Genetic recombination in Bacillus subtilis 168:: Effect of ΔhelD on DNA repair and homologous recombination

The B. subtilis Delta helD allele rendered cells proficient in transformational recombination and moderately sensitive to methyl methanesulfonate when present in an otherwise Rec(+) strain. The Delta helD allele was introduced into rec-deficient strains representative of the alpha (recF strain), beta (addA addB), gamma (recH), kappa (Delta recU), and zeta (Delta recS) epistatic groups. The Delta helD mutation increased the sensitivity to DNA-damaging agents of addAB, Delta recU, and Delta recS cells, did not affect the survival of recH cells, and decreased the sensitivity of recF cells. Delta helD also partially suppressed the DNA repair phenotype of other mutations classified within the alpha epistatic group, namely the recL, Delta recO, and recR mutations. The Delta helD allele marginally reduced plasmid transformation (three- to sevenfold) of mutations classified within the alpha, beta, and gamma epistatic groups. Altogether, these data indicate that the loss of helicase IV might stabilize recombination repair intermediates formed in the absence of recFLOR and render recFLOR, addAB, and recH cells impaired in plasmid transformation.