Host-gut microbiota interactions are more complex than good or bad. Both gut symbiotic bacteria and pathobionts can provide essential functions to their host in one scenario and yet be detrimental to host health in another. So, these gut-dwelling bacteria must be tightly controlled to avoid harmful effects on the host. However, how pathobionts and other symbiotic bacteria coordinate to establish a host immune defense system remains unclear. Here, using a Tephritidae fruit fly Bactrocera dorsalis, we report that both pathobionts and other gut symbiotic bacteria release tyramine, which is recognized by the host insects. These tyramines induce the formation of insect-conserved Malpighian tubules-gut countercurrent flow upon bacterial infection, which requires tyramine receptors and aquaporins. At the same time, pathobionts but not gut symbiotic bacteria induce the generation of reactive oxygen species, which are preserved by the countercurrent flow, promoting bacteria elimination through increasing gut peristalsis. More importantly, our results show that the Malpighian tubules-gut countercurrent flow maintains proper microbiota composition. Our work suggests a model where pathobiont-induced reactive oxygen species are preserved by Malpighian tubules-gut countercurrent flow involving both pathobionts and symbiotic bacteria. Furthermore, our work provides a Malpighian tubules-gut interaction that ensures efficient maintenance of the gut microbiota.

中文翻译：

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Pathobiont 和共生体通过 Bactrocera dorsalis 中的 Malpighian 小管-肠道逆流促进微生物群稳态


宿主-肠道微生物群的相互作用比好或坏更复杂。肠道共生细菌和病原体都可以在一种情况下为宿主提供基本功能，但在另一种情况下对宿主健康有害。因此，必须严格控制这些肠道细菌，以避免对宿主产生有害影响。然而，致病菌和其他共生细菌如何协调建立宿主免疫防御系统仍不清楚。在这里，使用 Tephritidae 果蝇 Bactrocera dorsalis，我们报告了病原体和其他肠道共生细菌都会释放酪胺，这被宿主昆虫识别出来。这些酪胺在细菌感染时诱导形成昆虫保守的马氏小管-肠道逆流，这需要酪胺受体和水通道蛋白。同时，致病菌而不是肠道共生菌诱导活性氧的产生，这些活性氧被逆流保留，通过增加肠道蠕动促进细菌消除。更重要的是，我们的结果表明 Malpighian 小管-肠道逆流保持适当的微生物群组成。我们的工作提出了一个模型，其中涉及致病菌和共生细菌的马尔皮根小管-肠道逆流保留了致病菌诱导的活性氧。此外，我们的工作提供了 Malpighian 小管-肠道相互作用，确保肠道微生物群的有效维持。