Seasonal variation and indirect monitoring of microcystin concentrations in Daechung reservoir, Korea

Microcystin Concentrations, Partitioning, and Structural Composition during Active Growth and Decline: A Laboratory Study

Microcystin can be present in variable concentrations, phases (dissolved and particulate), and structural forms (congeners), all which impact the toxicity and persistence of the algal metabolite. Conducting incubation experiments with six bloom assemblages collected from the Chowan River, North Carolina, we assessed microcystin dynamics during active growth and biomass degradation. Upon collection, average particulate and dissolved microcystin ranged between 0.2 and 993 µg L-1 and 0.5 and 3.6 µg L-1, respectively. The presence of congeners MC-LA, -LR, -RR, and -YR was confirmed with MC-RR and MC-LR being the most prevalent. Congener composition shifted over time and varied between dissolved and particulate phases. Particulate microcystin exponentially declined in five of six incubations with an average half-life of 10.2 ± 3.7 days, while dissolved microcystin remained detectable until the end of the incubation trials (up to 100 days). Our findings suggest that concerns about food-web transfer via intracellular toxins seem most warranted within the first few weeks of the bloom peak, while dissolved toxins linger for several months in the aftermath of the event. Also, it was indicated there were differences in congener profiles linked to the sampling method. We believe this study can inform monitoring strategies and aid microcystin-exposure risk assessments for cyanobacterial blooms.

Microcystis colony formation: Extracellular polymeric substance, associated microorganisms, and its application

Microcystis sp., amongst the most prevalent bloom-forming cyanobacteria, is typically found as a colonial form with multiple microorganisms embedded in the mucilage known as extracellular polymeric substance. The colony-forming ability of Microcystis has been thoroughly investigated, as has the connection between Microcystis and other microorganisms, which is crucial for colony development. The following are the key subjects to comprehend Microcystis bloom in depth: 1) key issues related to the Microcystis bloom, 2) features and functions of extracellular polymeric substance, as well as diversity of associated microorganisms, and 3) applications of Microcystis-microorganisms interaction including bloom control, polluted water bioremediation, and bioactive compound production. Future research possibilities and recommendations regarding Microcystis-microorganism interactions and their significance in Microcystis colony formation are also explored. More information on such interactions, as well as the mechanism of Microcystis colony formation, can bring new insights into cyanobacterial bloom regulation and a better understanding of the aquatic ecosystem.

Multi-class secondary metabolites in cyanobacterial blooms from a tropical water body: Distribution patterns and real-time prediction

Cyanobacterial blooms that produce toxins occur in freshwaters worldwide and yet, the occurrence and distribution patterns of many cyanobacterial secondary metabolites particularly in tropical regions are still not fully understood. Moreover, predictive models for these metabolites by using easily accessible water quality indicators are rarely discussed. In this study, we investigated the co-occurrence and spatiotemporal trends of 18 well-known and less-studied cyanobacterial metabolites (including [D-Asp3] microcystin-LR (DM-LR), [D-Asp3] microcystin-RR (DM-RR), microcystin-HilR (MC-HilR), microcystin-HtyR (MC-HtyR), microcystin-LA (MC-LA), microcystin-LF (MC-LF), microcystin-LR (MC-LR), microcystin-LW (MC-LW), microcystin-LY (MC-LY), microcystin-RR (MC-RR) and microcystin-WR (MC-WR), Anatoxin-a (ATX-a), homoanatoxin-a (HATX-a), cylindrospermospin (CYN), nodularin (NOD), anabaenopeptin A (AptA) and anabaenopeptin B (AptB)) in a tropical freshwater lake often plagued with blooms. Random forest (RF) models were developed to predict MCs and CYN and assess the relative importance of 22 potential predictors that determined their concentrations. The results showed that 11 MCs, CYN, ATX-a, HATX-a, AptA and AptB were found at least once in the studied water body, with MC-RR and CYN being the most frequently occurring, intracellularly and extracellularly. AptA and AptB were detected for the first time in tropical freshwaters at low concentrations. The metabolite profiles were highly variable at both temporal and spatial scales, in line with spatially different phytoplankton assemblages. Notably, MCs decreased with the increase of CYN, possibly revealing interspecific competition of cyanobacteria. The rapid RF prediction models for MCs and CYN were successfully developed using 4 identified drivers (i.e., chlorophyll-a, total carbon, rainfall and ammonium for MCs prediction; and chloride, total carbon, rainfall and nitrate for CYN prediction). The established models can help to better understand the potential relationships between cyanotoxins and environmental variables as well as provide useful information for making policy decisions.

Insight into Unprecedented Diversity of Cyanopeptides in Eutrophic Ponds Using an MS/MS Networking Approach

Man-made shallow fishponds in the Czech Republic have been facing high eutrophication since the 1950s. Anthropogenic eutrophication and feeding of fish have strongly affected the physicochemical properties of water and its aquatic community composition, leading to harmful algal bloom formation. In our current study, we characterized the phytoplankton community across three eutrophic ponds to assess the phytoplankton dynamics during the vegetation season. We microscopically identified and quantified 29 cyanobacterial taxa comprising non-toxigenic and toxigenic species. Further, a detailed cyanopeptides (CNPs) profiling was performed using molecular networking analysis of liquid chromatography-tandem mass spectrometry (LC-MS/MS) data coupled with a dereplication strategy. This MS networking approach, coupled with dereplication, on the online global natural product social networking (GNPS) web platform led us to putatively identify forty CNPs: fourteen anabaenopeptins, ten microcystins, five cyanopeptolins, six microginins, two cyanobactins, a dipeptide radiosumin, a cyclooctapeptide planktocyclin, and epidolastatin 12. We applied the binary logistic regression to estimate the CNPs producers by correlating the GNPS data with the species abundance. The usage of the GNPS web platform proved a valuable approach for the rapid and simultaneous detection of a large number of peptides and rapid risk assessments for harmful blooms.

