Response of the microbial community structure to the environmental factors during the extreme flood season in Poyang Lake, the largest freshwater lake in China.

Background: Poyang Lake is the largest freshwater lake in China, and there are several studies on the composition and diversity of bacteria in Poyang Lake, while few quantitative studies were carried out on the response of the bacterial community to environmental factors during the extreme flood season in Poyang Lake. Methods: The connected-lake heterogeneity of bacterial community composition (BCC) was investigated in Poyang Lake during the flood season in 2020. Illumina high-throughput sequencing technology was used in this study. Results: The bacterial community structure in the water was different from that in the sediment of Poyang Lake during extreme flood seasons. The bacterial diversity in water was much lower than that in sediment. In the water column, the dominant phyla were Actinobacteriota, while the composition of bacteria in sediment was more complex than that in water, and the dominant phyla in sediment were Proteobacteria, Chloroflexi, Acidobacteriota, and Actinobacteriota. The bacterial diversity in the water of Poyang Lake showed seasonal dynamics, while no seasonal variation of bacterial communities in sediment was observed. The bacterial community structure in the sediment from the two bays and channel areas of Poyang Lake can be distinguished from each other. The microbial diversity in sediment gradually increased from the Sancha Bay to the Zhouxi Bay and then to the channel, but the total nitrogen (TN) concentration in sediment (STN) and the total phosphorus (TP) concentration in sediment (STP) showed opposite trends. This might be due to the anthropogenic disturbances from the extreme flood. The bacterial community structure in, water column was significantly correlated with WT, NH4-N, STP, SOM, Chl a, DO, TP, and Eh, while the bacterial community structure in sediment was significantly correlated with SOM and STP. Conclusion: The bacterial community structure in water was greatly different from that in sediment in Poyang Lake during extreme flood seasons. The bacterial community structure in the water column was not only sensitive to the geochemical characteristics of the water but also affected by some nutrient concentrations in the sediment. During the wet seasons, bacterial diversity was only affected by SOM and STP.

Spatio-temporal variation of toxin-producing gene abundance in Microcystis aeruginosa from Poyang Lake.

Microcystis aeruginosa (M. aeruginosa) causes massive blooms in eutrophic freshwater and releases microcystin. Poyang Lake is the largest freshwater lake in China and has kept a mid-nutrient level in recent years. However, there is little research on microcystin production in Poyang Lake. In this study, water and sediment samples from ten sampling sites in Poyang Lake were collected from May to December in 2020, and from January to April in 2021 respectively. Microcystis genes (mcyA, mcyB, 16 s rDNA) were quantified by real-time fluorescence quantitative PCR analysis, and then the spatial and temporal variation of mcy genes, physicochemical factors, and bacterial population structure in the lake was analyzed. The relationship between the abundance of mcy genes and physicochemical factors in water column was also revealed. Results indicated that the microcystin-producing genes mcyA and mcyB showed significant differences in spatial and temporal levels as well, which is closely related to the physicochemical factors especially the water temperature (p < 0.05) and the nitrogen content (p < 0.05). The abundance of mcy genes in the sediment in December affected the abundance of mcy genes in the water column in the next year, while the toxic Microcystis would accumulate in the sediment. In addition to the toxic Microcystis, we also found a large number of non-toxic Microcystis in the water column and sediment, and the ratio of toxic to non-toxic species can also affect the toxicity production of M. aeruginosa. Overall, the results showed that M. aeruginosa toxin-producing genes in Poyang Lake distributed spatially and temporally which related to the physicochemical factors of Poyang Lake.

Pharmacokinetics, withdrawal time, and dietary risk assessment of enrofloxacin and its metabolite ciprofloxacin, and sulfachloropyridazine-trimethoprim in Taihe black-boned silky fowls.

Enrofloxacin (ENR) and sulfachloropyridazine combined with trimethoprim (TMP) were commonly used in poultries to treat bacterial infections. In this study, the pharmacokinetics of these antibiotics in four tissues of Taihe black-boned silky fowls was studied. The results showed that these drugs were absorbed and distributed rapidly, with the highest concentration showing in skin. Meanwhile, ENR and its metabolite ciprofloxacin (CIP) and TMP were depleted slowly, particularly in skin with the elimination half-lives being 37.1, 36.9, and 72.7 days, respectively. It may be attributed to the abundance of melanin in skin. The dietary risk assessment suggested that the long-term dietary intakes of ENR, CIP, and TMP showed a considerable threat to human health. Based on the experiment, the withdrawal times of 284 days for ENR + CIP and 159 days for TMP were acquired, which showed that these drugs are not appropriate for the application in Taihe black-boned silky fowls.

