Volatile ketone formation in bacteria: Release of 3-oxopentanoate by soil pseudomonads during growth on heptanoate

During enrichments to search for soil bacteria that form the volatile keton es, acetone and butanone, we isolated pure cultures of Pseudomonas aureofac iens, P. fluorescens, and P. putida that excrete the beta -keto-acid, 3-oxo pentanoate (3-OPA), when grown on heptanoic acid as carbon source. Analysis of 3-OPA used enzymatic decarboxylation by acetoacetate decarboxylase to y ield butanone, which was detected by headspace gas chromatography. The form ation of 3-OPA was strongly dependent on heptanoic acid concentration, the level of oxygen, and the state of growth, and was not seen with even-chain or other odd-chain fatty acids. Uptake of 3-OPA during stationary phase of growth is probably related to polyhydroxyalkanoate (PHA) formation in these isolates. A model for formation and release of 3-OPA is proposed.