Network analysis reveals succession of Microcystis genotypes accompanying distinctive microbial modules with recurrent patterns

Every member of the ecological community is connected via a network of vital and complex relationships, called the web of life. To elucidate the ecological network and interactions among producers, consumers, and decomposers in the Daechung Reservoir, Korea, during cyanobacterial harmful algal blooms (cyanoHAB), especially those involving Microcystis, we investigated the diversity and compositions of the cyanobacterial (16S rRNA gene), including the genotypes of Microcystis (cpcBA-IGS gene), non-cyanobacterial (16S), and eukaryotic (18S) communities through high-throughput sequencing. Microcystis blooms were divided into the Summer Major Bloom and Autumn Minor Bloom with different dominant genotypes of Microcystis. Network analysis demonstrated that the modules involved in the different phases of the Microcystis blooms were categorized into the Pre-Bloom, Bloom, Post-Bloom, and Non-Bloom Groups at all sampling stations. In addition, the non-cyanobacterial components of each Group were classified, while the same Group showed similarity across all stations, suggesting that Microcystis and other microbes were highly interdependent and organized into cyanoHAB-related module units. Importantly, the Microcystis genotype-based sub-network uncovered that Pirellula, Pseudanabaena, and Vampirovibrionales preferred to interact with specific Microcystis genotypes in the Summer Major Bloom than with other genotypes in the Autumn Minor Bloom, while the copepod Skistodiaptomus exhibited the opposite pattern. In conclusion, the transition patterns of cyanoHAB-related modules and their key components could be crucial in the succession of Microcystis genotypes and to enhance the understanding of microbial ecology in an aquatic environment.

Genomic and Metabolic Insights into Denitrification, Sulfur Oxidation, and Multidrug Efflux Pump Mechanisms in the Bacterium Rhodoferax sediminis sp. nov

This genus contains both phototrophs and nonphototrophic members. Here, we present a high-quality complete genome of the strain CHu59-6-5^T, isolated from a freshwater sediment. The circular chromosome (4.39 Mbp) of the strain CHu59-6-5^T has 64.4% G+C content and contains 4240 genes, of which a total of 3918 genes (92.4%) were functionally assigned to the COG (clusters of orthologous groups) database. Functional genes for denitrification (narGHJI, nirK and qnor) were identified on the genomes of the strain CHu59-6-5^T, except for N₂O reductase (nos) genes for the final step of denitrification. Genes (soxBXAZY) for encoding sulfur oxidation proteins were identified, and the FSD and soxF genes encoding the monomeric flavoproteins which have sulfide dehydrogenase activities were also detected. Lastly, genes for the assembly of two different RND (resistance-nodulation division) type efflux systems and one ABC (ATP-binding cassette) type efflux system were identified in the Rhodoferax sediminis CHu59-6-5^T. Phylogenetic analysis based on 16S rRNA sequences and Average Nucleotide Identities (ANI) support the idea that the strain CHu59-6-5^T has a close relationship to the genus Rhodoferax. A polyphasic study was done to establish the taxonomic status of the strain CHu59-6-5^T. Based on these data, we proposed that the isolate be classified to the genus Rhodoferax as Rhodoferax sediminis sp. nov. with isolate CHu59-6-5^T.

Ozonation of Microcystins: Kinetics and Toxicity Decrease

The ozonation of six microcystins (MCs) (MC-LR, MC-RR, MC-LA, MC-LF, MC-YR, and MC-LW) was investigated with a focus on the kinetics and decrease in toxicity. Second-order rate constants for the reactions of the six MCs with O₃ and ^•OH ( k_O3,MC and k_^•OH,MC) ranged from 7.1 × 10⁵ to 6.1 × 10⁶ M^-1 s^-1 ( k_O3,MC) and from 1.2 × 10¹⁰ to 1.8 × 10¹⁰ M^-1 s^-1 ( k_^•OH,MC), at pH 7.2 and 20 °C. The activation energies were calculated to be 21.6-34.5 and 11.6-13.1 kJ mol^-1 for k_O3,MC and k_^•OH,MC, respectively. The rate constants did not show an important pH dependency, except for k_O3,MC-YR, which increased at pH > 7. A kinetic model using the determined rate constants and the measured exposures of O₃ and ^•OH was able to precisely predict the removal of MCs in natural water. The hepatotoxicities of MCs were decreased by ozonation; the toxicities of the four MCs (MC-LR, MC-RR, MC-LA, and MC-LF) decreased nearly concurrently with decreases in their concentrations. However, MC-YR and MC-LW showed a gap between the concentration and toxicity as a result of the incomplete destruction of the Adda moiety (a key amino acid expressing the hepatotoxicity of MCs). A product study using liquid chromatography-mass spectrometry identified a number of oxidation products with an intact Adda moiety produced by the ozonation of MC-YR and MC-LW.

Adsorption of microcystin-LR onto kaolinite, illite and montmorillonite

In this study, microcystin-LR (MCLR) interactions with three representative silicate clays were studied using equilibrium batch experiments in order to provide insight into the role of clays on determining MCLR fate. The three tested clay minerals (kaolinite, montmorillonite and illite), saturated with sodium or calcium ions, were equilibrated with MCLR across a range of toxin concentrations at pH 5, 7 or 9. The results were fit to Freundlich and linear isotherm models, with the linear isotherm fits deemed most appropriate. In general, adsorption of MCLR was greater in the systems with Ca than in those with Na, however, regardless of the cation present, montmorillonite had the highest adsorption affinity for MCLR. Furthermore, except for Ca-montmorillonite, MCLR adsorption decreased with increasing pH. The pH-dependence of adsorption suggests the polar groups of MCLR, carboxylate associated with the glutamic acid and methylaspartic acid groups and amine associated with the arginine group, were more important in determining MCLR interactions with clays than the nonpolar ADDA group. Increased adsorption in systems enriched with calcium suggests Ca modified the clay interfacial properties and the availability of MCLR groups in a manner that increased MCLR affinity. Overall, the results suggest clays are capable of adsorbing MCLR from the aqueous phase, particularly at low pH and when saturated with Ca²⁺.

Spatiotemporal distribution and potential risk assessment of microcystins in the Yulin River, a tributary of the Three Gorges Reservoir, China

Microcystins (MCs) pose potential threat for both aquatic organisms and humans, whereas their occurrence in response to hydrodynamic alterations are not clearly understood. Here, spatiotemporal variations of dissolved MC-RR and MC-LR were evaluated monthly in 2016 in the Yulin River, a tributary of the Three Gorges Reservoir (TGR). The environmental factors that linked to MCs concentration were discussed. The results revealed that MC-RR maximumly reached 3.55 μg/L, and the maximum MC-LR concentration exceeded the threshold value of 1.0 μg/L recommended by the WHO. MCs concentrations were higher during the flood season and decreased from the estuary to the upstream reach of the Yulin River. Ecological risk assessment confirmed that MC-LR had significant adverse effects on the benthonic invertebrates Potamopyrgus antipodarum. MCs content in the sediment was 1.70- to 20-fold higher than that in suspended particulate matter (SPM). The impacts of environmental factors on the MCs profile differed between flood and dry seasons and the longitudinal differences of MCs were determined by the longitudinal profile of water velocity and SPM content, which were affected by TGR operations. This study suggested that the occurrence of MCs in the Yulin River were influenced by hydrologic regime in TGR.

