Fermentation of trans-aconitate via citrate, oxaloacetate, and pyruvate by Acidaminococcus fermentans

Growing cells of Acidaminococcus fermentans (DSM 20731 and ATCC 25085) fermented trans-aconitate via citrate, oxaloacetate, and pyruvate to approximately 2 CO2, 1.8 acetate, 0.1 butyrate and 0.9 H2. The carbon and electron recoveries were close to 100%. On citrate no growth was observed and washed cells were unable to ferment this tricarboxylate. In cell-free extracts, however, citrate as well as trans-aconitate were readily fermented to CO2 and acetate. Under these conditions, also cis-aconitate, oxaloacetate, and pyruvate were formed, whereas butyrate and intermediates of glutamate fermentation, 2-oxoglutatrate and glutaconate, could not be detected. Citrate Si-lyase, a Mg2+-dependent oxaloacetate decarboxylase, and pyruvate synthase were present in quantities that corresponded to the growth rate of the organism.