Temporal evolution and vertical stratification of Microcystis toxic potential during a first bloom event

In order to study the setup of a Microcystis bloom and the evolution of its toxic potential, we studied the temporal and vertical variations in Microcystis aeruginosa abundance, microcystins (MC) concentrations (intracellular and extracellular), and the relative proportion of potentially microcystin-producing cells (MC-producing cells) in relation to physicochemical parameters in the recently setup Moroccan reservoir “Yaacoub Al Mansour.” The Microcystis bloom appeared relatively late in the season and was associated with a low proportion of MC-producing cells in the water surface layer, probably related to non-limiting nutrient concentrations. Interestingly, the setup of the bloom leads to a vertical gradient, showing a decrease in Microcystis cell abundance inversely coupled with an increase in the proportion of MC-producing cells. Thus, this can be the result of the growth where non-MC-producing cells remain in the lighted water layer easier than MC-producing ones. Nevertheless, parameters other than light intensity may influence the toxic potential of bloom as no vertical pattern was observed concerning microcystins cellular quotas. The high microcystins concentrations measured in the deep water layer have also proved the importance of considering the deep part of aquatic ecosystem in the management of health risks associated with cyanobacterial proliferations.     

Molecular detection of potentially toxic cyanobacteria and their associated bacteria in lake water column and sediment

We investigated the molecular diversity of cyanobacteria and bacteria during a water bloom in a lake with a long history of toxic cyanobacterial blooms (Lake Kastoria, Greece). We also tested the hypothesis whether bloom-forming cyanobacteria are preserved in the lake’s sediment 2 years after the bloom. The dominant cyanobacteria during the bloom included the potentially toxin-producing Microcystis aeruginosa and several other Chroococcales forms closely related to the genus Microcystis. This suggests that the use of cyanobacterial-specific primers seems to be very informative in describing the cyanobacteria during the water blooms. The bacterial community showed high diversity, consisting mostly of singleton and doubleton phylotypes. The majority of the phylotypes were typical lake bacteria including some potential pathogens and toxin metabolising bacteria, suggesting that the dominant toxic cyanobacteria did not have any significant effect on the bacterial community structure. In the sediment, 2 years after the water bloom, no bloom-forming cyanobacteria were retrieved, suggesting that they cannot be preserved in the sediment. Similar to the water column, sediment bacterial diversity was also high, consisting mostly of yet-uncultured bacteria that are related to environments where organic matter degradation takes place.     

Temporal variations in the dynamics of potentially microcystin-producing strains in a bloom-forming Planktothrix agardhii (Cyanobacterium) population

The concentration of microcystins (MCs) produced during blooms depends on variations in both the proportion of strains containing the genes involved in MC production and the MC cell quota (the ratio between the MC concentration and the density of cells with the mcyA genotype) for toxic strains. In order to assess the dynamics of MC-producing and non-MC-producing strains and to identify the impact of environmental factors on the relative proportions of these two subpopulations, we performed a 2-year survey of a perennial bloom of Planktothrix agardhii (cyanobacteria). Applying quantitative real-time PCR to the mcyA and phycocyanin genes, we found that the proportion of cells with the mcyA genotype varied considerably over time (ranging from 30 to 80% of the population). The changes in the proportion of cells with the mcyA genotype appeared to be inversely correlated to changes in the density of P. agardhii cells and also, to a lesser extent, to the availability of certain nutrients and the abundance of cladocerans. Among toxic cells, the MC cell quota varied throughout the survey. However, a negative correlation between the MC cell quota and the mcyA cell number during two short periods characterized by marked changes in the cyanobacterial biomass was found. Finally, only 54% of the variation in the MC concentrations measured in the lake can be explained by the dynamics of the density of cells with the MC producer genotype, suggesting that this measurement is not a satisfactory method for use in monitoring programs intended to predict the toxic risk associated with cyanobacterial proliferation.     