Pathological and biochemical characterizations of microcystin-LR-induced liver and kidney damage in chickens after acute exposure.

Cyanobacteria contains considerable amounts of protein and other nutritive materials and are considered to be high-quality protein source and feed additive for livestock and poultry. However, some species of cyanobacteria are also able to produce toxins, and exposure to these toxins represents health risks to animals. In the present study, pathological changes and biochemical responses were examined in the liver and kidney of the Chongren chicken (Gallus gallus domesticus) after intraperitoneal (i.p.) injection with microcystin-LR (MC-LR) at dose of 5 µg kg-1 (Low dose group, LD group), 10 µg kg-1 (Medium dose group, MD group), and 20 µg kg-1 (High dose group, HD group), respectively. Results revealed that the high dose of MC-LR led to the irreversible liver damage, which was characterized by mononuclear infiltrations，necrotic changes and blood congestion, and obvious recovery of hepatocytes was observed in the low and medium dose groups. Across all groups, the MC-LR-induced injuries in the kidney were prominent since the first hour, and it did not get any better at the end of the experiments. The MC-related detoxification and antioxidant components (GSH, GPX, GST) in the liver made positive responses, which helped to alleviate the cytotoxicity of MC-LR. Our results showed that even at low concentrations of MCs (produced by cyanobacteria), pathological changes (such as necrosis and inflammation) were observed in liver and kidney of birds.

[Seasonal and Spatial Variations of Microcystins and Their Relationships with Physiochemical and Biological Factors in Poyang Lake].

Poyang Lake is the largest freshwater lake in China and an important drinking water source for Jiangxi Province. Since the year 2000, toxic cyanobacteria have been observed frequently in Poyang Lake. In this study, water samples were collected in the lake quarterly (April 2012, August 2012, October 2012, and January 2013) to examine the spatial and seasonal variations in the concentrations of microcystins (MCs; MC-RR, -YR, and -LR) and their relationships with physiochemical and biological factors. MCs were determined by ultra-high-performance liquid chromatography-electrospray ionization tandem triple quadrupole/mass spectrometry (UPLC-MS/MS). MC-RR (accounting for 75.01% and 71.34% of intracellular MC (IMC) and extracellular MC (EMC) concentrations, respectively) was the most dominant variant in Poyang Lake, followed by MC-LR (accounting for 21.95% and 24.97% of IMC and EMC concentrations, respectively), while MC-YR was detected in low concentrations (accounting for 3.01% and 3.69% of IMC and EMC concentrations, respectively). Total MC concentrations (IMC + EMC, TMC) ranged from 0.49 to 3517.85 ng·L-1, with an average of 337.43 ng·L-1 and only 2.53% (2 out of 79 water samples) of the water samples contained MCs concentrations exceeding the drinking water guideline level of 1 ng·L-1 for MC-LR proposed by World Health Organization (WHO). IMC concentrations showed significant relationships with Microcystis biomass (r=0.47, P<0.01), Oscillatoria biomass (r=0.68, P<0.01), Cyanobacteria biomass (r=0.56, P<0.01), and Chl-a (r=0.28, P<0.01), but no significant correlation was found between intracellular MC concentration and Anabena biomass (P>0.05), suggesting that Microcystis and Oscillatoria might be the main MCs-producing cyanobacteria in Poyang Lake. In addition, IMC concentrations were positively correlated with water temperature (r=0.51, P<0.01), transparence (r=0.69, P<0.01), Fe (r=0.43, P<0.01), and Zn contents (r=0.43, P<0.01), and negatively correlated with TN (r=-0.44, P<0.01), TP (r=-0.29, P<0.01), NH4+-N (r=-0.33, P<0.05), NO2--N (r=-0.28, P<0.05), Ca (r=-0.34, P<0.01), and Mg(r=-0.35, P<0.05), while no significant correlations were observed between IMC concentrations and pH, PO43--P, NO3--N, electrical conductivity, permanganate index, and Cu content (P>0.05). These results indicated that light intensity (represented by transparence), nitrogen, phosphorus, and water temperature might be the regulating factors of MCs production in Poyang Lake and trace elements (Fe, Zn, Ca, and Mg) can influence the MC production to a certain extent. IMCs and EMCs exhibited similar seasonal variations in Poyang Lake. The highest values of IMCs (531.87 ng·L-1) and EMCs (232.44 ng·L-1) were observed in summer. The concentrations of IMCs and EMCs in autumn were 31.97 ng·L-1 and 6.49 ng·L-1, respectively. Low concentrations were observed in spring (0.55 ng·L-1 and 0.88 ng·L-1 of IMCs and EMCs, respectively) and winter (0.69 ng·L-1 and 4.14 ng·L-1 of IMCs and EMCs, respectively). The highest IMCs and EMCs values of Poyang Lake in summer were 2298.08 ng·L-1 and 1219.77 ng·L-1, respectively, and the lowest values were 92.53 ng·L-1 and 38.80 ng·L-1, respectively. Overall, the concentrations of IMCs in eastern bays, the vicinity of Songmen Mountain, Banghu Lake, and its outlet were higher than those in other regions. However, the spatial distributions of EMCs in Poyang Lake were different from those of IMCs. EMCs concentrations in the vicinity of Songmen Mountain, Banghu Lake, and its outlet were higher than those in other regions.

