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

Abstract

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