Binary culture of microalgae as an integrated approach for enhanced biomass and metabolites productivity, wastewater treatment, and bioflocculation

Ecological studies of microalgae have revealed their potential to co-exist in the natural environment. It provides an evidence of the symbiotic relationship of microalgae with other microorganisms. The symbiosis potential of microalgae is inherited with distinct advantages, providing a venue for their scale-up applications. The deployment of large-scale microalgae applications is limited due to the technical challenges such as slow growth rate, low metabolites yield, and high risk of biomass contamination by unwanted bacteria. However, these challenges can be overcome by exploring symbiotic potential of microalgae. In a symbiotic system, photosynthetic microalgae co-exist with bacteria, fungi, as well as heterotrophic microalgae. In this consortium, they can exchange nutrients and metabolites, transfer gene, and interact with each other through complex metabolic mechanism. Microalgae in this system, termed as a binary culture, are reported to exhibit high growth rate, enhanced bio-flocculation, and biochemical productivity without experiencing contamination. Binary culture also offers interesting applications in other biotechnological processes including bioremediation, wastewater treatment, and production of high-value metabolites. The focus of the study is to provide a perspective to enhance the understanding about microalgae binary culture. In this review, the mechanism of binary culture, its potential, and limitations are briefly discussed. A number of queries are evolved through this study, which needs to be answered by executing future research to assess the real potential of binary culture.

Eutrophication, harmful algae and biodiversity - Challenging paradigms in a world of complex nutrient changes

Eutrophication is a complex process and often associated with not only a change in overall algal biomass but also with a change in biodiversity. Common metrics of eutrophication (e.g., chlorophyll a), total nitrogen (TN) and phosphorus (TP) are not adequate for understanding biodiversity changes, especially those associated with harmful algal bloom (HAB) proliferations. Harmful algae can increase disproportionately with eutrophication, depending on which nutrients change and in what proportion. This paper challenges several classic paradigms in our understanding of eutrophication and associated biodiversity changes. The underlying message is that nutrient proportions and forms can alter biodiversity, even when nutrients are at concentrations in excess of those considered limiting. The global HAB problem is on a trajectory for more blooms, more toxins, more often, in more places. Our approach to management of HABs and eutrophication must consider the broader complexity of nutrient effects at scales ranging from physiological to ecological.

Abundant iron and sulfur oxidizers in the stratified sediment of a eutrophic freshwater reservoir with annual cyanobacterial blooms

The microbial community in eutrophic freshwater sediment was investigated from a 67-cm-deep sediment core collected from the Daechung Reservoir in South Korea, where cyanobacterial blooms have occurred annually for the past 30 years. The majority of core sediments were characterized by dark-grayish, fine-grained mud with abundant gas-escaped and thinly laminated layers. Intervals of summer and winter seasons were represented by periodic peaks of geochemical profiles of parameters such as grain size and relative carbon mass ratios to various nutrients such as nitrogen, sulfur, and phosphorus. In bacteria, Proteobacteria (66.6%) was the most prevalent phylum, followed by Chloroflexi (8.9%), Bacteroidetes (5.1%), and Spirochaetes (2.6%). Archaea were also abundant, representing approximately half of the total prokaryotes in the sediments. Notably, three Bacteria (Sulfuricurvum, Sideroxydans, and Gallionella) and one Archaea (Thermoplasmata) accounted for 43.4% and 38.4% of the total bacteria and archaea, respectively, implying that iron and sulfur oxidizing microorganisms dominate in this eutrophic freshwater sediment. These results indicate that 1) eutrophic freshwater lakes in monsoon climates undergo a stratified sedimentary process with seasonal and annual variations in geochemical and microbial profiles, and 2) the microbial oxidative metabolism of iron and sulfur is notably active in sediments from a eutrophic lake.

Cyanobacterial Toxins in Freshwater and Food: Important Sources of Exposure to Humans

A recent ecological study demonstrated a significant association between an increased risk of nonalcoholic liver disease mortality and freshwater cyanobacterial blooms. Moreover, previous epidemiology studies highlighted a relationship between cyanotoxins in drinking water with liver cancer and damage and colorectal cancer. These associations identified cyanobacterial blooms as a global public health and environmental problem, affecting freshwater bodies that are important sources for drinking water, agriculture, and aquafarms. Furthermore, as a result of climate change, it is expected that our freshwater environments will become more favorable for producing harmful blooms that produce various cyanotoxins. Food is an important source of cyanotoxin exposure to humans, but it has been less addressed. This paper synthesizes information from the studies that have investigated cyanotoxins in freshwater and food on a global scale. We also review and summarize the health effects and exposure routes of cyanotoxins and candidates for cyanotoxin treatment methods that can be applied to food.

Impact of Microalgae-Bacteria Interactions on the Production of Algal Biomass and Associated Compounds

A greater insight on the control of the interactions between microalgae and other microorganisms, particularly bacteria, should be useful for enhancing the efficiency of microalgal biomass production and associated valuable compounds. Little attention has been paid to the controlled utilization of microalgae-bacteria consortia. However, the studies of microalgal-bacterial interactions have revealed a significant impact of the mutualistic or parasitic relationships on algal growth. The algal growth, for instance, has been shown to be enhanced by growth promoting factors produced by bacteria, such as indole-3-acetic acid. Vitamin B₁₂ produced by bacteria in algal cultures and bacterial siderophores are also known to be involved in promoting faster microalgal growth. More interestingly, enhancement in the intracellular levels of carbohydrates, lipids and pigments of microalgae coupled with algal growth stimulation has also been reported. In this sense, massive algal production might occur in the presence of bacteria, and microalgae-bacteria interactions can be beneficial to the massive production of microalgae and algal products. This manuscript reviews the recent knowledge on the impact of the microalgae-bacteria interactions on the production of microalgae and accumulation of valuable compounds, with an emphasis on algal species having application in aquaculture.

