| Very little is known about the role of DNA repair networks in the pathogenesis by Brucella abortus. Being an intracellular pathogen, its ability to survive within macrophages is crucial to infect the host; hence, the mechanisms used are central to pathogenesis. First, we investigated RecA, key protein of the SOS response. While many bacteria are hypersensitive to UV-radiation, B. abortus recA mutants, surprisingly, exhibited a moderate sensitivity. The presence of a second RecA protein was hypothesized, but even though a recA-like gene and gene product were detected, our efforts to clone this gene failed. An analysis of the genome of Brucella spp. confirmed the presence of one recA gene. A BLASTP search, however, showed some homology between RecA and another repair protein, RadA. The cloned B. abortus radA gene product was characterized both in E. coli and B. abortus . Our results indicated that RadA was a 38 kD MC-inducible protein, could perform homologous recombination and could substitute for RecA. However, the genetic requirements for recA suppression differed according to the host, suggesting different regulation mechanisms. Also, the deletion of radA barely impaired the ability of Brucella to replicate within macrophages, confirming its role as an auxiliary protein. Then, we investigated the effect of a non-cleavable mutant of E. coli , LexA(Ind-), another protein of the SOS response. Our results showed that, despite the distant phylogenetic relationship between B. abortus and E. coli, LexA(Ind-) was able to render B. abortus wild-type and repair-deficient mutants more sensitive to damage. Similar results were observed with other bacterial species, indicating a possible broad use of this mutant. In vitro studies with these repair-deficient strains showed an increased sensitivity to macrophages. Thus, these findings indicated that the SOS regulon, and more specifically, recombinational repair, was necessary for survival of Brucella to repair NO- and H2O2-induced lesions. Last, a preliminary computational analysis of Brucella spp. genome proposed a number of genes likely to participate in the SOS network of Brucella, divergent from the SOS regulon of E. coli and other bacteria. Thus, despite a highly conserved RecA protein, there is diversity in SOS repair networks among bacteria. |
