DNA recombination in Escherichia coli and Pseudomonas aeruginosa

MORO CAMILA; BORGOGNO MARÍA V; MONTI MARIELA R; ARGARAÑA CARLOS E

Congreso; LII Reunión Anual de SAIB; 2016

RecA is a central factor in the recombination between DNA molecules containing exact homology (homologous, HO) or very low divergence (homeologous, HE) sequences. Recombination of sequences containing low divergence is inhibited by the concerted action of the mismatch repair proteins MutS and MutL. We have built a genetic system to determine HO and HE recombination in Gram-negative bacteria. Using this system, we determined the recombination rate in the wild-type (WT) and mutant strains (recA and mutS) of Pseudomonas aeruginosa and Escherichia coli. In both bacteria, HO recombination rates were approximately 60-200-fold higher than HE recombination rates. The absence of MutS did not affect HO recombination levels, but raised HE recombination rates to values close to that of HO recombination, indicating that MutS controls the exchange between divergent sequences. In the E. coli RecA-deficient strain, both HO and HE recombination rates were 60-fold lower than that obtained for the WT strain. The P. aeruginosa recA strain showed 15 and 3-fold decreased HO and HE recombination rates respectively, compared with the WT strain. These results suggest that RecA is a key factor for recombination in E. coli whereas a RecA-independent recombination mechanism mainly functions in P. aeruginosa. At present we are analyzing the molecular structure of the recombinant products with the aim to elucidate this alternative mechanism.