Shifting in the Dominant Bacterial Group Endozoicomonas Is Independent of the Dissociation With Coral Symbiont Algae

Abstract

The coral-associated <i>Endozoicomonas</i> are dominant bacteria in the coral holobiont. Their relative abundance usually decreases with heat-induced coral bleaching and is proposed to be positively correlated with Symbiodiniaceae abundance. It remains unclear whether this phenomenon of decreased <i>Endozoicomonas</i> abundance is caused by temperature stress or a decreased abundance of Symbiodiniaceae. This study induced bleaching in the coral <i>Euphyllia glabrescens</i> using a dark treatment over 15 weeks. We examined shifts in <i>Endozoicomonas</i> abundance and experimentally reduced Symbiodiniaceae density. 16S rRNA gene amplicon sequencing was used to characterize the changes in bacterial community (incl. <i>Endozoicomonas</i>) over time, and the 16S rRNA gene copy number of <i>Endozoicomonas</i> was quantified by qPCR. We detected a high abundance of <i>Endozoicomonas</i> in <i>E. glabrescens</i> that underwent dark-induced bleaching. The results reveal that changes in the relative abundance of <i>Endozoicomonas</i> are unrelated to Symbiodiniaceae abundance, indicating that <i>Endozoicomonas</i> can be independent of Symbiodiniaceae in the coral holobiont.