Chambouvet et al. BMC Microbiology 2014, 14:110 http://www.biomedcentral.com/1471-2180/14/110 RESEARCH ARTICLE Open Access Diverse molecular signatures for ribosomally ‘active’ Perkinsea in marine sediments Aurélie Chambouvet1*, Cédric Berney2,3, Sarah Romac2,3, Stéphane Audic2,3, Finlay Maguire1, Colomban De Vargas2,3 and Thomas A Richards4 Abstract Background: Perkinsea are a parasitic lineage within the eukaryotic superphylum Alveolata. Recent studies making use of environmental small sub-unit ribosomal RNA gene (SSU rDNA) sequencing methodologies have detected a significant diversity and abundance of Perkinsea-like phylotypes in freshwater environments. In contrast only a few Perkinsea environmental sequences have been retrieved from marine samples and only two groups of Perkinsea have been cultured and morphologically described and these are parasites of marine molluscs or marine protists. These two marine groups form separate and distantly related phylogenetic 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 diversity and distribution of these protists in marine sediments and water column samples taken from the Deep Chlorophyll Maximum (DCM) and sub-surface using both DNA and RNA as the source template and sampling four European offshore locations. Results: We detected the presence of 265 sequences branching with known Perkinsea, the majority of them recovered from marine sediments. Moreover, 27% of these sequences were sampled from RNA derived cDNA libraries. 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 suggesting this diversity encompasses a range of biologically and ecologically distinct organisms. Conclusions: These results demonstrate that the 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 suggesting this diversity represents ribosomally ‘active’ and intact cells. Given the phylogenetic range of hosts infected by known Perkinsea parasites, these data suggest that Perkinsea either play a significant but hitherto unrecognized role as parasites in marine sediments and/or members of this group are present in the marine sediment possibly as part of the ‘seed bank’ microbial community. Keyword: 454 pyrosequencing, Perkinsus, Parvilucifera, Food web, Protist, Parasite Background (including both marine alveolate group I and II [also Environmental DNA (eDNA) analyses have demonstrated sometimes called MALVI & MALVII a]) [4,8]. that diversity records are missing significant data regarding Molecular surveys have shown that Perkinsea-like protists (reviewed in: [1-3]). Parasitic protists are a key sequences can be diverse and abundant in freshwater component of food webs, yet the role and diversity of lakes, suggesting this group plays an important role in these groups is often unknown (e.g. [4-6]). The protist freshwater food webs [5,9-11]. However, most freshwater ‘superphylum’ Alveolata includes numerous polyphyletic Perkinsea have still not been characterised ecologically or groups of parasites [7], for example: Apicomplexa, Perkinsea morphologically, with one exception, a recently identified (also named perkinsids or Perkinsozoa) and Syndiniales Perkinsea-like protist linked to local mortality events of the Southern Leopard frog Rana sphenocephala in the * Correspondence: [email protected] USA in 2003 [12]. Analysis of the SSU rDNA sequence 1Life Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK of this protist suggests that this infectious agent branches Full list of author information is available at the end of the article close to the Perkinsea in SSU rDNA phylogenies within © 2014 Chambouvet et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. Chambouvet et al. BMC Microbiology 2014, 14:110 Page 2 of 10 http://www.biomedcentral.com/1471-2180/14/110 a cluster consisting of only freshwater environmental using a custom-built pipeline developed by the BioMarKs sequences [12-14]. With the exception of the Perkinsea as- consortium (see [28]). This analysis identified 271 se- sociated with frog infections, all morphological descriptions quences preliminarily classified as Perkinsea. and cultured representatives of the Perkinsea are derived The taxonomic affiliation of these sequences was checked from two marine genera: Perkinsus and Parvilucifera. using phylogenetic analyses of a SSU rDNA dataset com- Perkinsus is a group of parasites infecting molluscs prising representative alveolate groups (Additional