Interaction of tetracycline with protein synthesizing system of Streptomyces aureofaciens

Molecular cloning of tetracycline resistance genes from Streptomyces rimosus in Streptomyces griseus and characterization of the cloned genes

Two tetracycline resistance genes of Streptomyces rimosus, an oxytetracycline producer, were cloned in Streptomyces griseus by using pOA15 as a vector plasmid. Expression of the cloned genes, designated as tetA and tetB was inducible in S. griseus as well as in the donor strain. The tetracycline resistance directed by tetA and tetB was characterized by examining the uptake of tetracycline and in vitro polyphenylalanine synthesis by the sensitive host and transformants with the resultant hybrid plasmids. Polyphenylalanine synthesis with crude ribosomes and the S150 fraction from S. griseus carrying the tetA plasmid was resistant to tetracycline, and, by a cross-test of ribosomes and S150 fraction coming from both the sensitive host and the resistant transformant, the resistance directed by tetA was revealed to reside mainly in crude ribosomes and slightly in the S150 fraction. However, the resistance in the crude ribosomes disappeared when they were washed with 1 M ammonium chloride. These results suggest that tetA specified the tetracycline resistance of the machinery for protein synthesis not through ribosomal subunits, but via an unidentified cytoplasmic factor. In contrast, S. griseus carrying the tetB plasmid accumulated less intracellular tetracycline than did the host, and the protein synthesis by reconstituting the ribosomes and S150 fraction was sensitive to the drug. Therefore, it is conceivable that tetB coded a tetracycline resistance determinant responsible for the reduced accumulation of tetracycline.

Susceptibility of ribosomes of the tetracycline-producing strain of Streptomyces aureofaciens to tetracyclines

Ribosomes from cells of Streptomyces aureofaciens producing tetracycline antibiotics (Tc-ribosomes) differ in electrophoretic mobility of ribosomal proteins S2, S10 and L19 from those of the same strain, where the production of tetracyclines was suppressed by changed cultivation conditions (C-ribosomes). Purified tight vacant couples C- and Tc-ribosomes are equally active in the translation of poly(U). Both types of S. aureofaciens ribosomes are more sensitive to tetracycline and chlortetracycline than ribosomes of Escherichia coli in the Phe-tRNA binding and the translation of poly(U).

[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.

Synthesis and degradation of proteins and DNA in Streptomyces aureofaciens

The rate of protein synthesis in Streptomyces aureofaciens, measured by incorporation of U-14C-L-leucine into cells, fluctuated during the production phase in the range of 10-15% of the values determined in the phase of intensive growth. Tetracycline partially inhibited the protein synthesis during the growth phase only. The proteins synthesized between the 6th and 18th hour of growth, were 75% degraded by the 48th hour. The DNA synthesis, measured by means of incorporation of 2-14C-thymine into the mycelium, occurred predominantly during the first 24 h of cultivation. Similarly, DNA synthesized between the 6th and 12th hour of cultivation was degraded by 75% after 48 h. The turnover of culture proteins is thus caused largely by degradation of old cells and growth of new ones which are more resistant to tetracycline. The activity of alanine aminotransferase and aspartate aminotransferase increase substantially towards the end of fermentation.

Properties of the ribosomes of antibiotic producers: effects thiostrepton and micrococcin on the organisms which produce them

Ribosomes of Streptomyces azureus, which produces thiostrepton, are resistant to thiostrepton by virtue of being unable to bind the antibiotic. These ribosomes are also resistant to a number of other antibiotics (the thiostrepton group) which may share a common ribosomal binding site and a common mode of action with thiostrepton. Conversely, Bacillus pumilis and a strain of micrococcus, which produce the (probably identical) antibiotics micrococcin P and micrococcin, respectively, possess ribosomes which are susceptible to these antibiotics in vitro, although the organisms themselves are resistant.

Properties of ribosomes from Streptomyces erythreus and Streptomyces griseus

Ribosomes from an erythromycin-producing strain, Streptomyces erythreus, lacked affinity for erythromycin and were also resistant to other macrolide antibiotics (leucomycin, spiramycin, and tylosin) and to lincomycin, whereas Streptomyces griseus B(3) ribosomes were susceptible to all of these antibiotics.