Anaerobic acetate oxidation to CO2 by Desulfobacter postgatei

Abstract

The strict anaerobe Desulfobacter postgatei oxidizes acetate to CO2 with sulfate as electron acceptor. During growth at 28°C with a doubling time of 16 h the oxidation and assimilation rate of acetate were 280 nmol and 20 nmol per min and mg protein, respectively. In cell extracts all the enzymes of the citric acid cycle were found (numbers in brackets=specific activities in nmol per min and mg protein at 28°C): Citrate (si)-synthase (250); aconitase (200); NADP-dependent isocitrate dehydrogenase (8500); 2-oxoglutarate: ferredoxin oxidoreductase (300); succinyl-CoA: acetate CoA transferase (160); membrane bound succinate dehydrogenase (3500); and membrane bound malate dehydrogenase with 2,3-dimethyl-1,4-naphthoquinone as artificial electron acceptor (54). The following enzymes catalyzing the synthesis of oxaloacetate from acetate and CO2 were also present: Acetyl-CoA synthetase (10); ferredoxin dependent pyruvate synthase (30); phosphoenolpyruvate synthetase (10); and phosphoenolpyruvate carboxylase (24). The key enzymes of the glyoxylate cycle were not detected. The order of magnitude of the observed enzyme activities was sufficient to account for an oxidation of acetate via the citric acid cycle and for a synthesis of oxaloacetate from acetate and CO2 as anaplerotic reaction.