Detecting chemical signals is important for identifying food sources and avoiding harmful agents. Like many animals, C. elegans use olfaction to chemotax towards their main food source, bacteria. However, little is known about the bacterial compounds governing C. elegans attraction to bacteria and the physiological importance of these compounds to bacteria. Here, we address these questions by investigating the function of a small RNA, P11, in the pathogen, Pseudomonas aeruginosa, that was previously shown to mediate learned pathogen avoidance. We discovered that this RNA also affects the attraction of untrained C. elegans to P. aeruginosa and does so by controlling production of ammonia, a volatile odorant produced during nitrogen assimilation. We describe the complex regulation of P. aeruginosa nitrogen assimilation, which is mediated by a partner-switching mechanism involving environmental nitrates, sensor proteins, and P11. In addition to mediating C. elegans attraction, we demonstrate that nitrogen assimilation mutants perturb bacterial fitness and pathogenesis during C. elegans infection by P. aeruginosa. These studies define ammonia as a major mediator of trans-kingdom signaling, implicate nitrogen assimilation as important for both bacteria and host organisms, and highlight how a bacterial metabolic pathway can either benefit or harm a host in different contexts.

检测化学信号对于识别食物来源和避免有害物质非常重要。与许多动物一样，线虫利用嗅觉对其主要食物来源细菌进行趋化。然而，人们对控制秀丽隐杆线虫对细菌的吸引力的细菌化合物以及这些化合物对细菌的生理重要性知之甚少。在这里，我们通过研究病原体铜绿假单胞菌中的小 RNA P11 的功能来解决这些问题，之前已证明这种小 RNA 可以介导习得性病原体回避。我们发现，这种 RNA 还影响未经训练的线虫对铜绿假单胞菌的吸引力，并通过控制氨的产生来实现这一点，氨是氮同化过程中产生的挥发性气味剂。我们描述了铜绿假单胞菌氮同化的复杂调节，这是由涉及环境硝酸盐、传感器蛋白和 P11 的伙伴转换机制介导的。除了介导秀丽隐杆线虫吸引力之外，我们还证明氮同化突变体在铜绿假单胞菌感染秀丽隐杆线虫期间扰乱细菌适应性和发病机制。这些研究将氨定义为跨界信号传导的主要介质，暗示氮同化对于细菌和宿主生物体都很重要，并强调细菌代谢途径如何在不同环境下有益或损害宿主。