MOBILIZATION OF BACILLUS-THURINGIENSIS PLASMID PTX14-3

The Bacillus thuringiensis subsp. israelensis (Bti) plasmid pTX14-3 ha s been reported to contain a gene, mob14-3, with considerable homology to genes encoding mobilization proteins from other gram-positive bact eria. We have used the aggregation-mediated conjugation system recentl y discovered in Bti to compare the mobilization kinetics of different derivatives of plasmid pTX14-3. Plasmid pTX14-3 has been found to repl icate by the rolling-circle mechanism and to contain a locus suppressi ng the formation of high-molecular-weight DNA. We found that deleting a DNA fragment containing this locus increased the transfer frequency about twofold. The mobilization frequency of the plasmid containing th e intact mob14-3 gene did not indicate a mobilization-enhancing activi ty of the encoded polypeptide. However, the presence of the mob14-3 ge ne seemed to increase the stability of the plasmid in exponential grow th. (C) 1995 Academic Press, Inc.