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

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

Response of Daphnia's Antioxidant System to Spatial Heterogeneity in Cyanobacteria Concentrations in a Lowland Reservoir

Many species and clones of Daphnia inhabit ecosystems with permanent algal blooms, and they can develop tolerance to cyanobacterial toxins. In the current study, we examined the spatial differences in the response of Daphnia longispina to the toxic Microcystis aeruginosa in a lowland eutrophic dam reservoir between June (before blooms) and September (during blooms). The reservoir showed a distinct spatial pattern in cyanobacteria abundance resulting from the wind direction: the station closest to the dam was characterised by persistently high Microcystis biomass, whereas the upstream stations had a significantly lower biomass of Microcystis. Microcystin concentrations were closely correlated with the cyanobacteria abundance (r = 0.93). The density of daphniids did not differ among the stations. The main objective of this study was to investigate how the distribution of toxic Microcystis blooms affects the antioxidant system of Daphnia. We examined catalase (CAT) activity, the level of the low molecular weight antioxidant glutathione (GSH), glutathione S-transferase (GST) activity and oxidative stress parameters, such as lipid peroxidation (LPO). We found that the higher the abundance (and toxicity) of the cyanobacteria, the lower the values of the antioxidant parameters. The CAT activity and LPO level were always significantly lower at the station with the highest M. aeruginosa biomass, which indicated the low oxidative stress of D. longispina at the site with the potentially high toxic thread. However, the low concentration of GSH and the highest activity of GST indicated the occurrence of detoxification processes at this site. These results demonstrate that daphniids that have coexisted with a high biomass of toxic cyanobacteria have effective mechanisms that protect them against the toxic effects of microcystins. We also conclude that Daphnia''s resistance capacity to Microcystis toxins may differ within an ecosystem, depending on the bloom''s spatial distribution.     

The potential use of bacterium strain R219 for controlling of the bloom-forming cyanobacteria in freshwater lake

Cyanobacterial blooms become a serious environmental threat to the freshwater ecosystem, and several physical and chemical methods have been developed for controlling the blooms. In order to develop a biocontrol agent for controlling the blooms, we isolated a bacterial strain R219 that exhibited strong algicidal activity against the dominant bloom-forming species of Microcystis aeruginosa from Lake Tai in China. Based on 16S rDNA sequence analysis we determined the strain R219 to be Pseudomonas aeruginosa by the virtue of its sharing about 99.8% similarity with reference strains in the DNA databases. Biochemical and morphological tests were used to support the accurate identification as that of the bacterium P. aeruginosa. We also tested culture filtrate and ethyl acetate extract of strain R219 and showed both of them exhibited strong algicidal effect on the growth of M. aeruginosa at mid-exponential phase when the R219 filtrate and ethyl acetate extract were applied at various cell densities. Moreover, the P. aeruginosa filtrate showed high potency in removal of the mixed species bloom-forming cyanobacteria collected directly from the Lake Tai. When adding the filtrate of the strain R219 to the mixed-species cyanobacteria, the content of chlorophyll-a of the algae were reduced by as much as 80–90%. Oral acute toxicity assessment for strain R219 demonstrated that all the mice that received the broth or filtrate in doses of 0.5 or 2.0 g kg^?1 were alive without any immediate behavioral changes within 14 days of administration of either broth or filtrate. These results indicate that the strain R219 may have potential for a use in controlling the bloom-forming cyanobacteria in freshwater ecosystems.     

