Abstract
The coral-associated Endozoicomonas 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 Endozoicomonas abundance is caused by temperature stress or a decreased abundance of Symbiodiniaceae. This study induced bleaching in the coral Euphyllia glabrescens using a dark treatment over 15 weeks. We examined shifts in Endozoicomonas abundance and experimentally reduced Symbiodiniaceae density. 16S rRNA gene amplicon sequencing was used to characterize the changes in bacterial community (incl. Endozoicomonas) over time, and the 16S rRNA gene copy number of Endozoicomonas was quantified by qPCR. We detected a high abundance of Endozoicomonas in E. glabrescens that underwent dark-induced bleaching. The results reveal that changes in the relative abundance of Endozoicomonas are unrelated to Symbiodiniaceae abundance, indicating that Endozoicomonas can be independent of Symbiodiniaceae in the coral holobiont.
Highlights
Coral-associated bacteria are commonly understood to affect coral health (Bourne and Webster, 2013; Bourne et al, 2016)
No significant variation was detected in the abundance of Endozoicomonas over the 15-week dark treatment, whereas the abundance of total bacteria significantly decreased at week 15
In the comparative Quantitative PCR (qPCR) results (Supplementary Figure S2B), there was a similar dynamic in the changes in Endozoicomonas 16S rRNA gene copy numbers normalized by the copy number of total bacterial 16S rRNA genes
Summary
Coral-associated bacteria are commonly understood to affect coral health (Bourne and Webster, 2013; Bourne et al, 2016). The bacteria genus Endozoicomonas, a putative core coral bacterial group (Bourne et al, 2016; Neave et al, 2016), is highly associated with coral bleaching. Genome analyses have revealed Endozoicomonas to function in DMSP degradation, testosterone degradation, probiotic mechanism, and the Embden-Meyerhof-Parnas (EMP) glycolytic pathway (Neave et al, 2014; Ding et al, 2016; Tandon et al, 2020). They can constitute >90% of the total bacterial community abundance (Pogoreutz et al, 2018; Shiu et al, 2018). Several studies have described a decrease in Endozoicomonas populations in corals during bleaching (Lee et al, 2015; Pantos et al, 2015; Glasl et al, 2016; Ziegler et al, 2017)
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