0023-6152

AA00697606

1685888

査読無

0023-6152

AA00697606

A new strain of Bacillus thuringiensis exhibiting activity in Spodoptera exigua was isolated and identified. Synergistic effects appeared when it was mixed with tannic acid, which is a protease inhibitor that enhances insecticidal activities. Substrate reactions with different types of proteases were analyzed, and according to the results, trypsin showed proteolytic activity levels of 91.4% and 89.4% on BApNA and BPVApNA substrates, respectively. When trypsin was treated with tannic acid, proteolytic activity levels of 62.2% and 54.5% appeared on BApNA and BPVApNA substrates, respectively, and tannic acid suppressed the trypsin–substrate reactions by 29.2% and 34.9%, respectively. Colorimetric activity assays of trypsin identified slightly lower activity levels in larvae that ate a combination of B. thuringiensis KB100 strain and 40 mM of tannic acid, when compared to larvae that died after eating the positive control, control, or the B. thuringiensis subsp. kurstaki KB100. The results of trypsin gene expression level analyses conducted using the qRT–PCR analyses indicated that trypsin 1 gene expression levels were lower when 40 mM of tannic acid was added to the B. thuringiensis KB100 strain, compared to the B. thuringiensis KB100 strain alone. Trypsin 2 gene expression levels were also lower when 40 mM of tannic acid was added to the B. thuringiensis KB100 strain. The results of immunofluorescence antibody experiments indicated that the addition of 40 mM of tannic acid to the B. thuringiensis KB100 strain, during decomposition by the mid–gut proteases of S. exigua, led to differences in expression levels and image analyses.