Spatial and temporal diversity of microcystins and microcystin-producing genotypes in Oneida Lake, NY

Oneida Lake is a shallow, eutrophic lake with a well-established cyanobacterial population with reported toxic blooms containing hepatotoxic microcystins (MC). Peak bloom events from the summers of 2002 and 2003 were analyzed to determine the principal cyanobacterial genera containing microcystin synthetase (mcy) genes. Sequence analysis of a partial mcyA amplicon targeting Microcystis, Anabaena and Planktothrix sp. indicated that Microcystis sp. was the dominant mcy genotype. This Microcystis clade was split into two distinct sub-clades. Bloom events contained members of both sub-clades with the higher MC concentrations found when both sub-clades were present in near equal proportions. The proportion of Microcystis containing the mcyD gene ranged from 0 to 37% of the total Microcystis population as determined by quantitative PCR (qPCR). The total concentration of Microcystis containing mcyD genes was linearly related to the concentration of MCs (r² = 0.63). The relationship between mcy genotype and physiochemical variables was examined to determine the factor(s) controlling the periodicity in MC production in Oneida Lake. Multivariate statistical analyses, used to correlate the continuous-response variables, revealed a strong relationship between chlorophyll a, MCs and total Microcystis.     

The Stream Inlet to a Shallow Bay of a Drinking Water Reservoir,a ‘Hot‐Spot’ for Microcystis Blooms Initiation

Stream inlets into shallow bays of reservoirs and lakes may be ‘hot‐spots’ for toxic cyanobacterial bloom initiation. These ‘hot‐spots’ may be connected with the permanent inflow of high nutrient concentrations from the catchment, optimal physical conditions (wind protected areas) that occur in shallow areas and/or ineffective top‐down control. Four sampling sites along a transect from stream to reservoir in a shallow bay of Sulejow Reservoir (Poland) were studied to test the above hypothesis, comprising a transition zone between lotic and pelagic habitats. Investigations showed that stream inlet into shallow bay acted as incubator for Microcystis blooms. The nutrient level, especially phosphorus, was identified as the major cause of cyanobacterial bloom growth. The increase of Microcystis biomass strongly correlated with increasing microcystin concentrations, however, a relationship with microcystin content was not observed. Toxicity of bloom demonstrated seasonal variability, reaching its maximum at the initial phase of bloom. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A Field Study to Investigate Environmental Factors that Could Effect Microcystin Synthesis of a Microcystis Population in the Bautzen Reservoir

Toxicity of Microcystis blooms to warm-blooded animals generated by microcystins has bew reported world wide. The ecological relevance of microcystin production for cyanobacteria remains unknown. The microcystin concentration in Microcystis blooms occurring in the Bautzen reservoir Was investigated. The microcystin content of samples were determined by HPLC and ranged from undetectabel to 14.7 μg mg⁻¹. Various chemical and physical parameters were monitored at the same time as Microcystis sampling, however, there was no correlation between these parameters and microcystin dynamics. The spatial distribution of microcystin in the Microcystis population was investigated once and showed no difference between samples taken at five stations. The microcystin concentration in ihc cell free water from the reservoir was below the detection threshold (< 1 μg L⁻¹). Size dependent Fractions of the Microcystis population analyzed for microcystin concentration correlated with colony sim. In the small fraction (>30 <66 μm) microcystin was not detected. In the medium fraction (> 6 h < 100μm) lower microcystin concentrations were detected than in large fraction (>100μm) in which the highest microcystin concentrations were found.     

Molecular confirmation of Planktothrix rubescens as the cause of intense,microcystin—Synthesizing cyanobacterial bloom in Lake Ziros,Greece

Cyanobacterial blooms occur increasingly often and raise ecological concerns worldwide. In Mediterranean freshwater ecosystems algal blooms are commonly attributed to Microcystis, Anabaena, and Aphanizomenon genera while Planktothrix is the most common bloom forming cyanobacterium in deep Northern and prealpine European oligotrophic to mesotrophic lakes. In the framework of an undertaken study of cyanobacterial species in lakes of Northwestern Greece we investigated the cyanobacterial diversity in Lake Ziros throughout a 15-month period (January 2006–March 2007) by using molecular methods. Surprisingly, a severe cyanobacterial bloom occurred during the study period, which upon microscopic examination and detailed molecular characterization found to be caused by Planktothrix rubescens species. The appearance of P. rubescens from November 2006 coincided with poor cyanobacterial diversity and resulted in a thick epilimnetic bloom in March 2007 (3.1 × 10⁸ cells/l and microcystin concentration 199 μg/l). Genotype composition of the total cyanobacterial community of the lake was analyzed by using denaturing gradient gel electrophoresis (DGGE) profiling of the intergenic transcribed spacer region of the rnn operon (rRNA-ITS). A P. rubescens strain closely related to Kpr strain from Lake Klinckenberg, The Netherlands, was found to dominate. The importance of this observation is expanded by the fact that microcystin concentrations recorded in Lake Ziros were the highest measured ever in Greek aquatic ecosystems examined so far and also found amongst the highest recorded worldwide.     

