ANTI-SOS EFFECTS INDUCED IN BACILLUS-SUBTILIS BY A PHI-105 MUTANT PROPHAGE

The presence of the mutant prophage phi105cts23 in Bacillus subtilis s trains strongly affected several biological parameters including the v iability of protoplasts and the establishment of plasmid pC194. A defe ctive inducibility of the prophage after treatments that de-repress th e SOS-like response were also observed. Although these alterations sug gested a Rec-deficient phenotype, homologous recombination was not imp aired in these lysogenic derivatives. In fact, chromosomal DNA transfo rmation in these competent cells was more efficient than in cells carr ying the wild type prophage: cell death due to prophage induction upon competence development was lower than expected. Alterations in the re sponse to SOS-inducing agents and to osmotic stress correlated with th e presence of this particular mutant prophage or the cloned thermosens itive repressor at the permissive temperature. The induction of an ant i-SOS effect is discussed.