Freshwater Blooms Research Articles

Progress and prospect in the study of <i>Cylindrospermopsis raciborskii</i> and its toxins

随着水体富营养化程度的加剧，淡水蓝藻水华在全球范围内频繁暴发. 拟柱孢藻（Cylindrospermopsis raciborskii）作为一类有害水华蓝藻，具有一定的产毒能力和较强的入侵性，日渐受到人们的广泛关注. 近年来，拟柱孢藻不断由热带、亚热带地区向温带地区扩张，并在众多水体中出现暴发现象，若其毒素进入到饮用水中，无疑将对人类健康造成潜在威胁. 本文从拟柱孢藻的分布演变、生态生理特征、毒性、检测和去除等研究前沿方面进行了综述，并对相关研究领域进行展望，为进一步研究拟柱孢藻的生态毒理、有效控制和去除提供科学依据.;With the aggravation of water eutrophication, harmful cyanobacterial bloom in fresh water becomes more and more serious on a global scale. Cylindrospermopsis raciborskii, a noxious cyanobacterial species that can form blooms in fresh water, has gradually received widespread attention for its potential ability of toxin production and strong invasiveness. In recent years, Cylindrospermopsis raciborskii has spread from the tropics and subtropics to temperate zones with associated blooms in many water bodies. If the toxins come into drinking water, it will undoubtedly pose a potential threat to human health. In this review, recent literatures concerning its geographic distribution, ecophysiology, toxicity, detection and removal processes are summarized. Meanwhile, we discussed the future research directions in related field, which will provide some scientific information for further studies on the ecological toxicology, effective controls and removal of Cylindrospermopsis raciborskii.

An experimental use of floating treatment wetlands (FTWs) to reduce phytoplankton growth in freshwaters

Eutrophication and the formation of phytoplankton blooms in freshwaters can be detrimental to water quality and biological health and produce organic matter that can be difficult to remove during water treatment processes. With the frequency of phytoplankton blooms increasing, remediation solutions are becoming increasingly popular. This study investigated the use of a peat-based floating treatment wetland (FTW) for reducing phytoplankton growth in eutrophic waters. Over a four-week period, the FTWs were able to reduce chlorophyll a concentrations by 80%, through sequestration of nitrate and phosphate and possibly due to the direct inhibitory properties of phenolic compounds. Although there are concerns about the leaching of dissolved organic carbon (DOC) from the FTWs, this may be more than offset by the beneficial suppression of phytoplankton growth and the resulting reduced input of ‘untreatable’ low molecular weight DOC.

Coagulation performance and floc characteristics of polytitanium tetrachloride (PTC) compared with titanium tetrachloride (TiCl 4 ) and ferric chloride (FeCl 3 ) in algal turbid water

Abstract Seasonal green algae blooms in freshwaters have raised attention on the need to develop novel effective treatment processes for the removal of algae in water. In the present study, the performance of newly developed polytitanium tetrachloride (PTC) coagulant for the removal of freshwater microalga Chlorella vulgaris has been investigated and compared with titanium tetrachloride (TiCl 4 ) coagulant and the conventional ferric chloride (FeCl 3 ) coagulant. The main benefit of using titanium-based coagulants is that the sludge produced after flocculation may be recycled into a valuable product: titanium dioxide photocatalyst. Both titanium-based coagulants achieved good flocculation over a broader pH range and coagulant dose compared to conventional FeCl 3 coagulant. All three coagulants achieved comparable performance in terms of turbidity removal (i.e. turbidity removal efficiency >97%); although TiCl 4 performed slightly better at the lower tested dose (i.e. 3 and also grew at a faster rate. This study indicates that Ti-based coagulants are effective and promising coagulants for algae removal in water.

Dominant genera of cyanobacteria in Lake Taihu and their relationships with environmental factors.

Cyanobacterial blooms in freshwaters have become one of the most widespread of environmental problems and threaten water resources worldwide. Previous studies on cyanobacteria in Lake Taihu often collected samples from one site (like Meiliang Bay or Zhushan Bay) and focused on the variation in patterns or abundance of Microcystis during the blooming season. However, the distribution of cyanobacteria in Lake Taihu shows differing pattern in various seasons. In this study, water samples were collected monthly for one year at five sites in Lake Taihu with different trophic status and a physicochemical analysis and denaturing gradient gel electrophoresis (DGGE) were conducted. DGGE fingerprint analysis showed that Microcystis (7/35 bands) and Synechococcus (12/35 bands) were the two most dominant genera present during the study period at all five sites. Cyanobium (3/35 bands) was the third most common genus which has seldom been previously reported in Lake Taihu. Redundancy analysis (RDA) indicated that the cyanobacterial community structure was significantly correlated with NO3 (-)-N, CODMn, and NH4 (+)-N in the winter and spring, whereas it was correlated with water temperature in the summer and autumn. Limiting the nutrient input (especially of N and C loading) in Lake Taihu would be a key factor in controlling the growth of different genera of cyanobacteria.

