Isolation and distribution of mosquito-larvicidal cry genes in Bacillus thuringiensis strains native to Saudi Arabia

摘要

A total of 157 environmental samples were collected from 11 ecological regionsacross Saudi Arabia to isolate native Bacillus thuringiensis (Bt) strains. Bt isolates (n=103)were recovered by the 50% (v/v) ethanol treatment method with Bt index range of 0.01 to 0.4.Most of Bt isolates showed spherical crystals (54%), while, irregular, bi-pyramidal, and sporeattachedcrystal constituted 27, 16 and 3% respectively. PCR analysis with eight general andspecific dipteran primers of Cry and Cyt genes, revealed positive amplification for cry4 &cyt1, and cry4A, cry4B and cyt2, and cry 10 and cry 11 genes in 28%, 26%, 22%, and 25% oftested strains respectively; whereas cry2 gene was not detected except with the referenceBt kurstaki HD-1 strain. Bioassays against Aedes caspuis and Culex pipiens larvae indicatedthat 11 strains displayed better larvicidal activity compared with Bacillus thuringiensis H14(Bti) reference (LC50 0.6 μg/ml) strain against Ae. caspuis, but only two strains (620A &633R1, LC50 of 0.09 μg/ml & 0.064 μg/ml) that gave significant enhancement. Additionally,one strain (633R1) showed LC50 similar to that of Bti H14 (LC50 0.064 μg/ml) against Cx.pipiens. With the exception of cyt primers, sequenced DNA of all positive primers ampliconsrevealed 95 to 99% identity in GenBank with Bacillus thuringiensis subsp. israelensis plasmidpBtoxis and also correlated with its SDS-PAGE expressed protein profiles analysis. It is hopedthat our wild bio-insecticide Bt strains can be explored in future in the control of mosquitovectorborne diseases in Saudi Arabia.