Microbe of the Week

1. Microbe of the Week Pseudomonas aeruginosa The Genus Pseudomonas…. • Gram negative obligate free-living aerobic organisms, often in water • Can oxidize many organic compounds to obtain energy • Pseudomonas aeruginosa is a human pathogen

2. Microbe of the Week Pseudomonas aeruginosa An opportunistic pathogen from the environment, infecting: • Burn patients • Cystic fibrosis patients • Immuno-compromised patients • Medically compromised hospitalized patients A naturally antibiotic-resistant organism

3. Pseudomonas aeruginosa An opportunistic pathogen from the HOT TUB ! Causing Folliculits

4. Microbial Metabolism Cellular Respiration and Fermentation

5. What happens after glycolysis?

6. What happens after glycolysis? • After glucose is broken down to pyruvic acid, pyruvic acid can be channeled into either • Aerobic Respiration OR Fermentation • Aerobic respiration • Uses the TCA cycle and electron transport chain • Final electron acceptor is O2 • Anaerobic respiration • Uses the TCA cycle and only PART of the electron transport chain • Final electron acceptor is an inorganic molecule other than O2, like nitrate or sulfate.

7. Aerobic Respiration • Tricarboxylic acid (TCA) cycle • Kreb’s cycle or citric acid cycle • A large amount of potential energy stored in acetyl CoA is released by a series of redox reactions that transfer electrons to the electron carrier coenzymes (NAD+ and FAD)

8. Acetyl CoA • Where does it come from? • Pyruvic acid, from glycolysis, is converted to a 2-carbon (acetyl group) compound (decarboxylation) • The acetyl group then combines with Coenzyme A through a high energy bond • NAD+ is reduced to NADH

9. Pyruvate NAD+ NADH CoA CO2 CoA Acetyl-CoA CoA ATP Oxaloacetate NADH Citrate P NAD+ Isocitrate NAD+ Malate NADH H2O CO2 Fumarate a -ketoglutarate NAD+ FADH2 CoA NADH CO 2 CoA FAD Succinyl-CoA Succinate CoA ADP TCA cycle • For every molecule of glucose (2 acetyl CoA) the TCA cycle generates • 4 CO2 • 6 NADH • 2 FADH2 • 2 ATP

10. Where to now? • All the reduced coenzyme electron carriers make their way to the electron transport chain • 2 NADH from glycolysis • 2 NADH from pyruvic acid to acetyl CoA conversion • 6 NADH and 2 FADH2 from the TCA cycle • The electron transport chain indirectly transfers the energy from these coenzymes to ATP

11. The electron transport chain • Sequence of carrier molecules capable of oxidation and reduction • Electrons are passed down the chain in a sequential and orderly fashion • Energy is released from the flow of electrons down the chain • This release of energy is coupled to the generation ATP by oxidative phosphorylation

12. Membrane location of the ETC • The electron transport chain is located in • the inner membrane of the mitochondria of eukaryotes • the plasma membrane of prokaryotes

13. The ETC players • Three classes of ETC carrier molecules • Flavoproteins • Contain a coenzyme derived from riboflavin • Capable of alternating oxidations/reductions • Flavin mononucleotide (FMN) • Cytochromes • Have an iron-containing group (heme) which can exist in alternating reduced (Fe2+) and oxidized (Fe3+) forms • Coenzyme Q (Ubiquinone) • Small non protein carrier molecule

14. Are all ETCs the same? • Bacterial electron transport chains are diverse • Particular carriers and their order • Some bacteria may have several types of electron transport chains • Eukaryotic electron transport chain is more unified and better described • All have the same goal to capture energy into ATP

15. The mitochondrial ETC • The enzyme complex NADH dehydrogenase starts the process by dehydrogenating NADH and transferring its high energy electrons to its coenzyme FMN • In turn the electrons are transferred down the chain from FMN to Q to cytochrome b • Electrons are then passed from cytochrome b to c1 to c to a and a3 with each cytochrome reduced as it gains electrons and oxidized as it loses electrons

