Geographical Distribution of Bacillus thuringiensis Strains and vip3 Genes in Different Climatic Zones in China

Vegetative Insecticidal Proteins(VIPs),a large family of insecticidal proteins,are produced from Bacillus thuringiensis (Bt) during the vegetative growth stage. VIPs represent the second generation of bio-insecticides that confer a wider insecticidal spectrum and have stronger activity.This work compared the geographical distribution of Bt strains and their vip3 genes in different climatic zones in China, the tropical (Hainan Province), subtropical (Guangxi Province) and temperate zones (Heilongjiang Province). A total of 156 Bt strains were isolated from 841 soil samples in Hainan Province tropical region, 356 Bt strains from 1 420 soil samples in Guangxi Province and 167 Bt strains from 1 010 soil samples in different geographical regions in Heilongjiang Province. Twenty-two out of 156 strains from tropical Hainan Province and two out of 356 from subtropical Guangxi Province were found to express vip3 genes,while vip3 genes were not expressed from temperate zone in Heilongjiang Province.Restriction Fragment Length Polymorphism(RFLP)was used to identify different types of vip 3 genes that were within the same family and three full-length vip3 genes were isolated.The genes cloned from Bacillus thuringiensis strain SL3 expressed in the transformed E.coli BL21 strain. Through SDS-PAGE, 88.6 ku insecticidal protein was expressed. The bioassays used two-instar larva of Lepidoptera insects (Spodoptera exigua and Agrotis ipsilon)were performed.The results of the bioassays showed that the protein strongly inhibited the body weight increasement on Spodoptera exigua and Agrotis ipsilon in a standard bioassay.Taken together,the results indicated that the distribution of Bt strains and vip3 genes had regional preference.Tropical and subtropical regions were the rich resources of Bt strains and vip3 genes compared with temperate region.These results would undoubtedly facilitate the studies of insecticidal proteins and expand the list of the pest-killing candidates to make fully use of the extremely rich microbial resources.The new vip 3 genes isolated in the current study might also help resolve the emerging insecticidal resistance problems.