Stability of toxigenic Microcystis blooms

This is the first detailed study on the occurrence of cyanobacterial toxins in India, where we studied five eutrophic, temple ponds in the vicinity of Varanasi city, Uttar Pradesh, which continuously supported blooms of Microcystis sp. for several years. Bloom material from all five ponds was sampled bi-monthly from September 2003 to August 2004. Analysis of extracts by high-performance liquid chromatography (HPLC) indicated that microcystin-RR (MC-RR) was present all year round at high concentrations (311–1540 μg/g, dry weight), posing a significant health hazard especially since all five ponds are widely used for bathing, washing, cattle drinking supply, irrigation and recreation. In addition, there was unusually low temporal variation in concentration of MC-RR in each pond, <20% variation in four out of five ponds throughout the year.Characterization of microcystin composition of several bloom samples from this study by HPLC–PDA/MS confirmed that additional microcystins were present in many of the samples. The rarely reported, MC-AR was frequently detected in bloom samples from three of the ponds (Adityanagar, Durgakund and Sankuldhara), where it typically represented 20% of the microcystin pool. MC-WR was frequently found in samples from Adityanagar and Sankuldhara, representing 5–10% of the microcystin pool. MC-LR, along with the previously unreported MC-AHar, each represented approximately 5% of the microcystin pool when present. Bloom samples from each pond had a characteristic microcystin profile, when sampled from 2003 to 2006, suggesting persistent species/strain domination.The perennial and consistent nature of the toxic Microcystis blooms in these ponds is highly unusual, in contrast to the commonly encountered temporal and spatial variation of toxigenic and non-toxigenic species. Laboratory isolates from several ponds were shown to produce microcystins, showing similar microcystin composition to the original bloom material.     

Grazing on toxic cyanobacterial blooms by tadpoles of edible frog Rana grylio

Tadpoles of Rana grylio were raised as edible frogs in fishponds of Guanqiao in Wuhan City, Hubei, China, during cyanobacterial blooms from June to October. The dominant cyanobacterial species was Microcystis, which was found to be lethally toxic by intraperitoneal (i.p.) mouse bioassay. Little is known about the effect of tadpoles on toxic cyanobacterial blooms. To evaluate the potential of the tadpoles to graze on cyanobacterial blooms, the tadpoles were fed on Microcystis collected from the field in the laboratory. The Microcystis cells decreased from 1.19 × 10⁷ cells mL^?1 to 3.23 × 10⁶ cells mL^?1, with a sharp reduction of 73% of the initial Microcystis population observed in the first 24 h after introduction of the tadpoles. The ponds containing tadpoles had a markedly lower density of Microcystis than those lacking tadpoles. Tadpoles exposed to either cultured Microcystis aeruginosa (NIES–90, 2.768 µg microcystins mg^–1 dw^–1) cells or lysed M. aeruginosa cells grew well, however, indicating that they were unaffected by Microcystis toxins. We found a significant increase in tadpole body weight after feeding on either field Microcystis or cultured M. aeruginosa. The mean increase in individual body weight was 20 mg day^?1 when fed on Microcystis from the pond, and 7 mg day^?1 when fed on M. aeruginosa from culture. Our study strongly suggested that there is a direct trophic relationship between R. grylio tadpoles and toxic Microcystis blooms and they possess the potential to graze on toxic Microcystis. The results imply that R. grylio tadpoles may play an important ecological role in reducing toxic cyanobacterial blooms caused by Microcystis.     

