Because environments are full of diverse microorganisms including parasites and pathogens, how to select and maintain a beneficial microbial partner is a critical issue for host organisms. The bean bug Riptortus pedestris (Heteroptera: Alydidae) acquires a specific gut symbiont, Burkholderia insecticola, from environmental soil in the second instar stage and houses it in a crypt-bearing midgut region called M4. To sort the Burkholderia symbiont from a wide variety of soil microbes, R. pedestris develops a specialized organ named “constricted region (CR)”. The CR, located in front of the crypt-bearing symbiotic region, is immediately closed after colonization of M4 by the Burkholderia symbiont to block any contamination of microbes ingested with food. By using a food coloring and a red fluorescent protein (RFP)-expressing Burkholderia symbiont, we here revealed that the closed CR is re-opened at a later developmental stage of R. pedestris. Although the CR was re-opened at the late phase of the fifth instar, oral administration of food coloring and green fluorescent protein (GFP)-expressing symbiont demonstrated that ingested food and bacteria were stopped at the M4B despite the opened CR. Observations using confocal microscopy revealed reverse flow of gut content from M4 to M3 through the opened CR, the flow pressure of which seemed to prevent any contamination of the symbiotic M4 region. The morphological change of the CR with aging may cause a risk of contamination, but another mechanism, the reverse flow, plausibly maintains the specificity of gut symbiont in R. pedestris.

由于环境充满了包括寄生虫和病原体在内的多种微生物，因此如何选择和维持有益的微生物伴侣是宿主生物的关键问题。bug虫Riptortus pedestris（Heteroptera：Alydidae）在第二龄期阶段从环境土壤中获得了一种特殊的肠道共生体Burkholderia insecticola，并将其安置在一个隐窝的中肠区域M4中。为了从多种土壤微生物中分类Burkholderia共生菌，R。pedestris开发了一种专门的器官，称为“限制区（CR）”。位于隐窝共生区前面的CR在伯克霍尔德菌（Burkholderia）侵染M4后立即关闭共生物，以阻止食物摄入的任何微生物污染。通过使用食用色素和表达红色荧光蛋白（RFP）的伯克霍尔德菌共生体，我们在这里揭示了封闭的CR在R. pedestris的后期发育阶段重新开放。尽管CR在第五龄期的后期重新打开，但口服施用食用色素和表达绿色荧光蛋白（GFP）的共生体表明，尽管打开了CR，但仍在M4B处停止了摄入的食物和细菌。使用共聚焦显微镜进行的观察显示，肠内容物通过打开的CR从M4向M3反向流动，其流动压力似乎可以防止共生M4区域受到任何污染。在CR的老化可能会引起污染的风险，但另一种机制，反向流动，形态变化振振有词维持肠道共生体中特异性R. pedestris。