Water Quality, Toxicity and Diversity of Planktonic and Benthic Cyanobacteria in Pristine Ancient Lake Khubsugul (Hövsgöl), Mongolia.

For the first time, microcystin-producing cyanobacteria have been detected in Khubsugul, which is ancient, pristine and one of the world's largest lakes. The microcystin synthetase genes belonged to the genera Nostoc, Microcystis and possibly Snowella spp. No microcystins were found in the water of the lake. Using the HPLC-HRMS/TOF, five microcystin congeners were identified in biofilms from stony substrates sampled in the coastal zone. The concentration of microcystins in biofilms was low: 41.95 µg g-1 d. wt. by ELISA and 55.8 µg g-1 d. wt. using HPLC. The taxonomic composition of planktonic and benthic cyanobacterial communities was determined by means of microscopy and high-throughput sequencing of 16S rDNA amplicons. Nostocales cyanobacteria dominated benthos of Lake Khubsugul and Synechococcales-plankton. The abundance of cyanobacteria was low both in plankton and benthos; there was no mass development of cyanobacteria. Hydrochemical and microbiological analyses showed that the water in the lake was clean; the number of faecal microorganisms was significantly below the acceptable guideline values. Hydrochemical and hydrophysical parameters, and the concentration of chlorophyll a, were low and within the range of values recorded in the 1970s to 1990s, and corresponded to the oligotrophic state of the lake. There were no signs of anthropogenic eutrophication of the lake and no conditions for the cyanobacterial blooms.

Lacustrine, wastewater, interstitial and fluvial water quality in the Southern Lake Baikal region.

The coastal area of the southern Lake Baikal with the population over 35,000 people remains an attractive spot for both tourists and local residents. Despite high anthropogenic impact, a detailed assessment of water quality in this area has not been performed so far. Here, we performed a comprehensive evaluation of the quality of the surface, bottom and interstitial water in rivers, lacustrine water and wastewater in the southern Lake Baikal region. We analyzed 37 samples for the presence of fecal enterococci, Escherichia coli and assessed their hydrochemical parameters: concentrations of nutrients (nitrate-N, nitrite-N, ammonium-N and phosphate-P), dissolved oxygen and amount of ions (HCO3- + SO42- + Cl- + Ca2+ + Mg2+ + Na+ + K+). In addition, the temperature, pH and electrical conductivity were also measured. We found that multiple areas around South Baikal suffer from microbiological and hydrochemical pollution. We conclude that ecological situation in this area requires immediate attention from local authorities, more efficient wastewater management systems should be constructed in the settlements. We also conclude that interstitial waters from the lake's splash zone represent an effective and sensitive indicator of sanitary-microbiological and hydrochemical pollution and their analysis can be included in the standard protocol of water quality assessment for all types of water bodies.

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

Although under-ice microbial communities are subject to a cold environment, low concentrations of nutrients, and a lack of light, they nevertheless take an active part in biogeochemical cycles. However, we still lack an understanding of how high their diversity is and how these communities are distributed during the long-term ice-cover period. Here, we assessed for the first time the composition and distribution of microbial communities during the ice-cover period in two subarctic lakes (Labynkyr and Vorota) located in the area of the lowest temperature in the Northern Hemisphere. The diversity distribution and abundance of main bacterial taxa as well as the composition of microalgae varied by time and habitat. The 16S rRNA gene sequencing method revealed, in general, a high diversity of bacterial communities where Proteobacteria (~ 45%) and Actinobacteria (~ 21%) prevailed. There were significant differences between the communities of the lakes: Chthoniobacteraceae, Moraxellaceae, and Pirellulaceae were abundant in Lake Labynkyr, while Cyanobiaceae, Oligoflexales, Ilumatobacteraceae, and Methylacidiphilaceae were more abundant in Lake Vorota. The most abundant families were evenly distributed in April, May, and June their contribution was different in different habitats. In April, Moraxellaceae and Ilumatobacteraceae were the most abundant in the water column, while Sphingomonadaceae was abundant both in water column and on the ice bottom. In May, the abundance of Comamonadaceae increased and reached the maximum in June, while Cyanobiaceae, Oxalobacteraceae, and Pirellulaceae followed. We found a correlation of the structure of bacterial communities with snow thickness, pH, Nmin concentration, and conductivity. We isolated psychrophilic heterotrophic bacteria both from dominating and minor taxa of the communities studied. This allowed for specifying their ecological function in the under-ice communities. These findings will advance our knowledge of the under-ice microbial life.

Bacterioneuston in Lake Baikal: Abundance, Spatial and Temporal Distribution.

An aquatic surface microlayer covers more than 70% of the world's surface. Our knowledge about the biology of the surface microlayer of Lake Baikal, the most ancient lake on Earth with a surface area of 31,500 km², is still scarce. The total bacterial abundance, the number of cultured heterotrophic temporal bacteria, and the spatial distribution of bacteria in the surface microlayer and underlying waters of Lake Baikal were studied. For the first time, the chemical composition of the surface microlayer of Lake Baikal was determined. There were significant differences and a direct relationship between the total bacterial abundance in the surface microlayer and underlying waters of Lake Baikal, as well as between the number of cultured heterotrophic bacteria in studied water layers in the period of summer stratification. In the surface microlayer, the share of cultured heterotrophic bacteria was higher than in the underlying waters. The surface microlayer was characterized by enrichment with PO43-, total organic carbon and suspended particulate matter compared to underlying waters. A direct relationship was found between the number of bacteria in the surface microlayer and environmental factors, including temperature, total organic carbon and suspended particulate matter concentration.