Germinant generation from δ-endotoxin of Bacillus thuringiensis strain 1.1.

The novel finding of this study is that the δ-endotoxin present in the spore coat of Bacillus thuringiensis strain 1.1 (Bt1.1), plays a central role in spore germination by generation of germinant via its β-glucosidase activity and is based on the following: (i) the crystals of Bt1.1 consist of the 140 kDa δ-endotoxin which exhibits β-glucosidase enzymatic activity. Besides crystals, δ-endotoxin is also located in the spore coat and at this site displays β-glucosidase activity, resulting in glucose production; (ii) glucose is an efficient germinant of both Bt1.1 and acrystalliferous Bt4.1 strain; (iii) substrates of β-glucosidase can activate the germination of Bt1.1 spores, but not those of the acrystalliferous Bt4.1 sister strain that do not contain the 140 kDa δ-endotoxin; (iv) Reduction or enhancement of enzymatic activity of δ-endotoxin, results in retardation or acceleration of germination and outgrowth, respectively. Bt1.1 cells secrete a 60 kDa polypeptide which displays β-glucosidase activity as indicated by zymogram analysis and which is immunologically related to the 140 kDa δ-endotoxin.