Improvement and Mechanism of Action of Microbial Pesticides (Bt)

The spore-forming, gram-positive bacterium, Bacillus thuringiensis (Bt), is a ubiquitous soil micro-organism. Since the first Bt was isolated as a pathogen of silkworm in 1901, it has become possible to group these isolates into 50 serovars. At present it has been estimated that over 60, 000 isolates are being maintained in culture collections worldwide. The delta-endotoxin products in Bt during spore-forming stage are most widely used as biological control agents and pesticides that do not pollute the enviroment. The delta-endotoxin is an insecticidal protein that be coded by cry gene to constructs a crystalline protein bodies. After a susceptible insect ingested these crystalline bodies, the proteins are dissolved in midgut by the digestive juice and changed to an active toxin protein. In this review, the mode of action of the delta-endotoxin, improvement of Bt products by gene manipulation for the development of biopesticides (recombinant microbes) against Bt-resistance pests and also transgenic plants incorporating the cry genes were introduced.