Modulation of Cry IV A toxin protein expression by glucose in Bacillus thuringiensis israelensis

Bacillus thuringiensis subsp. israelensis (Bti) produces Cry IV A protoxin protein as part of the insecticidal crystal toxin during sporulation. This study was conducted with the objective of identifying environmental signals which regulate toxin synthesis by Bti. Glucose was found to repress Cry IV A toxin induction at the mRNA level. The repressive effect of glucose was dependent on a phosphorylation step since protein kinase inhibitor calphostin c relieved the 130-kD protoxin synthesis at both the mRNA and protein level. Phosphorylation of HPr, the phosphocarrier protein of the phosphotransferase system, occurred during glucose repression of Cry IV A toxin synthesis in Bti cells was seen by Western blotting with anti-phosphoserine antibody and rabbit anti-HPr serum. Phosphorylation of HPr in vivo as well as in the in vitro assay was inhibited by calphostin c, a specific inhibitor of serine/threonine kinase. Calphostin c had no effect on sporulation efficiency of Bti cells.