Unicellular versus Filamentous: The Glacial Alga Ancylonema alaskana comb. et stat. nov. and Its Ecophysiological Relatedness to Ancylonema nordenskioeldii (Zygnematophyceae, Streptophyta).

Lenka Procházková,Linda Nedbalová,Daniel Remias,Tomáš Řezanka

doi:10.3390/microorganisms9051103

Abstract

Melting polar and alpine ice surfaces frequently exhibit blooms of dark pigmented algae. These microbial extremophiles significantly reduce the surface albedo of glaciers, thus accelerating melt rates. However, the ecology, physiology and taxonomy of cryoflora are not yet fully understood. Here, a Swiss and an Austrian glacier dominated either by filamentous Ancylonema nordenskioeldii or unicellular Mesotaenium berggrenii var. alaskanum, were sampled. Molecular analysis showed that both species are closely related, sharing identical chloroplast morphologies (parietal-lobed for Ancylonema vs. axial plate-like for Mesotaenium sensu stricto), thus the unicellular species was renamed Ancylonema alaskana. Moreover, an ecophysiological comparison of the two species was performed: pulse–amplitude modulated (PAM) fluorometry confirmed that they have a high tolerance to elevated solar irradiation, the physiological light preferences reflected the conditions in the original habitat; nonetheless, A. nordenskioeldii was adapted to higher irradiances while the photosystems of A. alaskana were able to use efficiently low irradiances. Additionally, the main vacuolar polyphenol, which effectively shields the photosystems, was identical in both species. Also, about half of the cellular fatty acids were polyunsaturated, and the lipidome profiles dominated by triacylglycerols were very similar. The results indicate that A. alaskana is physiologically very similar and closely related but genetically distinct to A. nordenskioeldii.

Highlights

Melting glaciers harbor diverse communities of specialized microorganisms [1], and the habitat can be regarded as extreme for photoautotrophic life, considering the prevailing conditions [2,3]
Microalgal ice surface blooms at Morteratsch Glacier in Switzerland were mainly caused by filaments of A. nordenskioeldii and some scattered unicells of M. berggrenii var
Based on the acquired morphological and genetic data from both field sites, the latter was moved to the genus Ancylonema and the rank of a variety is raised to species status

Summary

Introduction

Melting glaciers harbor diverse communities of specialized microorganisms [1], and the habitat can be regarded as extreme for photoautotrophic life, considering the prevailing conditions [2,3]. The current knowledge about biodiversity, distribution and adaptations of glacial algae were reviewed in [4] These habitats are dominated by few zygnematophycean species. Both species are closely related but morphologically distinguishable, the first being more roundish after cell cleavage and practically unicellular [5,6]; the latter cylindrical-elongate and forming filaments [7]. They are apparently cosmopolitan in polar and mid-latitude mountainous regions [8,9].

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