The success of the cyanobacterium Cylindrospermopsis raciborskii in freshwaters is enhanced by the combined effects of light intensity and temperature

<p>Toxic cyanobacterial blooms in freshwaters are thought to be a consequence of the combined effects of anthropogenic eutrophication and climate change. It is expected that climate change will affect water mixing regimes that alter the water transparency and ultimately the light environment for phytoplankton. Blooms of the potentially toxic cyanobacterium <em>Cylindrospermopsis raciborskii</em> are expanding from tropical towards temperate regions. Several hypotheses have been proposed to explain this expansion, including an increase in water temperature due to climate change and the high phenotypic plasticity of the species that allows it to exploit different light environments. We performed an analysis based on eight lakes in tropical, subtropical and temperate regions to examine the distribution and abundance of <em>C. raciborskii</em> in relation to water temperature and transparency. We then conducted a series of short-term factorial experiments that combined three temperatures and two light intensity levels using <em>C. raciborskii</em> cultures alone and in interaction with another cyanobacterium to identify its growth capacity. Our results from the field, in contrast to predictions, showed no differences in dominance (>40% to the total biovolume) of <em>C. raciborskii</em> between climate regions. <em>C. raciborskii</em> was able to dominate the phytoplankton in a wide range of light environments (euphotic zone = 1.5 to 5 m, euphotic zone/mixing zone ratio <0.5 to >1.5). Moreover, <em>C. raciborskii </em>was capable of dominating the phytoplankton at low temperatures (<15°C). Our experimental results showed that <em>C. raciborskii</em> growing in interaction was enhanced by the increase of the temperature and light intensity. <em>C. raciborskii </em>growth in high light intensities and at a wide range of temperatures, suggests that any advantage that this species may derive from climate change that favors its dominance in the phytoplankton is likely due to changes in the light environment rather than changes in temperature. Predictive models that consider only temperature as a drive factor can therefore fail in predicting the expansion of this potentially toxic cyanobacterium.<em></em></p>

토착 남세균 림노트릭스 속 KNUA012 균주의 바이오연료 원료로서의 특성 연구

A filamentous cyanobacterium, Limnothrix sp. KNUA012, was axenically isolated from a freshwater bloom sample in Lake Hapcheon, Hapcheon-gun, Gyeongsangnam-do, Korea. Its morphological and molecular characteristics led to identification of the isolate as a member of the genus Limnothrix. Maximal growth was attained when the culture was incubated at 25°C. Analysis of its lipid composition revealed that strain KNUA012 could autotrophically synthesize alkanes, such as pentadecane (C 15 H 32 ) and heptadecane (C 17 H 36 ), which can be directly used as fuel without requiring a transesterification step. Two genes involved in alkane biosynthesis－an acyl-acyl carrier protein reductase and an aldehyde decarbonylase－were present in this cyanobacterium. Some common algal biodiesel constituents－myristoleic acid (C 14:1 ), palmitic acid (C 16:0 ), and palmitoleic acid (C 16:1 )－were produced by strain KNUA012 as its major fatty acids. A proximate analysis showed that the volatile matter content was 86.0% and an ultimate analysis indicated that the higher heating value was 19.8 MJ kg -1 . The isolate also autotrophically produced 21.4 mg g -1 phycocyanin－a high-value antioxidant compound. Therefore, Limnothrix sp. KNUA012 appears to show promise for application in cost-effective production of microalga-based biofuels and biomass feedstock over crop plants.

Fast, rugged and sensitive ultra high pressure liquid chromatography tandem mass spectrometry method for analysis of cyanotoxins in raw water and drinking water—First findings of anatoxins, cylindrospermopsins and microcystin variants in Swedish source waters and infiltration ponds

