Genetics of thermotolerance in ciprofioxacin resistant mutant of

A ciprotloxacin resi stant mutant (Cf) of Rhizobium legulIlinossarulll bv phaseoli USDA 2695 which nodulates common bean plants (Phaseolus vulgaris L) was isolated after nitrous acid mutagenesis. Another m tant resistant to nalidi xic acid (NaIR) was isolated spontaneously. Both mutants showed thermotolerance as evident by their abi lity to grow at elevated (40°C) temperature, although the wi ld type (USDA 2695) failed to grow at this temperature. Transformation and plasmid curing experiments suggested the gene(s) controlling thermotolerance (TrR) and res istance to nalidixic acid or cipro tloxac in were located on the main chromosome and not on the plasmids. Hi gh frequency of co-transfer of TrR_CrR and TrR _NaI R during transformati on experiments indicated a close association of these gene(s). Role of DKA gyrase and supercoiling in these thermololerant mutants has been discussed.