Morphological and physicochemical diversity of snow algae from Alaska

Marta J Fiołka,Izabela Treska,Weronika Sofińska-Chmiel,Nozomu Takeuchi,Sylwia Mieszawska

doi:10.1038/s41598-020-76215-x

Marta J Fiołka, Izabela Treska + Show 3 more

Open Access

https://doi.org/10.1038/s41598-020-76215-x

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Abstract

Snow algae are photosynthetic microbes growing in thawing snow. They usually show various morphological cell types. The aim of this study was to carry out microscopic and spectroscopic analysis of different forms of cells of snow algae collected on glaciers in Alaska. Four different shapes of algal cells were observed with the use of bright field LM (Light Microscopy), DIC (Differential Interference Contrast), EDF (Extended Depth Focus), fluorescence microscopy, and SEM (Scanning Electron Microscopy). The cells exhibited the strongest autofluorescence after the exposure to 365-nm excitation light, and the intensity differed among the cell types. Zygotes (cysts) showed the most intense fluorescence. Acridine orange staining revealed the acid nature of the algal cells. The use of Congo red and Calcofluor white fluorochromes indicated differences in the structure of polysaccharides in the cell wall in the individual types of algal cells. FTIR (Fourier-Transform Infrared Spectroscopy) analyses showed the presence of polysaccharides not only in the algal cells but also in the fixative solution. The presence of polysaccharides in the extracellular algal fraction was confirmed by X-ray dispersion spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy imaging (SEM). The differences observed in the structure of the cell wall of the different forms of red snow algae prompt further analysis of this structure.

Highlights

Snow algae are photosynthetic microbes growing in thawing snow
Since snow algae are adapted to living in an environment with low temperatures in the alpine or polar regions, they possibly produce a number of compounds such as sugars, sugar alcohols, and lipids and form mucous casings and cysts to adapt to such environmental conditions
Based on the sequence data, Types 1 and 2 cells are likely to be S. nivaloides and Type 4 is likely to be Chloromonas sp. (Chloromonadia snow group G), which was identified by single cell sequencing[34]

Summary

Introduction

Snow algae are photosynthetic microbes growing in thawing snow. They usually show various morphological cell types. The red or pink color of snow caused by blooms of snow algae is commonly observed during summer in alpine and coastal polar regions. The red color of algae is associated with the carotenoid astaxanthin found in algal cells outside chloroplasts This secondary pigment probably protects photosynthetic pigment-protein complexes against damage by strong solar radiation[3,4,5,6]. Algae involved in the phenomenon of red snow represent various species; most often, Chlamydomonas nivalis is responsible for the red snow. This snow alga was described as dominant in the algal community colonizing Gulkana Glacier and Harding Icefield in Alaska[13,14]. Interpretations of experiments on field-collected cells are limited due to their short-term

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