Incidence of insect cell cytolytic activity amongBacillus thuringiensisserotypes

Abstract

Fourteen serotypes of Bacillus thuringiensis were surveyed for cytolytic activity toward established cell lines of two lepidopteran and one dipteran insect species. Toxic protein extracted from spore-crystal combinations from each serotype was examined by an in vitro cell bioassay for cytotoxicity. In general, a cell line from the tobacco hornworm (Manduca sexta) was more responsive to entomocidal protein than cells from the spruce budworm (Choristoneura fumiferana). Significant cytotoxicity toward either or both lepidopteran cell lines was present among all of the serotypes tested with the single exception of serotype 14 (B. thuringiensis subsp. israelensis). This serotype exhibited the only significant cytotoxicity towards dipteran cells (Anopheles gambiae). The degree of cytotoxicity among the soluble but unactivated preparations varied widely and may have resulted from endogenous protease activity. Activation by α-chymotrypsin digestion improved cytotoxicity by as much as 500-fold in some instances, but failed to significantly improve the activity of those serotypes which contained high initial cytotoxicity.