Acetone formation in the vibrio family: a new pathway for bacterial leucine catabolism

There is current interest in biological sources of acetone, a volatile orga nic compound that impacts atmospheric chemistry. Here, we determined that l eucine-dependent acetone formation is widespread in the Vibrionaceae, Sixte en Vibrio isolates, two Listonella species, and two Photobacterium angustum isolates produced acetone in the presence of L-leucine, Shewanella isolate s produced much less acetone, Growth of Vibrio splendidus and P, angustum i n a fermenter with controlled aeration revealed that acetone was produced a fter a lag in late logarithmic or stationary phase of growth, depending on the medium, and was not derived from acetoacetate by nonenzymatic decarboxy lation in the medium. L-Leucine, but not D-leucine, was converted to aceton e with a stoichiometry of approximately 0.61 mel of acetone per mel of L-le ucine, Testing various potential leucine catabolites as precursors of aceto ne showed that only alpha-ketoisocaproate was efficiently converted by whol e cells to acetone, Acetone production was blocked by a nitrogen atmosphere but not by electron transport inhibitors, suggesting that an oxygen-depend ent reaction is required for leucine catabolism. Metabolic labeling with de uterated (isopropyl-d(7))-L-leucine revealed that the isopropyl carbons giv e rise to acetone with full retention of deuterium in each methyl group. Th ese results suggest the operation of a new catabolic pathway for leucine in vibrios that is distinct from the 3-hydroxy-3-methylglutaryl-coenzyme A pa thway seen in pseudomonads.