The limit of the genetic adaptation to copper in freshwater phytoplankton

Copper is one of the most frequently used algaecides to control blooms of toxic cyanobacteria in water supply reservoirs. Among the negative impacts derived from the use of this substance is the increasing resistance of cyanobacteria to copper toxicity, as well as changes in the community structure of native phytoplankton. Here, we used the ratchet protocol to investigate the differential evolution and maximum adaptation capacity of selected freshwater phytoplankton species to the exposure of increasing doses of copper. Initially, a dose of 2.5 μM CuSO₄·5H₂O was able to completely inhibit growth in three strains of the toxic cyanobacterium Microcystis aeruginosa, whereas growth of the chlorophyceans Dictyosphaerium chlorelloides and Desmodesmus intermedius (represented by two different strains) was completely abolished at 12 μM. A significant increase in resistance was achieved in all derived populations during the ratchet experiment. All the chlorophyceans were able to adapt to up to 270 μM of copper sulfate, but 10 μM was the highest concentration that M. aeruginosa strains were able to cope with, although one of the replicates adapted to 30 μM. The recurrent use and increasing doses of copper in water reservoirs could lead to the selection of copper-resistant mutants of both chlorophyceans and cyanobacteria. However, under high concentrations of copper, the composition of phytoplankton community could undergo a drastic change with cyanobacteria being replaced by copper-resistant chlorophyceans. This result stems from a distinct evolutionary potential of these species to adapt to this substance.     

Role of Environmental Factors and Toxic Genotypes in the Regulation of Microcystins-Producing Cyanobacterial Blooms

The aim of this study was to understand: (1) how environmental conditions can contribute to formation of Microcystis-dominated blooms in lowland, dam reservoirs in temperate climate—with the use of quantitative molecular monitoring, and (2) what is the role of toxic Microcystis genotypes in the bloom functioning. Monitoring of the Sulejow Reservoir in 2009 and 2010 in two sites Tresta (TR) and Bronislawow BR), which have different morphometry, showed that physicochemical conditions were always favorable for cyanobacterial bloom formation. In 2009, the average biomass of cyanobacteria reached 13 mg L^?1 (TR) and 8 mg L^?1 (BR), and in the second year, it decreased to approximately 1 mg L^?1 (TR and BR). In turns, the mean number of toxic Microcystis genotypes in the total Microcystis reached 1 % in 2009, both in TR and BR, and in 2010, the number increased to 70 % in TR and 14 % in BR. Despite significant differences in the biomass of cyanobacteria in 2009 and 2010, the mean microcystins (MCs) concentration and toxicity stayed at a similar level of approximately 1 μg L^?1. Statistical analysis indicated that water retention time was a factor that provided a significant difference between the two monitoring seasons and was considered a driver of the changes occurring in the Sulejow Reservoir. Hydrologic differences, which occurred between two studied years due to heavy flooding in Poland in 2010, influenced the decrease in number of Microcystis biomass by causing water disturbances and by lowering water temperature. Statistical analysis showed that Microcystis aeruginosa biomass and 16S rRNA gene copy number representing Microcystis genotypes in both years of monitoring could be predicted on the basis of total and dissolved phosphorus concentrations and water temperature. In present study, the number of mcyA gene copies representing toxic Microcystis genotypes could be predicted based on the biomass of M. aeruginosa. Moreover, MCs toxicity and concentration could be predicted on the basic of mcyA gene copy number and M. aeruginosa (biomass, 16S rRNA), respectively. Present findings may indicate that Microcystis can regulate the number of toxic genotypes, and in this way adjust the whole bloom to be able to produce MCs at the level which is necessary for its maintenance in the Sulejow Reservoir under stressful hydrological conditions.     

Targeted deep sequencing reveals high diversity and variable dominance of bloom-forming cyanobacteria in eutrophic lakes

Cyanobacterial blooms in eutrophic lakes are severe environmental problems worldwide. To characterize the spatiotemporal heterogeneity of cyanobacterial blooms, a high-throughput method is necessary for the specific detection of cyanobacteria. In this study, the cyanobacterial composition of three eutrophic waters in China (Taihu Lake, Dongqian Lake, and Dongzhen Reservoir) was determined by pyrosequencing the cpcBA intergenic spacer (cpcBA-IGS) of cyanobacteria. A total of 2585 OTUs were obtained from the normalized cpcBA-IGS sequence dataset at a distance of 0.05. The 238 most abundant OTUs contained 92% of the total sequences and were classified into six cyanobacterial groups. The water samples of Taihu Lake were dominated by Microcystis, mixed Nostocales species, Synechococcus, and unclassified cyanobacteria. Besides, all the samples from Taihu Lake were clustered together in the dendrogram based on shared abundant OTUs. The cyanobacterial diversity in Dongqian Lake was dramatically decreased after sediment dredging and Synechococcus became exclusively dominant in this lake. The genus Synechococcus was also dominant in the surface water of Dongzhen Reservoir, while phylogenetically diverse cyanobacteria coexisted at a depth of 10 m in this reservoir. In summary, targeted deep sequencing based on cpcBA-IGS revealed a large diversity of bloom-forming cyanobacteria in eutrophic lakes and spatiotemporal changes in the composition of cyanobacterial communities. The genus Microcystis was the most abundant bloom-forming cyanobacteria in eutrophic lakes, while Synechococcus could be exclusively dominant under appropriate environmental conditions.     

