Abstract
Snow algae play crucial roles in cold ecosystems, however, many aspects related to their biology, adaptations and especially their diversity are not well known. To improve the identification of snow algae from colored snow, in the present study we used a polyphasic approach to describe a new Antarctic genus, Chlorominima with the species type Chlorominima collina. This new taxon was isolated of colored snow collected from the Collins Glacier (King George Island) in the Maritime Antarctic region. Microscopy revealed biflagellated ellipsoidal cells with a rounded posterior end, a C-shaped parietal chloroplast without a pyrenoid, eyespot, and discrete papillae. Several of these characteristics are typical of the genus Chloromonas, but the new isolate differs from the described species of this genus by the unusual small size of the cells, the presence of several vacuoles, the position of the nucleus and the shape of the chloroplast. Molecular analyzes confirm that the isolated alga does not belong to Chloromonas and therefore forms an independent lineage, which is closely related to other unidentified Antarctic and Arctic strains, forming a polar subclade in the Stephanosphaerinia phylogroup within the Chlamydomonadales. Secondary structure comparisons of the ITS2 rDNA marker support the idea that new strain is a distinct taxon within of Caudivolvoxa. Physiological experiments revealed psychrophilic characteristics, which are typical of true snow algae. This status was confirmed by the partial transcriptome obtained at 2°C, in which various cold-responsive and cryoprotective genes were identified. This study explores the systematics, cold acclimatization strategies and their implications for the Antarctic snow flora.
Highlights
The cryospheric biome is dominated by highly specialized microorganisms that thrive under extreme low temperatures at the interface between snow/ice and liquid water (Anesio and Laybourn-Parry, 2012)
Unlike Chloromonas arctica, in Chlorominima collina motility was only maintained at low temperatures
Considering that Cm. collina (i) forms an independent lineage within Stephanosphaerinia, (ii) it is sister to strains assigned to Chloromonas or Chlamydomonas, but which are not monophyletic with the type species of Chloromonas (Cr. reticulata) or Chlamydomonas (Cd. reinhardtii), so it is not can maintain the assigned generic identity and must be transferred to other genera (Pröschold et al, 2001), we propose a new genus Chlorominima, describing the type species Cm. collina, with the aim of generating a baseline to identify the rest of the members of this polar monophyletic lineage, contributing to the biodiversity in the snow algae Chlainomonas kolii and Chlainomonas rubra of Chlamydomonadales
Summary
The cryospheric biome is dominated by highly specialized microorganisms that thrive under extreme low temperatures at the interface between snow/ice and liquid water (Anesio and Laybourn-Parry, 2012). The basis of these microbial communities, and the precursors of inorganic carbon fixation and primary source of macromolecules, are snow and ice algae, and cyanobacteria (Boetius et al, 2015; Anesio et al, 2017). Snow algae play crucial ecological roles as foundation organisms sustaining a high diversity of heterotrophic micro-eukaryotes, bacteria, and archaea (Lutz et al, 2015; Havig and Hamilton, 2019). It has been suggested that such biological processes can promote horizontal exchange and recombination of genetic material, which enables the acquisition of new genes, enhancing diversity (Lyon and Mock, 2014; Liu et al, 2018)
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