Cloning and expression of the binary toxin gene from Bacillus sphaericus IAB872 in a crystal-minus Bacillus thuringiensis subsp israelensis

Bacillus sphaericus IAB872 has high toxicity against susceptible Culex spp. and medium larvicidal activity against binary toxin-resistant Culex spp. S equence analysis revealed that the sequence of the binary toxin gene from I AB872 was totally identical to that of the reference strain 2362. The recom binant plasmids were introduced into an acrystalliferous B. thuringiensis s train 4Q7, and the resulting transformants produced parasporal inclusion co mposed of 51 kDa and 42 kDa proteins during sporulation. SDS-PAGE and Weste rn blot further confirmed that B. thuringiensis transformants were able to express the binary toxin in a high level. Toxicity bioassays showed that th ey performed high toxicity to susceptible Culex spp. larvae, but no toxicit y to resistant Culex larvae. It was, therefore, suggested that other unknow n toxins perhaps existed in the wild strain IAB872 except the binary toxin. Their modes of action might be different from that of binary toxin, and th ey were possibly responsible for the activity of the wild strain IAB872 aga inst resistant mosquito larvae.