Antibiotic production improvement in the rare actinomycete Planobispora rosea by selection of mutants resistant to the aminoglycosides streptomycin and gentamycin and to rifamycin.

During a strain improvement program, spontaneous mutants with single or combined resistance to streptomycin (Str(r)), gentamycin (Gen(r)) or rifamycin (Rif(r)) were selected from the industrial strain of Planobispora rosea, which is the producer of thiazolylpeptide GE2270. Among the mutants resistant to each single antibiotic, higher producers occurred more frequently (60%) among Gen(r) than in Rif(r) (10%) and Str(r) (24%) populations. Two Gen(r) mutants showed up to 1.5-fold improvement in GE2270 production while single resistant mutants Str(r) and Rif(r) produced slightly more than the parental strains. The combination of Str(r) and Rif(r) in the same strain improved GE2270 yield up to 1.7-fold. Finally, a higher GE2270 producing strain (1.8-fold improvement with respect to the parental strain) was selected among those mutants with triple resistance to streptomycin, rifamycin and gentamycin. A hierarchical increase in aerial mycelium and spore formation was observed which paralleled GE2270 production improvement.