Algae-bacteria interactions: Evolution, ecology and emerging applications

Algae and bacteria have coexisted ever since the early stages of evolution. This coevolution has revolutionized life on earth in many aspects. Algae and bacteria together influence ecosystems as varied as deep seas to lichens and represent all conceivable modes of interactions - from mutualism to parasitism. Several studies have shown that algae and bacteria synergistically affect each other's physiology and metabolism, a classic case being algae-roseobacter interaction. These interactions are ubiquitous and define the primary productivity in most ecosystems. In recent years, algae have received much attention for industrial exploitation but their interaction with bacteria is often considered a contamination during commercialization. A few recent studies have shown that bacteria not only enhance algal growth but also help in flocculation, both essential processes in algal biotechnology. Hence, there is a need to understand these interactions from an evolutionary and ecological standpoint, and integrate this understanding for industrial use. Here we reflect on the diversity of such relationships and their associated mechanisms, as well as the habitats that they mutually influence. This review also outlines the role of these interactions in key evolutionary events such as endosymbiosis, besides their ecological role in biogeochemical cycles. Finally, we focus on extending such studies on algal-bacterial interactions to various environmental and bio-technological applications.

Long-Term Satellite Observations of Microcystin Concentrations in Lake Taihu during Cyanobacterial Bloom Periods

Microcystins (MCs) produced by cyanobacteria pose a serious threat to public health. Intelligence on MCs distributions in freshwater is therefore critical for environmental agencies, water authorities, and public health organizations. We developed and validated an empirical model to quantify MCs in Lake Taihu during cyanobacterial bloom periods using the atmospherically Rayleigh-corrected moderate resolution imaging spectroradiometer (MODIS-Aqua) (Rrc) products and in situ data by means of chlorophyll a concentrations (Chla). First, robust relationships were constructed between MCs and Chla (r = 0.91; p < 0.001; t-test) and between Chla and a spectral index derived from Rrc (r = -0.86; p < 0.05; t-test). Then, a regional algorithm to analyze MCs in Lake Taihu was constructed by combining the two relationships. The model was validated and then applied to an 11-year series of MODIS-Aqua data to investigate the spatial and temporal distributions of MCs. MCs in the lake were markedly variable both spatially and temporally. Cyanobacterial bloom scums, temperature, wind, and light conditions probably affected the temporal and spatial distribution of MCs in Lake Taihu. The findings demonstrate that remote sensing reconnaissance in conjunction with in situ monitoring can greatly aid MCs assessment in freshwater.

Long-term monitoring reveals carbon-nitrogen metabolism key to microcystin production in eutrophic lakes

The environmental drivers contributing to cyanobacterial dominance in aquatic systems have been extensively studied. However, understanding of toxic vs. non-toxic cyanobacterial population dynamics and the mechanisms regulating cyanotoxin production remain elusive, both physiologically and ecologically. One reason is the disconnect between laboratory and field-based studies. Here, we combined 3 years of temporal data, including microcystin (MC) concentrations, 16 years of long-term ecological research, and 10 years of molecular data to investigate the potential factors leading to the selection of toxic Microcystis and MC production. Our analysis revealed that nitrogen (N) speciation and inorganic carbon (C) availability might be important drivers of Microcystis population dynamics and that an imbalance in cellular C: N ratios may trigger MC production. More specifically, precipitous declines in ammonium concentrations lead to a transitional period of N stress, even in the presence of high nitrate concentrations, that we call the “toxic phase.” Following the toxic phase, temperature and cyanobacterial abundance remained elevated but MC concentrations drastically declined. Increases in ammonium due to lake turnover may have led to down regulation of MC synthesis or a shift in the community from toxic to non-toxic species. While total phosphorus (P) to total N ratios were relatively low over the time-series, MC concentrations were highest when total N to total P ratios were also highest. Similarly, high C: N ratios were also strongly correlated to the toxic phase. We propose a metabolic model that corroborates molecular studies and reflects our ecological observations that C and N metabolism may regulate MC production physiologically and ecologically. In particular, we hypothesize that an imbalance between 2-oxoglutarate and ammonium in the cell regulates MC synthesis in the environment.

Monitoring and removal of cyanobacterial toxins from drinking water by algal-activated carbon

Microcystins (MCs) are the most potent toxins that can be produced by cyanobacteria in drinking water supplies. This study investigated the abundance of toxin-producing algae in 11 drinking water treatment plants (DWTPs). A total of 26 different algal taxa were identified in treated water, from which 12% were blue green, 29% were green, and 59% were diatoms. MC levels maintained strong positive correlations with number of cyanophycean cells in raw and treated water of different DWTPs. Furthermore, the efficiency of various algal-based adsorbent columns used for the removal of these toxins was evaluated. The MCs was adsorbed in the following order: mixed algal-activated carbon (AAC) ≥ individual AAC > mixed algal powder > individual algal powder. The results showed that the AAC had the highest efficient columns capable of removing 100% dissolved MCs from drinking water samples, thereby offering an economically feasible technology for efficient removal and recovery of MCs in DWTPs.

Microcystin mcyA and mcyE Gene Abundances Are Not Appropriate Indicators of Microcystin Concentrations in Lakes

Cyanobacterial harmful algal blooms (cyanoHABs) are a primary source of water quality degradation in eutrophic lakes. The occurrence of cyanoHABs is ubiquitous and expected to increase with current climate and land use change scenarios. However, it is currently unknown what environmental parameters are important for indicating the presence of cyanoHAB toxins making them difficult to predict or even monitor on time-scales relevant to protecting public health. Using qPCR, we aimed to quantify genes within the microcystin operon (mcy) to determine which cyanobacterial taxa, and what percentage of the total cyanobacterial community, were responsible for microcystin production in four eutrophic lakes. We targeted Microcystis-16S, mcyA, and Microcystis, Planktothrix, and Anabaena-specific mcyE genes. We also measured microcystins and several biological, chemical, and physical parameters--such as temperature, lake stability, nutrients, pigments and cyanobacterial community composition (CCC)--to search for possible correlations to gene copy abundance and MC production. All four lakes contained Microcystis-mcyE genes and high percentages of toxic Microcystis, suggesting Microcystis was the dominant microcystin producer. However, all genes were highly variable temporally, and in few cases, correlated with increased temperature and nutrients as the summer progressed. Interestingly, toxin gene abundances (and biomass indicators) were anti-correlated with microcystin in all lakes except the largest lake, Lake Mendota. Similarly, gene abundance and microcystins differentially correlated to CCC in all lakes. Thus, we conclude that the presence of microcystin genes are not a useful tool for eliciting an ecological role for toxins in the environment, nor are microcystin genes (e.g. DNA) a good indicator of toxins in the environment.

