beta-Lactamase activity and resistance to penicillins in Myxococcus xanthus

Several mutants and other variants of Myxococcus xanthus HP100 were obtained with differences in their sensitivity to carbenicillin and other penicillin derivatives. The specific activities of beta-lactamase in different resistant organisms varied from strain to strain but were consistently higher than in HP100. The relative molecular mass (Mr) of the enzyme in M. xanthus HP100 was found to be 22,300. In certain carbenicillin resistant strains a second fraction of beta-lactamase activity of molecular weight 186,000 presumed to be an octamer of the other form was present. The enzyme was found in cell free extracts and also in culture supernatants of all carbenicillin resistant mutants but not in culture supernatants of strain HP100. In all the carbenicillin resistant mutants a part of the intracellular enzyme activity was released by osmotic shock and this activity may be periplasmic. The forms of the enzyme present in the culture supernatants and released by osmotic shock were monomeric. Carbenicillin resistance was not transferable between strains by conjugation. One resistance allele inhibited the transfer of the R factor Sa between myxococci.