Biocide gene(s) and biocidal activity in different strains of Bacillus sphaericus. Expression of the gene(s) in E. coli maxicells.

The recently cloned biocidal determinant of the highly toxic strain of B. sphaericus 1593M (Ganesan et al. 1983) was used as probe to investigate homologous sequences in different toxic and non-toxic strains of B. sphaericus. It was found that the potent strains we have analysed are characterised by the presence of DNA sequences (6.6, 6.4, 5.8, 1.6, 1.3 and 0.6 Kb) not found in the non-toxic strains. These results further show that one of the two weakly toxic strains analysed presents a hybridisation pattern completely different from that observed with the highly potent strains of B. sphaericus. When the DNA of the two non-toxic strains was analysed, SSII-I failed to hybridise to the probe and Rem4 exhibited mainly one hybridisable sequence of 2.3 Kb not detectable in the toxic strains. No region of homology to the probe was found in the DNA of two strains of B. thuringiensis (var. berliner and var. israeliensis) analysed. By dot blot hybridisation experiments it was estimated that the larvicidal determinant might be present in about one to three copies per genome. With the use of E. coli maxicells we have shown further that the toxin gene(s) encoded four polypeptides with molecular weights of 21, 19, 15 and 12 Kd. The significance of these findings is discussed.