Sulfur and chlorine compounds in water bodies of the Pymvashor subarctic hydrothermal system.

The results of the study of the behavior of redox-dependent sulfur and chlorine compounds in sediments of water bodies of the Pymvashor natural boundary (PNB) located in the Bolshezemelskaya Tundra (the Polar Cis-Ural Region, Nenets Autonomous Okrug, Russian Federation) are presented. Currently, the Pymvashor is the only known location in Continental Europe where hydrothermal springs function in the polar territories. Data on the quantitative characteristics of the geochemical parameters of bacterial sulfate reduction (reduced sulfur compounds, reactive iron forms, and organic matter) in the sediments of all studied Pymvashor water bodies have been obtained. It has been established that the revealed differences in the distribution and transformation of these parameters, in addition to the main reasons affecting the course of redox processes, were also caused by the thermal factor (warming effect of thermal waters on all ecosystems of the natural boundary). Thus, iron monosulphides dominated in the upper sediment layers of non-freezing watercourses, which distinguished them from the sediments of seasonally frozen lakes, where sulfur associated with organic matter dominated along the entire length of the sediment cores. The presence of chlorophenols (CPs) and their derivatives, including pentachlorophenol as a persistent organic pollutant, in the sediments of studied Pymvashor water bodies was established. It is shown that the chlorophenol composition is mainly induced by the occurrence of natural enzymatic and biochemical processes. The influence of microclimatic conditions of the subarctic hydrothermal system on the composition, levels, and distribution of chlorophenolic compounds in the sediments was revealed.

Metabolic Diversity and Evolutionary History of the Archaeal Phylum "Candidatus Micrarchaeota" Uncovered from a Freshwater Lake Metagenome.

Acidophilic archaea of the archaeal Richmond Mine acidophilic nanoorganisms (ARMAN) group from the uncultured candidate phylum "Candidatus Micrarchaeota" have small genomes and cell sizes and are known to be metabolically dependent and physically associated with their Thermoplasmatales hosts. However, phylogenetically diverse "Ca Micrarchaeota" are widely distributed in various nonacidic environments, and it remains uncertain because of the lack of complete genomes whether they are also devoted to a partner-dependent lifestyle. Here, we obtained nine metagenome-assembled genomes of "Ca Micrarchaeota" from the sediments of a meromictic freshwater lake, including a complete, closed 1.2 Mbp genome of "Ca Micrarchaeota" Sv326, an archaeon phylogenetically distant from the ARMAN lineage. Genome analysis revealed that, contrary to ARMAN "Ca Micrarchaeota," the Sv326 archaeon has complete glycolytic pathways and ATP generation mechanisms in substrate phosphorylation reactions, the capacities to utilize some sugars and amino acids as substrates, and pathways for de novo nucleotide biosynthesis but lacked an aerobic respiratory chain. We suppose that Sv326 is a free-living scavenger rather than an obligate parasite/symbiont. Comparative analysis of "Ca Micrarchaeota" genomes representing different order-level divisions indicated that evolution of the "Ca Micrarchaeota" from a free-living "Candidatus Diapherotrites"-like ancestor involved losses of important metabolic pathways in different lineages and gains of specific functions in the course of adaptation to a partner-dependent lifestyle and specific environmental conditions. The ARMAN group represents the most pronounced case of genome reduction and gene loss, while the Sv326 lineage appeared to be rather close to the ancestral state of the "Ca Micrarchaeota" in terms of metabolic potential.IMPORTANCE The recently described superphylum DPANN includes several phyla of uncultivated archaea with small cell sizes, reduced genomes, and limited metabolic capabilities. One of these phyla, "Ca Micrarchaeota," comprises an enigmatic group of archaea found in acid mine drainage environments, the archaeal Richmond Mine acidophilic nanoorganisms (ARMAN) group. Analysis of their reduced genomes revealed the absence of key metabolic pathways consistent with their partner-associated lifestyle, and physical associations of ARMAN cells with their hosts were documented. However, "Ca Micrarchaeota" include several lineages besides the ARMAN group found in nonacidic environments, and none of them have been characterized. Here, we report a complete genome of "Ca Micrarchaeota" from a non-ARMAN lineage. Analysis of this genome revealed the presence of metabolic capacities lost in ARMAN genomes that could enable a free-living lifestyle. These results expand our understanding of genetic diversity, lifestyle, and evolution of "Ca Micrarchaeota."

Sharp water column stratification with an extremely dense microbial population in a small meromictic lake, Trekhtzvetnoe.

Located on the shore of Kandalaksha Bay (the White Sea, Russia) and previously separated from it, Trekhtzvetnoe Lake (average depth 3.5 m) is one of the shallowest meromictic lakes known. Despite its shallowness, it features completely developed water column stratification with high-density microbial chemocline community (bacterial plate) and high rates of major biogeochemical processes. A sharp halocline stabilizes the stratification. Chlorobium phaeovibrioides dominated the bacterial plate, which reached a density of 2 × 108 cell ml-1 and almost completely intercepts H2 S diffusion from the anoxic monimolimnion. The resulting anoxygenic photosynthesis rate reached 240 µmol C l-1 day-1 , exceeding the oxygenic photosynthesis rate in the mixolimnion. The rates of other processes are also high, reaching 4.5 µmol CH4 l-1 day-1 for methane oxidation and 35 µmol S l-1 day-1 for sulfate reduction. Metagenomic analysis demonstrated that the Chl. phaeovibrioides population in the bacterial plate layer had nearly clonal homogeneity, although some fraction of these cells harbour a plasmid. The Chlorobium population was associated with bacteriophages that share homology with CRISPR spacers in the host. These features make the ecosystem of the Trekhtzvetnoe Lake a valuable model for studying regulation and evolution processes in natural high-density microbial systems.

Microbial processes of the carbon and sulfur cycles in an ice-covered, iron-rich meromictic lake Svetloe (Arkhangelsk region, Russia).

Biogeochemical, isotope geochemical and microbiological investigation of Lake Svetloe (White Sea basin), a meromictic freshwater was carried out in April 2014, when ice thickness was ∼0.5 m, and the ice-covered water column contained oxygen to 23 m depth. Below, the anoxic water column contained ferrous iron (up to 240 µµM), manganese (60 µM), sulfide (up to 2 µM) and dissolved methane (960 µM). The highest abundance of microbial cells revealed by epifluorescence microscopy was found in the chemocline (redox zone) at 23-24.5 m. Oxygenic photosynthesis exhibited two peaks: the major one (0.43 µmol C L-1  day-1 ) below the ice and the minor one in the chemocline zone, where cyanobacteria related to Synechococcus rubescens were detected. The maximum of anoxygenic photosynthesis (0.69 µmol C L-1  day-1 ) at the oxic/anoxic interface, for which green sulfur bacteria Chlorobium phaeoclathratiforme were probably responsible, exceeded the value for oxygenic photosynthesis. Bacterial sulfate reduction peaked (1.5 µmol S L-1  day-1 ) below the chemocline zone. The rates of methane oxidation were as high as 1.8 µmol CH4  L-1  day-1 at the oxi/anoxic interface and much lower in the oxic zone. Small phycoerythrin-containing Synechococcus-related cyanobacteria were probably involved in accumulation of metal oxides in the redox zone.