We previously determined that several diets used to rear Aedes aegypti and other mosquito species support the development of larvae with a gut microbiota but do not support the development of axenic larvae. In contrast, axenic larvae have been shown to develop when fed other diets. To understand the mechanisms underlying this dichotomy, we developed a defined diet that could be manipulated in concert with microbiota composition and environmental conditions. Initial studies showed that axenic larvae could not grow under standard rearing conditions (27 °C, 16-h light: 8-h dark photoperiod) when fed a defined diet but could develop when maintained in darkness. Downstream assays identified riboflavin decay to lumichrome as the key factor that prevented axenic larvae from growing under standard conditions, while gut community members like Escherichia coli rescued development by being able to synthesize riboflavin. Earlier results showed that conventional and gnotobiotic but not axenic larvae exhibit midgut hypoxia under standard rearing conditions, which correlated with activation of several pathways with essential growth functions. In this study, axenic larvae in darkness also exhibited midgut hypoxia and activation of growth signaling but rapidly shifted to midgut normoxia and arrested growth in light, which indicated that gut hypoxia was not due to aerobic respiration by the gut microbiota but did depend on riboflavin that only resident microbes could provide under standard conditions. Overall, our results identify riboflavin provisioning as an essential function for the gut microbiota under most conditions A. aegypti larvae experience in the laboratory and field.

我们之前确定用于饲养埃及伊蚊的几种饮食和其他蚊子物种支持具有肠道微生物群的幼虫的发育，但不支持无菌幼虫的发育。相比之下，无菌幼虫已被证明在喂食其他饮食时会发育。为了理解这种二分法背后的机制，我们开发了一种明确的饮食，可以根据微生物群组成和环境条件进行操作。初步研究表明，在标准饲养条件下（27 °C，16 小时光照：8 小时黑暗光周期）喂养确定的饮食时，无菌幼虫不能生长，但在黑暗中维持时可以发育。下游分析确定核黄素衰变为荧光色素是阻止无菌幼虫在标准条件下生长的关键因素，而肠道群落成员如大肠杆菌通过能够合成核黄素来挽救发育。早期的结果表明，常规和无菌幼虫在标准饲养条件下表现出中肠缺氧，这与具有基本生长功能的几种途径的激活相关。在这项研究中，黑暗中的无菌幼虫也表现出中肠缺氧和生长信号激活，但在光照下迅速转变为中肠常氧并阻止生长，这表明肠道缺氧不是由于肠道微生物群的有氧呼吸引起的，而是依赖于核黄素只有常驻微生物才能在标准条件下提供。总的来说，我们的结果确定在大多数情况下核黄素供应是肠道微生物群的基本功能埃及伊蚊幼虫在实验室和野外的经验。