Isolation of viable cell mass from frozen <Emphasis Type="Italic">Microcystis viridis</Emphasis> bloom containing microcystin-RR

Cyanobacterial species commonly occur in the phytoplankton of freshwater lakes and sometimes develop as toxin-producing blooms. Microcystis is one of the most common genera of freshwater cyanobacteria and is often the dominating phytoplankton of eutrophic lakes all over the world. In eutrophic lakes, large amounts of Microcystis may overwinter in the sediment and re-inoculate the water column in spring. In most cases, the overwintering pelagic population—if it exists—is small, and its role in re-inoculation has not been clear yet. In December 2005, we found large amounts of Microcystis on the surface, frozen in the ice cover in a eutrophic pond (Pond Hármashegy, Hungary). We identified the Microcystis species and investigated the viability and the toxicity of the frozen cells. The dominant species in the bloom samples was Microcystis viridis. Viability tests showed that the colonies isolated from the ice cover were composed of living cells. The isolated strain was found toxic, we analyzed the microcystin composition in the frozen planktonic Microcystis mass; in the investigated samples microcystin-RR was the main cyanotoxin.     

The involvement of α-proteobacteria Phenylobacterium in maintaining the dominance of toxic Microcystis blooms in Lake Taihu,China

Lake Taihu in China has suffered serious harmful cyanobacterial blooms for decades. The algal blooms threaten the ecological sustainability, drinking water safety, and human health. Although the roles of abiotic factors (such as water temperature and nutrient loading) in promoting Microcystis blooms have been well studied, the importance of biotic factors (e.g. bacterial community) in promoting and meditating Microcystis blooms remains unclear. In this study, we investigated the ecological dynamics of bacterial community, the ratio of toxic Microcystis, as well as microcystin in Lake Taihu. High-throughput 16S rRNA sequencing and principal component analysis (PCA) revealed that the bacteria community compositions (BCCs) clustered into three groups, the partitioning of which corresponded to that of groups according to the toxic profiles (the ratio of toxic Microcystis to total Microcystis, and the microcystin concentrations) of the samples. Further Spearman's correlation network showed that the α-proteobacteria Phenylobacterium strongly positively correlated with the toxic profiles. Subsequent laboratory chemostats experiments demonstrated that three Phenylobacterium strains promoted the dominance of the toxic Microcystis aeruginosa PCC7806 when co-culturing with the non-toxic PCC7806 mcyB⁻ mutant. Taken together, our data suggested that the α-proteobacteria Phenylobacterium may play a vital role in the maintenance of toxic Microcystis dominance in Lake Taihu.     

Strong effects of amoebae grazing on the biomass and genetic structure of a Microcystis bloom (Cyanobacteria)

Despite its importance for bloom toxicity, the factors determining the population structure of cyanobacterial blooms are poorly understood. Here, we report the results of a two‐year field survey of the population dynamics of Microcystis blooms in a small hypertrophic urban pond. Microscopic enumeration of Microcystis and its predators and parasites was combined with pigment and microcystin analysis and denaturing gradient gel electrophoresis of the ITS rDNA region to assess population dynamics and structure. Two main Microcystis morpho‐ and ITS types were revealed, corresponding to M. aeruginosa and M. viridis. In both years, high population densities of naked amoebae grazing on Microcystis coincided with rapid decreases in Microcystis biomass. In one year, there was a shift from heavily infested M. aeruginosa to the less‐infested M. viridis, allowing the bloom to rapidly recover. The preference of amoebae for M. aeruginosa was confirmed by grazing experiments, in which several amoeba strains were capable of grazing down a strain of M. aeruginosa, but not of M. viridis. Zooplankton and chytrid parasites appeared to be of minor importance for these strong and fast reductions in Microcystis biomass. These findings demonstrate a strong impact of small protozoan grazers on the biomass and genetic structure of Microcystis blooms.     

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

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Toxicity to Daphnia of a compound extracted from laboratory and natural Microcystis spp., and the role of microcystins

1. The microcystin content of a variety of Microcystis spp., from both laboratory strains and natural blooms, was analysed by HPLC. The microcystin content of laboratory strains ranged from 1.6 to 4.3μgmg^?1 dry weight. Yearly and seasonal variation was detected in an analysis of bloom material collected from Bautzen Reservoir over a 3-year period. The microcystin concentration in bloom material ranged from undetectable to 1.16 μg ml^?1 dry weight. 2. Toxicity of laboratory and natural Microcystis to Daphnia pulicaria was determined using an established LC₅₀ technique. Partially purified water extracts from different Microcystis samples exhibited a wide range of toxicity. The highest activity was found in natural Microcystis samples, with an LC₅₀ of 36 μgm^?1 dry weight of Microcystis, whereas one strain did not appear toxic at 1600 μg ml^?1. 3. No correlation was found between the concentrations of microcystins of different laboratory and natural Microcystis strains and the toxicity of extracts to Daphnia pulicaria from the same strains. Therefore, we discriminated between hepatotoxic microcystins and the compound(s) that is toxic to Daphnia, here termed DTC (Daphnia-toxic compound), which is independent of microcystins.     

