Construction and characterization of a Bacteroides thetaiotaomicron recA mutant: transfer of Bacteroides integrated conjugative elements is RecA independent.

We report the construction and analysis of a Bacteroides thetaiotaomicron recA disruption mutant and an investigation of whether RecA is required for excision and integration of Bacteroides mobile DNA elements. The recA mutant was deficient in homologous recombination and was more sensitive than the wild-type strain to DNA-damaging agents. The recA mutant was also more sensitive to oxygen than the wild type, indicating that repair of DNA contributes to the aerotolerance of B. thetaiotaomicron. Many Bacteroides clinical isolates carry self-transmissible chromosomal elements known as conjugative transposons. These conjugative transposons can also excise and mobilize in trans a family of unlinked integrated elements called nonreplicating Bacteroides units (NBUs). The results of a previous study had raised the possibility that RecA plays a role in excision of Bacteroides conjugative transposons, but this hypothesis could not be tested in Bacteroides spp. because no RecA-deficient Bacteroides strain was available. We report here that the excision and integration of the Bacteroides conjugative transposons, as well as NBU1 and Tn4351, were unaffected by the absence of RecA activity.