Identification and characterization of a new mosquitocidal Bacillus sphaericus and its toxin proteins

The bacterial insecticides have been used for the control of vector mosquitoes for more than five decades. Some strains of Bacillus sphaericus produce a highly toxic protein called binary toxins during sporulation. These toxins are composed of toxic BinA (41.9 kDa) and receptor binding BinB (51.4 kDa) proteins and show toxicity against mosquito larvae which vectors of malaria, dengue fever, and yellow fever. In this study, a new mosquitocidal B. sphaericus (MBI5) strain is identified. The toxicity of MBI5 is tested in laboratory bioassay that was able to kill the larvae of Culex pipiens. Bioassay test results showed that MBI5 was able to kill the larvae, but not pupa and adults of Culex pipiens. The BinA and BinB genes were cloned into pET-16b and expressed in Escherichia coli DH5α. The active form of BinA and BinB proteins were purified from the E. coli BL21. The purified BinA protein showed LC50 dose 206,8 ng ml-1 at 8 h against Culex pipiens larvae. The BinB protein was reported as non-toxic against Culex. The 1:1 molar ratio combination of BinA and BinB proteins showed LC50 dose 379,7 ng ml-1 at 8 h against Culex pipiens larvae. The results showed that newly isolated and identified B. sphaericus MBI5 strain can be used as a potential bacterial insecticide against laves of mosquito species.