The importance of recA mutant strains for the study of antifungal genes inPseudomonas aureofaciens PA147-2

Pseudomonas aureofaciens PA147-2 shows antifungal activity toward a variety of plant pathogenic fungi. We have been investigating the molecular mechan isms underlying the fungal inhibition, and during these studies it was obse rved that the use of pLAFR3-based cosmids for in trans complementation of m utants lacking antifungal activity is hindered by cosmid instability. It wa s hypothesised that the cosmid stability could be improved by inactivation of recA. The recA gene of PA147-2 was cloned and shown to complement recA m utants of E. coli, restoring RecA-dependent functions when expressed in tra ns. Two recA mutants of PA147-2 were constructed. Both of these mutants sho w sensitivity to DNA damage. Cosmid pPS2122 restores antifungal activity to a mutant by allele exchange, but is unstable in trans. The stability of pP S2122 is shown to be improved in a recA mutant of PA147-2 with respect to t he wild type.