Spherical parasporal inclusions of the Lepidoptera-specific and Coleoptera-specific Bacillus thuringiensis strains: A comparative electron microscopic study

Four Lepidoptera-specific Bacillus thuringiensis strains that belong to the four H serogroups (serovars sumiyoshiensis, fukuokaensis, darmstadiensis, and japonensis) and a Coleoptera (Scarabaeidae)specific strain belonging to serovar japonensis were examined for comparative ultrastructure of spheric al parasporal inclusions. The prominent feature of the inclusions of the Le pidoptera-specific strains was the existence of thick, highly electron-dens e envelopes surrounding a homogeneous protein matrix. The envelopes were 15 .0-66.7 nm thick and consisted of 5-12 layers of membrane. This is also the case with inclusions of a Coleoptera-specific strain. The ultrastructure o f inclusions from the five strains was in marked contrast to that of the bi pyramidal parasporal inclusions produced by a Lepidoptera-specific serovar sotto strain.