Microbiology Helmut Pospiech

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1 Microbiology Helmut Pospiech

2 Microbial Metabolism Different ways to make a living

3 Energy metabolism of Microorganisms Fermentation ADP +Pi Motility ATP Active transport (nutrient uptake)

4 Any Way to Catabolise Glucose Embden-Meyerhof pathway (glycolysis) Entner-Douderoff pathway Pentose phosphate pathway

5 Embden-Meyerhof pathway

6 The Entner-Doudoroff pathway Can be considered a variant of the Embden-Meyerhof pathway Utilised by many bacteria including Pseudomonads Stanier et al., General Microbiology, 5th ed. KDPG = 2-keto-3-deoxy- 6-phospho-gluconate Ł only 1 ATP / glucose Modified from Hal White,

7 The Pentose Phosphate Pathway Basically cycle where C 1 of glucose will be completely oxidised to CO 2 The resulting pentose will be rearranged to produce glucose again Transketolase Transaldolase Can be used to feed in pentoses (as carbon source) In eukaryotes mainly used to produce NADPH and precursors for anabolism Basically irreversible at the 3rd step of the reaction (6-P-G dehydrogenase), but can be reversible by introducing an additional step catalysed by the enzyme RubisCO (Calvin cycle) Irreversible step

8 Horton et al. Principles of Biochemistry, 4th ed.

9 The Fate of Pyruvate Krebs Cycle Anabolism or Complete oxidation CO 2 Pyruvate Fermentation Direct regeneration of NADH Respiration Regeneration of NADH Glyoxylate Cycle Anabolism

10 Krebs Cycle

11 Lactic Acid Fermentation Ł 2 ATP

12 Fermentation the Art of Effective NADH Regeneration In every fermentation, there has to be atomic and redox balance Simplest way to keep redox balance is to produce H 2 H 2 is then used by other microorganisms

13 Common Microbial Fermentations

14 Unusual Bacterial Fermentations

15 Lactic Acid Fermentation Lactic acid bacteria Homofermentative: Yoghurt Heterofermentative: Sauerkraut Sour milk (piimä)

16 Mixed Acid Fermentation Enterobacteria and closely related, e.g.: E. coli Salmonella spp. Shigella dysenteriae Klebsiella spp. Proteus spp.

17 Clostridial Fermentations I e.g. Clostridium acetobutylicum At neutral ph, butryate is the main fermentation product 3 ATP /glucose fermented Lowers ph of the medium When ph gets too low, fermentation is switched to acetone/butanol Neutral fermentation products But only 2 ATP /glucose fermented

18 Clostridial Fermentations II the Stickland Reaction Proteolytic clostridia, e.g. C. histolytica C. putrifaciens C. tetani C. botulinum Ferment pairs of amino acids: one as electron donor and one as electron acceptor Many foul-smelling byproducts: H2S Methylmercaptan Cadaverine Putrecine Clostridia are major putrefiers (Suom. mädäntyjät ) Many similar fermentations with other substrates

19 Clostridial Fermentations II the Stickland Reaction

20 Clostridial Fermentations III

21 Propionic Acid Fermentation Propionibacterium spp. Swiss (Emmental) cheese Makes the holes in the cheese Originally in the rumen (suom. pötsin) of cattle 1 ATP /Lactate fermented Secondary fermentation!

22 Fermentations lacking substrate level phosphorylations ΔG 0 = kj ΔG 0 = kj Succinate fermentation Propionigenium modestum Energy produced is not sufficient for direct ATP generation Na + ion is pumped across the cytoplasmic membrane Oxalate fermentation Oxalobacter formigenes Energy conserved as protomotoric force (H + gradient) The end of the line for fermentation?

23 No! Syntrophy Two different microorganisms cooperate to degrade a substance that neither can utilise alone Mainly secondary fermentations Interspecies H 2 transfer Keeps H 2 concentrations low and drives the reaction to the product side although the ΔG 0 is positive Mainly fermentation of alcohols and fatty acids