Study On Enhancment Of Zwittermicin A To Cry1Ac Against Spodoptera Exigua Hübner

Zwittermicin A(ZwA) is a linear aminopolyol antibiotic produced by Bacillus cereus (Bc) and Bacillus thuringiensis (Bt) with broad spectrums, and it inhibits many eukaryotes and prokaryotes. ZwA can enhance the toxicity of Bt Cry1 Ac protein. but the mechanism was still unknown.In this study, we did some primary research about histopathology, molecular biology and biochemistry on the mechanism of the enhancement.Cry1Ac protein was extracted by pH dependent precipitation method. Then feeded Spodoptera exigua Hübner (S.exigua) larvae with ZwA and Cry1Ac separately and corporately to improve the enhancement. The mortality was 90% at 48h after S.exigua larvae were treated with Cry1Ac in the presence of ZwA, which was higher than that without ZwA. All the 5th-instar larvae were dead at 84h after fed with 5μg of Cry1Ac plus 25μg of ZwA( per larvae).Microscopical observation of dissected midgut showed that at 12h post feeding with 5μg Cry1Ac and 25μg ZwA no PM were present in the treated larvae, in contrast to the presence of a fully formed PM in the midgut of control larvae. But after 36h, the midgut displayed normal and PM formed again. After being treated by 1% ZwA and Calcofluor individually in vitro, the PM protein of S.e was obveriously released by Calcofluor not ZwA.The effection of ZwA to Trypsin's activity was detected by the method of BAEE. The result was positive and it showed that ZwA had no effect on the prossess of Trypsin activing Cry1Ac protein. Through these results we presumed that ZwA could react withsome sites on the wall of Spodoptera exigua larvae's midgut.