Identification of quorum sensing-regulated Vibrio fortis as potential pathogenic bacteria for coral bleaching and the effects on the microbial shift

Coastal pollution, global warming, ocean acidification, and other reasons lead to the imbalance of the coral reef ecosystem, resulting in the increasingly serious problem of coral degradation. Coral bleaching is often accompanied by structural abnormalities of coral symbiotic microbiota, among which <i>Vibrio</i> is highly concerned. In this study, <i>Vibrio fortis</i> S10-1 (MCCC 1H00104), isolated from sea cucumber, was used for the bacterial infection on coral <i>Seriatopora guttatus</i> and <i>Pocillopora damicornis</i>. The infection of S10-1 led to coral bleaching and a significant reduction of photosynthetic function in coral holobiont, and the pathogenicity of <i>V. fortis</i> was regulated by quorum sensing. Meanwhile, <i>Vibrio</i> infection also caused a shift of coral symbiotic microbial community, with significantly increased abundant Proteobacteria and Actinobacteria and significantly reduced abundant Firmicutes; on genus level, the abundance of <i>Bacillus</i> decreased significantly and the abundance of <i>Rhodococcus</i>, <i>Ralstonia</i>, and <i>Burkholderia-Caballeronia-Paraburkholderia</i> increased significantly; S10-1 infection also significantly impacted the water quality in the micro-ecosystem. In contrast, S10-1 infection showed less effect on the microbial community of the live stone, which reflected that the microbes in the epiphytic environment of the live stone might have a stronger ability of self-regulation; the algal symbionts mainly consisted of <i>Cladocopium</i> sp. and showed no significant effect by the <i>Vibrio</i> infection. This study verified that <i>V. fortis</i> is the primary pathogenic bacterium causing coral bleaching, revealed changes in the microbial community caused by its infection, provided strong evidence for the "bacterial bleaching" hypothesis, and provided an experimental experience for the exploration of the interaction mechanism among microbial communities, especially coral-associated <i>Vibrio</i> in the coral ecosystem, and potential probiotic strategy or QS regulation on further coral disease control.