Transformation and Transduction in Recombination-defective Mutants of Bacillus subtilis

Abstract

The effects on transformation and transduction of an ultraviolet sensitivity ( uvr − ) and two ultraviolet sensitivity-recombination deficiency ( rec-1 − and rec-2 − ) mutations in isogenic strains of Bacillus subtilis were investigated. Transformation frequency in the rec-1 − and rec-2 − strains was reduced to approximately 5 and 25%, respectively, of the parental strains. Normal kinetics of deoxyribonucleic acid dose response in transformation were found for the rec-1 + and rec-2 − strains. Biphasic curves were obtained with the rec-1 − strains. Transduction frequency with bacteriophage SP-10 decreased parallel to transformation frequency in the rec-1 − and rec-2 − strains. This result suggests that transformation and SP-10 transduction share a common mechanism for genetic recombination. It also indicates that the reduction in transformation frequency of these strains was not due to altered competence. Transduction frequency with bacteriophage PBS-1 or 3NT, on the contrary, was not diminished in rec-1 − strains. This frequency was reduced in rec-2 − strains but not as severely as that of transformation or SP-10 transduction. Several hypotheses to interpret these differences are presented. Recombination frequency between linked markers was reduced more than 50% in transformation by the presence of the rec-1 − mutation. Linkage was unaffected in the rec-2 − strains. Neither the rec-1 − nor the rec-2 − mutation had an effect on linkage in PBS-1 or 3NT transduction. The uvr − strains were transformed at a frequency equal to or greater than that of the parental strains. These strains were transduced by all bacteriophage systems at frequencies about twofold higher than those of parental strains.