Quercetin is one of the most abundant flavonoids and the defense secondary metabolites in plants. In this study, the effect of quercetin on the growth of the silkworm larvae was investigated. Cytochrome P450 monooxygenases (P450s), glutathione S-transferases (GSTs), and carboxylesterases (COE) were assayed after exposure to different concentrations of quercetin for 3 d (short-term) and 7 d (long-term), respectively. The results showed that the weight gain of the silkworm larvae significantly decreased after the larvae were treated by different concentrations of quercetin except for the treatment with 0.5% quercetin. Activities of P450, GST, and COE were induced by 0.5 or 1% concentration of quercetin. In the midgut, the induction activity of P450s was reached to the highest level (2.3-fold) by 1% quercetin for 7 d, the highest induction activities of GSTs toward CHP and CDNB were 4.1-fold and 2.6-fold of controls by 1% quercetin after 7 d exposure, respectively. For COEs, the highest activity (2.3-fold) was induced by 0.5% quercetin for 7 d. However, P450s in whole body were higher inducible activities in short-term treatment than those in long-term treatment. The responses of eight cytochrome P450 (CYP) genes belonged to CYP6 and CYP9 families and seven GST genes were detected with real-time polymerase chain reaction. In addition, the genes induced by quercetin significantly were confirmed by qRT-PCR. CYP6AB5, CYP6B29, and GSTe8 were identified as inducible genes, of which the highest induction levels were 10.9-fold (0.5% quercetin for 7 d), 6.2-fold (1% quercetin for 7 d), and 7.1-fold (1% quercetin for 7 d), respectively.

The bacterial strain LP08 was isolated from soil collected from bay of Bohai, China. The sequence of 16S rDNA of strain LP08 showed 99% homology to Burkholderia cepacia. The lipase from Burkholderia cepacia LP08 was purified by ammonium sulphate precipitation, ion exchange chromatography and Sephadex G-75 chromatography. The characterization of the lipase exhibited maximum activity at 30 °C and pH 9.0. The lipase retained 63, 66, 74, and 95% of its maximum activity at 10, 15, 20 and 25 °C respectively. The lipase activity was promoted in the presence of commercial detergent, sodium cholate, sodium taurocholate, glycerine and NaCl, while was little inhibited in the presence of TritonX-100, Tween-20, Tween-80, SDS, saponin. The present lipase was highly stable towards oxidizing agents and was stable after 1 h at 25 °C in the presence of hydrogen peroxide, sodium hypochlorite and sodium perborate. The results suggest that the lipase from Burkholderia cepacia LP08 showed good potential for application in the detergent formulation.

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