Molecular evaluation on the distribution, diversity, and toxicity of Microcystis (Cyanobacteria) species from Lake Ulungur--a mesotrophic brackish desert lake in Xinjiang, China

Evaluation of the Effectiveness of the SED-BIO System in Reducing the Inflow of Selected Physical, Chemical and Biological Pollutants to a Lake

The aim of this study was to assess the efficiency of the innovative SED-BIO system in limiting the inflow of pollutants to Jelonek Lake. The analyses were conducted in the Gniezno Lake District in Greater Poland (the western part of Poland). Physical and chemical analyses were conducted in the years 2016–2019. The results demonstrate that the system is highly effective in the reduction of such nutrients as nitrogen (NO3−—63%; NH4+—14.9%) and phosphorus (PO43−—19.3%). Although the presence of cyanobacteria was confirmed practically throughout the whole monitoring period of the system (2016), the specimens found in most samples were not toxigenic genotypes with a potential to produce microcystins. Microcystins (3 µg·L−1) were detected only once, immediately after the SED-BIO system had been installed in the river and pond, which demonstrates that this natural toxin was eliminated from the additional pool of contaminants that might be transported to Jelonek Lake.

Effects of Microbial Activity and Environmental Parameters on the Degradation of Extracellular Environmental DNA from a Eutrophic Lake

Extracellular DNA (exDNA) pool in aquatic environments is a valuable source for biomonitoring and bioassessment. However, degradation under particular environmental conditions can hamper exDNA detectability over time. In this study, we analyzed how different biotic and abiotic factors affect the degradation rate of extracellular environmental DNA using 16S rDNA sequences extracted from the sediment of a eutrophic lake and Anabaena variabilis cultured in the laboratory. We exposed the extracted exDNA to different levels of temperature, light, pH, and bacterial activity, and quantitatively analyzed the concentration of exDNA during 4 days. The solution containing bacteria for microbial activity treatment was obtained from the lake sediment using four consecutive steps of filtration; two mesh filters (100 μm and 60 μm mesh) and two glass fiber filters (2.7 μm and 1.2 μm pore-sized). We found that temperature individually and in combination with bacterial abundance had significant positive effects on the degradation of exDNA. The highest degradation rate was observed in samples exposed to high microbial activity, where exDNA was completely degraded within 1 day at a rate of 3.27 day⁻¹. Light intensity and pH had no significant effects on degradation rate of exDNA. Our results indicate that degradation of exDNA in freshwater ecosystems is driven by the combination of both biotic and abiotic factors and it may occur very fast under particular conditions.

Dynamics and polyphasic characterization of odor-producing cyanobacterium Tychonema bourrellyi from Lake Erhai, China

The previous studies indicated that Tychonema-like strains from Lake Erhai could release geosmin so that the species was listed as the potential harmful cyanobacteria influencing the drinking water safety around Lake Erhai. But, the dynamics and biological information of this species were too limited. In this study, the polyphasic approach was used to reveal its biological characterization and the dynamics in Lake Erhai. The characters of trichomes, including filaments with solitary or bundle state, reddish-brown or blue-green color, planktonic habitat, and presence of keritomized content, were examined by the microscopic method. The 16S rDNA sequences of these strains were used for phylogenetic analysis and molecular identification. The strains were morphologically classified as Tychonema bourrellyi, and geosmin and β-ionone were identified as the major volatile substances using gas chromatography-mass spectrometry (GC-MS) analysis. No strains of T. bourrellyi were found to produce microcystin by the HPLC and mcy gene approaches. Cell numbers at 12 sampling sites in Lake Erhai were shown as an average of 3 × 10(4) cells L(-1) in 2009 and 2010. The obvious peaks occurred in July and August each year. This was the first report on occurrence of T. bourrellyi from outside of Europe, and T. bourrellyi was also a newly recorded species in China. Such a result demonstrated that T. bourrellyi could distribute extending from cold waters in North Europe to the warm waters in subtropical regions. It was interesting to observe the coincidence of the occurrence of T. bourrellyi with slightly eutrophicated waters since Lake Erhai had been regarded as an early phase of eutrophicated lake.

Spatiotemporal distribution pattern of cyanobacteria community and its relationship with the environmental factors in Hongze Lake, China

Hongze Lake, located in the east route of the South-to-North Water Diversion Project (SNWDP), is a potential drinking water source for the residents along this water diversion project. Based on a monthly sampling at 11 stations in three regions of Hongze Lake, the spatiotemporal distribution pattern of cyanobacteria community was comprehensively investigated from March 2011 to February 2013. A total of 23 cyanobacterial species which belong to 16 genera were identified, and Microcystis was the most predominant cyanobacterial genus mainly composed of Microcystis wesenbergii in Hongze Lake. The cyanobacterial abundance ranged from 0 to 2.6 × 10(7) cells/L, and the average cyanobacteria abundance of Northern region was significantly higher than those of Western region and Eastern region in the 2-year study. The total cyanobacteria abundance and the Microcystis abundance both took on a similar seasonal regularity in the three regions. The results of correlation analysis indicated that Microcystis abundance was correlated with water temperature, chemical oxygen demand (COD)Mn, nitrate (NO₃-N), and total nitrogen (TN)/total phosphorus (TP) mass ratio, among which water temperature had the highest correlation coefficient. In summer, cyanobacteria blooms may take place under suitable environmental conditions at some special areas in Hongze Lake, especially where the concurrence of slow water exchange and steady wind direction exists.

Variation of Microcystis and microcystins coupling nitrogen and phosphorus nutrients in Lake Erhai, a drinking-water source in Southwest Plateau, China

Lake Erhai is the second largest lake of Southwest China and an important drinking water source. The lake is currently defined as the preliminary stage of eutrophic states, but facing a serious threat with transfer into intensive eutrophication. The present study examined the dynamics of Microcystis blooms and toxic Microcystis in Lake Erhai during 2010, based on quantitative real-time PCR method using 16S rRNA gene specific for Microcystis and microcystin systhesis gene (mcy), and chemical analysis on microcystin (MC) concentrations. Total Microcystis cell abundance at 16 sampling sites were shown as an average of 1.7 × 10(7) cells l(-1) (1.3 × 10(2)-3.8 × 10(9) cells l(-1)). Microcystin LR (MC-LR) and microcystin RR (MC-RR) were the main variants. The strong southwesterly winds, anticlockwise circular flows and geographical characteristics of lake and phytoplankton community succession impacted the distribution patterns of Chl a and MC in the lake. The concentration of Chl a and MC and abundances of total Microsytis and MC-producing Microsystis (MCM) were shown to be positively correlated with pH, DO and TP, negatively correlated with SD, NO₃-N, TN/Chl a and TN/TP, and not correlated with NH₄-N, TN, dissolved total nitrogen (DTN) and water temperatures. When TN/TP decrease, Microcystis tended to dominate and MC concentrations tended to increase, suggesting that the "TN/TP rule" can be partially applied to explain the correlation between the cyanobacterial blooms and nutrients N and P only within a certain nutrient level. It is speculated that N and P nutrients and the associated genes (e.g., mcy) may jointly drive MC concentration and toxigenicity of Microcystis in Lake Erhai.