Effect of polymyxin B, tyrocidine, gramicidin D, and other antibiotics on the enzymatic hydrolysis of poly-beta-hydroxybutyrate.

Merrick, J. M. (State University of New York, Buffalo). Effect of polymyxin B, tyrocydine, gramicidin D, and other antibiotics on the enzymatic hydrolysis of poly-beta-hydroxybutyrate. J. Bacteriol. 90:965-969. 1965.-Previous studies have demonstrated that native poly-beta-hydroxybutyrate (PHB) granules isolated from Bacillus megaterium are surrounded by a discrete membranelike structure. Morphological alterations of PHB granules are mainly characterized by membrane fragmentation, and can be correlated with decreased susceptibility of the polymer to enzymatic hydrolysis by soluble factors. In the present investigation, the inhibitory effect of a variety of surface-active and other antibiotics on the enzymatic depolymerization of PHB was examined. The most potent inhibitors were polymyxin B, tyrocidine, and gramicidin D. These polypeptide antibiotics are known to attack other types of membranous structures. The results, therefore, support previous evidence that the membrane or similar constituents of PHB granules are intimately involved in its metabolism. Chlortetracycline was also found to be a potent inhibitor of the depolymerization, but its mechanism of action may be different from the other antibiotics. The polymer-synthesizing enzyme(s), also localized on the granules, is inhibited by tyrocidine and gramicidin D but not by polymyxin B or chlortetracycline.