16. O2, the terminal electron acceptor • Finally, cytochrome a3 passes its electrons to O2 which picks up protons to form H2O

17. How is ATP generated? • Electron transfer down the chain is accompanied at several points by the active pumping of protons across the inner mitochondrial membrane • This transfer of protons is used to generate ATP by chemiosmosis as the protons move back across the membrane

18. The ETC sets up a proton gradient • As energetic electrons are passed down the ETC some carriers (proton pumps) actively pump H+ across the membrane. • Proton motive force results from an excess of protons on one side of the membrane

19. Generation of ATP by chemiosmosis • Protons can only diffuse back along the gradient through special protein channels that contain the enzyme ATP synthase (Fo). • ATP synthase (Fo) uses the energy released by the diffusion of H+ across the membrane to synthesize ATP from ADP

20. ETC drives chemiosmosis NADH 3 ATP FADH2 2 ATP

21. Aerobic Respiration • Complete oxidation of 1 glucose molecule generates 38 ATP in prokaryotes • 2 from each of glycolysis and 2 from the TCA cycle by substrate level phosphorylation • 34 from oxidative phosphorylation as a result of 10 NADH and 2 FADH2 from glycolysis and the TCA cycle

22. Anaerobic Respiration • Like aerobic respiration, it involves glycolysis, the TCA cycle and an electron transport chain…. but, • The final electron acceptor is an inorganic molecule other than O2 • Some bacteria use NO3- and produce either NO2-, N2O or N2 (Pseudomonas and Bacillus) • Desulfovibrio use SO42- to form H2S • Methanogens use carbonate to form methane • The amount of ATP generated varies with the pathway • Only part of the TCA cycle operates under anaerobic conditions • Not all ETC carriers participate in anaerobic respiration • ATP yield never as high as aerobic respiration

23. Fermentation • Uses Glycolysis but does not use the TCA cycle or Electron Transport Chain • Releases energy from sugars or other organic molecules, but only 2 ATP for each glucose • Does not use O2 o or inorganic electron acceptors • Uses an organic molecule as the final electron acceptor • Produces only small amounts of ATP and most of the energy remains in the organic end product

24. Fermentation • In fermentation, pyruvic acid or its derivatives are reduced by NADH to fermentation end products • Ensures recycling of NAD+ for glycolysis

25. Why bother with fermentation? • Fermenting bacteria can grow as fast as those using aerobic respiration by markedly increasing the rate of glycolysis • Fermentation permits independence from molecular oxygen and allows colonization of anaerobic environments

26. Types of fermentation Acid Fermentation Homolactic • Only lactic acid • Streptococcus and Lactobacillus Heterolactic • Mixture of lactic acid, acetic acid and CO2 • Can result in food spoilage • Can produce • Yogurt • Sauerkraut • Pickles

27. Bring on the good stuff • Alcohol fermentation by the yeast Saccharomyces is responsible for some of the better things in life • CO2 produced causes bread to rise • Ethanol is used in alcoholic beverages

28. End products of fermentation

29. Metabolic pathways of Energy Use • The complete oxidation of glucose to CO2 and H2O is considered an efficient process • But, 45% of the energy from glucose is lost as heat • Cells use the remaining energy (in ATP) in a variety of ways • E.g., active transport of molecules across membrane or flagella motion • Most is used for the production of new cellular components

30. Integration of metabolic pathways • Carbohydrate catabolic pathways are central to the supply of cellular energy • However, rather than being dead end pathways, several intermediates in these pathways can be diverted into anabolic pathways • This allows the cell to derive maximum benefit from all nutrients and their metabolites • Amphibolic Pathways-integration of catabolic and anabolic pathways to improve cell efficiency

31. Amphibolic view of metabolism Glycolysis glyceraldehyde-3-phosphate pyruvate TCA cycle acetyl-CoA oxaloacetic acid α-ketoglutaric acid