Ultrastructural and molecular characterization of the parasporal crystal proteins of Bacillus thuringiensis subsp kurstaki S93 active against Spodoptera frugiperda

A Brazilian strain of Bacillus thuringiensis subsp. kurstaki (S93), which w as previously shown to be more toxic to Spodoptera frugiperda than the comm ercially available strain HD 1 DIPEL, was characterized. The S93 isolate wa s shown to produce bypiramidal and cuboidal shape crystals. SDS-PAGE of spo rulating cultures showed the presence of mainly two polypeptides of ca. 135 - and 65-kDa, respectively. The presence of these polypeptides was in agree ment with the type of crystals found, cryIA- and cryIIA-type genes were als o detected in the plasmidial DNA from this strains by using PCR. Furthermor e, plasmidial profile of this strain has a very similar content to the HD1 DIPEL strain. These results hint that the Brazilian strain is very similar to the HD1 in several aspects. However, the reasons for the increased activ ity of the Brazilian isolate towards S. frugiperda remain unknown.