Modeling the role of wind and warming on Microcystis aeruginosa blooms in shallow lakes with different trophic status

This study focuses on the role of wind exposure and storm events, in interaction with trophic status and temperature, on the competition between two species: Microcystis aeruginosa and a typical green alga. It is based on a water column model containing ecological and fluid mechanic features including mixing and shear stress at the bottom. This model addresses for the first time the impact of storm events (inducing sediment and nutrient resuspension) on algal dynamics. Simulations with realistic environmental forcings were performed with different sets of wind, temperature, and trophic conditions. With normal temperatures, conditions for dominance and bloom formation of M. aeruginosa in summer are restricted to hypertrophic waters with low wind exposure. Higher wind exposure (above 2 m s^?1) impairs the formation blooms even in favorable trophic conditions and enhances the dominance of green algae. Hotter temperatures allow the dominance of M. aeruginosa for lower phosphorus conditions and higher wind exposure and lead to the exclusion of green algae for high phosphorus content and low wind exposure. Nevertheless, high wind exposure (above 3 m s^?1) still prevents dense bloom formation and allows the coexistence of both species. Storm events bring two counterbalancing features: sediment and nutrient resuspension. The first leads to a decrease of phytoplankton density in response to high turbidity, and the second leads to an increase and better maintenance of M. aeruginosa blooms due to high phosphorus concentration released in the water. This result depends on the timing of the event and on general wind exposure as phosphorus release only benefits M. aeruginosa if exposure to wind is low.     

Alternative food sources of native and non-native bivalves in a subtropical eutrophic lake

The aim of this study was to evaluate the consumption of alternative food sources (water column and sediment) and the potential competition under different conditions between Diplodon parallelopipedon (native) and Corbicula fluminea (non-native). We evaluated filtration and ingestion rates of water column at 6 and 24 h, held with and without organic matter and different phytoplankton types: needle-shaped green algae (Ankistrodesmus sp.) and filamentous cyanobacteria (Planktothrix agardhii) dominated communities. Our results confirmed higher filtration and ingestion rates per biomass unit for C. fluminea in the presence of sediment without organic matter. However, when we compared the filtration of bivalves held in sediment with organic matter, D. parallelopipedon rates were not significantly different from C. fluminea values. Moreover, in the presence of filamentous cyanobacteria, only C. fluminea filtration and ingestion rates decreased significantly. Our experimental results and previous field evidence concur that C. fluminea were not able to outcompete the native bivalves in organic matter rich sediment and cyanobacteria blooms conditions. The differential responses to the eutrophication process between exotic and native bivalves, apparently favoring the later, might buffer the potential competition interactions allowing their coexistence.     

Flow of toxic metals in food-web components of tropical mangrove ecosystem,Southern India

The concentration of heavy metals in water, sediment, and various food-web components like plankton, shrimp, bivalve, and fishes were collected from Muthupet mangrove ecosystem. Heavy metal concentration in water samples was relatively lesser than the biological and sediment samples. Among the heavy metals studied, zinc showed highest concentration ranged from 1.81 to 81.5 mg/kg or mg/L, whereas Cd (0–26.06 mg/kg or mg/L) was found to be lesser in all the samples except a few organisms viz. Anadara sp. (26.06 mg/kg), Coilia sp. (10.09 mg/kg), Anguila sp. (9.14 mg/kg), and Tachysurus maculates (6.95 mg/kg) observed during this study. Pb and Cu were ranged from 10.29 to 14.99 mg/kg and 0.59 to 16.06 mg/kg, respectively. The reported values of heavy metals were several folds higher than permissible levels of international regulatory agencies like WHO, FAO, and USEPA. The order of accumulation of heavy metals in biological samples are as follows: Pb > Cu > Zn > Cd. All the biota showed a higher degree of bioconcentration factor for Zn, in the range of 3.90–34.39. Principal component analysis concluded that Muthupet was contaminated by lithogenic as well as anthropogenic activities.Therefore, field observation and sample analysis clearly indicated that sampling sites were polluted with both point and nonpoint source of pollution.     

