ROLE AND OXIDATION PATHWAY OF POLY-β-HYDROXYBUTYRIC ACID IN MICROCOCCUS HALODENITRIFICANS

Abstract

Cells of Micrococcus halodenitrificans have a high poly-β-hydroxybutyric acid (PHBA) content, the oxidation of which accounts for the high endogenous respiration of this organism. The amount of polymer in resting cells decreased with time, and viability could be correlated with the polymer content of the cells. PHBA-rich cells maintained their viability for longer periods than PHBA-poor cells. Cells oxidized PHBA in the presence of sodium chloride but not in water; optimal oxidation occurred in 0.33 to 0.75 M NaCl.The results suggest the following oxidation pathway. A diethyl p-nitrophenyl phosphate sensitive depolymerase catalyzes the hydrolysis of the polyester to β-hydroxybutyrate. This soluble substrate is oxidized by a DPN-linked D(−)-β-hydroxybutyric acid dehydrogenase to acetoacetate. Acetoacetate is further oxidized in the presence of oxalacetate, ATP, and coenzyme A. Citrate is formed, indicating the presence of the condensing enzyme, and PHBA oxidation is strongly inhibited by malonate. These findings suggest that oxidation proceeds via the tricarboxylic acid cycle.