Localization of toxicity for silkworm larvae in the parasporal inclusion of Bacillus cereus var. alesti.

Abstract

The parasporal protein inclusion of Bacillus cereus var. alesti accounts for one third of the dry weight of the washed products of sporulation. Although the spore:crystal ratio is 1:1, the weight ratio is 1.5:1. Like other parasporal crystals, those of var. alesti are swollen but not dissolved by alkalinity up to a critical pH (11.5–11.8); above this pH, dissolution occurs. Toxicity tests on extracts made at increasing pH levels indicated that the crystal protein itself is the toxic agent and not the carrier of it. The protein of actively dividing cells and of spores was non-toxic. Crystal-forming cells contained a toxic protein which would dissolve at a lower pH than would the free crystal.