High-frequency monitoring of the genetic diversity and the potential toxicity of a Microcystis aeruginosa bloom in a French shallow lake

During cyanobacterial blooms, processes influencing the population dynamics of blooming species remain partially unexplained. To provide new information, we performed a high-frequency monitoring – every 2 days at six sampling points – of a Microcystis aeruginosa population blooming in a shallow lake. At each sampling date, there was no spatial heterogeneity in the ITS genotypic composition of the population and in the proportion of potentially microcystin- producing (mcyB+) cells, whereas high variations were recorded in cell abundances. In contrast, when looking at the temporal evolution of these parameters, the ITS genotypic composition of the population and in a lesser extent the percentage of mcyB+ cells displayed high variations during the growth phase of the bloom, but not during the plateau phase or the subsequent decline. This suggests that during the development of the bloom, there was no directional selection leading to the dominance of a restricted number of genotypes and that a balancing selection process permitted the maintenance of a high genetic diversity in the Microcystis population. Finally, no relationship was found between these variations occurring in the Microcystis population and those recorded for several environmental parameters, suggesting that many factors and processes interacting together might be involved in these variations.     

Synergistic and species‐specific effects of climate change and water colour on cyanobacterial toxicity and bloom formation

相似文献   

Use of electrospray tandem mass spectrometry for identification of microcystins during a cyanobacterial bloom event

Drastic environmental conditions such as elevated temperature, abrupt pH variation, low turbulence, and high nutrient inputs can enhance the development of toxic cyanobacterial blooms in lakes and reservoirs. This study describes the occurrence of four microcystin variants (MC) in a bloom in the eutrophic reservoir Billings, in S?o Paulo City. The bloom sample was collected in October 2003, and Microcystis were the main genus found. The MC were separated and purified by reverse phase high performance liquid chromatography (RP-HPLC). Their structures were elucidated by electrospray ionization tandem mass spectrometry (ESI-MS/MS) and four MC variants were determined: MC-RR, MC-LR, MC-YR, and MC-hRhR. MC-hRhR is described for the first time as a new variant of MC with two homoarginines at positions 2 and 4 in its structure. ESI-MS/MS analysis thus provides a powerful and convenient tool for the determination of variants of MC. These results represent an important contribution to the knowledge of the biochemistry of toxic cyanobacteria and their toxins, specifically in S?o Paulo State.     

用鲢鳙直接控制微囊藻水华的围隔试验和湖泊实践

为了控制水体富营养化所形成的水华,国外经典的生物操纵论者提倡放养食鱼性鱼类以控制食浮游生物的鱼类,藉此壮大浮游动物种群,然后借助浮游动物遏制藻类.按照这条思路,以浮游生物为食的鲢和鳙应该是清除的对象.本文作者认为我国湖泊中危害性最大的是微囊藻水华,而浮游动物根本不能摄食这种水华,不如直接利用鲢鳙进行控制,因而1989-1992年间在武汉的东湖进行了三次原位围隔试验,2000年再度重复了一次围隔试验,结果证明,迄今在东湖中已消失18年的微囊藻水华,重新出现在不养鱼的围隔里.在养入一定密度的鲢或/和鳙的围隔中,就没有水华出现.已经出现水华的围隔,放入适当密度的鲢或/和鳙后,在短期内水华又复消失;而放入草鱼的围隔,则水华始终持续,不受影响.说明鲢和鳙能有效地遏制微囊藻水华.鲢、鳙遏制水华的有效放养密度(亦即有效生物量)为46-50g·m^-3.东湖湖泊中鲢、鳙的生物量,直到1985年才达到这个水平,所以1985年湖里反常地没有出现水华.往后的年份,东湖的鱼产量越来越高,也就是湖里鲢、鳙的生物量越来越大,所以迄今没有微囊藻卷土重来的机会.东湖的水质和其他非生物条件仍适于蓝藻水华的发生与发展,如果东湖鲢、鳙的产量下降到阈值以下,亦即降到1985年以前1000t水平,那么微囊藻及其它蓝藻水华的重来将是不可避免的.经典的生物操纵论学说和措施不能解决微囊藻水华猖獗的问题.相反,用滤食浮游生物的鲢和鳙直接遏制微囊藻却是有实验根据并已被渔业生产实践证明行之有效的.     