Cyanobacterial blooms and water quality in Greek waterbodies

The cyanobacterial species composition of nine Greek waterbodies of different type and trophic status was examined during the warm period of the year (May–October). Cyanobacterial water blooms were observed in all waterbodies. Forty-six cyanobacterial taxa were identified, 11 of which are known to be toxic. Eighteen species are reported for the first time in these waterbodies, 8 of which are known to produce toxins. Toxin producing species were found in all of the waterbodies and were primarily dominant in bloom formations (e.g., Microcystis aeruginosa, Anabaena flos-aquae, Aphanizomenon flos-aquae and Cylindrospermopsis raciborskii). Cosmopolitan species (e.g., M. aeruginosa), pantropic (e.g., Anabaenopsis tanganyikae) and holarctic species (e.g., Anabaena flos-aquae) were encountered. Shallow, eutrophic waterbodies had blooms dominated by Microcystis species and were characterized by phytoplankton association M. Anabaena and Aphanizomenon species of association H were dominant in waterbodies with low dissolved inorganic nitrogen and thermal stratification in the summer. Total cyanobacterial biovolumes (CBV) ranged from 7 to 9,507 cm³ m⁻³ and were higher than Alert Level 2 and Guidance Level 2 (10 cm³ m⁻³; World Health Organization; WHO) in seven of the waterbodies. Chlorophyll a concentrations ranged from 6 to 90,000 mg m⁻³ and were higher than Alert Level 2 and Guidance Level 2 (50 mg m⁻³; WHO) in eight of the waterbodies. There is also an elevated risk of acute toxicosis (Guidance Level 3; WHO) in five waterbodies. Water of an undesirable quality, hazardous to humans and animals occurs in several Greek waterbodies.     

Field and experimental studies on the combined impacts of cyanobacterial blooms and small algae on crustacean zooplankton in a large,eutrophic, subtropical,Chinese lake

Field and experimental studies were conducted to evaluate the combined impacts of cyanobacterial blooms and small algae on seasonal and long-term changes in the abundance and community structure of crustacean zooplankton in a large, eutrophic, Chinese lake, Lake Chaohu. Seasonal changes of the crustacean zooplankton from 22 sampling stations were investigated during September 2002 and August 2003, and 23 species belonging to 20 genera were recorded. Daphnia spp. dominated in spring but disappeared in mid-summer, while Bosmina coregoni and Ceriodaphnia cornuta dominated in summer and autumn. Both maximum cladoceran density (310 ind. l⁻¹) and biomass (5.2 mg l⁻¹) appeared in autumn. Limnoithona sinensis, Sinocalanus dorrii and Schmackeria inopinus were the main species of copepods. Microcystis spp. were the dominant phytoplankton species and formed dense blooms in the warm seasons. In the laboratory, inhibitory effects of small colonial Microcystis on growth and reproduction of Daphnia carinata were more remarkable than those of large ones, and population size of D. carinata was negatively correlated with density of fresh large colonial Microcystis within a density range of 0–100 mg l⁻¹ (r = −0.82, P< 0.05). Both field and experimental results suggested that seasonal and long-term changes in the community structure of crustacean zooplankton in the lake were shaped by cyanobacterial blooms and biomass of the small algae, respectively, i.e., colonial and filamentous cyanobacteria contributed to the summer replacement of dominant crustacean zooplankton from large Daphnia spp. to small B. coregoni and C. cornuta, while increased small algae might be responsible for the increased abundance of crustacean zooplankton during the past decades.     

Microcystins Induce Morphological and Physiological Changes in Selected Representative Phytoplanktons

Dissolved microcystins (MC) are regularly present in water dominated by microcystin-producing, bloom-forming cyanobacteria. In vitro experiments with environmentally feasible concentrations (5 × 10⁻⁷ M) of the three most common microcystins, MC-LR, -RR, and -YR, revealed that they influence the metabolism of different representative phytoplanktons. At light intensities close to the cyanobacterial bloom environment (50 μmol m⁻² s⁻¹), they produce morphological and physiological changes in both microcystin-producing and nonproducing Microcystis aeruginosa strains, and also have similar effects on the green alga Scenedesmus quadricauda that is frequently present in cyanobacterial blooms. All three microcystin variants tested induce cell aggregation, increase in cell volume, and overproduction of photosynthetic pigments. All three effects appear to be related to each other, but are not necessarily caused by the same mechanism. The biological activity of microcystins toward the light-harvesting complex of photobionts can be interpreted as a signal announcing the worsening of light conditions due to the massive proliferation of cyanobacteria. Although the function of microcystins is still unknown, it is evident that they have numerous effects on phytoplankton organisms in nature. These effects depend on the individual organism as well as on the various intracellular and extracellular signaling pathways. The fact that dissolved microcystins also influence the physiology of microcystin-producing cyanobacteria leads us to the conclusion that the role of microcystins in the producing cells differs from their role in the water environment.     