Bioaccumulation of heavy metals in local edible plants near a municipal landfill and the related human health risk assessment

ABSTRACT

The increase in municipal solid waste generation, along with high concentrations of heavy metals in environments near municipal landfill, has led to human health hazards. This study investigated heavy metal contamination in water, sediment, and edible plants near a municipal landfill, including the bioaccumulation factor (BAF) and potential health risks. The heavy metal concentrations in the samples were analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES). The concentrations of arsenic (As), lead (Pb), cadmium (Cd), and chromium (Cr) in water samples were not detected (ND), ND, 0.006 ± 0.01 mg/L, and ND, respectively, and in sediment samples, the concentrations were 1.19 ± 0.44, 3.20 ± 0.62, 0.46 ± 0.21, and 6.97 ± 0.34 mg/kg, respectively. The highest concentrations of As (5.03 ± 0.38), Pb (1.81 ± 0.37), and Cd (1.93 ± 0.13) were found in Marsilea crenata, whereas that of Cr (5.68 ± 0.79) was detected in Ipomoea aquatica. The Cr concentration in all plant species exceeded the standard for vegetables. The BAF values followed the heavy metal concentrations. All plant species have a low potential for accumulating Pb and Cr. The edible plants in this study area might cause health hazards to consumers from As, Pb, and Cd contamination.     

Metal Contamination in Sediment of One of the Upper Reaches of the Yangtze River: Mianyuan River in Longmenshan Region,Southwest of China

Metal contamination in sediment of the Mianyuan River (one of the major upper reaches of the Yangtze River) in Longmenshan Region (China) was investigated in 2012. Means of metal concentrations in sediment (<74μm) were Cr: 59.93 ± 19.8% mg/kg; As: 7.21 ± 50.2% mg/kg; Se: 0.45 ± 66.3% mg/kg; Pb: 19.89 ± 29.3% mg/kg; Zn: 78.98 ± 31.9% mg/kg; Cd: 0.69 ± 28.3% mg/kg; Ba: 0.71 ± 34.0% g/kg; Mn: 0.55 ± 62.2% g/kg. This study suggested: (1) concentrations of Cd, As, Cr, and Pb in Mianyuan River sediment were lower than those of the middle and lower reaches of the Yangtze River; (2) the increase of metals during the period from 2006 to 2009 was probably related to the destruction of tailings piles by the Wen Chun earthquake in 2008; (3) organic materials decided the distribution of Cd, Se, As, Ba, and Mn in the upstream sediment, while the iron and manganese minerals controlled the distribution of Ba, Cr, and Zn in the downstream sediment; (4) sources of Cd, Se, and As were geogenic, while sources of Cr, Zn, Ba, and Mn were anthropogenic; (5) the source of Pb in the upstream sediment was probably automobile exhaust, but that of Pb in the downstream sediment was geogenic.     

A freshwater bacterial strain,Shewanella sp. Lzh-2, isolated from Lake Taihu and its two algicidal active substances,hexahydropyrrolo[1,2-a]pyrazine-1,4-dione and 2, 3-indolinedione