不同生活型大型植物对浮游植物群落的影响

湖泊加速富营养化是世界范围内的普遍现象,由此造成水质恶化,藻类大量增生,水生植被特别是沉水植物衰退乃至消失,生物多样性降低,严重影响湖泊主要功能的发挥。大型植物与浮游植物都是浅水湖泊的初级生产者,其间存在复杂的相互关系,如除竞争作用外,还可能存在相生...     

Effects of the microcystin profile of a cyanobacterial bloom on growth and toxin accumulation in common carp Cyprinus carpio larvae

A 12 day growth trial was conducted to compare the effect of the variation in microcystins (MC) composition of two bloom samples of Microcystis aeruginosa on the growth performance and microcystin accumulation in common carp Cyprinus carpio larvae. Two M. aeruginosa natural bloom samples with different MC profiles were collected and larvae were exposed to cyanobacterial cells through their diet. Three diets, a basal control diet and two diets prepared from the basal diet plus the same toxins content (60 ng MC g^?1 diet) of each cyanobacterial bloom, were given at the same ration level to three groups of larvae during the experimental period. Larval mass and standard length from day 9 were significantly different between cyanobacterial treatments and in both cases lower than that of the control. The MC accumulation by larvae, inversely correlated with the growth performance, was also significantly different between cyanobacterial treatments (26·96 v. 17·32 ng g^?1 at the end of the experimental period). These results indicate that MC variants profile may have effects on the toxin uptake and toxicity. To date, this is the first laboratory study to show that fish accumulate MC depending on the toxin profile of the cyanobacterial bloom.     

Diversity of <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> isolates (Chroococcales,Cyanobacteria) from East-African water bodies

With exception of South Africa, very little is known about the presence and abundance of toxic cyanobacteria and cyanobacterial blooms on the African continent. The close proximity between society and nature, and the use of the sparse water resources as drinking water in large parts of Africa, lead to the recognition that more knowledge on toxic cyanobacterial blooms is of major importance. The bloom forming cyanobacterium Microcystis aeruginosa is known to produce cyclic heptatoxins (microcystins) which can be toxic to humans. In this study the morphological, genetic, and chemical characters of 24 strains of M. aeruginosa from several water bodies in Kenya and Uganda, some of them used as drinking water sources, were examined. The M. aeruginosa strains possessed different levels of diversity depending on characterisation method. Four morphotypes were identified based on the traditional morphological approach, 10 genotypes by DNA sequence comparison of the PC-IGS and ITS1 rDNA regions, and 10 chemotypes based on MALDI-TOF-MS oligopeptide analysis. Only 4 of the 24 isolated strains from East Africa were found to produce microcystins, while oligopeptides belonging to the aeruginosin and cyanopeptolin class were detected in most strains.     

Molecular characterization of potential microcystin-producing cyanobacteria in Lake Ontario embayments and nearshore waters

The distribution and genotypic variation of potential microcystin (MC) producers along the southern and eastern shores of Lake Ontario in 2001 and 2003 were examined using a suite of PCR primers. Cyanobacterial, Microcystis sp., and Microcystis-specific toxin primer sets identified shoreline distribution of cyanobacterial DNA (in 97% of the stations) and MC synthetase genes (in 50% of the stations). Sequence analysis of a partial mcyA amplicon targeting Microcystis, Anabaena, and Planktothrix species indicated that the Microcystis sp. genotype was the dominant MC genotype present and revealed a novel Microcystis-like sequence containing a 6-bp insert. Analysis of the same samples with genus-specific mcyE primers confirmed that the Microcystis sp. genotype was the dominant potential MC producer. Genotype compositions within embayments were relatively homogenous compared to those for shoreline and tributary samples. MC concentrations along the shoreline exhibited both temporal and spatial differences as evidenced by the protein phosphatase inhibition assay, at times exceeding the World Health Organization guideline value for drinking water of 1.0 microg MC-LReq liter(-1). MC genotypes are widespread along the New York State shoreline of Lake Ontario, appear to originate nearshore, and can be carried through the lake via wind and surface water current patterns.     