The establishment of preliminary safety threshold values for cyanobacteria based on periodic variations in different microcystin congeners in Lake Chaohu, China

As harmful cyanobacterial proliferation threatens the safety of drinking water supplies worldwide, it is essential to establish a safety threshold (ST) for cyanobacteria to control cyanobacterial density effectively in water sources. For this purpose, cyanobacterial abundance, microcystin (MC) production, and environmental parameters were monitored monthly from September 2011 to August 2012 in one drinking water source of Lake Chaohu. The cyanobacterial density ranged from 1400 to 220 000 cells per mL with the succession of two dominant species Microcystis and Dolichospermum, which was determined by water temperature and nutrient loading. The MC concentrations were correlated significantly with the cyanobacterial density and they varied between 0.28 and 8.86 μg L(-1). Therefore, the characteristics of MC cell quotas were classified according to four stages of the development of cyanobacteria, namely: recruitment, multiplication, decline and dormancy. The ST for cyanobacteria was established for different periods based on the MC cell quota and its guideline wherein three commonly monitored MC congeners (MC-LR, -RR and -YR) were considered in the present study. Its reliability was verified in the water source using the data collected between June 2013 and May 2014. The results highlighted the necessity to classify the ST-values in different periods referring to the main MC congeners rather than MC-LR, which will facilitate the management and control of toxic cyanobacterial proliferation in drinking water sources.

Status, alert system, and prediction of cyanobacterial bloom in South Korea

Bloom-forming freshwater cyanobacterial genera pose a major ecological problem due to their ability to produce toxins and other bioactive compounds, which can have important implications in illnesses of humans and livestock. Cyanobacteria such as Microcystis, Anabaena, Oscillatoria, Phormidium, and Aphanizomenon species producing microcystins and anatoxin-a have been predominantly documented from most South Korean lakes and reservoirs. With the increase in frequency of such blooms, various monitoring approaches, treatment processes, and prediction models have been developed in due course. In this paper we review the field studies and current knowledge on toxin producing cyanobacterial species and ecological variables that regulate toxin production and bloom formation in major rivers (Han, Geum, Nakdong, and Yeongsan) and reservoirs in South Korea. In addition, development of new, fast, and high-throughput techniques for effective monitoring is also discussed with cyanobacterial bloom advisory practices, current management strategies, and their implications in South Korean freshwater bodies.

Temporal variations in microcystin-producing cells and microcystin concentrations in two fresh water ponds

The relationship between microcystin production, microcystin-producing cyanobacteria, including Microcystis spp., and various biological and physicochemical parameters in Sankuldhara and Lakshmikund, situated in the same geographical area was studied over a period of 1.5 years. Seasonal variation in cyanobacterial 16S rRNA, Microcystis spp. 16S rRNA, mcyA and mcyB genes were quantitatively determined by real-time PCR. Microcystis was the dominant microcystin producer in both study sites constituting 67% and 97% of the total microcystin-producing cyanobacteria at Sankuldhara and Lakshmikund, respectively. Microcystin concentrations were 2.19-39.60 μg/L and 15.22-128.14 μg/L at Sankuldhara and Lakshmikund, respectively, as determined by LC-MS. Principal component analysis revealed a strong positive correlation between microcystin concentration and the copy number of mcyA and mcyB, chlorophyll a and cyanobacterial biomass at both sites. The higher microcystin concentrations in Lakshmikund pond were attributed to the high copy number of mcy genes present coupled with the pond's eutrophication status, as indicated by high total algal biomass, high chlorophyll a content, high nutrient load and low DO. Therefore, a significant difference in microcystin concentrations, correlating with these various biological and physicochemical parameters, confirms the importance of local environmental variables in the overall regulation of microcystins production.

Temporal distribution of cyanobacteria in the coast of a shallow temperate estuary (Río de la Plata): some implications for its monitoring

The aim of this study was to analyze the temporal distribution of phytoplanktonic cyanobacteria in a site located in the freshwater tidal zone near the extraction point for the drinking water supply. Samples were taken considering three timescales as follows: hours, days, and weeks, during the period of highest development of cyanobacteria. The phytoplankton density, microcystin concentration (LR, RR, YR), and chlorophyll-a were related to meteorological variables (wind and temperature), tidal high, and physical-chemical variables (nutrients, pH, conductivity, light penetration). The results obtained in this study showed that the variables that primarily modulate the temporal distribution of cyanobacteria were temperature, pH, light penetration, conductivity, and nutrients (particularly NO3 (-) and NH4 (+)), while the winds and tide had a secondary effect, only evidenced at an hourly scale. Therefore, this timescale would be the most suitable for monitoring cyanobacterial populations, when the amount of cyanobacterial cells exceeds the alert I level proposed by the World Health Organization. This recommendation is particularly important for the water intake zones in Río de la Plata, which are vulnerable to the damage generated by cyanobacteria on the water quality.

Nitrogen availability increases the toxin quota of a harmful cyanobacterium, Microcystis aeruginosa

An important objective in understanding harmful phytoplankton blooms is determining how environmental factors influence the toxicity of bloom-forming species. We examined how nutrients and grazers (dreissenid mussels) affect the production of microcystin (a liver toxin) by the cyanobacterium Microcystis aeruginosa, via a combination of field and laboratory experiments, and field observations in Lake Erie. The field experiment revealed no effect of mussel density on microcystin quota (particulate microcystin per unit Microcystis biomass). In contrast, in both field and laboratory experiments, nitrogen-limited conditions led to substantially reduced microcystin quota relative to phosphorus-limited or nutrient-saturated conditions. In the field experiment, microcystin per unit of mcyB gene was strongly reduced under nitrogen-limited conditions, indicating a phenotypic response. Results from a seasonal survey in the western basin of Lake Erie revealed a similar negative influence of nitrogen limitation (as indexed by nitrate concentration) on microcystin quota. Our results are consistent with stoichiometric considerations in that the cell quota of a nitrogen-rich secondary metabolite, microcystin, was reduced disproportionately under nitrogen limitation.

