The distinct microbiome of Hydrurus foetidus, the dominant algae in glacier-fed streams

Hydrurus foetidus is a major primary producer at the base of the food web in glacier-fed streams across the globe. Although it has been reported since 200 years, little is known about this unicellular alga which is able to form long filaments (up to 30 cm) and bloom under oligotrophic conditions. In this study, we hypothesise H. foetidus harbours a distinct microbiome with which it may have symbiotic-like interactions, enabling it to thrive under the hard conditions of glacier-fed streams. Various streams of the Swiss Alps were screened and sampled for H. foetidus specimens and streamwater samples across two seasons. After DNA extraction, full-length 16S rRNA genes were sequenced using Nanopore technology to evaluate the microbiome composition within H. foetidus and streamwater. Preliminary results suggest H. foetidus indeed harbours its own microbiome, which differs from the streamwater one with an enrichment in Rhodoferax, Polaromonas, Flavobacterium genera, as well as a genus from the Oxalobacteraceae family (CM1G08), a family associated with nitrogen-fixation processes. Further analyses will be performed to determine the community assembly processes driving both microbiomes as well as how the distance from the glacier affects H. foetidus microbiome composition. Due to climate change and glacier disappearance, glacier-fed streams are now changing towards conditions to which H. foetidus may not be adapted. Therefore, it is crucial to intensify research about this alga to better understand its relevance for the ecosystem and the effects climate change will have on its prevalence in glacier-fed streams.