SUMMARY: An extracellular-protease-deficient mutant, ME142, was isolated from as a spontaneous erythromycin-resistant (Ery) clone. This mutant showed conditional sporulation and only sporulated normally in the absence of erythromycin. In the presence of the antibiotic, sporulation was greatly reduced. Production of extracellular proteases by ME142 also exhibited conditional deficiency, possibly due to pleiotropic effects of the sporulation deficiency. The production of protease was 2-10% that of the wild-type level in the presence of erythromycin. ME142 showed poor competence for transformation even in the absence of erythromycin; however, derivatives of ME142 were isolated which had the same Ery phenotype but which exhibited normal competence. One such mutant, ME162, was used as a host for the secretion of coli β-lactamase. The amount of β-lactamase in the culture supernatants of ME162 increased significantly when the cells were cultured with erythromycin, suggesting that proteolysis of the β-lactamase in the supernatants of ME162 was greatly reduced as compared to that in the supernatants of the wild-type strain.


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