THE RECA GENE OF LACTOCOCCUS-LACTIS - CHARACTERIZATION AND INVOLVEMENT IN OXIDATIVE AND THERMAL-STRESS

The role of recA in Lactococcus lactis, a microaerophilic fermenting o rganism, was examined by constructing a recA-disrupted strain. This si ngle alteration had a surprisingly pleiotropic effect. In addition to its roles in homologous recombination and DNA repair, recA is also inv olved in responses to oxygen and heat stresses. We found that oxygen s tress induced by aeration causes reductions in growth and stationary-p hase survival of the recA strain. Toxicity is a consequence of hydroxy l radical production via the Fenton Reaction and is alleviated by cata lase or Ferrozine addition. These results suggest that oxygen radicals are not efficiently eliminated and accumulate in lactococcal cultures , and that RecA is needed to deal with the damage they incur. Unexpect edly, thermal stress arrested growth of the recA strain. Immunological data indicate that the recA mutant is deficient in heat-shock protein s DnaK, GroEL, and GrpE, Poor growth at elevated temperature is theref ore due to a diminished heat-shock response in the recA strain. In con trast, levels of a novel heat-shock protein, HflB, are elevated. In Es cherichia coli, HflB downregulates the heat-shock response by promotin g degradation of the transcription factor sigma(32). We propose that r ecA regulates the heat-shock response via HflB. This work provides the first evidence showing that two major pathways of stress response, in duced by heat shock and DNA damage, are interactive.