Studies on Bacillus thuringiensis H-14 strains isolated in Egypt. VI: Correlation between specific plasmids and δ-endotoxin production

The crystal-producing (cry+) strains M1 and S128 of Bacillus thuringiensis H-14, and several noncrystal-producing (cry−) mutants derived from them, were analyzed for the presence of plasmid DMA in attempts to correlate δ-endotoxin production with the presence of a specific plasmid(s). Plasmid analysis of both parent strains revealed the presence of several plasmids in the size range of 3.2–130 megadalton (Mdal). The two strains were found to have identical plasmid profiles, except that strain M1 contained an additional plasmid of 68 Mdal. All the cry− mutants derived from the cry+ parental strains had lost at least a 75 Mdal plasmid. On the other hand, plasmid analysis of cry+ derivatives cured of one or more plasmids revealed that they all harbored the 75 Mdal plasmid. This correlation was further confirmed by a plasmid transfer experiment in which strain M1 transmitted the crystal-producing phenotype to a noncrystal-producing B. thuringiensis recipient. Agarose gel electrophoresis showed that the 75 Mdal plasmid was present in all the isolated cry+ transcipients and absent in all the isolated cry− transcipients. These results demonstrate that the structural genes for the δ-endotoxin in the isolated strains of B. thuringiensis H-14 are borne on the 75 Mdal plasmid. © 1994 by John Wiley & Sons, Inc..