Metabolism of poly-beta-hydroxybutyrate and acetoin in Bacillus cereus.

Kominek, Leo A. (University of Illinois, Urbana), and H. Orin Halvorson. Metabolism of poly-beta-hydroxybutyrate and acetoin in Bacillus cereus. J. Bacteriol. 90:1251-1259. 1965.-The synthesis of poly-beta-hydroxybutyrate (PHB) in Bacillus cereus strain T begins after the cessation of logarithmic growth. Its accumulation is preceded by the formation of acetoacetyl coenzyme A reductase, an enzyme used for its biosynthesis. Exogenous acetic acid present in the medium owing to incomplete glucose oxidation serves as the carbon source for polymer formation during the initial stages of its synthesis. Pyruvic acid is converted to acetoin by an enzyme system that is formed during vegetative growth. The formation of this enzyme system is dependent on a low pH in the medium. As the cells enter the sporulating stage, they lose the ability to form acetoin. The acetoin that accumulates is utilized via the 2,3-butanediol cycle which begins to function late in the sporulation stage. This cycle generates acetic acid which is used for PHB synthesis and is also oxidized to carbon dioxide. PHB accumulation reaches a maximum just prior to the formation of spores, and it is degraded during the process of sporulation. The effect of sporulation inhibitors and pH on PHB and acetoin metabolism are discussed.