Seasonal and spatial variations of microcystins in Poyang Lake, the largest freshwater lake in China.

Poyang Lake is the largest freshwater lake in China and an important drinking water source. Since the year 2000, toxic cyanobacteria have been observed frequently in Poyang Lake. In the present study, spatial and seasonal variations of microcystins (MCs; MC-RR, MC-YR, and MC-LR) in water column were examined monthly from January to December (except the months of March, May, and November) in 2013, by using ultra-high-performance liquid chromatography-electrospray ionization tandem triple quadrupole/mass spectrometry (UPLC-MS/MS). MC-RR was the most dominant variant, followed by MC-LR, while MC-YR was detected in low concentration. Total MC concentrations (intracellular + extracellular MCs) ranged from 1.26 to 9916.05 ng/L, with an average of 469.99 ng/L, and only 3.14% (6 out of 192 samples) of the water samples contained MC concentrations that exceeded the drinking water guideline level of 1 µg/L for MC-LR proposed by the World Health Organization (WHO). MC concentrations in water column showed obvious seasonal variations in Poyang Lake. Intracellular and extracellular MCs were both at a low level from January to April but increased quickly from June to August and decreased dramatically thereafter. Intracellular MCs exhibited similar spatial distribution pattern with extracellular MCs. Both intracellular and extracellular MC concentrations in eastern bays and around Songmen Mountain of Poyang Lake were higher than other regions. Intracellular MC concentrations were positively correlated with Chl a (r = 046, P < 0.01), pH (r = 0.25, P < 0.01), cyanobacterial biomass (r = 0.40, P < 0.01), and temperature (r = 0.36, P < 0.01) but negatively correlated with TN (r = - 0.28, P < 0.01), suggesting that TN, cyanobacteria biomass, pH, and temperature might be regulating factors for MC production in Poyang Lake.

Occurrence and spatial distributions of microcystins in Poyang Lake, the largest freshwater lake in China.

Occurrence and spatial distributions of microcystins (MCs; MC-RR, -YR, -LR, -LA, -LF, -LW) in Poyang Lake were studied during the period from July 6 to July 18, 2012, by using ultra-high-performance liquid chromatography-electrospray ionization tandem triple quadrupole/mass spectrometry (UPLC-MS/MS). MC-RR was the most dominant variant (94.70 and 84.73 % for intracellular (cellular MCs) and extracellular (dissolved MCs) MCs, respectively) in Poyang Lake, followed by MC-LR (4.65 and 13.17 %, respectively), MC-YR (0.8 and 2.63 %, respectively), and MC-LA (0.02 and 0.00 %), while MC-LW and MC-LF were not detected. Total MCs concentrations (intracellular +extracellular MCs) ranged between 0.0036 and 7.97 µg/L, with an average of 0.79 µg/L, and only two sampling stations with the total MCs concentrations exceeded the drinking water guideline level of 1 µg/L for MC-LR proposed by World Health Organization. The overall spatial pattern of intracellular and extracellular MCs in Poyang Lake demonstrates decreasing trends from east to west, and the south part higher than the north part. Intracellular MCs content was negatively correlated with total nitrogen (r = -0.34, p < 0.01) and NO3 (r = -0.35, p < 0.01), while no significant correlation was found between intracellular MCs concentration and total phosphorus, NH4, and NO2 (p > 0.05), suggesting that NO3 might be a regulating factor for MCs production in Poyang Lake. In addition, intracellular MCs concentrations were positively correlated with wind speed, Microcystis and Cyanobacteria biomass (r = 0.34-0.51, p < 0.05), indicating that wind speed plays an important role in the spatial distributions of MCs, and NO3, toxic cyanobacteria (mainly Microcystis), and wind speed seem to be the important forcing factors driving MCs spatial distributions in Poyang Lake.