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chapter five: microbial metabolism

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1 chapter five: microbial metabolism

2 oxidation-reduction redox reaction: coupled reactions
e- removed as part of H atom

3 redox reactions aerobic respiration oxygenic photosynthesis

4 nutritional classification: metabolic strategy
aerobic respiration iron oxidizers E source to oxidize e- light/chemical light energy phototroph chemical energy chemotroph carbon source org./inorganic photoheterotroph photoautotroph chemoheterotroph chemoautotroph electron source organic/inorganic photoorgano- heterotroph photolitho- chemoorgano- inorganic autotroph oxygen other inorganic electron acceptor org./inorganic fermentation butanediol mixed acid lactic acid alcohol respiration chemolitho- anoxygenic photosynthesis anaerobic respiration sulfur oxidizers oxygenic photosynthesis e- acceptor oxygen/other Purple non- Sulfur bacteria PSB, GSB, GNSB Cyanobacteria (plants) We categorize based on carbon, energy, and electron source NSP bacteria grow photoheterotrophically using malate or succinate as e-, C and light

5 classifying respiration & photosynthesis

6 complementary metabolism

7 acquiring ATP: substrate level phosphorylation

8 acquiring ATP: oxidative phosphorylation & chemiosmosis

9 heterotrophy: respiration
The ETC process The ETC overview Factors affecting the ETC Switching to fermentation electron path (oxidation)

10 heterotrophy: respiration & fermentation
C6H12O6 CO2 NAD+ NADH ETC ADP + P lots of ATP 2 H+ reduced e- acceptor inorganic e- acceptor C6H12O6 pyruvate NAD+ NADH substrate P few ATP lactic acid ethanol & CO2 mixed acids butanediol organic ferm

11 heterotrophy: respiration & fermentation
inorganic e- acceptor does NOT mean O2 organic mole.  CO2 fermentation organic e- acceptor organic  organic mole. incomplete H stripping, lower ATP yield The Kreb’s Cycle The Kreb’s Cycle in detail

12 metabolism & media

13 Chapter Five Learning Objectives
Discuss redox reactions in biological systems. Identify the redox partners in aerobic and anaerobic respiration and oxygenic and anoxygenic photosynthesis. Correctly identify the carbon, energy and electron source for an organism when given its nutritional classification (e.g., chemoorganoheterotroph). How is ATP generated in both substrate level and oxidative phosphorylation? Why is it so important that the electron transport chain is housed in a lipid bilayer membrane? Why is a terminal electron acceptor so important? What happens in a microorganism if the terminal electron acceptor of the ETC is not available? What molecules build up? What is done with these molecules? Discuss the major differences between respiration and fermentation. What are the four basic kinds of fermentation?

14 autotrophy: chemosynthesis
chemo-: conversion of chemical E  ATP iron oxidation sulfur oxidation -synthesis: carbon fixation (CO2  organic molecule) ADP + P ETC ATP NAD NADH carbon fixation 2 H+ 2Fe2+ 2Fe3+ heterotrophy 2 H+ ADP + P ETC ATP NAD NADH carbon fixation H2S SO42- heterotrophy

15 chemosynthesis: iron oxidation
Thiobacillus ferrooxidans chemolithoautotrophy energy = Fe2+  Fe3+ electron = same carbon = CO2  CH2O

16 chemosynthesis: sulfur oxidation
Sulfolobus acidocaldarius chemolithoautotrophy energy = S2- (sulfide) / S2O32- (thiosulfate)  SO32- (sulfite) electron = same carbon = CO2  CH2O

17 autotrophy: photosynthesis
photo: light E  chemical E light-dependent (light) reactions ATP & NAD(P)H “reducing power” synthesis: light-independent (dark) reactions carbon fixation: piling e- onto CO2 H2S/H2O ADP + P chlorophyll ETC ATP NAD(P) NAD(P)H carbon fixation oxidized heterotrophy

18 photosynthetic electron flow & chemiosmosis
cyclic photosynthesis in the purple sulfur bacteria non-cyclic photosynthesis in the cyanobacteria Comparing Eukaryotic & Prokaryotic photosynthesis

19 microbial CO2 fixation

20 photosynthesis compared
Eukaryotes Prokaryotes Algae, Plants Cyanobacteria Green Bacteria Purple Bacteria electron donor H2O H2O or H2S sulfur compounds O2 production oxygenic oxygenic anoxygenic anoxygenic environment aerobic aerobic anaerobic anaerobic CO2 fixation Calvin-Benson Reverse Citric Acid (Reverse Kreb’s)

21 amphibolism & ATP 21


23 metabolic diversity: the non-sulfur purple bacteria
chemoheterotrophic growth aerobic respiration fermentation photoautotrophic growth anaerobic, anoxygenic photosynthesis H2 for e- & CO2 for C photoheterotrophic growth anaerobic, anoxygenic photosynthesis C6H6O4 (succinate) for both

24 chapter 5 learning objectives
How is ATP generated in chemosynthesis, photosynthesis and respiration? How is the process different for each and how is it the same? Discuss the redox partners of sulfur and iron oxidizing bacteria. How do non-cyclic and cyclic photosynthesis differ? How does each produce ATP and NADPH/NADH? What is each used for? How is carbon fixed during chemosynthesis and photosynthesis? How is the process similar and how is it different? How do amphibolism, catabolism and anabolism relate to growth and repair in cells?

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