Microcystins Induce Morphological and Physiological Changes in Selected Representative Phytoplanktons

Dissolved microcystins (MCs) are regularly present in water dominated by microcystin-producing, bloom-forming cyanobacteria. In vitro experiments with environmentally feasible concentrations (5 × 10⁻⁷ M) of the three most common microcystins, MC-LR, MC-RR, and MC-YR, revealed that they influence the metabolism of different representative phytoplanktons. At light intensities that are close to the cyanobacterial bloom environment (50 μmol m⁻² s⁻¹), they produce morphological and physiological changes in both microcystin-producing and -nonproducing Microcystis aeruginosa strains and also have similar effects on the green alga Scenedesmus quadricauda that is frequently present in cyanobacterial blooms. All three microcystin variants tested induce cell aggregation, increase in cell volume, and overproduction of photosynthetic pigments. All three effects appear to be related to each other but are not necessarily caused by the same mechanism. The biological activity of microcystins toward the light-harvesting complex of photobionts can be interpreted as a signal announcing the worsening of light conditions due to the massive proliferation of cyanobacteria. Although the function of microcystins is still unknown, it is evident that they have numerous effects on phytoplankton in nature. These effects depend on the individual organism as well as on the various intracellular and extracellular signaling pathways. The fact that dissolved microcystins also influence the physiology of microcystin-producing cyanobacteria leads us to the conclusion that the role of microcystins in the producing cells differs from the role in the water environment.     

Effects of the Distribution of a Toxic Microcystis Bloom on the Small Scale Patchiness of Zooplankton

Toxic cyanobacterial blooms can strongly affect freshwater food web structures. However, little is known about how the patchy occurrence of blooms within systems affects the spatial distribution of zooplankton communities. We studied this by analysing zooplankton community structures in comparison with the spatially distinct distribution of a toxic Microcystis bloom in a small, shallow, eutrophic lake. While toxic Microcystis was present at all sites, there were large spatial differences in the level of cyanobacterial biomass and in the zooplankton communities; sites with persistently low cyanobacterial biomass displayed a higher biomass of adult Daphnia and higher zooplankton diversity than sites with persistently high cyanobacterial biomass. While wind was the most likely reason for the spatially distinct occurrence of the bloom, our data indicate that it was the differences in cyanobacterial biomass that caused spatial differences in the zooplankton community structures. Overall, our study suggests that even in small systems with extensive blooms ‘refuge sites’ exist that allow large grazers to persist, which can be an important mechanism for a successful re-establishment of the biodiversity in an ecosystem after periods of cyanobacterial blooms.     

FATE OF THE TOXIC CYCLIC HEPTAPEPTIDES,THE MICROCYSTINS,FROM BLOOMS OF MICROCYSTIS (CYANOBACTERIA) IN A HYPERTROPHIC LAKE1

The in situ fate of the toxic cyclic heptapeptides, the microcystins, produced by blooms of Microcystis was examined at two stations in a hypertrophic Japanese lake. Microcystins were detected in all samples of Microcystis with quantities varying seasonally and spatially (230–950 μg · g dry wt^?1 at St. 1 and 160–746 μg · g dry wt^?1 at St. 2) and composed of microcystin-LR, -RR, and-YR. Microcystin-RR was the dominant toxin in most samples. A large amount of microcystin (1.1 μg · L^?1) was detected in only one sample of filtered lake water. Accumulation of microcystin in zooplankton was indirectly estimated from a newly developed equation model. Large amounts of microcystin (75–1387 μg · g dry wt^?1) were accumulated in the zooplankton community, which consisted of two cladocerans, Bosmina fatalis Burckhardt and Diaphanosoma brachyurum Lieve, and a copepod, Cyclops vicinus Uljanin, that co-occurred with the toxic Microcystis blooms. The maximum percent of microcystin content in zooplankton to that in Microcystis was 202%. Among the three species of zooplankton, only B. fatalis seemed to be responsible for accumulation of the microcystins because C. vicinus appeared to avoid contact with Microcystis cells and D. brachyurum did not consume colonies of Microcystis. Microcystins may be transferred to higher trophic levels through B. fatalis.     

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.     

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

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