Variability of Microbial Communities in Two Long-Term Ice-Covered Freshwater Lakes in the Subarctic Region of Yakutia, Russia

Microbial difference and its influencing factors in ice-covered lakes on the three poles

Most lakes in the world are permanently or seasonally covered with ice. However, little is known about the distribution of microbes and their influencing factors in ice-covered lakes worldwide. Here we analyzed the microbial community composition in the waters of 14 ice-covered lakes in the Hoh Xil region of northern Qing-Tibetan Plateau (QTP), and conducted a meta-analysis by integrating published microbial community data of ice-covered lakes in the tripolar regions (the Arctic, Antarctica and QTP). The results showed that there were significant differences in microbial diversity, community composition and distribution patterns in the ice-covered tripolar lakes. Microbial diversity and richness were lower in the ice-covered QTP lakes (including the studied lakes in the Hoh Xil region) than those in the Arctic and Antarctica. In the ice-covered lakes of Hoh Xil, prokaryotes are mainly involved in S-metabolic processes, making them more adaptable to extreme environmental conditions. In contrast, prokaryotes in the ice-covered lakes of the Arctic and Antarctica were predominantly involved in carbon/nitrogen metabolic processes. Deterministic (salinity and nutrients) and stochastic processes (dispersal limitation, homogenizing dispersal and drift) jointly determine the geographical distribution patterns of microorganisms in ice-covered lakes, with stochastic processes dominating. These results expand the understanding of microbial diversity, distribution patterns, and metabolic processes in polar ice-covered lakes.

Investigating eukaryotic and prokaryotic diversity and functional potential in the cold and alkaline ikaite columns in Greenland

The ikaite columns in the Ikka Fjord, SW Greenland, represent a permanently cold and alkaline environment known to contain a rich bacterial diversity. 16S and 18S rRNA gene amplicon and metagenomic sequencing was used to investigate the microbial diversity in the columns and for the first time, the eukaryotic and archaeal diversity in ikaite columns were analyzed. The results showed a rich prokaryotic diversity that varied across columns as well as within each column. Seven different archaeal phyla were documented in multiple locations inside the columns. The columns also contained a rich eukaryotic diversity with 27 phyla representing microalgae, protists, fungi, and small animals. Based on metagenomic sequencing, 25 high-quality MAGs were assembled and analyzed for the presence of genes involved in cycling of nitrogen, sulfur, and phosphorous as well as genes encoding carbohydrate-active enzymes (CAZymes), showing a potentially very bioactive microbial community.

Microeukaryotic Communities of the Long-Term Ice-Covered Freshwater Lakes in the Subarctic Region of Yakutia, Russia

Currently, microeukaryotic communities of the freshwater arctic and subarctic ecosystems are poorly studied. Still, these are of considerable interest due to the species biogeography and autecology as well as global climate change. Here, we used high-throughput 18S rRNA amplicon sequencing to study the microeukaryotic communities of the large subarctic freshwater lakes Labynkyr and Vorota in Yakutia, Russia, during the end of the ice cover period, from April to June. By applying the statistical methods, we coupled the microeukaryotic community structure profiles with available discrete factor variables and hydrophysical, hydrochemical, and environmental parameters. The sub-ice layer and the water column communities were differentiated due to the temporal change in environmental conditions, particularly temperature regime and electric conductivity. Additionally, the community composition of unicellular eukaryotes in lakes Labynkyr and Vorota was changing due to seasonal environmental factors, with these alterations having similar patterns in both sites. We suggest the community developed in the sub-ice layer in April serves as a primer for summer freshwater microeukaryotes. Our results extend the current knowledge on the community composition and seasonal succession of unicellular eukaryotes within subarctic freshwater ecosystems.

Under-Ice Development of Silica-Scaled Chrysophytes with Different Trophic Mode in Two Ultraoligotrophic Lakes of Yakutia

Silica-scaled chrysophytes are a widespread group of microeukaryotes, an important component of aquatic habitats. They belong to different evolutionary lineages and they are characterized by the presence of siliceous scales, but differ in trophic mode. We studied the diversity of these organisms in different months of the ice cover period in two subarctic lakes of Yakutia, Labynkyr and Vorota. Silica-scaled chrysophytes, due to various trophic modes, have a competitive advantage in conditions of a long period of ice cover. Statistical analysis has shown the relationship between the relative abundance of mixotrophic and photoautotrophic representatives of silica-scaled chrysophytes with the thickness of the snow cover and the transparency of the ice. An increase in snow cover thickness and the process of melting ice with a decrease in its transparency reduce the relative abundance of photoautotrophic and mixotrophic species. Photoautotrophic representatives of silica-scaled chrysophytes begin to develop already in April, when a thick, solid, and transparent layer of ice and a small layer of snow were observed. During the research period, from April to June, the relative abundance of colorless heterotrophic silica-scaled chrysophytes genera Paraphysomonas and Lepidochromonas was more or less stable. A new species of Spiniferomonas heterospina sp. nov. has been discovered in Lake Labynkyr.