ULTRAVIOLET-LIGHT, MITOMYCIN-C AND NITROUS-ACID INDUCE GENETIC INSTABILITY IN STREPTOMYCES-AMBOFACIENS ATCC23877

In Streptomyces ambofaciens ATCC23877, pigment-negative (Pig-) mutants occur at high frequency (about 0.7 X 10(-2)) in the progenies of wild -type colonies. Furthermore, the offspring of these Pig- mutants can e ither be phenotypically homogeneous or hypervariable (with no preponde rant phenotype). Pig- mutants can also lack antibiotic production and present aerial mycelium deficiency, auxotrophy for arginine, oversensi tivity to either ultraviolet (UV) light or mitomycin C and resistance to either novobiocin or nosiheptide. This genetic instability is relat ed to both amplified DNA sequences and deletions. Mutagens such as UV light, mitomycin C and nitrous acid induced genetic instability and in creased the Pig- mutant frequency to almost 30% even at a high surviva l rate. Induced Pig- mutants exhibited the same features as the sponta neous ones at both phenotypic and molecular levels. The frequency of d etected genomic rearrangements after treatment was higher than 10%. We postulate that an SOS-like system is involved in the induction of gen etic instability in S. ambofaciens.