The nourseothricin producer Streptomyces noursei is resistant to its own antibiotic in submerged as well as in surface culture. The strain shows no cross-resistance to miscoding inducing aminoglycoside antibiotics. Cell free extracts of Streptomyces noursei inactivate nourseothricin by enzymatic acetylation. The pattern of cross-resistance of Streptomyces noursei correlates well with the substrate specificity of the nourseothricin acetyltransferase. Furthermore, the acetyltransferase activity parallels the resistance level in nourseothricin-producing strains and nonproducing mutants. The results suggest that the nourseothricin acetyltransferase is important in the self-defence strategy of the nourseothricin-producing strain.
Streptothricin antibiotics (nourseothricin) are potent inhibitors of procaryotic protein synthesis and, in addition, inducers of miscoding ( . The nourseothricin producer Streptomyces noursei is, however, highly resistant t o its own antibiotic. Possible self-resistance mechanisms of antibiotic producers are : inactivation of the antibiotic by modifying enzymes, alteration of the target site, and reduced uptake of the antibiotic , CUNDLIFFE 1984).
Recent investigations revealed that cell free extracts of Streptornyces noursei inactivate nourseothricin by enzymatic acetylation (HAUPT and THRUM 1985). The results presented in this paper demonstrate a correlation between nourseothricin resistance and nourseothricin acetyltransferase activity of Streptomyces noursei.