蝇类幼虫抗球孢白僵菌侵染的微生态学机制

The intestinal symbiotic bacteria have important functions on the development, reproduction, immunity and ecological adaptation of insects. The results of our previous research showed that, oral secretions of Musca domestica larvae could strongly inhibit the spore germination of Beauveria bassiana. But the inhibition effects of oral secretions from the ciprofloxacin fed larvae is weakened. It shows that, there were some matters in the oral secretions of Musca domestica larvae could inhibit the spore germination of Beauveria bassiana, and the matters had relations with the intestinal symbiotic bacteria from the larvae. So we speculate that the larvae oral secretion matters are one of the most important factors on maggots’ anti-infection to Beauveria bassiana. In support of this scientific hypothesis, we used 16s rDNA high-throughput sequencing and analysis technology, combinating intestinal bacteria culture and function identification, researching the key groups of symbiotic bacteria in intestines of Boettcheriaca peregrine，Lucilia sericat and Musca domestica maggots inhibiting the spore germination of Beauveria bassiana. To explore the micro-ecology mechanism of maggots’ anti-infection to the Beauveria bassiana. The results will demonstrate the functions of intestinal symbiotic bacteria in host stage choice of Beauveria bassiana, and lay the foundations on Beauveria bassiana resource utilization and flies’ biological control.

昆虫与肠道共生细菌在长期的进化过程中，建立了密切联系，构成了昆虫微生态。肠道共生细菌在昆虫的发育、繁殖、免疫、生态适应等方面起着重要作用，是昆虫学研究的热点之一。我们已有研究结果表明，家蝇幼虫口腔分泌物能强烈抑制球孢白僵菌孢子的萌发，而喂食含环丙沙星的饲料后，家蝇幼虫口腔分泌物的抑制作用相对减弱，说明口腔分泌物中有抑制球孢白僵菌孢子萌发的活性物质，且其合成与肠道共生细菌有关，我们推测这可能也是球孢白僵菌不能寄生蝇类幼虫的重要原因之一。为证明此科学假设，我们拟采用蝇蛆肠道细菌16S rDNA高通量测序与分析等技术，结合肠道细菌的体外培养及功能鉴定等方法，研究棕尾别麻蝇、丝光绿蝇和家蝇蝇蛆肠道共生细菌中抑制球孢白僵菌孢子萌发的关键菌群，探索蝇蛆抗球孢白僵菌感染的微生态学机制。研究的开展，可在新的角度研究球孢白僵菌对寄主昆虫虫态选择的机制，为球孢白僵菌资源开发利用及蝇类生物防治奠定理论基础。

首先通过传统分离方法和16S rDNA高通量测序法，分别明确了家蝇幼虫肠道可培养细菌和所有细菌的组成，通过利用不同抗生素分别去除家蝇幼虫肠道中的革兰氏阳性菌、革兰氏阴性菌和全部细菌，再进行转录组学测序表明，家蝇幼虫肠道中的革兰氏阴性细菌在其发育过程中起着更为重要的作用。而肠道中的铜绿假单胞菌Y12对球孢白僵菌有很强的拮抗作用，推测其可能是家蝇幼虫抗白僵菌感染的重要微生物因子。通过将铜绿假单胞菌Y12与球孢白僵菌共培养后，进行转录组测序表明，Y12主要影响球孢白僵菌的免疫与应激，并通过干扰球孢白僵菌的氧化应激、非生物刺激和氧化还原过程等通路影响其生长；家蝇成虫感染球孢白僵菌后，其肠道细菌的组成与球孢白僵菌菌株致病力相关，致病力超强的菌株对肠道细菌的调控能力越强。总之，家蝇幼虫肠道细菌中的铜绿假单胞菌是其抗球孢白僵菌感染的重要因子，家蝇幼虫在聚集孳生过程中，不断分泌消化液，并不断排出粪便，而粪便中的铜绿假单胞菌与其它细菌在幼虫孳生地周围形成一层细菌保护膜，从而抑制球孢白僵菌孢子侵染。