Esterase electrophoretic polymorphism of Bacillus thuringiensis and Bacillus cereus reference strains

The genomic diversity and relationship among 61 Bacillus thuringiensis and Bacillus cereus reference strains were investigated by electrophoretic analysis of esterase enzymes on native polyacrylamide gel. Polymorphism of the esterolytic bands revealed seven esterases, designed as Est A to Est G in order of decreasing anodal migration. Each esterase showed two to three mobility variants that assigned the analysed strains into 35 electrophoretic types (ETs). This high diversity allowed the identification of several serovar or strain-specific ETs. Cluster analysis of ETs showed three major groups in which the strains belonging to the serovar tolworthi were the most distant. The ETs distribution showed that B. thuringiensis and B. cereus are intermingled in the dendrogram with the resolution of some common serovars of B. thuringiensis in tight phylogenetic lineages. These results indicate that the esterase enzyme electrophoresis, applied as a sole typing method for the closely related species B. thuringiensis and B. cereus is suitable to highlight the intraspecific genetic diversity.