Genetic Recombination in Bacillus subtilis 168: Effect of ΔhelD on DNA Repair and Homologous Recombination

The B. subtilis ΔhelD allele rendered cells proficient in transformational recombination and moderately sensitive to methyl methanesulfonate when present in an otherwise Rec(+) strain. The ΔhelD allele was introduced into rec-deficient strains representative of the α (recF strain), β (addA addB), γ (recH), ɛ (ΔrecU), and ζ (ΔrecS) epistatic groups. The ΔhelD mutation increased the sensitivity to DNA-damaging agents of addAB, ΔrecU, and ΔrecS cells, did not affect the survival of recH cells, and decreased the sensitivity of recF cells. ΔhelD also partially suppressed the DNA repair phenotype of other mutations classified within the α epistatic group, namely the recL, ΔrecO, and recR mutations. The ΔhelD allele marginally reduced plasmid transformation (three- to sevenfold) of mutations classified within the α, β, and γ 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.