Guoxiang Wang

Non-microcystin producing Microcystis wesenbergii (Komárek) Komárek (Cyanobacteria) representing a main waterbloom-forming species in Chinese waters

It is well known that several morphospecies of Microcystis, such as Microcystis aeruginosa (Kützing) Lemmermann and Microcystis viridis (A. Brown) Lemmermann can produce hepatotoxic microcystins. However, previous studies gave contradictory conclusions about microcystin production of Microcystis wesenbergii (Komárek) Komárek. In the present study, ten Microcystis morphospecies were identified in waterblooms of seven Chinese waterbodies, and Microcystis wesenbergii was shown as the dominant species in these waters. More than 250 single colonies of M. wesenbergii were chosen, under morphological identification, to examine whether M. wesenbergii produce hepatotoxic microcystin by using multiplex PCR for molecular detection of a region (mcyA) of microcystin synthesis genes, and chemical analyses of microcystin content by ELISA and HPLC for 21 isolated strains of M. wesenbergii from these waters were also performed. Both molecular and chemical methods demonstrated that M. wesenbergii from Chinese waters did not produce microcystin.

Genetic diversity of Microcystis populations in a bloom and its relationship to the environmental factors in Qinhuai River, China

Cyanobacterial blooms, forming massive scum and various cyanotoxins, increasingly spread in a wide range of freshwater ecosystems. One heavy Microcystis bloom occurred in the entire Qinhuai River basin in 2010 summer for the first time. To determine the Microcystis populations and their spatial distributions along Qinhuai River, a molecular approach was applied by sequencing the DNA library based on the internal transcribed spacer sequences of 16-23S rRNA (ITS). The parsimony network (TCS) analysis showed that 9 groups were formed based on the main 24 genotypes, and each group was dominated by one highly represented root sequence. Marked changes in the composition and proportion of the Microcystis ITS genotype were detected from the upper to the lower reaches. The seed sources forming the bloom were probably located at 4 different locations. Furthermore, it was found that pH was the primary factor affecting the spatial distribution of the main genotype group among samples.

Insights into tetracycline adsorption onto kaolinite and montmorillonite: experiments and modeling

Adsorption of tetracycline (TC) on kaolinite and montmorillonite was investigated using batch adsorption experiments with different pH, ionic strength, and surface coverage. As a result, pH and ionic strength-dependent adsorption of TC was observed for the two clay minerals. The adsorption of TC decreased with the increase of pH and ionic strength, and high initial TC concentration had high adsorption. In addition, a triple-layer model was used to predict the adsorption and surface speciation of TC on the two minerals. As a result, four complex species on kaolinite (≡X−∙H3TC+, ≡X−∙H2TC±, ≡SOH0∙H2TC±, and ≡SOH0∙HTC−) and three species on montmorillonite (≡X−∙H3TC+, ≡X−∙H2TC±, and ≡SOH0∙HTC−) were structurally constrained by spectroscopy, and these species were also successfully fitted to the adsorption edges of TC. Three functional groups of TC were involved in these adsorption reactions, including the positively charged dimethylamino group, the C=O amide I group, and the C=O group at the C ring. Combining adsorption experiments and model in this study, the adsorption of TC on kaolinite and montmorillonite was mainly attributed to cation exchange on the surface sites (≡X−) compared to surface complexation on the edge sites (≡SOH) at natural soil pH condition. Moreover, the surface adsorption species, the corresponding adsorption modes, and the binding constants for the surface reactions were also estimated.

Effects of chlorpyrifos on the gut microbiome and urine metabolome in mouse (Mus musculus).

In this study, the toxic effects of clorpyrifos (CPF) on the gut microbiome and related urine metabolome in mouse (Mus musculus) were investigated. Mice were exposed to a daily dose of 1 mg kg(-1) bodyweight of CPF for 30 d. As a result, CPF significantly altered the gut microbiota composition in terms of the relative abundance of key microbes. Meanwhile, CPF exposure induced the alterations of urine metabolites related to the metabolism of amino acids, energy, short-chain fatty acids (SCFAs), phenyl derivatives and bile acids. High correlations were observed between perturbed gut microbiome and altered metabolic profiles. These perturbations finally resulted in intestinal inflammation and abnormal intestinal permeability, which were also confirm by the histologic changes in colon and remarkable increase of lipopolysaccharide (LPS) and diamine oxidase (DAO) in the serum of CPF-treated mice. Our findings will provide a new perspective to reveal the mechanism of CPF toxicity.

