Species Specificity of Bacteria Associated to the Brown Seaweeds Lobophora (Dictyotales, Phaeophyceae) and Their Potential for Induction of Rapid Coral Bleaching in Acropora muricata

Abstract

While reef degradation is occurring worldwide, it is not uncommon to see phase shifts from coral to macroalgal dominated reefs. Numerous studies have addressed the mechanisms by which macroalgae may outcompete corals and a few recent studies highlighted the putative role of bacteria at the interface between macroalgae and corals. Some studies suggest that macroalgae may act as vectors and/or foster proliferation of microorganisms pathogenic for corals. Using a combination of high throughput sequencing, bacterial culturing, and in situ bioassays we question if the adversity of macroalgal-associated bacteria to corals is mediated by specific bacterial taxa. Using Illumina sequencing, we characterized and compared the bacterial community from two Lobophora (Dictyotales, Phaeophyceae) species. The two species presented distinctive bacterial communities. Both species shared approximately half of their OTUs, mainly the most abundant bacteria. Species-specific OTUs belong to Planctomycetes, Proteobacteria, and Bacteroidetes. In total, 16 culturable bacterial strain were isolated and identified from the Lobophora surface, consisting of 10 genera (from nine families, four classes, and three phyla), some of which are not known as, but are related to pathogens involved in coral diseases, and others are naturally associated to corals. When patches of marine agar with 24 h cultures of each of these bacteria were placed in direct contact with the branches of the scleractinian coral Acropora muricata, they caused severe bleaching after 24 h exposure. Results suggest that regardless of taxonomic affinities, increase in density of these bacteria can be adverse to corals. Nevertheless, the microbial community associated to macroalgal surface may not represent a threat to corals, because the specific bacterial screening and control exerted by the alga preventing specific bacterial proliferation.

Niche-based assembly of bacterial consortia on the diatom Thalassiosira rotula is stable and reproducible

“…Cumulative evidence suggests that epibiotic microbial communities are characteristic to their living hosts [52,53]. Yet, compared with a number of detailed microbiome studies of multicellular marine macroalgae [22,52,[54][55][56], there is currently no unifying scheme or theory for bacterial community assembly on unicellular algae that underpins the divergent observations of distinct core communities on phylogenetically different microalgae to spatially and/or temporally diverse communities on conspecific microalgae [57].…”

Allelochemicals Produced by Brown Macroalgae of the Lobophora Genus Are Active against Coral Larvae and Associated Bacteria, Supporting Pathogenic Shifts to Vibrio Dominance

“…cover increasing from 15% in 2001 to 92% in 2009 (15). Direct contact with Lobophora macroalgae has already been shown to cause a negative physiological effect on corals in the form of tissue necrosis and bleaching (7,9,14,15,47,48). Previous studies have also shown that crude extracts from Caribbean L. variegata, particularly hydrophilic compounds, have broadspectrum antibacterial activity that causes significant shifts in coral-associated microbial communities (13,21).…”

Climate Change Impacts on Seagrass Meadows and Macroalgal Forests: An Integrative Perspective on Acclimation and Adaptation Potential

“…However, bacterial communities associated to marine macrophytes are not fixed and can change temporally and spatially across seasons, lifespan, life stages and tissue types by biotic and abiotic factors (Staufenberger et al, 2008;Aires et al, 2016;Mancuso et al, 2016). While bacterial communities of some macroalgae appear species-or even lineage-specific Vieira et al, 2016), this is yet unclear for kelps and seagrasses due to the low number of studies with inter-species comparisons. Recent results (Cúcio et al, 2016) suggest that sympatric seagrass species (in this case Z. marina, Z. noltei, and Cymodocea nodosa) might share largely the same rhizosphere community.…”