Microbiota and metabolic disturbance caused by sulfamethoxazole exposure in the scleractinian coral Pocillopora damicornis

The overuse of antibiotics in aquaculture causes severe contamination in the coral reef environments, leading to the degradation of this vulnerable ecosystem. In the present study, 16S rRNA, transcriptomic and physiological approaches were employed to reveal the impacts of sulfamethoxazole (SMX), one of the common and widely distributed antibiotics in South China Sea, on the keystone sclerectinian coral Pocillopora damicornis holobiont. It was revealed that low-concentration SMX exposure (0.1 µg L −1 ) induced immune responses in coral hosts by activating the tumor necrosis factor (TNF) signaling pathway, and the synthesis of heat shock proteins. The symbiotic Symbiodiniaceae also enhanced their stress resistance by up-regulating oxygen metabolism and translation-related genes. Low-concentration SMX could also increase energy reserve and suppress energy allocation in the coral host. Moreover, results from 16S rRNA sequencing suggested that SMX exposure caused broad functional shifts in bacterial communities, including microbial infection, degradation of environmental pollutants, cyanoamino acid metabolism, carbon storage and glutathione metabolism. These findings illustrate that coral holobionts are highly sensitive to SMX exposure, which alters bacterial symbiont community to disturb energy metabolism, triggers immune responses, and ultimately affects corals’ survival.