Roles of streptomycin 6 -kinase and ribosomal affinity to streptomycin in self-protection of streptomycin producer

Molecular cloning and expression in Streptomyces lividans of a streptomycin 6-phosphotransferase gene from a streptomycin-producing microorganism

The gene encoding streptomycin 6-kinase involved in the self-resistance of the streptomycin-producing Streptomyces griseus HUT 6037 was cloned in the plasmid vector pIJ703. The resulting plasmid, pSP6, contained 2.5 kb inserts of S. griseus DNA. When streptomycin-susceptible S. lividans 1326 was retransformed with pSP6, all transformants produced streptomycin 6-kinase. Addition of streptomycin to the culture medium of S. lividans carrying pSP6 plasmid brought about a remarkable increase in streptomycin 6-kinase activity in the cell extracts. It is suggested from the results that the production of streptomycin 6-kinase in streptomycin producer was induced by streptomycin accumulated during cultivation.

Influence of nourseothricin on growth and secondary metabolism of Streptomyces noursei JA 3890b

The nourseothricin-producing S. noursei strain JA 3890b possessed a high degree of resistance to its own antibiotic when grown in submerged cultures started from mycelium samples as inocula. In contrast, both the outgrowth of spores and the development of surface colonies from mycelium samples were severely inhibited in the presence of relatively low concentrations of nourseothricin, suggesting that the producer organism is susceptible to the autotoxic metabolite in particular stages of its development. Nourseothricin production by submerged cultures has been found to be independent of negative feedback regulation by the antibiotic.

[Secondary metabolites as endogenous effectors of microbial cytodifferentiation]

The present survey covers the regulatory role of microbial secondary metabolites and related compounds as endogenous signals of cell differentiation of the producing organisms. Several antibiotics have been shown to exert autoregulatory effects on differentiation-associated functions. The mechanisms of self-protection of the producing cells against the autotoxicity of secondary metabolites are discussed in terms of an integral part of the modulation of signal strength. As a further topic, the review deals with the hormone-like interference of particular metabolites with differentiating cells. Conclusive discussion concerns the potential use of microbial signal molecules either as tools for directed manipulations of product syntheses or as pharmaceutics.