Derepression of F-lacinSalmonella typhimuriumby a determinant for kanamycin resistance

SUMMARY When a determinant for neomycin-kanamycin resistance (K) was transferred by an F-lacfactor intoSalmonella typhimurium, the resulting KF-lacstrain was sensitive to the male-specific phage μ2and F-lacwas derepressed. However, F-lacalone is repressed inS. typhimurium. When kanamycin resistance is spontaneously lost fromS. typhimuriumKF-lacan element persists which derepresses F-lacinS. typhimurium. The results are consistent with the hypothesis that a locusder, for derepression of F-lacinS. typhimurium, lies on the K plasmid. The R factor Rldrd19 is derepressed in K12 but is repressed inS. typhimurium. It also is derepressed byder. In contrast to F-lacand R1, another R factor, R136drdH8, is derepressed in both K12 andS. typhimurium, so that the intervention ofderis unnecessary for its derepression in the salmonella host.