Freshwater blooms of cyanobacteria (blue–green algae) in source waters are generally composed of several different strains with the capability to produce a variety of toxins. The major exposure routes for humans are direct contact with recreational waters and ingestion of drinking water not efficiently treated. The ultra high pressure liquid chromatography tandem mass spectrometry based analytical method presented here allows simultaneous analysis of 22 cyanotoxins from different toxin groups, including anatoxins, cylindrospermopsins, nodularin and microcystins in raw water and drinking water. The use of reference standards enables correct identification of toxins as well as precision of the quantification and due to matrix effects, recovery correction is required. The multi-toxin group method presented here, does not compromise sensitivity, despite the large number of analytes. The limit of quantification was set to 0.1μg/L for 75% of the cyanotoxins in drinking water and 0.5μg/L for all cyanotoxins in raw water, which is compliant with the WHO guidance value for microcystin-LR. The matrix effects experienced during analysis were reasonable for most analytes, considering the large volume injected into the mass spectrometer. The time of analysis, including lysing of cell bound toxins, is less than three hours. Furthermore, the method was tested in Swedish source waters and infiltration ponds resulting in evidence of presence of anatoxin, homo-anatoxin, cylindrospermopsin and several variants of microcystins for the first time in Sweden, proving its usefulness.

Microcystin production in Microcystis aeruginosa: effect of type of strain, environmental factors, nutrient concentrations, and N:P ratio on mcyA gene expression

Blooms affect water quality mainly due to the release of microcystins (MCs) by cyanobacteria. The synthesis of MCs is influenced by factors such as nutrient concentration, temperature, pH, light intensity, salinity, turbidity, and the presence of xenobiotics. In this study, we evaluated the effect of environmental factors (temperature and light intensity), the concentration of three nutrients (NaNO3, K2HPO4, and FeCl3), and the N:P ratio on the growth of two Microcystis aeruginosa strains (Ch10 and UTEX LB2385), as well as on mcyA gene expression and intracellular MC concentration. Under similar conditions, the population growth and chlorophyll a concentration per cell of both strains were different. The mcyA gene was significantly up-regulated from the early growth phase (5 days) to the stationary phase (15 days) in most cases, whereas intracellular MC concentrations varied depending on the assessed factor. The N:P ratio affected the development of both strains and MCs production differently. High concentration of intracellular MCs was recorded at low nitrogen and iron concentrations, low temperature, and high light intensity. The response in mcyA gene expression, related to the incubation time, of both strains was different, because strain Ch10 responded in most cases starting at 5 days of growth, whereas UTEX LB2385 responded until 10 and 15 days. This difference reflects physiological plasticity that could help to understand the permanence and dominance of Microcystis genus blooms in eutrophic freshwaters. The variability in response to the tested environmental factors confirms that population growth, genetic expression, and microcystin production are not related to a single factor but to an array of conditions that, when combined, stimulate MCs production. These conditions can be both stress-causing and favorable; hence, monitoring of environmental factors aimed at alerting against health risks provoked by cyanotoxins is a very complex task.

A field application feasibility assessment of naphthoquinone derivatives for the mitigation of freshwater diatom Stephanodiscus blooms

Although many algicidal substances have been developed, their field application remains a serious challenge due to their high toxicity in the ecosystem and also due to economic reasons. Therefore, we evaluated the claim that naphthoquinone (NQ) derivatives can be used for the efficient mitigation of natural Stephanodiscus hantzschii blooms in freshwater. We tested a total of 23 algicidal NQ compounds to select the best based on the algicidal activity of S. hantzschii species. Among them, NQ 4–6 showed the highest algicidal activities (96 % at ≥0.2 μM). We conducted an acute toxicity assessment of the new algicide and found that NQ 4–6 had advanced solubility and lower toxicity, as represented by the survival rates of Selenastrum capricornutum, Daphnia magna, and Danio rerio, which are interconnected components of the freshwater ecosystem. None of these organisms seemed to be affected by the highest NQ concentration (2 μM), indicating a lack of significant toxic effects. These results indicate that the NQ 4–6 compound is promising for use as a selective control agent for S. hantzschii that does not cause negative side effects in the freshwater ecosystem. To evaluate the possibility of field application of NQ 4–6, we first performed microcosm tests. In the microcosm tests (60 L), S. hantzschii was completely eliminated 10 days after inoculation with the NQ 4–6 compound (0.2 μM). In the microcosm experiments, the dynamics of the biotic (except the phytoplankton) and abiotic factors showed similar trends in the control and treatment groups. Therefore, the NQ 4–6 compound has potential as an alternative algicidal substance to effectively mitigate natural S. hantzschii blooms.