Sphingomonas daechungensis sp. nov., isolated from sediment of a eutrophic reservoir

Strain CH15-11T, isolated from a sediment sample taken from Daechung Reservoir, South Korea, during the late-blooming period of cyanobacteria, was found to be a Gram-stain-negative, non-motile, non-spore-forming, rod-shaped and aerobic bacterium. Strain CH15-11T grew optimally at pH 7 and 28–30 °C. According to a phylogenetic tree based on 16S rRNA gene sequences, strain CH15-11T belonged to the genus Sphingomonas and clustered with Sphingomonas sediminicola Dae 20T, with which it shared the highest 16S rRNA gene sequence similarity (97.6 %). Chemotaxonomic analysis showed that strain CH15-11T had characteristics typical of members of the genus Sphingomonas , such as the presence of sphingoglycolipid, ubiquinone Q-10 and sym-homospermidine. Plus, strain CH15-11T included summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) and C16 : 0 as the major fatty acids. The genomic DNA G+C content was 65.6 mol%. Sequence data showed that strain CH15-11T was most closely related to Sphingomonas sediminicola Dae 20T (97.6 %), Sphingomonas ginsengisoli Gsoil 634T (97.2 %) and Sphingomonas jaspi TDMA-16T (97.0 %). However, the DNA–DNA relatedness values between strain CH15-11T and the most closely related type strains were within a range of 35–59 %. Thus, based on the phylogenetic, phenotypic and genetic data, strain CH15-11T was classified as a member of the genus Sphingomonas as a representative of a novel species, for which the name Sphingomonas daechungensis sp. nov. is proposed. The type strain is CH15-11T ( = KCTC 23718T = JCM 17887T).

Early physiological and biochemical responses of rice seedlings to low concentration of microcystin-LR

Microcystin-leucine and arginine (microcystin-LR) is a cyanotoxin produced by cyanobacteria like Microcystis aeruginosa, and it's considered a threat to water quality, agriculture, and human health. Rice (Oryza sativa) is a plant of great importance in human food consumption and economy, with extensive use around the world. It is therefore important to assess the possible effects of using water contaminated with microcystin-LR to irrigate rice crops, in order to ensure a safe, high quality product to consumers. In this study, 12 and 20-day-old plants were exposed during 2 or 7 days to a M. aeruginosa extract containing environmentally relevant microcystin-LR concentrations, 0.26-78 μg/L. Fresh and dry weight of roots and leaves, chlorophyll fluorescence, glutathione S-transferase and glutathione peroxidase activities, and protein identification by mass spectrometry through two-dimensional gel electrophoresis from root and leaf tissues, were evaluated in order to gauge the plant's physiological condition and biochemical response after toxin exposure. Results obtained from plant biomass, chlorophyll fluorescence, and enzyme activity assays showed no significant differences between control and treatment groups. However, proteomics data indicates that plants respond to M. aeruginosa extract containing environmentally relevant microcystin-LR concentrations by changing their metabolism, responding differently to different toxin concentrations. Biological processes most affected were related to protein folding and stress response, protein biosynthesis, cell signalling and gene expression regulation, and energy and carbohydrate metabolism which may denote a toxic effect induced by M. aeruginosa extract and microcystin-LR. The implications of the metabolic alterations in plant physiology and growth require further elucidation.

In situ studies on growth, oxidative stress responses, and gene expression of juvenile bighead carp (Hypophthalmichthys nobilis) to eutrophic lake water dominated by cyanobacterial blooms

Cyanobacterial blooms have received increasing attention as a public biohazard for human and animal health. To assess the effect of cyanobacteria-dominant lake water on juvenile fish, we measured the responses of specific growth rate, condition factor, body weight and body length, oxidative stress, and related gene expression of juvenile bighead carp Hypophthalmichthys nobilis exposed to in situ eutrophic lake (Chl a was around 7.0μgL(-1)). Results showed in situ cyanobacteria-dominant lake water had no effect on the growth performance, but significantly elevated the contents of malondialdehyde, the expression of heat shock protein 70, and the activity of superoxide dismutase, indicating that oxidative stress occurred. Meanwhile in situ lake water significantly decreased the expression of catalase and glutathione S-transferase genes. We conclude that in situ cyanobacteria-dominated lake water was harmful to juvenile bighead carp based on the oxidative stress and changes in the related gene expression levels.

Monitoring approaches for a toxic cyanobacterial bloom

Cyanobacterial blooms, dominated by Microcystis sp. and associated microcystin variants, have been implicated in illnesses of humans and animals. Little is known regarding the formation of blooms and the presence of cyanotoxin variants in water bodies. Furthermore, the role played by ecological parameters, in regulating Microcystis blooms is complicate and diverse. Local authorities responsible for water management are often faced with the challenging task of dealing with cyanobacterial blooms. Therefore, the development of suitable monitoring approaches to characterize cyanobacterial blooms is an important goal. Currently, various biological, biochemical and physicochemical methods/approaches are being used to monitor cyanobacterial blooms and detect microcystins in freshwater bodies. Because these methods can vary as to the information they provide, no single approach seemed to be sufficient to accurately monitor blooms. For example, immunosensors are more suited for monitoring the presence of toxins in clear water bodies while molecular methods are more suited to detect potentially toxic strains. Thus, monitoring approaches should be tailored for specific water bodies using methods based on economic feasibility, speed, sensitivity and field applicability. This review critically evaluates monitoring approaches that are applicable to cyanobacterial blooms, especially those that focus on the presence of Microcystis, in freshwater bodies. Further, they were characterized and ranked according to their cost, speed, sensitivity and selectivity. Suggested improvements were offered as well as future research endeavors to accommodate anticipated environmental changes.

Dissolved microcystins in surface and ground waters in regions with high cancer incidence in the Huai River Basin of China

Microcystins (MCs) are potent hepatotoxins and have also implicated in liver tumor promotion. The present study investigates the temporal and spatial variations of MCs in different water bodies in the Huai River Basin in China. Water samples including rivers, ponds and wells were collected every quarter during December 2008 and December 2009. MCs were determined by high pressure liquid chromatography after solid phase extraction. MCs concentrations in river samples were 0.741±0.623μgL(-1) with maximum of 1.846μgL(-1). MCs in pond were 0.597±0.960μgL(-1) with maximum of 2.298μgL(-1). MCs were also detected in 51.7% of the groundwater samples, MCs in groundwater were 0.060±0.085μgL(-1) with maximum of 0.446μgL(-1). MCs concentrations in groundwater did not differ significantly among different depths or towns (Wilcoxon test, p>0.05). The average MCs in groundwater in each sampling period were 0.068μgL(-1), 0.118μgL(-1), 0.052μgL(-1), 0.059μgL(-1) and 0.020μgL(-1). Through multi linear regression, the best fit model was built on MCs in groundwater with River B (R(2)=0.13, p<0.05), rather than with pond water. The results suggested that MCs contamination in groundwater originated from rivers, causing potential health risk on population who drink groundwater directly.

