昆虫病原线虫共生菌BP品系杀虫毒素基因xptA2的杀虫活性分析

为进一步研究嗜线虫致病杆菌Xenorhabdus nematophila杀虫毒素基因簇中各基因的功能,从BP品系的粘粒文库中筛选出一个粘粒克隆XnBP83包含全部的xpt基因,对该粘粒克隆进一步亚克隆得到一个亚克隆菌株Sub9.0,只有一个xpt基因xptA2.以Sub9.0为研究对象,对xptA2的功能作了进一步研究.结果表明,xptA2基因的表达产物与其它xpt基因的表达产物物理混合后无明显增效作用,而将xptA2转入缺失xptA2的粘粒克隆XnBP6和XnBP203后,也同样无明显增效作用.对xptA2的序列分析发现,BP品系的xptA2预测氨基酸序列与已发表序列相比明显存在2个变异区.进一步BLAST分析发现,这2个变异区同昆虫病原线虫共生菌中与口服毒性有关的杀虫毒素蛋白具有同源性.

Insecticidal activity of insecticidal toxin gene xptA2 in Xenorhabdus nematophila BP

The insecticidal toxin genes in Xenorhabdus nematophila BP can express toxin proteins that have high insecticidal activity to many Lepidoptera larvae. As a kind of candidate toxin gene for transgenic insect-resistant plants, it is very important to found out the relationships of these genes. Subg. 0, one subclone of a cosmid clone XnBP83 from Xenorhabdus nematophila BP which has all xpt insecticidal genes, was used for studying the function of xptA2 in X. nematophila because only xptA2 presented in this subclone. It was found that protein expressed by xptA2 had oral toxicity to Heliothis armigera but the full oral toxicity of XnBP83 could not be restored when physical mixing of toxins expressed by the 3 genes, xptB1, xptC1 and xptA2. The full oral toxicity of XnBP83 could not be restored when xptA2 was transformed into XnBP76 or XnBP203. Two varied regions were found in the deduced amino acid of xptA2 of X. nematophila BP comparing with that in PMFI296. BLAST results showed that the two regions had homology with XptA1 in X. nematophila PMF1296 and TcdA in P. luminescens W14 which were thought to be associated with oral toxicity to insects.