Part-Per-Trillion Level Detection of Microcystin-LR Using a Periodic Nanostructure

Accelerated eutrophication of surface water sources has resulted in an increased presence of cyanobacterial blooms in fresh water. The release of hepatotoxins like microcystins from such blooms can have a catastrophic impact on local human and wildlife ecosystems. Therefore, a rapid, low-cost, reliable, and highly sensitive method for low-concentration detection of microcystins is needed to minimize risks to public health. In this paper, we report the first experimental demonstration of microcystin-leucine-arginine (MC-LR) detection in water at low part-per-trillion levels using a portable optical sensor. The demonstrated biosensor utilizes a highly sensitive electromagnetic surface wave in periodically coupled artificial nanostructures to directly probe the interaction between immobilized antibodies and MC-LR. The surface customization reported here uses a layer-by-layer polyelectrolyte adsorption process to provide highly stable and site-directed immobilization of target antibodies. Steady-state analysis of the sensor’s response confirms that the plasmonic sensor can detect the presence of MC-LR antigens at part-per-trillion levels. The demonstrated sensor is an important first step toward realizing a lab-on-a-chip sensing system for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$in~situ$ </tex-math></inline-formula> , autonomous, real-time, distributed environmental monitoring of MC levels in drinking water.

Inhibitory mechanisms of Acacia mearnsii extracts on the growth of Microcystis aeruginosa.

Our previous work revealed that Acacia mearnsii extract can inhibit the growth of Microcystis aeruginosa, the common species forming toxic cyanobacterial blooms in eutrophic freshwater. In the present study, we demonstrated that this plant extract can significantly increase cell membrane permeability and Ca²⁺/Mg²⁺-ATPase activity on the membrane. Long-term exposure to concentrations of 20 ppm A. mearnsii extract led to algal cell membrane leakage or even lysis. Comparison of expression of three photosynthesis-related genes (rbcL, psaB and psbD) in M. aeruginosa with and without plant extract treatment revealed that their expression was remarkably reduced in the presence of the extract. Down-regulation of photosynthesis-related genes could indicate the inhibition of the photosynthetic process. Thus, our results suggested that both photosynthetic systems and membranes of M. aeruginosa are potentially damaged by A. mearnsii extract.

产毒与不产毒铜绿微囊藻对模拟酸雨及紫外辐射的生理响应

PDF HTML阅读 XML下载 导出引用 引用提醒 产毒与不产毒铜绿微囊藻对模拟酸雨及紫外辐射的生理响应 DOI: 10.5846/stxb201405211049 作者: 作者单位: 黄山学院生命与环境科学学院;厦门大学近海海洋环境科学国家重点实验室,黄山学院,黄山学院,黄山学院,黄山学院,厦门大学,黄山学院,厦门大学 作者简介: 通讯作者: 中图分类号: 基金项目: 安徽省自然科学基金青年项目(1508085QC67);黄山学院博士启动项目(2014xkjq002);安徽省大学生创新创业项目(AH2014103753126);近海海洋环境科学国家重点实验室(厦门大学)访问学者基金(MELVisitingFellowship)(MELRS1314) Physiological responses of toxigenic and non-toxigenic strains of Microcystis aeruginosa to simulated acid rain and UV radiation Author: Affiliation: Huangshan University,,,,,,,Xiamen University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了比较研究酸雨与紫外辐射对淡水水体常见藻华蓝藻的生理学影响,选取铜绿微囊藻(Microcystis aeruginosa)产毒(FACHB-905)与不产毒(FACHB-469)株系作为实验材料,通过人工模拟酸雨,研究了不同pH处理后2藻株的光合生理变化以及对紫外辐射的敏感性的异同。实验设置3个pH梯度,pH7.10为对照组(正常培养基培养的藻体),两模拟酸雨处理组(pH5.65和pH4.50);两种辐射处理,可见光处理(PAR)以及全波长辐射处理(PAB)。