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Hydrurus foetidus is a cold-water golden alga (Chrysophyceae) found in fast-flowing rivers mainly during time of snowmelt. It has primarily been studied by scientists located near alpine or northern locations, but there are also observations both in south and north America, Russia, Japan, in the Hope Bay area (Antarctica) and Himalaya. If and where environmental conditions are appropriate, Hydrurus may be distributed "worldwide." More information is wanted from areas where its presence may be expected. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The psychrophilic freshwater alga Hydrurus foetidus (Villars) Trevisan has previously resisted laboratory culturing in liquid media. We investigated the use of microbiological techniques adapted to specific requirement for low temperature and high turbulence of the alga. We found that successful culturing required cleaning steps, where pieces of the alga were dissected out and plated on agar under cold conditions. From here, unialgal colonies could be isolated and inoculated into liquid media under appropriate conditions. Turbulence, created by a laboratory shaker, is critical. Sufficient light (30-100 µmol m s) and low temperature (here 2-3°C) are necessary. This rather common but highly under-investigated freshwater alga has potential for basic and applied research when available as laboratory cultures. [ABSTRACT FROM AUTHOR]

A silicon requirement for growth is demonstrated for an alga other than a diatom. Concentrations of less than 1 μM silicate greatly decreased the growth rate of Synura petersenii Korshikov and caused morphological changes. Half of maximum growth rate (μ[submax] = 1.12 divisions/day) appeared at a concentration of only 0.23 μM silicate. Germanium dioxide inhibited growth considerably; the degree of inhibition varying from non to almost 100% depending upon both Si and Ge concentrations. The amount of silicon deposited in the external scales of S. petersenii is comparable per unit area to that of diatoms. S. petersenii is able to deplete the medium of silicate to very low levels. The feasibility of batch culture techniques for this kind of work is discussed briefly. [ABSTRACT FROM AUTHOR]