Exploring the cold-water coral holobiont: characterizing the bacterial associates of the octocorals Paragorgia arborea and Primnoa resedaeformis

Corals are among the world’s most biodiverse symbiotic ecosystems, and recent work has highlighted the importance of microbes to the health and resilience of reef-building tropical corals. Cold-water corals (CWCs) constitute crucial ecosystems in both shallow and deeper waters, and also form symbioses with microbes. Here, we describe the bacterial associates of two CWCs, Paragorgia arborea and Primnoa resedaeformis, sampled from the Gulf of Maine. Unique bacterial communities were found in the mucus and the tissues of P. arborea, and anatomically distinct bacterial biomarkers were identified. We speculate that some P. arborea-associated bacteria may participate in nitrogen cycling, and other contributors such as the dominant taxa Mycoplasma may play a role in host health. While bacterial sequences in the mucus of P. resedaeformis were low in abundance and diversity, our findings were supported by the recently published P. resedaeformis microbiome. The information provided here serves to detail novel findings in CWC microbiome research and promotes future exploration of CWCs