDECO2ETHANOL+NADHNAD+Used to make bread, wine, and beer.Making ATP without an e- transport chain or ATPases…Substrate-level phosphorylationSee figures……Types of fermentations in a little more detail - See overheads….1) Mixed acid fermentation - organisms excrete ethanol and amixture of acids including acetic, lactic, succinic, and formicacids.Seen in Escherichia, Salmonella, Proteus, andsome others2) Butanediol fermentation - Pyruvate converted toacetoin, which is then reduced to 2,3-butanediol aswell as ethanol. Characteristic of Enterobacter,Serratia, and some Bacillus Basis of some diagnostic tests,including Voges-Proskauer.3) Stickland reaction… found in many clostridiathat live in rich environments…. Use 2amino acids - one as an e- donor and one asan e- acceptorLast examples of important fermentations:Heterolactic fermentation:Glucose ----> 1 ethanol + 1 lactateHomolactic fermentation:Glucose ----> 2 lactatesSee overhead for details of NAD+ regenerationThat was all fermentation - the generation ofenergy without terminal electron acceptors.Why did fermentation yield so little ATP?1) The carbon compounds are only partiallyoxidized.2) The reduction potentials between primaryelectron donor and terminal electron acceptorare small.If O2 or another terminal electron acceptor isused, the carbon can be oxidized completely toCO2.If O2 is used = aerobic respirationAnabolic reactions:Require energy input, used for making biomassFig. 6.29Fig. 6.30. A. Amine incorporation to form glutamate. B. transanimation reaction to form other amino acidsFig. 6.31Fig. 6.32Many bacteria can biosynthesize all of their biomassfrom simple molecules (e.g. nitrate, phosphate,glucose etc)….. e.g. E. coli can grow in mediacontaining only glucose and six inorganic salts….Others are more “fastidious” and require the presenceof exogenous amino acids and other organiccompounds, e.g. many pathogens and symbionts arefastidious….. e.g. Some Neisseria spp. can only begrown in the lab in the presence of all 20 amino acidsand 7 vitamins…. (Please read page 91)Non-fastidious microbes often need anapleroticreactions to replenish intermediates in biosyntheticpathways……. These reactions are especiallyimportant during the lag phase to “prime the pump”See overhead…… Anaplerotic reaction, an exampleof starting the TCA cycle in an awakeningbacterium…Pyruvate + ATP + CO2 ---> Oxaloacetate +
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