The role of nitrogen fixation in cyanobacterial bloom toxicity in a temperate, eutrophic lake

Toxic cyanobacterial blooms threaten freshwaters worldwide but have proven difficult to predict because the mechanisms of bloom formation and toxin production are unknown, especially on weekly time scales. Water quality management continues to focus on aggregated metrics, such as chlorophyll and total nutrients, which may not be sufficient to explain complex community changes and functions such as toxin production. For example, nitrogen (N) speciation and cycling play an important role, on daily time scales, in shaping cyanobacterial communities because declining N has been shown to select for N fixers. In addition, subsequent N pulses from N₂ fixation may stimulate and sustain toxic cyanobacterial growth. Herein, we describe how rapid early summer declines in N followed by bursts of N fixation have shaped cyanobacterial communities in a eutrophic lake (Lake Mendota, Wisconsin, USA), possibly driving toxic Microcystis blooms throughout the growing season. On weekly time scales in 2010 and 2011, we monitored the cyanobacterial community in a eutrophic lake using the phycocyanin intergenic spacer (PC-IGS) region to determine population dynamics. In parallel, we measured microcystin concentrations, N₂ fixation rates, and potential environmental drivers that contribute to structuring the community. In both years, cyanobacterial community change was strongly correlated with dissolved inorganic nitrogen (DIN) concentrations, and Aphanizomenon and Microcystis alternated dominance throughout the pre-toxic, toxic, and post-toxic phases of the lake. Microcystin concentrations increased a few days after the first significant N₂ fixation rates were observed. Then, following large early summer N₂ fixation events, Microcystis increased and became most abundant. Maximum microcystin concentrations coincided with Microcystis dominance. In both years, DIN concentrations dropped again in late summer, and N₂ fixation rates and Aphanizomenon abundance increased before the lake mixed in the fall. Estimated N inputs from N₂ fixation were large enough to supplement, or even support, the toxic Microcystis blooms.

Analysis of factors affecting the ratio of microcystin to chlorophyll-a in cyanobacterial blooms using real-time polymerase chain reaction

Chlorophyll-a concentration has been used as an indicator to estimate microcystin levels in water bodies. This study examined the microcystin to chlorophyll-a ratio in a fishpond in Japan. The ratio varied spatially and temporally during the six-month field survey, which is consistent with reports by other researchers. We investigated the causes of the variability of the ratio by quantifying microcystin synthetase (mcy) A gene with real-time PCR, so as to observe the growth of microcystin-producing cyanobacteria and Microcystis strains in natural cyanobacterial blooms. The application of real-time PCR enabled corroboration of the relationship between the toxigenicity and the toxicity of the blooms. The microcystin to chlorophyll-a ratio was influenced by the combined effects of the durability of the toxic bloom, and the quantity of microcystin-producing cyanobacteria carrying the mcy A gene, especially toxic Microcystis strains. Cyanobacterial blooms produced more microcystin when high concentrations of microcystin-producing Microcystis aggregated in a stationary state with low growth rates. The variable toxicity of blooms needs to be reflected in accurate and efficient alert systems for toxic cyanobacteria and cyanotoxins.

Temporal variation in density and diversity of cyanobacteria and cyanotoxins in lakes at Nagpur (Maharashtra State), India

Toxic cyanobacteria (TCB) are known worldwide for the adverse impacts on humans and animals. Species composition and the seasonal variation of TCB in water bodies depend on interactions between physical and chemical factors. The present investigation delineates temporal variations in physico-chemical water quality parameters, viz. nutrients and density, diversity, and distribution of toxic cyanobacteria and cyanotoxins in Lake Ambazari (21 degrees 7'52''N, 79 degrees 2'22''E) and Lake Phutala (21 degrees 9'18''N, 79 degrees 2'37''E) at Nagpur (Maharashtra State), India. These lakes are important sources of recreational activities and fisheries. Toxic cyanobacterial diversity comprised Anabaena, Oscillatoria, Lyngbya, Phormidium, and Microcystis, a well-known toxic cyanobacterial genus, as dominant. Chlorophyll-a concentrations in the lakes ranged from 1.44 to 71.74 mg/m(3). A positive correlation of Microcystis biomass existed with orthophosphate-P (p < 0.05) and nitrate-N (p > 0.05). Identification and quantification of microcystin variants were carried out by high performance liquid chromatography equipped with photodiode array detector. Among all the tested toxin variants, microcystin-RR (arginine-arginine) was consistently recorded and exhibited a positive correlation (p < 0.05) with Microcystis in both the water bodies. Microcystis bloom formation was remarkable between post-monsoon and summer. Besides nutrient concentrations governing bloom formation, the allelopathic role of microcystins needs to be established.

Natural photodegradation of the cyanobacterial toxins microcystin and cylindrospermopsin

Microcystins (MC) and cylindrospermopsin (CYN) are potent toxins produced by diverse cyanobacterial genera found in waterbodies throughout the world. In the present study, and in order to achieve a better understanding of the fate of cyanobacterial toxins in the environment, we assessed the photodegradation of MC and CYN along the water column and by different radiation bands of the natural solar spectrum: photosynthetic active radiation (PAR), UV-A, and UV-B. Photodegradation of CYN seemed to be highly dependent on UV-A and was very low under natural conditions. This fact could be one of the reasons explaining the high extracellular CYN concentration found in diverse waterbodies. Microcystin photodegradation was higher, all three radiation bands (PAR, UV-A, and UV-B) being responsible for its degradation, although PAR and UV-A were more efficient because of their high natural irradiance. Modeling of MC photodegradation along the watercolumn was performed, using specific MC breakdown rates for the different radiation bands and including calculated attenuation coefficients for these bands. As a result, we suggest that rapid and efficient MC photodegradation may be expected in shallow systems or thin mixed layers.

