Molecular and morphological diversity of Zygnema and Zygnemopsis (Zygnematophyceae, Streptophyta) from Svalbard (High Arctic)

Abstract

Filamentous conjugating green microalgae (Zygnematophyceae, Streptophyta) belong to the most common primary producers in polar hydro-terrestrial environments such as meltwater streamlets and shallow pools. The mats formed by these organisms are mostly composed of sterile filaments with Zygnema morphology, but the extent of their diversity remains unknown. Traditional taxonomy of this group is based on reproductive morphology, but sexual reproduction (conjugation and formation of resistant zygospores) is very rare in extreme conditions. In the present study we gave the first record of zygospore formation in Svalbard field samples, and identified conjugating filaments as Zygnemopsis lamellata and Zygnema cf. calosporum. We applied molecular phylogeny to study genetic diversity of sterile Zygnema filaments from Svalbard in the High Arctic. Based on analysis of 143 rbcL sequences, we revealed a surprisingly high molecular diversity: 12 Arctic Zygnema genotypes and one Zygnemopsis genotype were found. In addition, we characterized individual Arctic genotypes based on cell width and chloroplast morphology using light and confocal laser scanning microscopy. Our findings highlight the importance of a molecular approach when working with sterile filamentous Zygnematophyceae, as hidden diversity might be very beneficial for adaptation to harsh environmental conditions, and experimental results could be misinterpreted when hidden diversity is neglected.

Metatranscriptomic and metabolite profiling reveals vertical heterogeneity within a Zygnema green algal mat from Svalbard (High Arctic)

“…The mat can be clearly described as Zygnema dominated, and the strain investigated in this study has been previously characterized as Zygnema sp. V by rbc L phylogeny (Pichrtová et al ., ).…”

“…V, belonging to the Z . circumcarinatum clade (Pichrtová et al ., ). The mat was sampled in early August during the Arctic growing season when water is readily available from melting snowfields.…”

“…Both samples contained young vegetative cells and belonged to genotype V, previously described by Pichrtová et al . (). Three independent biological replicates were measured with all methods described below.…”

“…Algae of the genus Zygnema are commonly found in Polar ecosystems, forming extensive mats in shallow pools, meltwater streams or on moist soil surfaces (Kim et al, 2008;Zidarova, 2008;Holzinger et al, 2009;Pichrtová et al, 2018). These habitats are characterized by extreme environmental conditions, including high seasonality.…”

“…to form different specialized cell types such as parthenospores, akinetes and so-called pre-akinetes, which are modified vegetative cells, supports survival under unfavourable conditions (McLean and Pessoney, 1971;Stancheva et al, 2012;Herburger et al, 2015). This is especially important in polar environments, as the formation of diploid zygospores is an extremely rare event in Zygnematophyceae from Arctic regions (Elster et al, 1997;Pichrtová et al, 2018). In addition, Zygnema uses diverse strategies to protect itself from high levels of irradiation, both ultraviolet radiation (UVR) and photosynthetically active radiation (PAR) (Holzinger et al, 2009;Pichrtová et al, 2013;Pierangelini et al, 2017).…”