Cyanobacterial blooms have become a serious problem in Lake Taihu during the last 20 years, and Microcystis aeruginosa and Synechococcus sp. are the two dominant species in cyanobacterial blooms of Lake Taihu. A freshwater bacterial strain, Shewanella sp. Lzh-2, with strong algicidal properties against harmful cyanobacteria was isolated from Lake Taihu. Two substances with algicidal activity secreted extracellularly by Shewanella sp. Lzh-2, S-2A and S-2B, were purified from the bacterial culture of strain Lzh-2 using ethyl acetate extraction, column chromatography, and high performance liquid chromatography (HPLC) in turn. The substances S-2A and S-2B were identified as hexahydropyrrolo[1,2-a]pyrazine-1,4-dione and 2, 3-indolinedione (isatin), respectively, based on liquid chromatography-mass spectrometry (LC-MS), gas chromatography-mass spectrometry (GC-MS), and hydrogen-nuclear magnetic resonance (H-NMR) analyses, making this the first report of their algicidal activity toward cyanobacteria. S-2A (hexahydropyrrolo[1,2-a]pyrazine-1,4-dione) had no algicidal effects against Synechococcus sp. BN60, but had a high level of algicidal activity against M. aeruginosa 9110. The LD50 value of S-2A against M. aeruginosa 9110 was 5.7 μg/ml. S-2B (2, 3-indolinedione) showed a potent algicidal effect against both M. aeruginosa 9110 and Synechococcus sp. BN60, and the LD50 value of S-2B against M. aeruginosa 9110 and Synechococcus sp. BN60 was 12.5 and 34.2 μg/ml, respectively. Obvious morphological changes in M. aeruginosa 9110 and Synechococcus sp. BN60 were observed after they were exposed to S-2A (or S-2B) for 24 h. Approximately, the algicidal activity, the concentration of S-2A and S-2B, and the cell density of Lzh-2 were positively related to each other during the cocultivation process. Overall, these findings increase our knowledge about algicidal substances secreted by algicidal bacteria and indicate that strain Lzh-2 and its two algicidal substances have the potential for use as a bio-agent in controlling cyanobacterial blooms in Lake Taihu.     

Detection of <Emphasis Type="Italic">Planktothrix rubescens</Emphasis> (Cyanobacteria) associated with microcystin production in a freshwater reservoir

So far, the presence of microcystins in Portuguese freshwater resources has always been attributed to the bloom-forming cyanobacteria Microcystis aeruginosa. In 2005, however, microcystins were detected at the Beliche reservoir (Algarve, South Portugal), following the development of a bloom dominated by Planktothrix rubescens. The identity of the causative organism was confirmed by combining both morphological and 16S rRNA gene sequence analysis. Its ability to produce microcystins was confirmed by HPLC and MALDI-TOF MS. Unlike M. aeruginosa that usually accumulates near the water surface, P. rubescens found at the Beliche reservoir accumulated only at deep water levels. Being invisible from the surface, the occurrence of toxic P. rubescens in freshwater resources requires special attention when designing site inspection and sampling procedures for the correct risk assessment and management of cyanobacterial blooms in the field. Handling editor: D. Hamilton     

Ecophysiological responses of the mangrove Avicennia marina to trace metal contamination

Growth responses of Avicennia marina seedlings to contamination by different concentrations of two essential (Cu, Zn) and two non-essential (Pb, Hg) trace metals were studied under glasshouse conditions. We tested the hypothesis that soil retention and root ultrafiltration would exclude most of the trace metals, and that those that are absorbed and translocated to the shoots would interfere with plant performance and be excreted via leaf salt glands. One-month-old seedlings were subjected to Cu, Zn, Pb and Hg at concentrations of 0, 40, 80, 120 and 160 μg g⁻¹ sediment for 12 months in a randomized complete block design (n = 6). Photosynthesis was measured at the end of 12 months of trace metal exposure with a portable gas exchange system and chlorophyll fluorescence with a pulse-modulated fluorometer. After morphometric measurements, plants were harvested and analyzed for Cu, Zn, Pb and Hg by atomic absorption spectroscopy. Total dry biomass decreased with increasing trace metal concentration for all metals. In the 160 μg g⁻¹ Cu, Zn, Hg and Pb treatments, total biomass was significantly lower than the control value by 43%, 37%, 42% and 40%, respectively. Decreases in plant height and number of leaves followed trends similar to those for total biomass and ranged from 37% to 60%, compared to the controls. Decreases in chlorophyll content in the trace metal treatments ranged from 50% to 58% compared to the control. Carbon dioxide exchange, quantum yield of photosystem II (PSII), electron transport rate (ETR) through PSII and photosynthetic efficiency of PSII (F_v/F_m) were highest in the control treatment and decreased with increasing trace metal concentrations. Decreases in CO₂ exchange in the 160 μg g⁻¹ treatments for all trace metals ranged from 50% to 60%. Concentrations of all trace metals in plant organs increased with increasing metal concentrations and were higher in roots than in shoots, with concentrations of Cu and Zn being considerably higher than those of Hg and Pb. Qualitative elemental analyses and X-ray mapping of crystalline deposits over the glands at the leaf surfaces indicated that Cu and Zn were excreted from the salt glands, while Hg and Pb were absent, at least being below the limits of detection. These results demonstrate that growth processes are sensitive to trace metals and therefore can be considered as a cost of metal tolerance, but salt glands of this mangrove species do contribute eliminating at least part of physiologically essential trace metals if taken up in excess.     

