recB recJ mutants of Salmonella typhimurium are deficient in transductional recombination, DNA repair and plasmid maintenance

recB recJ mutants of Salmonella typhimurium are deficient in transduction of chromosomal markers and ColE1-derived plasmids, and also in the maintenance of ColE1 and F plasmids. Plasmid instability is less severe in recD recJ strains; ColE1 plasmid DNA preparations from these strains show an increased yield of high molecular weight (HMW) linear multimers and a concomitant reduction in plasmid monomers compared to the wild type. Plasmids remain unstable in recA recD recJ mutants; since these do not produce HMW linear concatemers, we propose that a decrease in monomer production leads to plasmid instability, recB recJ strains also display decreased viability, a component of which may be related to their deficiency in DNA repair. In contrast to their severe defects in recombination, DNA repair and plasmid maintenance, recB recJ mutants of S. typhimurium behave similarly to the wild type in the segregation of chromosome duplications, The latter observation suggests that neither RecBCD nor RecJ functions are required for chromosomal recombination events that do not involve the use of free ends as recombination substrates.