Eingegangen arn 27. 5. 1983) Arsenate-resistant (AsR) clones were obtained with high frequency from colony populations of streptothricin-producing strains of Streptomyces noursei by the paper strip method. Whereas in the AsR-strains obtained from both wild type and mutant NG 13 the antibiotic production was reduced to approx. 60% of the parental level, the AsR clones isolated from colony populations of mutant UV 12 displayed increased productivity (5150%).However, their improved capacity to produce streptothricins was lost rapidly after repeated cell propagation in submerged cultures, suggesting that unstable genetic elements were involved in enabling S. noursei to grow in the presence of toxic concentrations of arsenate.Many reports on antibiotic fermentations attest that excessive supply with inorganic phosphate suppresses the production of secondary metabolites of streptomycetes and PeniciZZium species (DEMAIN 1982). Therefore, most fermentations of antibiotics require the addition of inorganic phosphate in growth-limiting amounts, if high yields are to be obtained (MARTIN 1978, INOUE et al. 1982, OMURA et al. 1981).The molecular mechanism of the so-called 'phosphate effect' appears to be complex and may also depend on the particular microorganism (MARTIN 1977). Among the possible mechanisms are the inhibition and repression of the antibiotic-specific pathway as well as interference with the energy metabolism and the system of precursor generation (MARTLN and DEMAIN 1976).In order to release antibiotic fermentations from the regulation by inorganic phosphate, efforts have been mainly directed to the control of the phosphate pool in the medium. Recent results show that mutants deregulated in their response to inorganic phosphate can be obtained from the candicidine-producing Streptomyces griseus by either the conventional screening techniques or selection of arsenateresistant (AsR) strains (MARTIN etal. 1979, NAHARRO et aZ. 1981). Because corresponding data for other antibiotic-producing streptomycetes are missing, the general value of the latter methods for the isolation of superior producers of antibiotics cannot he assessed.I n the present work, we report on the isolation and some properties of arsenateresistant strains of Streptomyces noursei, a microorganism producing streptothricintype antibiotics (BRADLER and THRUM 1963).
Materials and methodsStrains: Streptomyces ltoursei J A 3890b (BRADLER and THRUM 1963) was received from the culture collection of the Central Institute of Microbiology and Experimental Therapy, Jena.Mutant strains UV 12 and NG 13 were obtained by random selection for high antibiotic activity after using UV light and nitrosomethyl guanidine, respectively, as mutagens. The latter strains showed a 2-3 fold higher capacity to produce streptothricins (nourseothricin) than the parental strain.
