Ammonia nitrogen stress increases susceptibility to bacterial infection via blocking IL-1R–Relish axis mediated antimicrobial peptides expression in shrimp

Ammonia nitrogen (ammonia-N) accumulation is pointed out as an environmental stress factor in the aquatic culture system, and has been shown to increase the susceptibility of aquatic organisms to infection. However, the mechanism by which ammonia-N stress induces a higher susceptibility to infection or disease outbreak remains largely unknown. Herein, we cloned and identified an interleukin-1 receptor homolog from the shrimp Litopenaeus vannamei (designated as LvIL-1R), and uncovered a LvIL-1R–LvRelish axis mediated antibacterial signaling that could induce the expression of antimicrobial peptides (AMPs) and thus conferred protection against Vibrio parahaemolyticus infection. Besides, we observed that shrimps became more susceptible to bacterial infection under ammonia-N stress, which attributed to that the LvIL-1R–LvRelish-AMPs antibacterial axis was restrained by the elevated ammonia-N concentration in hemolymph. Our results reveal how environmental (ammonia-N) stress increases shrimp susceptibility to infection, thereby providing some insights into the development of an effective environmental control strategy for disease prevention and treatment in aquaculture.