The 18S and 28S rDNA identity and phylogeny of the common lotic chrysophyteHydrurus foetidus

Abstract

Hydrurus foetidus is a geographically widespread alga commonly detected as 2-10 cm thalli in mountain streams in early spring, and also in lowland rivers at latitudes where seasonal conditions are appropriate for this cold-water species. Reaching macroscopic dimensions but with a pronounced phenotypic plasticity, this species is not typical for the golden algae (Chrysophyceae) -they are almost exclusively microscopic organisms, best known as micro-or nanoplankton in fresh water. Other sessile multicellular members are less conspicuous in nature, and rarely detected and sampled for further investigation. Therefore, the phylogenetic position of Hydrurus within the Chrysophyceae is not clear and has been disputed. We determined the 18S and 28S rDNA subunit sequences from a typical H. foetidus sampled at Finse, Hardangervidda mountain plateau, in south Norway. Phylogenetic trees inferred from concatenated 18S and 28S sequences, including representatives of all known groups of heterokonts, safely confirmed Hydrurus as a chrysophyte. Extending the taxon sampling to include nearly all available 18S chrysophyte sequences from cultured species and environmental DNA, our analysis placed H. foetidus within a separate, well-defined clade (here named the Hydrurus-clade) dominated by environmental sequences and poorly defined strains of chrysophytes in culture, mostly from cold environments. The environmental sequences derived from other mountainous regions showed high similarity and may represent homologous or closely related species. However, the phylogenetic relationship to the closest morphologically described chrysophyte clades remains unresolved. Genetic tools for investigating the Hydrurus complex are now available. An increased sampling of Hydrurus-like heterokont species as well as chrysophytes in general is crucial for understanding the evolution of this lineage and its relations to other chrysophyte clades.

Developments in the taxonomy of silica‐scaled chrysophytes – from morphological and ultrastructural to molecular approaches

“…Two different alignments were constructed for the phylogenetic analyses, based on the SSU rDNA and rbc L sequences. The sequences were selected according to the publications of Andersen (2007) and Klaveness et al (2011) to encompass all chrysophycean lineages. After including newly determined sequences, the final matrices contained 111 SSU rDNA and 91 rbc L sequences, respectively.…”

“…The analysis revealed the presence of significant hidden diversity within the genus Paraphysomonas and placed Synurophyceae nested within several Chrysophycean clades. Finally, Klaveness et al (2011) published the so far most detailed SSU rDNA phylogeny of chrysophyte algae, based on a data set including nearly all available sequences from cultured species and environmental DNA. The Synurophyceae did not obtain statistical support in ML and Bayesian analyses; although a relative large number of Mallomonas and Synura species were included in the analysis, only the latter genus obtained moderate statistical support.…”

Hydrurus‐related golden algae (Chrysophyceae) cause yellow snow in polar summer snowfields

“…Sequence alignment of 64 sequences selected from the publication of Klaveness et al . and our own isolates was constructed with the alignment program MAFFT (Katoh et al . ) and subsequently processed manually and corrected where necessary.…”

“…Klaveness et al . () showed that chrysophycean sequences, isolated from snow and sampled at many different locations worldwide, almost exclusively belong to the Hydrurus ‐clade. However, the ecology of these snow habitats and the physiology of cells living there have not been described closer yet.…”

Chrysophyceae and Phaeothamniophyceae

“…(Adapted and redrawn from Klaveness et al (2011) with permission from the authors). Note the close affinity between the Chrysophyceae and the Synurophyceae and the remote locations of the bicosoecids and haptophytes, both once considered "close relatives" of the Chrysophyta.…”