Bactrerial metabolism

Bactrerial metabolism

1. BACTERIAL METABOLISM Santosh Yadav M.Sc. Clinical Microbiology Dept. of Microbiology Institute of Medicine Tribhuvan Univarsity Teaching Hospital, Nepal

2. Metabolism Sum total of all the chemical reactions occuring in the cell ( i.e. biosynthetic and degradative ) Metabolism in bacteria is essential for their existance , for environment , and products are commercially and medically important for human beings. 2

3. CATABOLIC AND ANABOLIC REACTIONS Reactions that cause breakdown of complex molecules into simpler form with relase of energy is catabolic reactions. Energy requiring reactions that build up complex organic molecules from simpler ones is anabolic reactions . 3

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5. Components of metabolism COMPONENTS FUNCTIONS Enzymes Biological catalyst, fascilitates each step of metabolic reaction by lowering the activation energy of reaction. Adenosine triphosphate (ATP) serves as energy currency of cell , Energy source Compund that is oxidised to release energy , also called an electron donor. Electron carriers carry the electrons that are removed during the oxidation of energy source ( NAD⁺, NADP⁺ , and FAD ( their reduced form NADH , NADPH , and FADH₂) . Precursor metabolites Intermediate metabolite that link anabolic and catabolic pathways, like pyruvate , acetyl-coA, glucose -6-p, etc. 5

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8. Role of ATP Is energy currency of cell, serving as ready and immediate donor of free energy. Energy is releases when phosphate bond is broken, hence it is called high energy phosphate bond. Synthesis and breakdown of ATP continuously occurs in cell during degradative and synthetic process. 8

9. Generation of ATP Bacteria uses three mechanism of phosphorylation to generate ATP from ADP. 1)Substrate level phosphorylation C-C-C-P + ADP C-C-C + ATP In this mechanism , a high energy phosphate from a phosphorylated substrate is directly transferred to to ADP . 9

10. Contd … 2) Oxidative phosphorylation : ATP generation duting ETC. 3) Photophosphorylation Occurs in phototrophs . Derive ATP using radiant energy of the sun. These ATP are then utilized to synthesize mainly glucose . 10

11. METABOLIC PATHWAYS OF ENERGY GENERATION 11

12. GLYCOLYSIS Embden-Mayerhof Parnas pathway. Stepwise Conversion of glucose to pyruvate and each step require specific enzyme. Occurs in cytosol . Does not require oxygen and hence occur in both aerobic and anaerobic bacteria. Three phases :- preparatory phase, splitting phase and energy generation phase. 2 molecules of pyruvic acids are formed from each glucose . Net gain of 2 ATP by substrate level phosphorylation and formation of 2 reduced substrate i.e. NADH(6 ATP) . 12

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14. Pathways alternative to glycolysis Many bacteria have another pathway in addition to glycolysis for degradation of glucose. 1) Pentose phosphate pathway, and 2) Entner Doudoroff pathway. 14

15. Pentose phosphate pathway Hexose monophosphate shunt. Occurs simultaneously with glycolysis and provides breakdown of both pentose sugar and glucose. Important Feature :- intermediate pentoses are used for nucleic acid synthesis, amino acid synthesis and glucose from CO 2 in photosynthetics . Important producer of reduced coenzyme i.e. NADPH , used for biosynthetic reactions. 15

16. Entner – Doudoroff pathway Bacteria having enzyme for Entner – Doudoroff pathway can metabolize without glycolysis or PPP. Found in some Gram negative bacteria like Psedomonas spp , Rhizobium,etc .. and generally not found in Gram positive bacteria. Produces 1 molecule NADH, 1 molecule NADPH and 1 molecule of ATP ( from 1 glucose). 16

17. Cellular respiration and fermentation Pyruvate obatained from glucose breakdown are channeled either to respiration or to fermentation. RESPIRATION :- is ATP generating process in which molecules are oxidized and the final electron acceptor is an inorganic molecules. TYPES OF RESPIRATION :- Aerobic respiration :- final electron acceptor is O₂ and occurs in aerobes. Anaerobic respiration : final electron acceptor is inorganic molecule other than O₂ . 17

18. Krebs cycle or TCA cycle Is second phase of aerobic respiration. Cytoplasmic membrane. Pyruvate formed enters TCA cycle only after converted into acetylCoA by decarboxylation rxn ( transition phase). Starts with condensaion of acetylCoA and oxaloacetate . AcetylCoA is oxidized and released as CO 2 and oxaloacetate is regenerated. 18

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20. Contd … From TCA cycle, oxidation of one acetylCoA molecule produce 3 NADH , 1 FADH₂ and 1 GTP . ( 1 lucose =2 pyruvate = 2 acetylCoA ) All the NADH and FADH2 enters into electron transport chain and finally ATP are generated. 20

21. Electron transport chain Last phase of respiration which generates ATP from reduced substrates. Consists of a sequence of carrier molecules though which electrons passes. Occurs in plasma membrane ( eukaryotic cell- inner mitochondrial membrane). 21

22. Contd … Three classes of carrier molecules 1) Flavoprotein :- coenzyme derived from viatmin B2 (riboflavin) and perform alternating oxidation and reduction reaction. 3) Ubiquinones :- small non protein carriers. 2) Cytochromes :-protein with iron containing group ( heme ). 22

23. 23 Electron transport chain is different in different bacteria , even a single bacteria have more than one type of ETC but their target is to derive energy in the form of ATP. Contd …

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26. Anaerobic respiration Final electron acceptor is NO 3 ⁻ , NO 2 ⁻ , N₂O, SO₄⁻⁻,CO₃ ⁻⁻, etc. and occurs in strict anaeres and facultative anaerobes. Sometimes Pseudomonas sps and Bacillus sps can use nitrate as final e⁻ acceptor. ATP generation varies from bacteria to bacteria and always less than aerobic respiration. Alternative electron carriers are used in the ETC. 26

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28. Fermentation Used by organisms that cannot respire because of either lack of inorganic electron acceptor or absence of ETS. Terminal electron acceptor is always organic compound. End product depends on type of microrganisms . Analysis of end product is valuable in identifying particular bacteria. ATP generating pathway is usually glycolysis ( 2ATP). 28

29. Products of fermentation 29

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31. Lactic acid fermentation Homolactic fermenters use the glycolytic pathway and directly reduce almost all their pyruvate to lactate with the enzyme lactate dehydrogenase ( eg . Lactobacillus spp ) Heterolactic fermenters form substantial amounts of products other than lactate; many produce lactate, ethanol, and CO2( Escherichia coli). 31

32. Catabolism of other substrates 32

33. Anabolism 33

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