Insight into the microbial community structure of a Norwegian deep-water coral reef environment

Deep-water coral reefs support rich biological communities below the photic zone of fjords and continental shelves around the world. In this environment, life is enclosed within cold permanent darkness, in stark contrast to life in tropical coral reefs. We collected samples of water, sediment and a Desmacidon sp. sponge from a deep-water coral reef off the coast of Norway, and characterised bacterial communities with focus on primary producers in the dark. Following DNA extraction, PCR amplification and 16S rRNA gene library sequencing, bioinformatic analyses demonstrated significant differences between bacterial communities associated with the three samples. The finding that 50% of the clones showed <90% identity to cultured bacteria reflects the novel and uncharacterised diversity associated with these deep-water coral reefs. A total of 13 bacterial phyla were identified. Acidobacteria dominated the sponge library and Proteobacteria dominated the bacterioplankton and sediment libraries. Phylogenetic analysis revealed a possible new clade of sponge-associated Acidobacteria, which includes representatives from the Desmacidon sp. (Norway), Rhopaloeides odorabile (Australia) and Discodermia dissoluta (Curacao). Furthermore, the targeted recovery of a particulate methane monooxygenase (pmoA) gene from the Desmacidon sp. DNA extract suggests that as yet uncultivated type I methanotrophs may mediate methane oxidation in this deep-water coral reef. Methanotrophs were not identified in the 16S rRNA gene libraries, but the presence of a high number (8%) of clones related to sulfide-, nitrite- and iodide-oxidising bacteria suggests chemosynthesis to be involved with maintenance of the deep-water coral reef ecosystem.