Sulfide causes histological damage, oxidative stress, metabolic disorders and gut microbiota dysbiosis in juvenile sea cucumber Apostichopus japonicus Selenka.

Sulfide is a common harmful substance in sediments, with an especially high risk for deposit feeder organisms. The sea cucumber Apostichopus japonicus is a typical benthic feeder, and its intestine is the first line of defense and serves as a crucial barrier function. In this study, histological, physiological, gut microbiota, and metabolomic analyses were performed to explore the toxic response in the intestine of juvenile A. japonicus exposed to 0, 0.8, and 1.6 mg/L sulfide stress for 96 h. The results revealed sulfide-induced intestinal inflammatory symptoms and oxidative stress. Moreover, gut bacterial composition was observed after sulfide exposure, with an increase in Proteobacteria and a decrease in Cyanobacteria and Planctomycetes. Specifically, sulfide increased a set of sulfide-removing bacteria and opportunistic pathogens while decreasing several putative beneficial substance-producing bacteria. The metabolomic analysis indicated that sulfide also disturbed metabolic homeostasis, especially lipid and energy metabolism, in intestine. Interestingly, several intestinal bacteria were further identified to be significantly correlated with metabolic changes; for example, the decreased abundance levels of Bacillus, Corynebacterium, and Psychromonas were positively correlated with important energy metabolites, including maleic acid, farnesyl pyrophosphate, thiamine, butynoic acid, and deoxycholic acid. Thus, our research provides new insights into the mechanisms associated with the intestinal metabolic and microbiota response involved in sulfide stress adaptation strategies of juvenile A. japonicus.