FIGURE 1.

(I) Timeline. A brief history of the use of homologous and heterologous chitinases to increase the insecticidal activity of B. thuringiensis. (II) Different options for the development of recombinant strains of B. thuringiensis expressing chitinases. (a) The bacterium can be transformed with heterologous chitinase genes obtained from bacteria other than B. thuringiensis. Chitinases harbor signal peptides and are secreted from the cells. (b) The bacterium can be transformed with homologous chitinase genes obtained from different strains of B. thuringiensis. Chitinases harbor signal peptides and are secreted from the cells. (c) Chitinase genes from B. thuringiensis are engineered and the signal peptide is deleted. Chitinases are expressed inside the cells as inclusion bodies along with the spores and insecticidal Cry proteins. (d) Chitinase genes lacking signal peptides are transcriptionally fused to the C-terminal encoding moiety of cry1 genes, facilitating the formation of disulfide bridges between the chimeric construct and Cry proteins. This strategy putatively allows the formation of chimeric crystals made of Cry and chitinases. Bt, B. thuringiensis; Chi, chitinases; Bt Chi, chitinases from Bt, Cry crystals, parasporal bodies made of Cry proteins; ChiΔsp, chitinase lacking signal peptide; Bt ChiΔsp, chitinase from Bt lacking a signal peptide.