Protistan microbial observatory in the Cariaco Basin: an examination of species richness, habitat specialization, and biogeography.

• Online Access: http://hdl.handle.net/2047/d20002083

The largest 18S rRNA Sanger sequence dataset from an oceanographic regime is combined with pyrosequencing to interrogate protistan diversity in the Cariaco Basin. A multiple PCR primer approach was applied to a total of 16 samples from 3 locations across the Basin and 4 depths along the basin's geochemical gradients. Phylogenetic analyses identify new clades at multiple levels of taxonomic hierarchy, revealing increased ecological and geographic distributions. Several clades were detected only in anoxic samples, suggestive of habitat specialization. This is supported by multivariate analyses and parametric richness estimations showing a division between communities present in different geochemical layers of the water column and at the different geographic locations sampled. In situ fixed samples were obtained to enumerate protists from different biogeochemical habitats using fluorescent in situ hybridization and scanning electron microscopy, and show that 90% of cells in deep anoxic layers of the Cariaco Basin do not hybridize with a universal probe. This suggests divergence in one of the most conserved regions of the 18S gene, and thus substantial novelty. Within anoxic in situ samples, a new class-level lineage within the phylum Ciliophora is identified and described here as "candidatus Cariacotrichea."