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J. Bacteriol., 01 1995, 277-282, Vol 177, No. 2
Copyright © 1995, American Society for Microbiology

Catabolic and anabolic enzyme activities and energetics of acetone metabolism of the sulfate-reducing bacterium Desulfococcus biacutus

PH Janssen and B Schnik
Fakultat fur Biologie, Universitat Konstanz, Germany.

Acetone degradation by cell suspensions of Desulfococcus biacutus was CO2 dependent, indicating initiation by a carboxylation reaction, while degradation of 3-hydroxybutyrate was not CO2 dependent. Growth on 3- hydroxybutyrate resulted in acetate accumulation in the medium at a ratio of 1 mol of acetate per mol of substrate degraded. In acetone- grown cultures no coenzyme A (CoA) transferase or CoA ligase appeared to be involved in acetone metabolism, and no acetate accumulated in the medium, suggesting that the carboxylation of acetone and activation to acetoacetyl-CoA may occur without the formation of a free intermediate. Catabolism of 3-hydroxybutyrate occurred after activation by CoA transfer from acetyl-CoA, followed by oxidation to acetoacetyl-CoA. In both acetone-grown cells and 3-hydroxybutyrate-grown cells, acetoacetyl- CoA was thioyltically cleaved to two acetyl-CoA residues and further metabolized through the carbon monoxide dehydrogenase pathway. Comparison of the growth yields on acetone and 3-hydroxybutyrate suggested an additional energy requirement in the catabolism of acetone. This is postulated to be the carboxylation reaction (delta G(o)' for the carboxylation of acetone to acetoacetate, +17.1 kJ.mol- 1). At the intracellular acyl-CoA concentrations measured, the net free energy change of acetone carboxylation and catabolism to two acetyl-CoA residues would be close to 0 kJ.mol of acetone-1, if one mol of ATP was invested. In the absence of an energy-utilizing step in this catabolic pathway, the predicted intracellular acetoacetyl-CoA concentration would be 10(13) times lower than that measured.(ABSTRACT TRUNCATED AT 250 WORDS)

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