稻水象甲入侵过程中肠道细菌群落的变化及其功能研究

Gut bacteria of insects play important roles in multiple physiological processes of hosts. The rice water weevil (RWW), Lissorhoptrus oryzophilus Kuschel, is an alien invasive species in China, and has spread rapidly in this country in recent years. Our preliminary survey revealed that this insect differs markedly in their gut bacterial composition among various geographic populations, however, it is not clear what causes such an difference and what it would contribute to the population development of this weevil. This project will collect RWW populations from various native and invasive regions and compare their gut bacteria community in terms of bacterial diversity and richness as well as the major bacterial taxa. The bacteria community in rice roots and rhizospheric soils and on diverse plant leaves was also surveyed to clarify the possibility of certain bacteria transferring to RWW and residing in its guts. Moreover, diverse factors, including insect developmental stage, bacterial density, host plants and ambient temperatures, on the transfer to and residence in the RWW gut were studied. We will also clarify functions of gut bacteria, including cellulolytic activity, contributions to insect host's feeding, growth, reproduction and survival, and tolerance to environmental stress (tolerance to low or high temperature, pathogen, etc.). Our overall objectives are to find the potential of changes in bacterial community of RWW guts and its effects on populations development of the insect. The results are expected to provided a research model for the future studies concerning relations of gut bacteria and population development of alien species.

昆虫肠道细菌在宿主的多种生理过程中起重要作用。稻水象甲(Lissorhoptrus oryzophilus, RWW)是一种外来入侵水稻害虫，近年在我国扩张十分迅速。申请者初步研究发现，该虫肠道细菌的种类构成存在地区间差异，但该差异的产生原因及其与该虫种群增长的关系尚不清楚。本项目拟基于细菌16S rRNA基因序列，系统比较RWW多个原产地、入侵地种群内肠道细菌群落的多样性、丰富度及细菌种类的差异，研究环境中的细菌通过取食进入RWW体内并定殖于肠道的可能性，确定初侵染源；研究细菌侵染和定殖与宿主生育期、环境中细菌浓度、RWW寄主植物种类、环境温度等因子的关系；研究肠道细菌水解纤维素能力，对宿主取食、生长发育、生殖和存活的影响，以及与宿主抗逆能力(耐热、耐寒性和抗病能力)的关系。由此探明RWW扩张过程中肠道细菌群落的变化及相关机制，以及对该虫种群发展的影响，从而揭示肠道细菌与其入侵的关系。

稻水象甲是一种世界性的入侵性害虫，在我国部分稻区危害严重。鉴于该虫具有寄主植物种类多、对环境适应能力强的特点，且其肠道细菌可在宿主的多种生命过程中起重要作用，本项目研究了稻水象甲肠道细菌的群落多样性及其随入侵过程的变化，以及部分细菌的功能。在稻水象甲中发现的主要肠道细菌有Rickettsia、Lactococcus、Wolbachia、Pantoea和Lactococcus等，其中Rickettsia在整个细菌群落中的相对丰度达到70%以上。其肠道细菌结构存在地理差异。例如在浙江乐清种群中Rickettsia主要为R. felis，而在河北唐海、美国加州Biggs种群中是R. bellii。此外，肠道细菌群落多样性与结构可随环境温度、寄主植物种类变化：与不适宜温度（19C和31C）相比，在适宜温度（23C和27C）下的细菌群落的丰富度、多样性明显较高；取食李氏禾、稗（适宜寄主）的成虫细菌群落丰富度明显高于取食水稻和双穗雀稗者，但细菌群落多样性则以取食稗的成虫为最高；取食双穗雀稗（不甚适宜寄主）的成虫菌群丰富度和多样性均明显较低。优势菌Rickettsia和Lactococcus的相对丰度与温度、食料条件关系密切：当成虫处于适宜温度并取食水稻时，Rickettsia的丰度随时间明显下降，而Lactococcus则上升。因此，该象甲在扩张的过程中其肠道细菌群落多样性和结构已发生明显变化，存在从环境中获得某些细菌并将其定殖于肠道的可能；温度、寄主植物等因子对肠道细菌群落产生显著影响，适宜的温度和食料条件有利于肠道细菌群落的发展。.对细菌功能的研究发现，抗生素处理后的成虫对球孢白僵菌的感染率显著上升，暗示肠道中的某些细菌极可能具有提高宿主抗病力的作用。成团泛菌转化株可在成虫肠道中定殖，在自然种群中其浓度在成虫羽化后显著上升，表明此细菌在成虫的食物消化和（或）营养吸收过程中起作用。.本研究首次在象甲类昆虫中发现Rickettsia是肠道中的优势菌，也是发现众多共生细菌共存于同种昆虫中的少数案例之一。研究发现其肠道细菌群落可随环境条件而变化，部分细菌与宿主的抗病性有关。研究结果丰富了我们对象甲类昆虫中肠道细菌群落多样性、功能及昆虫入侵机制的认识。