昆虫病原线虫共生菌BP品系杀虫毒素基因簇中各基因与杀虫活性的关系

昆虫病原线虫共生菌Xenorhabdus nematophilus BP的多个杀虫毒素基因集中在一起形成一个约40kb的基因簇。为研究这个基因簇中各基因与杀虫活性的关系，对该共生菌粘粒文库中5个粘粒克隆XnBP76、XnBP83、XnBP203、XnBPp378 和XnBP414及XnBP83的3个亚克隆插入DNA片段的基因结构和它们对棉铃虫的杀虫活性进行了比较，结果显示，xptB1, xptC1和xptA2 3个基因或后两者的联合表达产物具有最强的杀虫效果，缺失其中的任何1个或2个会使杀虫活力大幅度地下降或完全消失；而xptD1和xptA1的缺失对毒素基因簇的表达产物的杀虫活力影响很小；杀虫毒素的物理混合没有明显的增效作用。

Importance of Five Genes Presented in Xenorhabdus nematophilus BP Toxin Gene Cluster to Its Insecticidal Activity

Importance of five genes, named as xptA1, xptD1, xptB1, xptC1 and xptA2 presented in the toxin gene cluster of X. nematophilus BP strain, to its insecticidal activity against the neonate of Helicorvepa armigera was examined. This was achieved by analyzing and comparing the presence or absence of these five genes in and the insecticidal activity of each of the five clones screened from genomic cosmid library of X. nematophilus BP by in situ hybridization and another three subclones constructed from the enzyme-digested plasmid DNA of one of the insecticidal cosmid clones. The insecticidal activity of the clone or subclone was estimated by the 50% lethal concentration ( LC _ 50 ) of the neonate of H. armigera feed with the mixture of artificial diet and the cells of the clone or subclone examined. The presence or absence of each of the five genes in the clone or subclone was determined by the results of PCR amplification of the whole or the two ends of the targeted gene. The results indicated that: 1 the presence of xptC 1 and xptA 2 was critical for the full insecticidal activity of the toxin gene cluster while absence of xptD 1 and/or xptA 1 had little effect on the insecticidal activity against the neonate of H. armigera ; 2. mixing cosmid clone XnBP76 and subclone Sub20k, which had a gene structure of ( xptA1 +, xptD1 +, xptB1 +, xptC1 + and xptA2 -) and (xptA1 -, xptD1 -, xptB1 -, xptC1 - and xptA2 +), respectively, did not achieve the full insecticidal activity. The functions of these five genes in the insecticidal process were discussed briefly.