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Lecture 6, 2005 Fig. 6.24. Catabolism of other organic compounds Physiology cont. Table 6.8. Aerobic respiration in chemoautotrophs. 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) Phenolic respiration same as sugar (Fig. 6.8).. See Figure 6.25. and i.e. Overheads…. in 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 back Aerobic vs. anaerobic respiration in E. coli The order of catabolic reactions in a sediment….. Differences: Note oxygenase step needed to break ring Fermentation Internally balanced oxidation-reduction reaction Regeneration of NAD+ Different from respiration because no etransport 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 on the organism… Fig. 6.23. Endproducts (primary metabolites) of fermentation reactions in various microbes… Fig. 06.22Fig. 6.22 Regeneration of NAD+ without an e- transport chain……. Lactic Acid Fermentation Alcoholic Fermentation - 2 step process PYRUVATE PYRUVATE NADH NAD+ LacticAcid ACETALDEHYDE + CO2 NADH Used to make yogurt, sauerkraut and pickles. ETHANOL NAD+ Used to make bread, wine, and beer. Types of fermentations in a little more detail - See overheads…. Making ATP without an e- transport chain or ATPases… 1) Mixed acid fermentation - organisms excrete ethanol and a mixture of acids including acetic, lactic, succinic, and formic acids. Seen in Escherichia, Salmonella, Proteus, and some others Substrate-level phosphorylation See figures…… 2) Butanediol fermentation - Pyruvate converted to acetoin, which is then reduced to 2,3-butanediol as well as ethanol. Characteristic of Enterobacter, Serratia, and some Bacillus Basis of some diagnostic tests, including Voges-Proskauer. 3) Stickland reaction… found in many clostridia that live in rich environments…. Use 2 amino acids - one as an e- donor and one as an e- acceptor Last examples of important fermentations: Heterolactic fermentation: Glucose ----> 1 ethanol + 1 lactate That was all fermentation - the generation of energy without terminal electron acceptors. Why did fermentation yield so little ATP? Homolactic fermentation: Glucose ----> 2 lactates 1) The carbon compounds are only partially oxidized. See overhead for details of NAD+ regeneration 2) The reduction potentials between primary electron donor and terminal electron acceptor are small. If O2 or another terminal electron acceptor is used, the carbon can be oxidized completely to CO2. Anabolic reactions: If O2 is used = aerobic respiration Require energy input, used for making biomass Fig. 6.29 Fig. 6.30. A. Amine incorporation to form glutamate. B. transanimation reaction to form other amino acids Fig. 6.31 Fig. 6.32 Many bacteria can biosynthesize all of their biomass from simple molecules (e.g. nitrate, phosphate, glucose etc)….. e.g. E. coli can grow in media containing only glucose and six inorganic salts…. Non-fastidious microbes often need anaplerotic reactions to replenish intermediates in biosynthetic pathways……. These reactions are especially important during the lag phase to “prime the pump” Others are more “fastidious” and require the presence of exogenous amino acids and other organic compounds, e.g. many pathogens and symbionts are fastidious….. e.g. Some Neisseria spp. can only be grown in the lab in the presence of all 20 amino acids and 7 vitamins…. (Please read page 91) See overhead…… Anaplerotic reaction, an example of starting the TCA cycle in an awakening bacterium… Pyruvate + ATP + CO2 ---> Oxaloacetate + ADP