Diversity and dynamics of microcystin—Producing cyanobacteria in China's third largest lake, Lake Taihu

Microcystins (MC), the most prevalent group of harmful cyanobacterial hepatotoxins, are primarily produced by strains of cyanobacteria in Microcystis, Anabaena and Planktothrix. Lake Taihu, which is the third largest freshwater lake in China, is a hypertrophic shallow lake in eastern China that has experienced lake-wide cyanobacterial blooms annually during the last few decades. In this study, PCR-DGGE was used to evaluate the diversity of potential MC-producing cyanobacteria and real-time PCR was used to analyze the dynamics of this population based on the presence of the mcy gene in samples collected during a year long study. The results revealed that all MC-producing genotypes detected belonged to the genus Microcystis. In addition, the MC-producing genotype communities were more diverse during the bloom season than the non-bloom season, and the diversity in the late bloom period was lower than the diversity in the early bloom period. Furthermore, the abundance of MC-producing genotypes increased dramatically during the bloom development period, reaching its peak in late summer (September). The results also suggested that the highest mcy gene concentration lagged behind the highest MC concentration, and the potential MC-producing cyanobacterial community shift lagged behind the development of blooms.     

Effects of freshwater input on nutrient loading, phytoplankton biomass, and cyanotoxin production in an oligohaline estuarine lake

Pulsed river water events can increase nutrient levels potentially translating into enhanced primary production, phytoplankton community shifts, and bloom formation. The Bonnet Carré Spillway is a managed river diversion which can be used to redirect a significant amount of Mississippi River water into Lake Pontchartrain, reducing the risks of flood in the downstream communities during runoff seasons. We investigated nutrient enrichment and consequent changes in phytoplankton biomass, including toxic species in Lake Pontchartrain during and after a 1-month Bonne Carré Spillway opening in 2008. Water samples were collected along a 30 km transect. A freshwater plume was found to have formed by the strong river input that had limited mixing with the lake during the opening. The plume and lake water gradually mixed together after the Spillway was closed, indicated by the reduction of the horizontal salinity gradient. The river pulse increased the lake nitrate and dissolved reactive phosphorus concentrations to more than five times the lake background in the plume stations. Nutrient concentrations decreased rapidly after the Spillway closure as the plume dissipated. Diatoms and chlorophytes dominated the system during the opening. After the Spillway closure, there was a shift over time from diatom dominance to toxic cyanobacteria dominance that corresponded to more stable, warmer, and nutrient-limited water conditions. Associated toxins were present and varied over time and space. Further research on the phytoplankton assemblages on the lake is needed in subsequent, non-Spillway opening years to evaluate the impact of river water pulses on the development of these toxic cyanobacterial blooms.     

Detection of microcystin-producing cyanobacteria in Finnish lakes with genus-specific microcystin synthetase gene E (mcyE) PCR and associations with environmental factors

We studied the frequency and composition of potential microcystin (MC) producers in 70 Finnish lakes with general and genus-specific microcystin synthetase gene E (mcyE) PCR. Potential MC-producing Microcystis, Planktothrixand Anabaena spp. existed in 70%, 63%, and 37% of the lake samples, respectively. Approximately two-thirds of the lake samples contained one or two potential MC producers, while all three genera existed in 24% of the samples. In oligotrophic lakes, the occurrence of only one MC producer was most common. The combination of Microcystis and Planktothrix was slightly more prevalent than others in mesotrophic lakes, and the cooccurrence of all three MC producers was most widespread in both eutrophic and hypertrophic lakes. The proportion of the three-producer lakes increased with the trophic status of the lakes. In correlation analysis, the presence of multiple MC-producing genera was associated with higher cyanobacterial and phytoplankton biomass, pH, chlorophyll a, total nitrogen, and MC concentrations. Total nitrogen, pH, and the surface area of the lake predicted the occurrence probability of mcyE genes, whereas total phosphorus alone accounted for MC concentrations in the samples by logistic and linear regression analyses. In conclusion, the results suggested that eutrophication increased the cooccurrence of potentially MC-producing cyanobacterial genera, raising the risk of toxic-bloom formation.     

