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Dissimilatory sulphate reduction with acetate as electron donor
Summary
Sulphate-reducing bacteria like Desulfobacter postgatei oxidize acetate via the citric acid cycle. This process is more efficient than methane production, explaining sulphate
Area of Science:
- Microbiology
- Biochemistry
- Environmental Science
Background:
- Acetate oxidation is a key metabolic process in anaerobic environments.
- Sulphate reduction and methanogenesis are competing pathways for acetate utilization.
- Understanding these pathways is crucial for biogeochemical cycling.
Purpose of the Study:
- To elucidate the mechanism of acetate oxidation by sulphate using Desulfobacter postgatei.
- To compare the efficiency of acetate utilization by sulphate reducers and methanogens.
- To explain the inhibition of methane formation by sulphate in natural habitats.
Main Methods:
- Studied acetate oxidation in cell extracts of Desulfobacter postgatei.
- Assayed activities of key enzymes involved in the citric acid cycle and related pathways.
- Determined in vivo kinetic parameters (apparent Ks) for acetate utilization.
Main Results:
- Desulfobacter postgatei possesses high activities of citric acid cycle enzymes and pyruvate synthase.
- Acetate oxidation in D. postgatei proceeds via the citric acid cycle with pyruvate synthesis.
- The apparent Ks for acetate oxidation by D. postgatei (0.2 mM) is significantly lower than that for methanogens (3 mM).
Conclusions:
- Acetate oxidation in D. postgatei occurs through the citric acid cycle, utilizing an anaplerotic reaction for pyruvate synthesis.
- The higher affinity for acetate in sulphate reducers explains their competitive advantage over methanogens.
- Sulphate presence inhibits acetate fermentation to methane due to the more efficient acetate metabolism by sulphate-reducing bacteria.