研究结果表明,905藻株细胞粒径在各pH处理下都要显著高于469藻株,模拟酸雨处理显著降低了两藻株细胞的平均粒径及体积,但叶绿素含量显著提高;酸雨处理同时也引起细胞死亡率的增加,表现为藻体有效光化学效率显著降低,生长速率显著受到抑制,低pH下呈负增长,且这种抑制程度在469下更为显著。高的可见光以及紫外辐射处理,使两株系有效光化学效率随pH的降低而呈降低趋势,其中469藻株降低至更低的水平,且高光辐射以及紫外诱导的抑制率要显著高于905藻体,这可能与469藻株较低的光保护色素有关(较低的类胡萝卜素以及紫外吸收物质)。在未来全球变化背景下,不同种类的浮游植物对环境变化的响应及适应能力不同,可改变水体的群落结构和种群丰度,铜绿微囊藻905较469较强的耐受酸雨以及紫外辐射的能力,可能会使该株系在竞争力上占据优势。 Abstract:Acid precipitation from natural and human activities can lead to different extents of acidification in different freshwater ecosystems, with noticeable changes in the carbonate system and aquatic chemistry. For example, acidification is known to decrease the ionic concentrations of magnesium and calcium, but enhance aluminum concentrations. The changes to chemicals associated with freshwater acidification could induce physiological disturbance to most aquatic organisms, which would then need to spend additional energy to cope with acidic stress. Phytoplankton species with different sensitivities to acid stress may have differential physiological responses;thus, acid stress may lead to altered community structure and species richness. Alternatively, UV-B (280-320 nm) irradiance has been increasing due to stratospheric ozone depletion, which would also impact freshwater phytoplankton. Meanwhile, significantly decreased dissolved organic matter as a result of acid rain may further enhance the penetration of solar UV radiation (UVR, 280-400 nm) in the water column due to decreased light attenuation. Therefore, freshwater acidification and solar UVR may interact to influence phytoplankton physiology. This study examined the physiological responses of a freshwater bloom forming cyanobacterium, Microcystis aeruginosa, to acidification and UVR. Two strains were used for the experiments;a toxigenic strain (FACHB-905) and a non-toxigenic strain (FACHB-469). Microcystis aeruginosa cells were grown under simulated acid rain (with a mole ratio of H2SO4 : HNO3 = 8 : 1) under a solar simulator with and without UVR, to observe whether photosynthetic performance and sensitivity to UV irradiance differed between the two strains. Three pH levels were used, pH 7.10 (regular BG11+N medium), 5.65, and 4.50, with the latter two pH levels reflecting acidification conditions. Two solar radiation treatments were carried out, including: photosynthetically active radiation alone (PAR, 400-700 nm) and PAR+ UV-A+UV-B (PAB, 295-700 nm). Our results indicate that the mean cell size and cell volume of the 905 strain was significantly higher than those of the 469 strain in all pH treatments. Acidification treatment significantly lowered mean cell size and volume, but enhanced the chlorophyll a content in both strains. Under the lowest pH (4.50), higher mortality rates were observed for both strains, with decreased effective quantum yield. The inhibition of the growth rate was more pronounced in the non-toxigenic strain. The effective quantum yield declined with decreasing pH level when cells were exposed to high levels of PAR and PAR+UVR. UV-induced inhibition of effective quantum yield was much higher in the non-toxigenic strain compared to the toxigenic strain. This differential response may be attributed to different contents to UV absorbing compounds and carotenoids. Under the global climate change scenario, increasing aquatic acidification and UV irradiance might decrease the competence of the non-toxigenic strain over the toxigenic one. 参考文献 相似文献 引证文献