Ecological Dynamics of Toxic Microcystis spp. and Microcystin-Degrading Bacteria in Dianchi Lake,China

Toxic cyanobacterial blooms directly threaten both human safety and the ecosystem of surface waters. The widespread occurrence of these organisms, coupled with the tumor-promoting properties of the microcystin toxins that they produce, demands action to mitigate their potential impacts and, thus, a robust understanding of their ecological dynamics. In the present work, the abundance of toxic Microcystis spp. and microcystin (MC)-degrading bacteria in Dianchi Lake, located in Yunnan Province, China, was studied using quantitative PCR. Samples were taken at monthly intervals from June 2010 to December 2011 at three sampling stations within this freshwater lake. Results revealed that variation in the abundance of both total Microcystis spp. and toxic Microcystis spp. exhibited similar trends during the period of the algal bloom, including the reinvasion, pelagic growth, sedimentation, and overwintering periods, and that the proportion of toxic Microcystis was highest during the bloom and lowest in winter. Importantly, we observed that peaks in mlrA gene copy numbers of MC-degrading bacteria occurred in the months following observed peaks in MC concentrations. To understand this phenomenon, we added MCs to the MC-degrading bacteria (designated strains HW and SW in this study) and found that MCs significantly enhanced mlrA gene copy numbers over the number for the control by a factor of 5.2 for the microcystin-RR treatment and a factor of 3.7 for the microcystin-LR treatment. These results indicate that toxic Microcystis and MC-degrading bacteria exert both direct and indirect effects on each other and that MC-degrading bacteria also mediate a shift from toxic to nontoxic populations of Microcystis.     

洱海微囊藻水华的水生态风险评估研究

以洱海微囊藻水华为研究对象, 借鉴生态毒理学风险评估思路对藻类水华的水生态风险进行评价。研究通过暴露实验以及查阅文献获取了微囊藻水华对底栖动物、浮游动物、鱼类和沉水植物的效应数据, 采用毒性百分数排序法推导了洱海微囊藻水华的急性和慢性效应藻密度, 用风险商值评估微囊藻水华密度的水生态风险。进一步结合水华盖度和持续时间制定了微囊藻水华的急性、慢性生态风险评价表。研究结果表明, 微囊藻水华的急性生态风险分为低中高三级, 分别为微囊藻藻密度小于3.4×106 cells/L为低风险,微囊藻藻密度在3.4×106—3.4×107 cells/L之间为中风险,微囊藻密度大于3.4×107 cells/L为高风险。慢性生态风险同样分为低中高三级, 分别为微囊藻藻密度小于1.1×106 cells/L为低风险,微囊藻藻密度在1.1×106—1.1×107 cells/L为中风险,微囊藻密度大于1.1×107 cells/L为高风险。实际应用中需综合微囊藻水华密度、面积和持续时间, 制定洱海微囊藻水华水生态风险评价标准。当微囊藻水华处于中风险状态时, 应启动预警、强化水质管理和生物抑制措施, 当处于高风险状态时, 应采取水华的应急处理措施。研究结果有助于洱海微囊藻水华的科学管理。     

微囊藻毒素研究进展

随着大量含氮和磷的废水流入湖泊和江河,导致淡水蓝藻水华污染现象日趋严重。蓝藻水华污染的最主要危害是释放以微囊藻毒素（Ｍｉｃｒｏｃｙｓｔｉｎ,ＭＣ）为主的多种藻毒素,因此如何有效控制蓝藻水华污染和去除ＭＣ是摆在中外环境科学领域的一个难题。主要针对ＭＣ的产生、物化性质、毒性、分析方法和迁移转化方面的国内外最新研究进展进行了综述,并对重要的研究领域进行了展望。     

