Acetone carboxylation as a model reaction for anaerobic activation of hydrocarbons

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In the past funding period, acetone carboxylases of several nitrate-reducing bacteria turned out to be similar to those of aerobic bacteria, i.e., they require 2 ATP equivalents for acetone carboxylation to acetoacetate. From methanogenic enrichment cultures with acetone as sole substrate, acetone-fermenting bacteria were isolated and assigned to the genus Desulfosporosinus, closely related to D. orientis. With the sulfate-reducing bacterium Desulfococcus biacutus, strong evidence for a novel type of acetone activation was obtained in which acetone is carbonylated with CO to form acetoacetaldehyde. In the upcoming funding period, this new type of “acetone carbonylation” is to be studied in detail. The reaction partners have to be identified, the involved enzyme(s) to be enriched and purified, and its genetic coding to be identified via proteomic and genomic analysis of specifically expressed proteins. The entire reaction chain is to be elucidated by enzyme measurements with respect to the overall energy balance of this metabolism, and similar studies are to be extended to Desulfobacterium cetonicum and the recently isolated Desulfosporosinus sp.