Chromosomal instability in Streptomyces glaucescens: mapping of streptomycin-sensitive mutants

Streptomyces glaucescens strain GLAO (=ETH 22794) produces hydroxystreptomycin and has a high natural resistance to hydroxystreptomycin, dihydrostreptomycin and streptomycin. The wild-type strain gives rise spontaneously to streptomycin-sensitive (StrS-) variants at a frequency of 0 . 2 to 1 . 4%. These mutants lack streptomycin phosphotransferase activity responsible for the wild-type resistance to streptomycin group antibiotics and are unable to produce detectable amounts of hydroxystreptomycin. Mapping experiments showed that the strS marker lies between the chromosomal markers lys-2 and ura-3 on the linkage map of S. glaucescens. The molecular basis for instability of this marker is as yet unknown.