不同氮、磷浓度对铜绿微囊藻生长、光合及产毒的影响

对一株从野外分离得到的铜绿微囊藻产毒株进行分批培养,在不同的氮磷条件下研究其生长、光合荧光及毒素含量的变化。结果表明:正磷酸盐浓度不变时,铵氮浓度的改变对铜绿微囊藻的生长有明显影响。叶绿素a(Chl.a)含量在铵氮浓度为1.83-18.3mg/L时明显较大;微囊藻毒素(包括MC-LR和MC-RR)的含量在铵氮浓度为1.83mg/L时达到最大;当铵氮浓度为0-1.83mg/L时,随着铵氮浓度升高,可变荧光FV和MC的产量均增大,同时MC异构体的种类增多;铵氮浓度过大对M.aeruginosa的生长、生理和产毒均有抑制作用。在另一组实验中,即铵氮浓度不变而正磷酸盐浓度增大时,Chl.a含量呈总体下降的趋势,并且与FV/Fm呈显著正相关关系(P<0.01,r=0.97),MC(MC-LR和MC-RR)的含量在正磷酸盐浓度小于0.56mg/L时明显升高,MC-LR与FV/Fm呈显著正相关关系(P<0.01,r=0.967)。       

Nitrogen Forms Influence Microcystin Concentration and Composition via Changes in Cyanobacterial Community Structure

The eutrophication of freshwaters is a global health concern as lakes with excess nutrients are often subject to toxic cyanobacterial blooms. Although phosphorus is considered the main element regulating cyanobacterial biomass, nitrogen (N) concentration and more specifically the availability of different N forms may influence the overall toxicity of blooms. In this study of three eutrophic lakes prone to cyanobacterial blooms, we examined the effects of nitrogen species and concentrations and other environmental factors in influencing cyanobacterial community structure, microcystin (MC) concentrations and MC congener composition. The identification of specific MC congeners was of particular interest as they vary widely in toxicity. Different nitrogen forms appeared to influence cyanobacterial community structure leading to corresponding effects on MC concentrations and composition. Total MC concentrations across the lakes were largely explained by a combination of abiotic factors: dissolved organic nitrogen, water temperature and ammonium, but Microcystis spp. biomass was overall the best predictor of MC concentrations. Environmental factors did not appear to affect MC congener composition directly but there were significant associations between specific MC congeners and particular species. Based on redundancy analyses (RDA), the relative biomass of Microcystis aeruginosa was associated with MC-RR, M. wesenbergii with MC-LA and Aphanizomenon flos-aquae with MC-YR. The latter two species are not generally considered capable of MC production. Total nitrogen, water temperature, ammonium and dissolved organic nitrogen influenced the cyanobacterial community structure, which in turn resulted in differences in the dominant MC congener and the overall toxicity.     

Longitudinal Differences of Phytoplankton Community during a Period of Small Water Level Fluctuations in a Subtropical Reservoir Bay (Xiangxi Bay,Three Gorges Reservoir,China)

The Three Gorges Reservoir (TGR) had a great inflow discharge with small water level fluctuations in the flood season of the year 2008, when a large‐scale cyanobacterial bloom broke out in Xiangxi Bay (a tributary bay behaving like a lake) for the first time after the construction of the TGR impoundment. To compare spatiotemporal longitudinal differences of phytoplankton community structure during this period, weekly surveys were performed in Xiangxi Bay. The cyanobacterial bloom lasted from June 6 to July 18, 2008, with Microcystis aeruginosa as the dominant species. During this bloom the species diversity, evenness and community change rate was relatively low. The probable causes for the interruption of the bloom were precipitation and water temperature. In the non‐cyanobacterial bloom period (July 25 to September 26, 2008) many other species dominated the community including Stephanodiscus hantzschii and Cryptomonas ovata, with higher values of species diversity, evenness and community change rate. As for the longitudinal differences, the community structure in the riverine zone was different from that in other zones, indicating the important effect of inflow from the upstream of Xiangxi Bay. The management actions in Xiangxi Bay should prevent blooms in the mainstream, lacustrine and transitional zone. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)