Characterization of Bacillus spharicus binary proteins for biological control of Culex quinquefasciatus mosquitoes: a review

The larvicidal action of the entomopathogen Bacillus sphaericus towards Culex quinquefasciatus is due to the binary (Bin) toxin protein present in crystals, which are produced during bacterial sporulation. However, the molecular basis for binary and receptor recognition is not well understood. In this review we attempted to discuss the general biology of this species and concentrate on the genetics and physiology of toxin production and it's processing for the production of biopesticides. In addition, larvicide of B. sphaericus is unique in that it consists of two proteins of 42 (BinA) and 51(BinB) kDa, both of which are required for toxicity to mosquito larvae midgut and these binary proteins are cleaved by proteases, yielding peptides of 39 kDa and 43 kDa, respectively that form the active toxin. These associate bind to the receptor, a α-glucosidase on the midgut microvilli, and cause lysis of midgut cells after internalization. Besides, Bin toxin can increase the toxicity of other mosquitocidal proteins and may be useful for both increasing the activity of commercial bacterial larvicides. Recently, recombinant DNA techniques have been used to improve bacterial insecticide efficacy by markedly increasing the synthesis of mosquitocidal proteins and by enabling new endotoxin combinations from different bacteria to be produced within single strains. Finally, the availability of Bin toxins of B. sphaericus and newly discovered mosquitocidal protein offers the potential for constructing recombinant bacterial insecticides for more effective biopesticides for the biological control of mosquito vectors.