Insect Cell Cultures as Tools in the Study of Bacterial Protein Toxins

Abstract

Publisher Summary This chapter discusses insect cell cultures as tools in the study of bacterial protein toxins. Two toxin-producing bacilli, namely, Bacillus thuringiensis and Bacillus sphaericus, are among the most promising microbial agents for control of agricultural and public health insect pests. These bacteria share a number of common features. Each produces a protein toxin of relatively high molecular weight at sporulation that accumulates in a parasporal body or crystal. In B. thuringiensis, this toxin is called the δ-endotoxin. These toxins act as stomach poisons, first affecting the midgut of the insect. Each of these toxins is produced as a relatively inactive, high molecular weight precursor or protoxin that is activated by proteolytic degradation in the bacterial culture and in the larval gut. The activated form, that is, the toxin, is then relatively resistant to further proteolysis. Only insects with midgut environment containing the proper proteases at high pH are susceptible to these toxins, and among those insects, there is marked variation in susceptibility. Recently, it has been shown that toxins from many of the B. thuringiensis strains and from B. sphaericus bind to glycoprotein receptors. The presence or absence of these receptors may play a significant role in determining the susceptiblity or resistance of the insect.