Membrane-bound and extracellular β-lactamase production with developmental regulation in Streptomyces griseus NRRL B-2682

Abstract

A new type ofβ-lactamase has been isolated and characterized in Streptomyces griseus NRRL B-2682. The enzyme has membrane-bound and extracellular forms. Biochemical characterization of some of the properties of the enzyme showed that it belongs to the class A group of penicillinases. Comparison of the membrane-bound and extracellular forms of theβ-lactamases suggests that they seem to be differently processed forms of the same enzyme. The N-terminal amino acid sequence of the extracellular form of the β-lactamase showed a high degree of similarity to a D-aminopeptidase of another Streptomyces griseus strain. Secretion of the β-lactamase was affected by the differentiation state of the strain since in spontaneous non-sporulating mutants only the membrane-bound form was present. In accordance with this when sporulation of the wild-type strain was inhibited it failed to secrete extracellular β-lactamase. Addition of globomycin to the non-sporulating cells liberated the enzyme from the membrane, indicating that the protein is processed normally by signal peptidase II and a glyceride-thioether group, together with a fatty acid amide-linkage, is responsible for the attachment of the enzyme to the cellular membrane. Under sporulation-repressed conditions addition of peptidoglycan fragments and analogues or inhibition of cell wall biosynthesis by penicillin-G induced β-lactamase secretion and also restored sporulation both in solid and submerged cultures. These results confirm that β-lactamase secretion is tightly coupled to the sporulation process in S. griseus.