Hemocyanin-modulated niacinamide shapes the hemolymph microbiota of penaeid shrimp

In aquatic invertebrates, the hemolymph functions as a conduit between the host and its environment, hence, maintaining hemolymph microbial homeostasis significantly influences disease pathogenesis. This study examined the critical role of the respiratory glycoprotein hemocyanin as a host factor in modulating hemolymph microbial composition in penaeid shrimp. Shrimp depleted of hemocyanin followed by Vibrio parahaemolyticus infection had a disruption in the niacinamide salvage pathway, which consequently increased total bacteria and relative abundance of the conditional pathogens Vibrio and Shewanella in the hemolymph. Moreover, in vivo knockdown of hemocyanin followed by niacinamide supplementation restored hemolymph microbial homeostasis, mitigating the competitive advantage of Vibrio. Overall, our data present novel insights into the pivotal role of niacinamide metabolism in modulating shrimp hemolymph microbial composition through hemocyanin.