Protistan community analysis: key findings of a large-scale molecular sampling.

Protists are perhaps the most lineage-rich of microbial lifeforms, but remain largely unknown. High-throughput sequencing technologies provide opportunities to screen whole habitats in depth and enable detailed comparisons of different habitats to measure, compare and map protistan diversity. Such comparisons are often limited by low sample numbers within single studies and a lack of standardisation between studies. Here, we analysed 232 samples from 10 sampling campaigns using a standardised PCR protocol and bioinformatics pipeline. We show that protistan community patterns are highly consistent within habitat types and geographic regions, provided that sample processing is standardised. Community profiles are only weakly affected by fluctuations of the abundances of the most abundant taxa and, therefore, provide a sound basis for habitat comparison beyond random short-term fluctuations in the community composition. Further, we provide evidence that distribution patterns are not solely resulting from random processes. Distinct habitat types and distinct taxonomic groups are dominated by taxa with distinct distribution patterns that reflect their ecology with respect to dispersal and habitat colonisation. However, there is no systematic shift of the distribution pattern with taxon abundance.

Novel virus discovery and genome reconstruction from field RNA samples reveals highly divergent viruses in dipteran hosts.

We investigated whether small RNA (sRNA) sequenced from field-collected mosquitoes and chironomids (Diptera) can be used as a proxy signature of viral prevalence within a range of species and viral groups, using sRNAs sequenced from wild-caught specimens, to inform total RNA deep sequencing of samples of particular interest. Using this strategy, we sequenced from adult Anopheles maculipennis s.l. mosquitoes the apparently nearly complete genome of one previously undescribed virus related to chronic bee paralysis virus, and, from a pool of Ochlerotatus caspius and Oc. detritus mosquitoes, a nearly complete entomobirnavirus genome. We also reconstructed long sequences (1503-6557 nt) related to at least nine other viruses. Crucially, several of the sequences detected were reconstructed from host organisms highly divergent from those in which related viruses have been previously isolated or discovered. It is clear that viral transmission and maintenance cycles in nature are likely to be significantly more complex and taxonomically diverse than previously expected.

Phylogeny and evolution of Planomonadida (Sulcozoa): eight new species and new genera Fabomonas and Nutomonas.

Planomonads are widespread gliding zooflagellates from marine and freshwater sediments with seven species. We cultured 13 new strains; morphology and 18S and ITS2 rDNA sequences show that 11 represent eight new species described here. The 15 species form four robust clades, corresponding to revised Planomonas and Ancyromonas and new genera Fabomonas (marine) and Nutomonas (freshwater). Fabomonas tropica differs in shape and is genetically very distant from previously known planomonads, yet ultrastructurally similar. Anterior cilium morphology maps simply onto the rDNA tree forming the basis for two revised families: Ancyromonadidae (Ancyromonas, Nutomonas) have a uniformly thin, entirely acronematic anterior cilium; Planomonadidae (Fabomonas, Planomonas micra, and new species Planomonas elongata, bulbosa, and brevis) have a more conspicuous emergent basal region of the anterior cilium of normal thickness. ITS2 secondary structure is clade-specific, differing most sharply in the main Nutomonas subclade from all marine species, being exceptionally short compared with earlier-diverging marine clades. Nutomonas longa is very distant but Nutomonas howeae subsp. lacustris differs from Nutomonas (Planomonas) howeae and limna (new combinations) mainly by ITS2 compensatory and/or hemi-compensatory mutations. Ancyromonas indica, atlantica, and kenti are genetically more distinct from Ancyromonas sigmoides (=Planomonas mylnikovi). The first soil planomonad (new Nutomonas limna subspecies) was isolated.

The novel marine gliding zooflagellate genus Mantamonas (Mantamonadida ord. n.: Apusozoa).

Mantamonasis a novel genus of marine gliding zooflagellates probably related to apusomonad and planomonad Apusozoa. Using phase and differential interference contrast microscopy we describe the type species Mantamonas plasticasp. n. from coastal sediment in Cumbria, England. Cells are ∼5µm long, ∼5µm wide, asymmetric, flattened, biciliate, and somewhat plastic. The posterior cilium, on which they glide smoothly over the substratum, is long and highly acronematic. The much thinner, shorter, and almost immobile anterior cilium points forward to the cell's left. These morphological and behavioural traits suggest thatMantamonasis a member of the protozoan phylum Apusozoa. Analyses of 18S and 28S rRNA gene sequences of Mantamonas plasticaand a second genetically very different marine species from coastal sediment in Tanzania show Mantamonasas a robustly monophyletic clade, that is very divergent from all other eukaryotes. 18S rRNA trees mostly placeMantamonaswithin unikonts (opisthokonts, Apusozoa, and Amoebozoa) but its precise position varies with phylogenetic algorithm and/or taxon and nucleotide position sampling; it may group equally weakly as sister to Planomonadida, Apusomonadida or Breviata. On 28S rRNA and joint 18/28S rRNA phylogenies (including 11 other newly obtained apusozoan/amoebozoan 28S rRNA sequences) it consistently strongly groups with Apusomonadida (Apusozoa).

Closely related protist strains have different grazing impacts on natural bacterial communities.

Heterotrophic protists are abundant in most environments and exert a strong top-down control on bacterial communities. However, little is known about how selective most protists are with respect to their bacterial prey. We conducted feeding trials using cercomonad and glissomonad Cercozoa by assaying them on a standardized, diverse bacterial community washed from beech leaf litter. For each of the nine protist strains assayed here, we measured several phenotypic traits (cell volume, speed, plasticity and protist cell density) that we anticipated would be important for their feeding ecology. We also estimated the genetic relatedness of the strains based on the 18S rRNA gene. We found that the nine protist strains had significantly different impacts on both the abundance and the composition of the bacterial communities. Both the phylogenetic distance between protist strains and differences in protist strain traits were important in explaining variation in the bacterial communities. Of the morphological traits that we investigated, protist cell volume and morphological plasticity (the extent to which cells showed amoeboid cell shape flexibility) were most important in determining bacterial community composition. The results demonstrate that closely related and morphologically similar protist species can have different impacts on their prey base.