Inhibition of Camellia sinensis (L.) O. Kuntze on Microcystis aeruginosa and isolation of the inhibition factors

Low concentration of tea (Camellia sinensis (L.) O. Kuntze) was shown to inhibit the growth of the toxic cyanobacterium Microcystis aeruginosa. The inhibition efficiency was 40 % at 0.1 g dry tea/L and 90 % at 0.2 g/L after a 12-day culture. All varieties of tea used in the test could inhibit Microcystis growth, in which the inhibitory effect of green tea was greater than that of black tea. Antialgal allelochemicals were isolated from tea by solvent extraction, gel-chromatography and high performance liquid chromatography. Two algal-inhibition compounds were identified by liquid chromatography/mass spectrometry as epigallocatechin-3-gallate, epicatechin-3-gallate respectively. These are the main polyphenols in tea that have inhibitory effects on the growth of cyanobacteria. The combined effect of these polyphenols makes tea a promising source of algicide to inhibit the growth of algal blooms.     

Isolation of toxic metal-tolerant bacteria from soil and examination of their bioaugmentation potentiality by pot studies in cadmium- and lead-contaminated soil

Heavy metals, also regarded as toxic metals, are the important environmental pollutants that affect all forms of life. Accumulation of toxic metals in plants results in various biochemical, physiological and structural disturbances, leading to inhibited growth and sometimes plant death. Toxic metal contamination disturbs the soil ecology as well as the agricultural productivity. Several indigenous microbes can withstand the effect of toxic metal and play a vital role in the revival of tarnished soil. In the present study, soil samples were collected from contaminated crop field of Cachar district of Assam, India. Segregation, enumeration and identification of bacteria from soil samples were performed. Among all the tested isolates, very few were able to withstand a high concentration of Cd and Pb in nutrient agar plates. Toxic metal-tolerant bacteria were identified as Pseudomonas aeruginosa and Bacillus cereus. The isolates having a higher tolerance for Cd and Pb were taken into consideration for pot studies. P. aeruginosa strain SN4 and strain SN5 showed significant results at Cd- and Pb-contaminated soil, evidenced by the healthy growth of Oryza sativa seedlings. However, B. cereus strain SN6 showed high tolerance towards Cd and Pb, but pot experimental studies showed adverse effects on seedling germination and shoot growth of O. sativa. P. aeruginosa strains were significantly able to reduce the negative impact of Cd and Pb in the soil, thus finding an alternative in removal, recovery and remediation of toxic metal-contaminated crop field.     

Genetic characterization of <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> isolates from Portuguese freshwater systems

Cyanobacteria are microorganisms that pose a serious threat to the aquatic waterways through the production of dense blooms under eutrophic conditions and the release of toxic secondary metabolites—cyanotoxins. Within cyanobacteria, the colonial planktonic Microcystis aeruginosa is widely distributed in both fresh and brackish aquatic environments throughout the world being frequently observed in the Portuguese water systems. Apart from the well-established distribution of M. aeruginosa in Portugal, knowledge of its genetic diversity and population structure is unknown. Therefore, in this study twenty-seven strains were obtained from the North, Centre and South regions of Portugal and were subjected to extensive phylogenetic analyses using simultaneously four distinct genetic markers (16S rRNA, 16S-23S ITS, DNA gyrase subunit ß and cell division protein (ftsZ)) encompassing in total 2834 bp. With this work we characterized the phylogenetic relationship among the Portuguese strains, with the southern strains showing higher genetic structure relatively to the North and Centre strains. A total of fifteen genotypes were determined for M. aeruginosa in Portuguese water systems revealing a high genetic diversity. This is also the first study to report geographic variation on the population structure of the Portuguese M. aeruginosa.     

