| Abstrakt: |
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 (LC50) 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 xptC1 and xptA2 was critical for the full insecticidal activity of the toxin gene cluster while absence of xptD1 and/or xptA1 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. |
