Microbial Community Compositional Shifts in Bleached Colonies of the Brazilian Reef-Building Coral Siderastrea stellata

Abstract

The association of metazoan, protist, and microbial communities with Scleractinian corals forms the basis of the coral holobiont. Coral bleaching events have been occurring around the world, introducing changes in the delicate balance of the holobiont symbiotic interactions. In this study, Archaea, bacteria, and eukaryotic phototrophic plastids of bleached colonies of the Brazilian coral Siderastrea stellata were analyzed for the first time, using 16S rRNA gene libraries. Prokaryotic communities were slightly more diverse in healthy than in bleached corals. However, the eukaryotic phototrophic plastids community was more diverse in bleached corals. Archaea phylogenetic analyses revealed a high percentage of Crenarchaeota sequences, mainly related to Nitrosopumilus maritimus and Cenarchaeum symbiosum. Dramatic changes in bacterial community composition were observed in this bleaching episode. The dominant bacterial group was Alphaproteobacteria followed by Gammaproteobacteria in bleached and Betaproteobacteria in healthy samples. Plastid operational taxonomic units (OTUs) from both coral samples were mainly related to red algae chloroplasts (Florideophycea), but we also observed some OTUs related to green algae chloroplasts (Chlorophyta). There seems to be a strong relationship between the Bacillariophyta phylum and our bleached coral samples as clones related to members of the diatom genera Amphora and Nitzschia were detected. The present study reveals information from a poorly investigated coral species and improves the knowledge of coral microbial community shifts that could occur during bleaching episodes.

Eukarya associated with the stony coral Oculina patagonica from the Mediterranean Sea

“…Although the lack of retrieval of fungal 18S rRNA gene sequences is often related to the low efficiency of DNA extraction protocols due to the extremely resistant fungal cell walls, this is most likely not the case in this work, since previous studies on coral diversity that retrieved fungal sequences used the same extraction protocol used here (Wegley et al, 2007) Eukaryotic phototrophic plastids were detected in O. patagonica samples by bacterial 16S rRNA gene DGGE (Rubio-Portillo et al, unpublished results) using DNA extracted from the skeletal matrix, being their proportion higher in bleached (57.5%) than in healthy (11.3%) corals, in good agreement with the previous studies that showed an increase in phototrophs other than zooxanthellae in bleached corals (Lins-de- Barros et al, 2013). These phototrophs included a photosynthetic cocolithophorid that showed a 99% identity in the 16S rRNA analyzed sequence with Ochrosphaera sp.…”

“…One of them, with no matches in databases, was more frequently retrieved from Harbour samples where it was detected in 33.7% of bleached corals. The other sequence, distantly related (91%) to a marine diatom and previously detected in bleached corals (Lins-de- Barros et al, 2013), was found in 41.7% of bleached colonies from Tabarca.…”

“…have been previously detected in the coral Montrastraea franksi (Rohwer et al, 2001), and in the coral Siderastrea stellata (Lins-de- Barros et al, 2013), showing that plastid communities could play an important role during bleaching events. Previous studies also detected a shift in the endolithic community of O. patagonica associated with coral (Ainsworth et al, 2008).…”

“…The diversity of such phototrophs can increase in bleached (i.e. zooxanthellae-less) corals (Lins-de- Barros et al, 2013) since the Symbiodinium loss experienced during the disease allows a deeper penetration of light within the coral skeleton and the subsequent secondary colonization of Chlorophyta and Streptophyta (Garcia et al, 2013). For instance, an increase in filamentous endolithic green algae of the genus Ostreobium has been observed during coral bleaching Littman et al, 2011) together with a higher transference of photoassimilates to the overlying coral tissue, that can use them as an energy source during bleaching Schlichter et al, 1996).…”

Structural and functional diversity of free-living microorganisms in reef surface, Kra island, Thailand

“…Changing of microbial associates could help the coral animals adapt to altering coral niches [15,17]. In contrast, coral bleaching causes change to the microbial community balance [18]. Thus, it is of importance to understand these dramatically fruitful marine microbial communities.…”