Characterization of one novel cry8 gene from Bacillus thuringiensis strain Q52-7

Bacillus thuringiensis ( Bt ) is the most widely used insecticidal microbe due to its specific toxicity and safe use with respect to animals and the environment. In this study, we isolated Bt strain Q52-7 from a soil sample collected in the Qian Shan District, Liao Ning Province, China. We observed that the Q52-7 strain produced spherical crystals. The Bt Q52-7 strain had high toxicity against Asian Cockchafer (Holotrichia parallela ), exhibiting an LC 50 of 3.80 × 10 9 cfu/g, but is not toxic for Anomala corpulenta Motschulsky and Holotrichia oblita. Using general cry8 primers, we amplified a 1.3 kb fragment with the polymerase chain reaction. Specific primers were designed for the amplified fragment to clone the full-length coding region. A novel gene, cry8Na1 , had 69 % sequence similarity with cry8Ca1 . cry8Na1 gene was successfully expressed in the HD-73 – acrystalliferous mutant of Bt subsp . Kurstaki HD-73. Bioassays demonstrated that the Cry8Na1 protein is highly toxic for the H. parallela , with a 50 % lethal concentration of 8.18 × 10 10 colony forming units per gram.