Genetic segregation in a high‐yielding streptomycin‐producing strain of Streptomyces griseus

Abstract

The streptomycin-producing Streptomyces griseus HP spontaneously segregated non-reverting derivatives with altered phenotypes. Clones characterized by increased spore formation and decreased streptomycin production were found. Two other types of derivatives were defective in aerial mycelium and streptomycin formation as well, but differed in the capacity to synthesize a yellow pigment. These derivatives were examined with respect to further properties.The stability of S. griseus HP was investigated in relation to conditions of continuous culture. Both a t 26 and 30 "C, under glycerol and NH,Cl limitation a rapid segregation and enrichment of streptomycin-non-producing derivatives occurred. At 34 "C and glycerol limitation segregation began only after about 35 generations of continuous culture. I n NH,CI-limited chemostats the original strain was stable during 80 generations. I n the course of the continuous culture experiments it was shown that the onset of genetic segregation within mycelia can be detected before it becomes obvious in colonies grown from the mycelia. This was achieved by fractionation of the mycelia by protoplast formation and subsequent plating on regeneration medium allowing colony growth and differentiation.The frequent degeneration of high-yielding Streptomyces strains used in coniinercial antibiotic fermentations is a well-known phenomenon (for review see REUSSER 1963).However, the molecular meLhanisms causing the genetic instability or variability, respectively, of streptomycetes are not fully understood. Loss of plasniids in cases of extrachromosomally determined antibiotic production may be one reason for strain degeneration (HOPWOOD 1978).In order to avoid serious problems in industrial fermentations it is necessary to circumvent culture degeneration. Continuous selection of the respective phenotypes and storage of the strains in a viable but non-reproducing state, e. g. in lyophilized preserves, are usual methods for this purpose (REUSSER 1963). In spite of these measures strain degeneration can nevertheless occur in the course of long-term fernient at ion processes. The original strain can be overgrown by a few faster growing non-productive segregants which appear spontaneously.Therefore it would be useful to know culture conditions promoting or inhibiting strain degeneration. In this connection the properties of degenerated variants or mutants play an important role. Furthermore it would be favourable to have a method to detect the beginning of genetic segregation or degeneration in industrial Streptomyces strains, e . g. during preparation of biomass for lyophilization and in preserves used as inocula for fermentations. In our investigations concerning these probleins we used a high-yielding streptomycin-producing Streptomyces griseus strain. Both the frequency of spontaneous appearance of non-producers in agar slant cultures and the strain stability during culture in chemostats under different conditions, as described recently (ROTH and NOACK 1982), were examined. Derivatives of th...