Ecological development and genetic diversity of <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> from artificial reservoir in Russia

Microcystis aeruginosa is a well-known Cyanobacterium responsible for the formation of toxic water blooms around the world. Shallow, warm, and eutrophic reservoirs provide the most favourable conditions for M. aeruginosa development. Numerous studies have been devoted to this species, but there still is a necessity to develop additional approaches for the monitoring of cyanobacteria in reservoirs. In this study, M. aeruginosa in the water column of a hypereutrophic Siberian reservoir was investigated by fluorescence, light, and electron microscopy as well as genetic analysis using a mcyE marker. Here, we demonstrate the genetic diversity and features of the fluorescence spectra for different ecotypes of this species. We suggest that a fluorescence approach can be used to identify M. aeruginosa in a natural environment in order to increase the effectiveness of ecological monitoring and water quality evaluation.     

The diversity and distribution of toxigenic Microcystis spp. in present day and archived pelagic and sediment samples from Lake Erie

The reoccurrence of significant cyanobacterial blooms in Lake Erie during the last 13 years has raised questions concerning the long-term persistence of microcystin-producing cyanobacteria and the presence of natural sediment reservoirs for potentially toxic cyanobacteria in this large lake system. To address these questions, we analyzed phytoplankton and sediment samples which were collected and preserved in the 1970s as well as samples collected in 2004 from locations within Lake Erie. The identification of microcystin-producing cyanobacteria in Lake Erie was examined via PCR amplification of the mcyA gene fragment. Based on the high % sequence similarity, the mcyA sequences from all 1970s phytoplankton and sediment samples were determined to belong to Microcystis spp., in spite of reports suggesting that Lake Erie was dominated by filamentous cyanobacteria in the 1970s. In sediment samples from 2004, signature genes for Microcystis were distributed and preserved not only in the surface sediments but also up to 10–12 cm in depth. Based on cell quantities determined by a quantitative polymerase chain reaction (qPCR) method, 0.18% of eubacteria in the sediments were Microcystis cells, of which 4.8% were potential microcystin producers. In combination with experiments showing that Microcystis cells can be cultured from Lake Erie surface sediments, this paper demonstrates the potential for these sediments to act as a reservoir for pelagic Microcystis populations and that the composition of the population of microcystin-producing cyanobacteria in Lake Erie has not changed remarkably since the 1970s.     

Roles of dilution rate and nitrogen concentration in competition between the cyanobacterium <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> and the diatom <Emphasis Type="Italic">Cyclotella</Emphasis> sp. in eutrophic lakes

In Lake Tega, Japan, the shift of dominant algal species was caused as a result of discharging water from the adjacent river into the lake. The transition from cyanobacteria (mainly the genus Microcystis) to diatoms (mainly the genus Cyclotella) resulted in a disappearance of algal blooms. Although some environmental conditions such as flow rate, nutrient concentration, and transparency were changed by the project, the decisive factor for the transition has not been clarified yet. For the effective control of algal blooms by water discharge, this study aimed to elucidate the effects of daily renewal rate and nitrogen concentration on the interspecific competition between Microcystis aeruginosa and Cyclotella sp. Monoculture experiments were conducted to obtain growth characteristics for each species and mixed culture experiments were performed to examine their competitive abilities under various daily renewal rates of the culture medium (15 and 30 %) and nitrate concentrations (71.4, 178, and 357 μM). In addition to prepared medium, Lake Tega water was also used for mixed culture experiments. The results showed that the increase in a daily renewal rate contributed to the dominance of Cyclotella sp., while a nitrate concentration had little influence on the competition. We conclude that algal blooms composed of the genus Microcystis would be controlled by maintaining a daily renewal rate up to 30 % or more, which corresponded to the dilution rate of 0.36 day^?1, under a nitrate concentration of ≤357 μM. The study would include essential information for the management of lakes suffering from frequent occurrences of algal blooms.