file 1: and includes P. marinus, the main cause of mortality of Figure S1 and Additional file 2: Table S1) and environ- bivalves leading to the economically important shellfish mental sequences retrieved from GenBank (Additional disease ‘Dermo’ [15]. Parvilucifera spp. are known to file 3: Table S2). Of the 271 sequences initially identified infect up to 26 different dinoflagellates, playing a role in as Perkinsea, alignment based analyses and phylogeny species succession, for example, infecting dinoflagellates confirmed that 265 individual 454 ‘tag’ sequences were that cause red-tides [16]. Taken together these data not chimeras [29] and branched with known Perkinsea se- suggest that the Perkinsea phylum is a diverse group of quences. Moreover, a large number of the 265 sequences parasites infecting a wide range of species such as: mol- were highly similar and so were clustered at 99% identity luscs, amphibians and dinoflagellates [14]. resulting in 150 unique V4 sequences branching within, or Numerous clone library surveys of eukaryotic diversity close to, Perkinsea taxonomic groups (Additional file 1: in marine waters have now been published (e.g. [17-22]) Figure S1). Table 1 summarises the provenance of the se- yet only a few Perkinsea sequences have been identified. quences sampled and provides information regarding the Specifically, only nine sequences belonging to Perkinsea total % of Perkinsea sequences within each V4 sequence that are distinct from either Perkinsus or Parvilucifera clus- dataset, which ranges from 0.244% to 0.006% of the 454 ter groups are currently available in GenBank (May-2013). sequencing effort from each of the environments sampled. To our knowledge, most of the environmental surveys of marine environments have, however, focused on sub- Diversity within marine Perkinsea surface or deep chlorophyll maximum (DCM) water To investigate the diversity and environmental distribution column samples, with only a few studies sampling sedi- of the Perkinsea-like sequence tags, we conducted a phylo- ments (e.g. [18,23,24]). As such, marine sediments are genetic analysis focusing on the V4 region and including often thought of as a ‘black box’ in terms of microbial di- the 150 sequence clusters identified (Figures 2 and 3). The versity and function [25], lacking in eukaryotic-specific regions flanking the variable V4 region are relatively con- molecular surveys (e.g. [18,23]). Furthermore, the majority served, while V4 stems and loops are variable [27,30]. The of these publications use clone library survey methods and phylogeny was derived from a masked alignment of 330 therefore give only a partial view of biodiversity. In con- characters and included a mixture of sites with fast and trast second-generation sequencing of environmental se- slow patterns of variation. As our analysis was limited quence tags theoretically allow deeper surveys of to the V4 region the deep and intermediate nodes of microbial biodiversity allowing the detection of low abun- the phylogeny are poorly resolved so that the tree is only dance microbes [26,27]. In this paper we use second helpful for demonstrating the diversity of Perkinsea-like generation sequencing methods to evaluate the diver- sequences and not the internal topology of the Perkinsea sity of the Perkinsea in multiple marine environments group, consistent with the aim of this study. and test the hypothesis that the Perkinsea are hitherto To identify a conservative picture of Perkinsea diver- under sampled group in marine environments. sity we classified the sequence diversity into ‘cluster- groups’ on the basis of two restrictive criteria: 1) mod- Results and discussion erate topology support (>0.6/60%/60%) and 2) posses- Processing of sequence data sion of two sequences from separate samples. Using this Using 454 pyro-sequencing, we investigated the diversity approach we identified 38 phylogenetic clusters labeled of Perkinsea in a selection of European marine samples, as cluster 1-38 on Figures 2 and 3 in addition to the sequencing the V4 region of the SSU rDNA [27] using morphologically characterised Perkinsus and Parviluci- both rDNA and rRNA as template. A similar DNA-based fera groups. 30 of these clusters represent previously approach has been used to investigate freshwater Perkinsea undescribed marine diversity-groups. Additionally, 42 [14]. We obtained sequence data