Dominance and succession of Microcystis genotypes and morphotypes in Lake Taihu, a large and shallow freshwater lake in China.

Lake Taihu, which is the third largest freshwater lake in China, has experienced extensive cyanobacterial (Microcystis spp.) blooms over the past two decades. However, the distribution, dynamics and succession of the blooms have not been fully studied. To better understand the basic characteristics of Microcystis blooms in Lake Taihu, samples were collected from December 2008 to December 2009. The distribution and dynamics of different Microcystis morphotypes were characterized. Microcystis genotypes were analyzed also by sequencing the clone library of the internal transcribed spacer of the rRNA operon (ITS). The abundance of total Microcystis and the proportion of microcystin-producing subpopulation were estimated by using a quantitative PCR assay. Marked succession in both morphotypes and genotypes of the Microcystis population occurred during the course of the Microcystis bloom. The 2337 ITS sequences were obtained and were revealed to contain 618 Microcystis genotypes, which was the highest Microcystis genetic diversity reported in Lake Taihu. The T1 genotype, which was characterized by strains of Microcystis flos-aquae, was the most dominant genotype during winter and spring around the entire lake and likely acted as the main inoculum for forming blooms the following year. Water temperature periodically affected the succession of both Microcystis genotypes and morphotypes, whereas the micro-environment influenced the spatial distribution of Microcystis genotypes and morphotypes. High ratios of mcyD containing Microcystis subpopulations were detected during the onset and later bloom phases. A redundancy analysis (RDA) indicated that the water temperature and PO4-P were the major factors controlling both the total Microcystis abundance and the proportion of microcystin-producing Microcystis in hyper-eutrophic waters.

Reproduction capacity of Potamogeton crispus fragments and its role in water purification and algae inhibition in eutrophic lakes

The role of fragments in restoring eutrophic lakes remains unclear despite the importance of re-establishing submerged macrophytes via fragments. This study established a manipulative experiment using different biomass fragments of Potamogeton crispus. This approach was adapted to study the reproductive capacity, nutrient removal efficiency, and algae inhibitory effect of fragments. Results showed that fragments could grow throughout a 49-day experiment by maintaining the stable photosynthesis efficiency of leaves and lengthening the stems. These floating fragments could regenerate by producing turions for the maintenance of their species. Moreover, the increasing removal efficiency of TP, TN, NH4+-N, and NO3--N in water with the increase of fragment biomass indicates that the fragments could effectively purify water quality. Floating fragments competed with algae for nutrients, occupied a favorable ecological niche, and reduced algae biomass. They altered the structure of algae community and shifted the dominated green algae to cyanobacteria, the green algae of phytoplankton, and benthic algae. Findings imply that the postponable regulation of fragments is necessary for the ecological restoration of eutrophic lakes.

Spatial distributions of β-cyclocitral and β-ionone in the sediment and overlying water of the west shore of Taihu Lake.

After large-scale outbreaks of algal blooms in eutrophic water, considerable amounts of algae residue accumulate in near-shore zones before fermenting rapidly and becoming malodorous. Taste and odor pollution caused by secondary metabolites from cyanobacterial blooms has become a serious and widespread environmental problem. Two typical odorous compounds, β-cyclocitral and β-ionone, have gained increasing attention in recent years. In this paper, the spatial distributions of β-cyclocitral and β-ionone in the sediments and overlying water off the west shore of Taihu Lake were investigated. The results showed that β-cyclocitral, β-ionone and nutrients are released during the degradation of fresh cyanobacteria, especially in the early stages. The odorous compounds and nutrients greatly decreased as the depth of sediment increased, indicating that reed roots can absorb β-cyclocitral, β-ionone and nutrients. Furthermore, removing cyanobacteria and dredging sludge might reduce the release of β-cyclocitral and β-ionone.

