Recombination-deficient mutants of Bacillus subtilis

Abstract

Two mutant strains of B. subtilis Marburg, NIG43 and NIG45, were isolated. They showed high sensitivities to .gamma. rays, UV light and chemicals. Deficiencies in genetic recombination of these 2 mutants were shown by the experiments on their capacity in transformation, SPO2 transfection, PBS1 phage transduction and on their radiation and drug sensitivities and their Hcr+ capacity for UV-exposed phage M2. Some of these characteristics were compared with those of the known strains possessing the recA1 or recB2 alleles. Mapping studies revealed that the mutation rec-43 of strain NIG43 lies in the region of chromosome replication origin. The order was purA dna-8132 rec-43. Another mutation, rec-45, of strain NIG45 was tightly linked to recA1. The mutation rec-43 reduced mainly the frequency of PBS1 transduction. The mutation rec-45 reduced the frequency of recombination involved both in transformation and PBS1 transduction. The mutation rec-43 of strain NIG43 is conditional, but rec-45 of strain NIG45 is not. The UV impairment in cellular survival of strain NIG43 was gradually reverted at higher salt or sucrose concentrations, suggesting cellular possession of a mutated gene product whose function is conditional. In contrast to several other recombination-deficient strains, SPO2 lysogens of strains NIG43 and NIG45 were not inducible, indicating involvement of rec-43+ or rec-45+ gene product in the development of SPO2 prophage to a vegetative form. The UV-induced DNA degradation in vegetative cells was higher in rec-43 and rec-45 strains.