Phylogeny and lipid profiles of snow-algae isolated from Norwegian red-snow microbiomes

Snow algae blooms often form green or red coloured patches in melting alpine and polar snowfields worldwide, yet little is known about their biology, biogeography, and species diversity. We investigated eight isolates collected from red snow in northern Norway, using a combination of morphology, 18S rRNA gene and internal transcribed spacer 2 (ITS2) genetic markers. Phylogenetic and ITS2 rRNA secondary structure analyses assigned six isolates to the species Raphidonema nivale, Deuterostichococcus epilithicus, Chloromonas reticulata, and Xanthonema bristolianum. Two novel isolates belonging to the family Stichococcaceae (ARK-S05-19) and the genus Chloromonas (ARK-S08-19) were identified as potentially new species. In laboratory cultivation, differences in the growth rate and fatty acid profiles were observed between the strains. Chlorophyta were characterized by abundant C18:3n-3 fatty-acids with increases in C18:1n-9 in the stationary phase, whilst Xanthonema (Ochrophyta) was characterized by a large proportion of C20:5n-3, with increases in C16:1n-7 in the stationary phase. In a further experiment, lipid droplet formation was studied in C. reticulata at the single-cell level using imaging flow cytometry. Our study establishes new cultures of snow algae, reveals novel data on their biodiversity and biogeography, and provides an initial characterization of physiological traits that shape natural communities and their ecophysiological properties. Norwegian red snow microbiomes host phylogenetically diverse culturable microalgae that exhibit different growth strategies and accumulate lipids under physiological stress.

Automated summary

Snow algae blooms in melting snowfields are poorly understood in terms of their biology, biogeography, and species diversity. This study investigated eight isolates from red snow in northern Norway using morphology and genetic markers. Six isolates were assigned to known species, while two isolates were potentially new species. Further experiments revealed differences in growth rate and fatty acid profiles among strains, as well as the accumulation of lipids under physiological stress. This study provides new insights into the biodiversity and biogeography of snow algae, as well as their physiological traits and ecological properties.