CHARACTERIZATION OF LACTOCOCCUS-LACTIS UV-SENSITIVE MUTANTS OBTAINED BY ISS1 TRANSPOSITION

Studies of cellular responses to DNA-damaging agents, mostly in Escher ichia coli, have revealed numerous genes and pathways involved in DNA repair. However, other species, particularly those which exist under d ifferent environmental conditions than does E. coli, may have rather d ifferent responses. Here, we identify and characterize genes involved in DNA repair in a gram-positive plant and dairy bacterium, Lactococcu s lactis. Lactococcal strain MG1363 was mutagenized with transposition vector pG(+)host9::ISS1, and 18 mutants sensitive to mitomycin and UV were isolated at 37 degrees C. DNA sequence analyses allowed the iden tification of 11 loci and showed that insertions are within genes impl icated in DNA metabolism (polA, hexB, and deoB), cell envelope formati on (gerC and dltD), various metabolic pathways (arcD, bglA, gidA, hgrP , metB, and proA), and, for seven mutants, nonidentified open reading frames. Seven mutants were chosen for further characterization. They w ere shown to be UV sensitive at 30 degrees C (the optimal growth tempe rature of L. lactis); three (gidA, polA, and uvs-75) were affected in their capacity to mediate homologous recombination. Our results indica te that UV resistance of the lactococcal strain can be attributed in p art to DNA repair but also suggest that other factors, such as cell en velope composition, may be important in mediating resistance to mutage nic stress.