Physiology and molecular biology of aquatic cyanobacteria.

Cyanobacteria thrive in every illuminated aquatic environment known, contributing at least 25% of primary productivity worldwide. Given their importance in carbon and nutrient cycles, cyanobacteria are essential geochemical agents that have shaped the composition of the Earth's crust, oceans and atmosphere for billions of years. The high diversity of cyanobacteria is reflected in the panoply of unique physiological adaptations across the phylum, including different strategies to optimize light harvesting or sustain nitrogen fixation, but also different lifestyles like psychrotrophy, and oligotrophy. Some cyanobacteria produce secondary metabolites of cryptic function, many of which are toxic to eukaryotes. Consequently, bloom-forming toxic cyanobacteria are global hazards that are of increasing concern in surface waters affected by anthropogenic nutrient loads and climate change. While focusing on cyanobacteria in aquatic environments, the collection of papers herein touches on this broad range of topics. Regarding the role of cyanobacteria in the ocean, the importance of the unicellular picocyanobacteria is paramount. Indeed, Synechococcus and Prochlorococcus are the abundant genera in the oligotrophic open sea. Given that cyanobacteria are under regular assault imposed by photooxidative stresses, and that such stresses constrain photosynthetic performance, the paper by Mella-Flores et al. (2012) describes different strategies employed by model strains of Synechococcus and Prochlorococcus to high light and UV. Nonetheless, in the ocean, Synechococcus is composed of several clades that likely define particular ecotypes. Detection and enumeration of distinct Synechococcus clades is essential in understanding how these organisms co-exist with one another. To this end, Ahlgren and Rocap (2012) developed a suite of qPCR tools enabling a thorough analysis of Synechococcus community structure and dynamics. Nitrogen fixation by the unicellular Crocosphaera watsonii is now recognized to be a significant source of new N to marine environments. Two papers describe physiological properties of Crocosphaera relevant to their ecological importance. Sohm et al. (2011) demonstrate that a strain of C. watsonii produces high amounts of extracellular polysaccharides. The high level of organic carbon production suggests that this strain may directly support significant heterotrophy in the marine C cycle. Given that arsenate is a toxic anion that can interfere with the transport and metabolism of phosphate, Dyhrman and Haley (2011) report mechanisms of arsenate resistance in Crocosphaera, whose habitat includes P-limited ocean gyres. Such regions often have high arsenate:phosphate ratios, thus detoxification mechanisms are an important strategy for N fixation in these oligotrophic regions. The structure and physiological performance of arctic cyanobacterial mats is of particular interest, given their dominant contribution to biomass at high latitudes, and the stresses imposed by global warming on such fragile environments. Lionard et al. (2012) examine the composition of an artic microbial mat, and demonstrate the robust adaptation of the cyanobacteria to osmotic stress, a likely outcome of climate change. The characterization of chlorophyll-b containing Prochlorothrix spp. by Pinevich et al. (2012) indicate that despite the scarcity of this genus in aquatic environments, molecular methods suggest it is more widely distributed. The authors compare the physiological characteristics of the two known species and discuss the evolution of their light harvesting apparatus. Four papers explore the physiology of bloom-forming and toxic cyanobacteria. Kaplan et al. (2012) address the enigmatic function of the microcystins and cylindrospermopsins, describing experimental evidence for their role in cell-cell communication among bloom-formers. Sukenik et al. (2012) explore the spread of Aphanizomenon and Cylindrospermopsis to temperate freshwater environments. The appearance of such blooms is a likely consequence of global warming along with anthropogenic nutrient load, leading to a sustained invasion of into the middle latitudes. Given that management of phosphorus inputs is a strategy for limiting algal blooms in freshwaters, Saxton et al. (2012) describe the phosphorus quotas (intracellular and total) of the toxic colonial cyanobacterium, Microcystis aeruginosa. In response to increased phosphorus, Microcystis exhibited a higher cell P quota, yet a stable growth rate compared to lower phosphorus treatments. Such work has implications in modeling Microcystis blooms from P loadings into freshwaters. Gagnon and Pick (2012) contribute a study showing that the potent neurotoxin anatoxin-a is associated with nitrogen availability in Aphanizomenon. Understanding environmental cues for toxin production is essential in ultimately mitigating bloom toxigenicity. Together, these important contributions cover many of the issues tackled in the field today: the role of cyanobacteria in the global carbon and nutrient cycles, cyanobacterial evolution, the adaptation of cyanobacteria to climate change and the consequences of toxigenicity. The studies described in this collection provide an excellent introduction to these topics, while providing important clues regarding the future directions that studies of cyanobacteria will take.

Draft Genome Sequence of the Toxic Bloom-Forming Cyanobacterium Aphanizomenon flos-aquae NIES-81

Aphanizomenon flos-aquae is a toxic filamentous cyanobacterium that causes water blooms in freshwaters across the globe. We present the draft genome sequence of the A. flos-aquae strain NIES-81, which was determined by 454 pyrosequencing technology. The draft genome is ~5.7 Mb, containing 5,802 predicted protein-coding genes and 58 RNA genes, with a G+C content of 38.5%.

The Response of Macrophytes to Nutrients and Implications for the Control of Phytoplankton Blooms in East Taihu Lake, China

When macrophytes are growing in the eutrophicated aquatic ecosystem, the vegetation induces important effects to the water quality and phytoplankton concentrations in the water which affected by macroscopic physical, chemical and biological processes and the effects are the results of direct and indirect interactions of the aquatic plants and water body. The interactions between macrophytes, nutrients and phytoplankton blooms were examined in the water and sediments of a shallow, eutrophic and typical East Taihu, China. The importance of macrophytes as a sink for nutrients, and the inhibitory effect of macrophytes on phytoplankton bloom potential were assessed through three different seasons. Luxuriant aquatic plants growth in this system led to decrease available nutrients for phytoplankton and prevented bloom development. Uptake of N and P by aquatic plants accounted for a major portion of the observed N and P loss from the water column and sediments. Luxury uptake of N and P were indicated by high biomass and tissues N and P concentrations, indicating the capacity of macrophytes to act as a nutrient sink in midsummer. Dissolved inorganic N (DIN) and soluble reactive phosphorous (SRP) in water were reduced in midsummer in the presence of macrophytes. The use of macrophytes to reduce the nutrients in water system and thereby inhibit freshwater phytoplankton blooms should be considered as an effective management strategy in shallow eutrophicated lakes. As aquatic macrophytes also develops considerable indirect effects that could have a vital impact than the direct uptake the nutrients into the plant biomass.