Quantification of toxic Microcystis and evaluation of its dominance ratio in blooms using real-time PCR

Microcystins are produced by cyanobacteria carrying microcystin synthetase (mcy) genes in blooms. The present study investigated seasonal variations in concentrations of mcy A and 16S rRNA genes, encoded in the genus Microcystis using real-time PCR, and measured the water quality variables and microcystin concentrations in a hypereutrophic fish pond between June and November 2007. Prior to field survey, the relationship between axenic Microcystis aeruginosa NIES 102 cell abundance and concentrations of mcy A and 16S rRNA genes was determined by real-time PCR in the laboratory. Based on the quantitative relationship, microcystin-producing and total Microcystis cell numbers in the study site were estimated. The average dominance ratio of microcystin-producing strains in the total Microcystis population was approximately 80% and microcystin concentration was highly associated with toxic Microcystis cell numbers equivalent of mcy A gene. It was also observed that total nitrogen concentration was associated with development of Microcystis blooms, and high concentrations of NOx and NH4 increased microcystin production by promoting growth of microcystin-producing Microcystis strains.

Seasonal variations in microcystin concentrations in Lake Taihu, China

An enzyme-limited immunosorbent assay (ELISA) was used to monitor spatial and temporal variation of microcystins (MCs) in Lake Taihu. MC concentrations were higher in summer and autumn than in other seasons. Maximal MC concentration was 15.6 microg L(-1). Compared to central Lake Taihu and Wuli Bay, Meiliang Bay had higher MC concentrations due to high biomass of Microcystis.

Topology and enhanced toxicity of bound microcystins in Microcystis PCC 7806

The cyanobacterium Microcystis is a potent producer of microcystins and cyanopeptolins and causes most of the toxicity outbreaks in freshwaters worldwide. Microcystins are mainly stored in the cells and little is found in the water. The intracellular concentration of microcystins in Microcystis PCC 7806 was at least 0.9 mM, although the solubility of microcystins in water was only about 10 microM. This low solubility does not allow the solubilisation of such high amounts of microcystins in the cytosol of Microcystis. Differential fractionation of cell constituents showed that microcystins and cyanopeptolins were bound to a protein fraction primarily composed of phycobilins. The percentage of microcystins and cyanopeptolins found in the thylakoid membranes was very low. Phycobilins may be the major proteins that have binding sites for these oligopeptides. A molar ratio near to 6 was observed for microcystins to the phycobilin (alphabeta) monomer. The binding of the microcystins to the protein was rather weak and allowed rapid dissociation of microcystins from the protein-matrix. Toxicity assays with Thamnocephalus platyurus showed that native microcystin when still bound to cyanobacterial protein was more toxic than an equivalent amount that has been desorbed from the protein by treatment with methanol. It is suggested that phycobilins serve in the gut of grazers as carrier molecules for the rapid transport of microcystin from lysed cells of Microcystis to the epithelium where the uptake of microcystins occurs. Because protein-bound microcystin does not bind to C18 cartridges, this behaviour can be the cause of many analytical discrepancies observed. The blue-coloured water observed upon the collapse of Microcystis blooms may be extremely toxic because the released phycobilins may carry the major fraction of microcystins.

Rapid Analytical Detection of Microcystins Using Gold Colloidal Immunochromatographic Strip

Routine monitoring of microcystin in natural waters is difficult because the concentration of the toxin is low and the detection method is usually complicated. We developed a rapid analytical detection method of microcystins gold colloidal immunochromatogeraphic strip. The sensitivity of the strip is about 1 ng/mL for microcystin LR; it is able to distinguish visually among different concentrations of microcystin solutions. The developed gold colloidal strip can detect microcystins within 15 min and does not require either a complicated extraction system, or trained or qualified experts.

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.

Determination of cyanobacterial diversity during algal blooms in Daechung Reservoir, Korea, on the basis of cpcBA intergenic spacer region analysis

The detection and prevention of cyanobacterial blooms are important issues in water quality management. As such, the diversity and community dynamics of cyanobacteria during cyanobacterial bloom in the Daechung Reservoir, Korea, were studied by analyzing the intergenic spacer (IGS) region between phycocyanin subunit genes cpcB and cpcA (cpcBA IGS). To amplify the cpcBA IGS from environmental samples, new PCR primers that could cover a wider range of cyanobacteria than previously known primers were designed. In the samples taken around the bloom peak (2 September 2003), seven groups of cpcBA IGS sequences were detected, and none of the amplified cpcBA IGSs was closely related to the cpcBA IGS from chloroplasts. Apart from the Microcystis-, Aphanizomenon (Anabaena)-, Pseudanabaena-, and Planktothrix (Oscillatoria)-like groups, the three other groups of cpcBA IGS sequences were only distantly related to previously reported sequences (<85% similarity to their closest relatives). The most prominent changes during the bloom were the gradual decrease and eventual disappearance of the Aphanizomenon (Anabaena)-like group before the bloom peak and the gradual increase and sudden disappearance of Planktothrix (Oscillatoria)-like groups right after the bloom peak. The community succession profile obtained based on the cpcBA IGS analysis was also supported by a PCR-denaturing gradient gel electrophoresis analysis of the 16S rRNA genes.

Occurrence of toxic blue-green algae in the Kucukcekmece lagoon (Istanbul, Turkey)

The concentration of microcystin (MC) in the Kucukcekmece Lagoon, Istanbul, Turkey, and the physicochemical and biological parameters of water quality were investigated from October 2000 to June 2003. Water samples were collected from surface waters at three sites. Most bloom samples were dominated by Microcystis aeruginosa. The major microcystin variants detected by HPLC-PDA were microcystin-YR and microcystin-LR. Microcystin concentration increased dramatically from early summer to early autumn and thereafter tended to decrease. The toxin concentration found in the filtered samples from surface waters varied between 0.06 and 24.2 microg L(-1) microcystin-LR equivalents. Each year extensive fish mortality was recorded between mid-June and early October, coinciding with heavy algal blooms. A comparison of the conditions associated with cyanotoxin episodes in 2000, 2001, and 2002 showed that the microcystin increase was related to temperature, high concentration of dissolved nutrients, high light intensity (PAR). The highest MC concentrations were recorded at temperatures between 24 degrees C and 28.5 degrees C. Field data showed that the highest MC concentration (>3 microg L(-1)) and the highest cyanobacterial biomass (>30 mg L(-1)) corresponded to a total nitrogen:total phosphorus ratio greater than 7:1. The highest concentrations of M. aeruginosa biomass (173 mg L(-1)) and MC (24.2 microg L(-1) MC-LR equiv.) and the highest salinity (8.8%) were measured concurrently in the lagoon. To our knowledge, this is the first evidence of cyanobacterial toxins in the Kucukcekmece Lagoon.