Diverse molecular signatures for ribosomally ‘active’ Perkinsea in marine sediments. PerkMarSed

Background: Perkinsea are a parasitic lineage within the eukaryotic superphylum Alveolata. Recent studies making use of small sub-unit ribosomal RNA gene (SSU rDNA) methodologies have detected a significant diversity and abundance of Perkinsea-like phylotypes mainly in freshwater environments. Only a few Perkinsea sequences have been retrieved from marine waters while, in contrast, the only two groups of Perkinsea cultured and morphologically described are parasites of marine molluscs or other marine protists. These two marine groups form separate and distantly related clusters, composed of closely related lineages on SSU rDNA trees. Here, we test the hypothesis that Perkinsea are a hitherto under-sampled group in marine environments. Using 454 diversity ‘tag’ sequencing we investigate the genetic diversity and distribution of these protists in marine sediments and water column samples taken from the Deep Clorophyll Maximum (DCM) and sub-surface using both DNA and RNA as template and sampling four European offshore marine sites. Results: We detected the presence of 265 sequences branching with known Perkinsea, the majority of them recovered from marine sediments. Phylogenetic analyses classify a large proportion of these sequences into 38 cluster groups (including 30 novel marine cluster groups), which share less than 97% sequence similarity as to suggest this diversity encompasses a range of biologically and ecologically distinct organisms. Moreover 27% of these sequences were derived from RNA derived cDNA libraries. Conclusions: These results demonstrate that Perkinsea lineage is considerably more diverse than previously detected in marine environments. This wide diversity of Perkinsea-like protists is largely retrieved in marine sediment with a significant proportion detected in RNA derived libraries as to suggest this diversity represents ribosomally ‘active’ and intact cells present in these sediment environments. Given the phylogenetic range of hosts infected by known Perkinsea parasites, these data suggest that Perkinsea either play a significant but hitherto unrecognized role in marine sediment communities and/or members of this group are occupying the marine sediment possibly as ‘seed bank’.