Submerged macrophytes shape the abundance and diversity of bacterial denitrifiers in bacterioplankton and epiphyton in the Shallow Fresh Lake Taihu, China

AbstractnirK and nirS genes are important functional genes involved in the denitrification pathway. Recent studies about these two denitrifying genes are focusing on sediment and wastewater microbe. In this study, we conducted a comparative analysis of the abundance and diversity of denitrifiers in the epiphyton of submerged macrophytes Potamogeton malaianus and Ceratophyllum demersum as well as in bacterioplankton in the shallow fresh lake Taihu, China. Results showed that nirK and nirS genes had significant different niches in epiphyton and bacterioplankton. Bacterioplankton showed greater abundance of nirK gene in terms of copy numbers and lower abundance of nirS gene. Significant difference in the abundance of nirK and nirS genes also existed between the epiphyton from different submerged macrophytes. Similar community diversity yet different community abundance was observed between epiphytic bacteria and bacterioplankton. No apparent seasonal variation was found either in epiphytic bacteria or bacterioplankton; however, environmental parameters seemed to have direct relevancy with nirK and nirS genes. Our study suggested that submerged macrophytes have greater influence than seasonal parameters in shaping the presence and abundance of bacterial denitrifiers. Further investigation needs to focus on the potential contact and relative contribution between denitrifiers and environmental factors.

Cyanobacteria blooms: A neglected facilitator of CH4 production in eutrophic lakes

Lakes are regarded as one of the important sources of atmospheric CH4. However, the role of cyanobacteria blooms (CBBs) play in the CH4 production in eutrophic lakes is not fully clear. In this study, the spatial distribution characteristics of CH4 concentrations in surface water and sediment columns were investigated in Zhushan Bay of Taihu lake, China. Results showed that CH4 concentrations in CBBs accumulated zones were much higher than that in the open lake areas, with the highest values of 3.79 μmol·L-1 and 2261.88 μmol·L-1 in surface water and sediment columns, respectively. CH4 concentrations were strongly influenced by various factors. In surface water, the occurrence of CBBs greatly contributed to CH4 productions, as evidenced by the well-predicting for CH4 concentrations using Chl-a and NH4+ concentrations. In the sediments, the Ignition Loss and C:N ratio values were two indicators of CH4 contents, suggesting that the methanogenesis processes were influenced by not only the quantities, but also the qualities of organic matter. The labile substrates produced during the CBBs decomposition processes promoted the CH4 production and migration from sediments to the water column, resulting in the coherence in CH4 concentrations between the sediments and the surface water. The high-resolution determinations of CH4 concentrations in surface water and sediments clarified that the CBBs were a neglected facilitator of CH4 productions, which should be considered in the future estimation of CH4 emissions in eutrophic lakes.

Approach deliberation for source identification of sedimentary organic matters via comparing freshwater lakes with multi-ecotypes

Despite of the importance of understanding the sediment quality for lacustrine management, the source evaluation of sedimentary organic matter (SOM) in freshwater lakes is still insufficient. In this study, two shallow eutrophic lakes of Lake Taihu, China and Lake Izunuma, Japan were systematically investigated. Results of fatty acid profiles demonstrated that a wide range of organic matters, varying ecotypically, was inputted into the sediments of both lakes. Interestingly, there was a strong contribution from terrestrial plants to the sediments across ecotypes, with an approximate input from bacteria, and a relatively minor input from microalgae mainly included cyanobacteria, green algae, diatom and dinoflagellates. In addition, isotopic mixing model depicted a complementary picture that a significant, but spatially variable, amount of organic matter was derived from emergent and floating-leaf plants of Phragmites, Nelumbo, Nymphoides and Trapa L in Lake Izunuma. A general indicator selection procedure for the source assignments of SOM in freshwater ecosystems was therefore proposed: fatty acids could be a valid biomarker when the potential sources are unknown or unavailable; stable isotopes could be an effective supplement approach when assessing the special or defined organic sources.