Abstract
Cold-water corals, similar to tropical corals, contain diverse and complex microbial assemblages. These bacteria provide essential biological functions within coral holobionts, facilitating increased nutrient utilization and production of antimicrobial compounds. To date, few cold-water octocoral species have been analyzed to explore the diversity and abundance of their microbial associates. For this study, 23 samples of the family Anthothelidae were collected from Norfolk (n = 12) and Baltimore Canyons (n = 11) from the western Atlantic in August 2012 and May 2013. Genetic testing found that these samples comprised two Anthothela species (Anthothela grandiflora and Anthothela sp.) and Alcyonium grandiflorum. DNA was extracted and sequenced with primers targeting the V4–V5 variable region of the 16S rRNA gene using 454 pyrosequencing with GS FLX Titanium chemistry. Results demonstrated that the coral host was the primary driver of bacterial community composition. Al. grandiflorum, dominated by Alteromonadales and Pirellulales had much higher species richness, and a distinct bacterial community compared to Anthothela samples. Anthothela species (A. grandiflora and Anthothela sp.) had very similar bacterial communities, dominated by Oceanospirillales and Spirochaetes. Additional analysis of core-conserved bacteria at 90% sample coverage revealed genus level conservation across Anthothela samples. This core included unclassified Oceanospirillales, Kiloniellales, Campylobacterales, and genus Spirochaeta. Members of this core were previously recognized for their functional capabilities in nitrogen cycling and suggest the possibility of a nearly complete nitrogen cycle within Anthothela species. Overall, many of the bacterial associates identified in this study have the potential to contribute to the acquisition and cycling of nutrients within the coral holobiont.
Highlights
Cold-water coral ecosystems contribute to vital biodiversity hotspots within the deep sea
Because some tropical coral species have shown correlation between their bacterial composition and environmental parameters, similar relationships were anticipated within the host–microbe interactions of the cold-water corals collected during this study
Our study provides insight into the previously uncharacterized microbiome of cold-water octocorals classified under the family Anthothelidae
Summary
Cold-water coral ecosystems contribute to vital biodiversity hotspots within the deep sea. Research addressing the microbial communities associated with coldwater corals has been limited due to the expense of sampling, which can be directly linked to the difficulty of sample retrieval at depth. While many of these corals have been identified since the 1800s, the first microbial study of cold-water corals was not published until 2006. That same year, Penn et al (2006) evaluated bacterial communities associated with a black coral and several bamboo corals in the Gulf of Alaska These two studies were the first to describe the microbial communities associated with stony and soft cold-water coral species as well as demonstrate differentiation between these deepsea coral-associated communities and those of their surrounding environments (sediment and water column). Studies have characterized the microbial diversity of additional coldwater corals: L. pertusa (Kellogg, 2008; Neulinger et al, 2008; Hansson et al, 2009; Kellogg et al, 2009; Schottner et al, 2009; Galkiewicz et al, 2011), Madrepora oculata (Hansson et al, 2009), and octocorals Paragorgia arborea, Plumarella superba, and Cryogorgia koolsae (Gray et al, 2011)
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