Lysogenic infection in sub-tropical freshwater cyanobacteria cultures and natural blooms

Lysogeny has been reported for a few freshwater cyanobacteria cultures, but it is unknown how prevalent it is in freshwater cyanobacteria in situ. Here we tested for lysogeny in (a) cultures of eight Australian species of subtropical freshwater cyanobacteria; (b) seven strains of one species: Cylindrospermopsis raciborskii; and (c) six cyanobacterial blooms in drinking water reservoirs in South East Queensland, Australia. Lysogenic infection in the cyanobacteria was induced through mitomycin C addition. By measuring the decline in host cell numbers and the concomitant increase in cyanophages over the course of the experiment, we observed lysogenic infection in five of the eight species of cyanobacteria (i.e. Nodularia spumigena, Anabaena circinalis, Anabaenopsis arnoldii, Aphanizomenon ovalisporum, Microcystis botrys, Microcystis aeruginosa, C. raciborskii and Anabaena spp., and in four of the seven strains of C. raciborskii) but only in two of the six natural cyanobacteria blooms. Lysogeny dominated laboratory culture strains whereas in natural blooms of cyanobacteria few species were lysogenic (i.e. not mitomycin C inducible). Thus, lysogenic laboratory cultures may not necessarily reflect the genetics nor the physiology of a natural cyanobacterial population, and more information on both forms is needed to understand better how cyanobacteria behave and exist in their natural habitat.

Functional Analysis of Environmental DNA-Derived Microviridins Provides New Insights into the Diversity of the Tricyclic Peptide Family

Microviridins represent a unique family of ribosomally synthesized cage-like depsipeptides from cyanobacteria with potent protease-inhibitory activities. The natural diversity of these peptides is largely unexplored. Here, we describe two methodologies that were developed to functionally characterize cryptic microviridin gene clusters from metagenomic DNA. Environmental samples were collected and enriched from cyanobacterial freshwater blooms of different geographical origins containing predominantly Microcystis sp. Microviridins were produced either directly from fosmid clones or after insertion of environmental DNA-derived gene cassettes into a minimal expression platform in Escherichia coli. Three novel microviridin variants were isolated and tested against different serine-type proteases. The comparison of the bioactivity profiles of the new congeners allows deduction of further structure-function relationships for microviridins. Moreover, this study provides new insights into microviridin processing and gene cluster organization.

微囊藻毒素对陆生植物的污染途径及累积研究进展

微囊藻毒素(Microcystins,MCs)是全世界范围内普遍存在、且随着水体污染的加剧而在自然环境中大量积聚的蓝藻毒素之一,对多种生物有着严重的毒性作用。MCs在生物体内富集并通过食物链传递,对人类健康造成威胁。近些年,MCs对陆生植物的毒害作用及累积研究尤为引人关注,取得了一批重要的研究成果。MC-LR(L为亮氨酸)和MC-RR(R为精氨酸)是淡水水体中普遍存在且危害较大的两种MCs异构体。针对这两种毒素,重点介绍其对陆生植物的污染途径、毒性作用及其在作物体内的累积量,对今后的研究进行了展望。;The occurrence of toxic cyanobacterial blooms in eutrophic lakes, reservoirs and recreational waters has become a worldwide problem. In the last 20 years, the occurrence of toxic freshwater blooms of cyanobacteria has been frequently reported in many water bodies in China, such as Taihu Lake, Chaohu Lake and Dianchi Lake. Some of the cyanobacterial genera such as <em>Microcystis</em>, <em>Anabaena</em>, <em>Nostoc</em> and <em>Aphanizomenon</em> can produce a wide range of potent toxins, including a family of hepatotoxins called microcystins (MCs) that comprise the most frequently encountered MCs in freshwater. Microcystins are produced mainly by freshwater cyanobacterial blooms, which produce mass populations in water bodies commonly produce a range of toxic effects. Some reports suggest that the incidence of human primary liver cancer in the eastern region of China is related to the presence of MCs found in drinking water. The toxic effects and mechanism of MCs on animals have been well studied. Microcystins can potently inhibit protein phosphatase type-1 and 2A after the toxin was transported to cytoplasm by the bile acid transporter in the cell membrane of hepatocytes. Microcystins can also induce the oxidative stress <em>in vitro</em> cultured rat and fish cells. In recent years, the toxic effect of MCs on terrestrial plants and their bioaccumulation became an attracting area of research, which had made quite a number of important achievements. The growth inhibitory phenomenon of MCs on plant was firstly observed in <em>Sinapis alba</em>. Thereafter, many reports demonstrated that the growth, development and physiological pathway of plants could be affected by MCs. The commonly accepted toxic mechanism of MCs on plants is that MCs inhibit protein phosphatase type-1 and 2A. At present, there has some evidence suggesting that oxidative stress might be involved in the toxicity of MCs on plants. It was reported that the activity of peroxidase (POD) and superoxide dismutase (SOD), two of antioxidant enzymes, were changed in rape (<em>Brassica napus</em>) and rice (<em>Oryza sativa</em>) seedlings when exposed to MCs. Recently, some attentions also have been paid to the toxic effects of MCs irrigated with water contained cyanobacteria on plants. The effect of irrigation with contaminative lake water containing a variety of MCs on accumulation of toxins, or toxin metabolites, and growth in plants (e.g. ryegrass, clover, rape, and some vegetables) was investigated by many studies via field experiment or indoor test. Microcystins could accumulate in living organisms and transfer through the food chain, consequently threatening human health. These problems are beginning to be addressed via water quality management programs in some countries. Hazard characterization and risk assessment of cyanobacterial toxins in relation to human health requires the identification of exposure routes. Among more than 80 isomers of MCs, MC-LR (L indicated leucine) and MC-RR (R indicated arginine) are two common and dangerous ones existing in freshwater bodies. This study was aimed at MC-LR and MC-RR, including stressing their pollution ways to terrestrial plants, toxic effect and bioaccumulation amount in plants. Furthermore, the research directions in the future, such as the transfer and degradation mechanism of MCs in soils, dose-respones relationship of MCs and its ecological risk in agriculture were discussed.

