A glimpse into the dark – the bacterial and archaeal diversity of tropical anchialine cave sediments

Using ion torrent sequencing of the V4 region of the 16S rRNA gene, we investigated the sediment from four anchialine caves on Eleuthera (Bahamas). Anchialine caves are secluded, landlocked marine ecosystems, with high degrees of endemism. In the cave sediments, the bacterial and archaeal communities differ from marine communities and between caves, while often resembling those from low oxygen or anaerobic marine sediments. The waters of all caves investigated here were mostly saline and oxygenated, with Windermere Abyss differing from the other caves. This was mirrored by the bacterial and archaeal communities, with members of the wb1-A12 clade, Nitrosopumilaceae , members of the NB1-j phylum, and Actinomarinales being dominant in Preacher’s Blue Hole, Valentine’s Cave, and Bung Hole while Desulfatiglans , Bathyarchaeia, and members of the GIF3 and Sva0485 clades were dominant in Windermere Abyss. All communities showed taxa found in oxygenated and anoxic sediments, thus indicating a variety of chemoautotrophic lifestyles, including methane-, nitrogen- and sulphur cycling. The communities were different from other caves and included understudied or otherwise rare taxa, partially from deep sea sediments, implying that the isolation might be an evolutionary factor, and indicating that anchialine caves could be a window into the deep sea.