The Arctic Cylindrocystis (Zygnematophyceae, Streptophyta) Green Algae are Genetically and Morphologically Diverse and Exhibit Effective Accumulation of Polyphosphate

Abstract

The green algal genus Cylindrocystis is widespread in various types of environments, including extreme habitats. However, very little is known about its diversity, especially in polar regions. In the present study, we isolated seven new Cylindrocystis-like strains from terrestrial and freshwater habitats in Svalbard (High Arctic). We aimed to compare the new isolates on a molecular (rbcL and 18S rDNA), morphological (light and confocal laser scanning microscopy), and cytological (Raman microscopy) basis. Our results demonstrated that the Arctic Cylindrocystis were not of a monophyletic origin and that the studied strains clustered within two clades (tentatively named the soil and freshwater/glacier clades) and four separate lineages. Morphological data (cell size, shape, and chloroplast morphology) supported the presence of several distinct taxa among the new isolates. Moreover, the results showed that the Arctic Cylindrocystis strains were closely related to strains originating from the temperate zone, indicating high ecological versatility and successful long-distance dispersal of the genus. Large amounts of inorganic polyphosphate (polyP) grains were detected within the chloroplasts of the cultured Arctic Cylindrocystis strains, suggesting effective luxury uptake of phosphorus. Additionally, various intracellular structures were identified using Raman microscopy and cytochemical and fluorescent staining. This study represents the first attempt to combine molecular, morphological, ecological, and biogeographical data for Arctic Cylindrocystis. Our novel cytological observations partially explain the success of Cylindrocystis-like microalgae in polar regions.

Sunscreen mucilage: a photoprotective adaptation found in terrestrial green algae (Zygnematophyceae)

“…14). This is in line with recent findings about cell width stability in genotypes of the structurally similar saccoderm desmid Cylindrocystis (Barcytė et al, 2020). Interestingly, the strains DEL.1 and KH.1 with identical rbcL gene sequences showed marked differences in cell width as well (Fig.…”

Polyphosphate: A Multifunctional Metabolite in Cyanobacteria and Algae

“…Some algae accumulate polyP upon exposure to elevated temperatures, but very little is known about this phenomenon in photosynthetic organisms. A Cylindrocystis-like alga isolated from the High Arctic, where temperatures oscillate from −12 to +5°C, showed elevated polyP accumulation when cultivated at 20°C (Barcyte et al, 2020). However, another Cylindrocystis-like strain that inhabits the desert and grows at elevated temperatures did not accumulate polyP under the same conditions.…”

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

“…Two different alignments were constructed for the phylogenetic analyses, based on the 18S rRNA and rbcL gene sequences. The sequences were selected according to [10,11,21] to encompass all the zygnematophycean lineages. The 18S rDNA alignment contained 56 sequences (1777 bp), the rbcL matrix consisted of 49 sequences (1290 bp); Embryophytes (Sphagnum palustre, Phaeoceros laevis, Marchantia polymorpha) were selected as the outgroup.…”

“…The 18S rDNA and rbcL phylogenies showed a very close relationship between A. nordenskioeldii and A. alaskana, pointing to a common ancestor, and they formed the Ancylonema clade. In contrast, the third prominent species of glacial algae, Cylindrocystis brebissonii, is situated in its own zygnematophycean clade which was named after this organism [10].…”

“…They are apparently cosmopolitan in polar and mid-latitude mountainous regions [8,9]. In addition, Cylindrocystis is a third zygnematophycean genus with members causing or participating in glacial blooms, and cells can be distinguished by cell size, shape and chloroplast morphology [10]. Cytologically, all of these species share abundant brownish phenols in vacuoles; the main constituent, a glycosylated purpurogallin derivative pigment, is believed to play a significant role for tolerating high visible and ultraviolet irradiance, thus preventing either photoinhibition or DNA mutation effects [11,12].…”