Transgenerational effects of microcystin-LR onDaphnia magna

Anthropogenic and climate factors increase the frequency of problematic cyanobacterial blooms in freshwater. Among other toxins, some cyanobacteria produce microcystins (MCs), which inhibit phosphatases type 1 and type 2A and provokes oxidative stress. Toxic cyanobacteria affect the growth, survival and reproduction of zooplankton, particularly those from the genus Daphnia, which have a central position in pelagic food webs. However, one possibility to ameliorate effects is to biotransform MC via glutathione S transferase (GST) to a less toxic glutathione conjugate. This process was hypothesised to underlie the ability of Daphnia to withstand MC and to explain the enhanced tolerance of the offspring from mothers exposed to toxic cyanobacteria. Thus we conducted multigenerational experiments with D. magna, exposing the parental generation to MC for 1 or 7 days and determining the enzyme-mediated tolerance to MC in their offspring by assessing the acute effect of MC on biotransformation and antioxidant and metabolism enzymes, and through 21 day chronic tests on toxicity and growth. Seven days of exposure of the parental generation to MC induced higher activity of GST and malate dehydrogenase in the offspring and enabled them to increment the catalase activity when challenged with MC, whereas 1 day of exposure of the parental generation did not. Offspring from non-exposed and 1-day-exposed mothers suffered decreased survival when exposed to MC compared with offspring from 7-day-exposed mothers; survival was correlated with the elevated activity of GST, malate dehydrogenase and catalase, suggesting maternal transfer of activation factors. However, increased survival occurred at the expense of individual growth. These results suggest that transgenerational effects are provoked by MC in D. magna, which may explain the observed acquirement of enhanced tolerance over generations.

Removal of algal blooms from freshwater by the coagulation–magnetic separation method

This research investigated the feasibility of changing waste into useful materials for water treatment and proposed a coagulation-magnetic separation technique. This technique was rapid and highly effective for clearing up harmful algal blooms in freshwater and mitigating lake eutrophication. A magnetic coagulant was synthesized by compounding acid-modified fly ash with magnetite (Fe(3)O(4)). Its removal effects on algal cells and dissolved organics in water were studied. After mixing, coagulation, and magnetic separation, the flocs obtained from the magnet surface were examined by SEM. Treated samples were withdrawn for the content determination of chlorophyll-a, turbidity, chemical oxygen demand (COD), total nitrogen, and total phosphorus. More than 99 % of algal cells were removed within 5 min after the addition of magnetic coagulant at optimal loadings (200 mg L(-1)). The removal efficiencies of COD, total nitrogen, and phosphorus were 93, 91, and 94 %, respectively. The mechanism of algal removal explored preliminarily showed that the magnetic coagulant played multiple roles in mesoporous adsorption, netting and bridging, as well as high magnetic responsiveness to a magnetic field. The magnetic-coagulation separation method can rapidly and effectively remove algae from water bodies and greatly mitigate eutrophication of freshwater using a new magnetic coagulant. The method has good performance, is low cost, can turn waste into something valuable, and provides reference and directions for future pilot and production scale-ups.