A Bacillus sphaericus gene encoding a novel type of mosquitocidal toxin of 31.8 kDa

A size-fractionated genomic library of Bacillus sphaericus strain SSII-1 was constructed and screened for toxicity against larvae of the mosquito Culex quinquefasciatus (Cq). One toxin-producing clone, pS35, was identified and a 2.7-kb subclone was completely sequenced. An open reading frame of 879 bp encoding a 31.8-kDa protein (designated Mtx2) was identified. Purified, recombinant Mtx2 was toxic to Cq larvae. Mtx2 shows no significant homology to known insecticidal toxins, but has homology to two toxins active against mammalian cells, namely the E-toxin of Clostridium perfringens and the cytotoxin of Pseudomonas aeruginosa. Thus, Mtx2 represents a new type of mosquitocidal toxin.