取食不同食物对小菜蛾幼虫肠道细菌多样性的影响

【目的】植食性昆虫肠道细菌的组成与其食物密切相关。本研究旨在探究小菜蛾Plutella xylostella幼虫肠道细菌多样性与其取食食物之间的关系以及它们之间相互适应的过程。【方法】本研究选取小菜蛾人工饲料品系(S)及其转寄主到结球甘蓝Brassica oleracea var. capitata、结球白菜Brassica rapa subsp. pekinensis和花椰菜Brassica olerocea var. botrytis饲养后第1代(分别为G1C, G1CC和G1WC)和第3代(分别为G3C, G3CC和G3WC)的4龄幼虫，提取小菜蛾肠道细菌基因组DNA，利用Illumina MiSeq二代高通量测序技术，分析其肠道细菌多样性和丰度。【结果】α多样性指数分析发现，取食不同食物的小菜蛾4龄幼虫肠道细菌多样性高低顺序为G1WC>G1CC>S>G1C。在菌群组成上，以人工饲料为食的S样品肠道细菌主要由厚壁菌门(Firmicutes)组成，转寄主植物后的G1C, G1CC和G1WC肠道中厚壁菌门(Firmicutes)相对丰度显著下降，G1C和G1CC小菜蛾肠道中变形菌门(Proteobacteria)相对丰度显著上升成为优势菌群，G1WC肠道中拟杆菌门(Bacteroidetes)成为优势菌群。在寄主植物上连续饲养3代后，与第1代相比，小菜蛾肠道细菌α多样性指数没有显著性改变，但在结球甘蓝和结球白菜上小菜蛾肠道菌群结构却发生了变化，相比G1C，G3C肠道中芽孢杆菌目(Bacillales)的相对丰度显著下降；相比G1CC， G3CC肠道中放线菌门(Proteobacteria)、芽单胞菌门(Gemmatimonadetes)和硝化螺旋菌门(Nitrospirae)的相对丰度均显著上升。【结论】取食人工饲料和不同寄主植物的小菜蛾幼虫肠道细菌多样性和群落构成存在显著差异，寄主植物对小菜蛾肠道微生物的结构组成具有重要的影响，且小菜蛾肠道微生物对寄主植物可能存在一个长期适应的过程。本研究为进一步探讨影响小菜蛾肠道细菌变化的因素，以及后续研究肠道细菌与寄主植物之间的互作奠定了良好的基础。

Effects of different diets on the diversity of larval gut bacteria of the diamondback moth,Plutella xylostella (Lepidoptera: Plutellidae)

【Aim】 The composition of the gut bacteria in herbivorous insects is closely related to their foods. This study aims to address the relationship and mutual adaptation between the diversity of larval gut bacteria of Plutella xylostella and its diets. 【Methods】 The gut bacterial DNA was extracted from the 4th instar larvae of P. xylostella feeding on artificial diet (S) and the larvae shifted from artificial diet to feeding on cabbage Brassica oleracea var. capitata, Chinese cabbage Brassica rapa subsp. pekinensis and cauliflower Brassica oleracea var. italic for one generation (G1C, G1CC and G1WC, respectively), and three generations (G3C, G3CC and G3WC, respectively). The diversity and abundance of gut bacteria was then analyzed based on Illumina MiSeq of the 2nd generation high-throughput sequencing technology. 【Results】 The α-diversity index analysis indicated that the gut bacterial diversity of the 4th instar larvae of P. xylostella feeding on different diets was ranked as G1WC>G1CC>S>G1C. Firmicutes was the major phylum of the gut bacteria in sample S, while the relative abundance of Firmicutes in G1C, G1CC and G1WC decreased significantly. The relative abundance of Proteobacteria increased as the major phylum in G1C and G1CC, and that of Bacteroidetes increased as the dominant phylum in G1WC. No significant differences in terms of the α-diversity index of gut bacteria of P. xylostella were observed between the 1st and the 3rd generation of larvae feeding on all the host plants. However, the relative abundance of a few bacterial phyla had significant differences between the 1st and the 3rd generation of larvae feeding on cabbage and Chinese cabbage. Compared with G1C, G3C had a significantly reduced relative abundance of Bacillales. Similarly, the relative abundance of Proteobacteria, Gemmatimonadetes and Nitrospirae in G3CC was significantly increased as compared with that in G1CC. 【Conclusion】 The gut bacterial diversity and community composition of P. xylostella larvae reared on artificial diet and different host plants vary significantly. Host plants have a great influence on the structure and composition of the gut microbes of P. xylostella, which may have a long-term adaptation process to host plants. This should be a case study for the factors that influence gut bacteria of P. xylostella, and may provide insights into the interactions between gut bacteria and different host plants.