Concentrations Of Microcystis Research Articles

Colonial Microcystis' biomass affects its shift to diatom aggregates under aeration mixing.

The effect of hydrodynamic mixing on controlling Microcystis blooms or changing the algal community to diatom dominance has been widely studied; however, the effects of colonial Microcystis biomass on the development of the algal community are poorly known. Here, in order to study the changes in Microcystis blooms under continuous aeration mixing, an experiment was carried out in a greenhouse with factors of varying biomass of Microcystis and inorganic nitrogen and phosphorus enrichment in summer. There were three chlorophyll a (Chl-a) levels in six treatments: low Chl-a level of 68.4μgL-1 (treatments L, L-E), medium Chl-a level of 468.7μgL-1 (treatments M, M-E), and high Chl-a level of 924.1μgL-1 (treatments H, H-E). Treatments L-E, M-E and H-E were enriched with the same inorganic nitrogen and phosphorus nutrients. During the experiment of 30days, the concentration of Microcystis and Chl-a decreased, and diatom Nitzschia palea cells appeared in all the treatments, which became dominant in treatments M, M-E, H and H-E, with the highest biomass of 9.41 ± 1.96mgL-1 Nitzschia in treatment H-E on day 30. The rank order of the biomass of Nitzschia from low to high was (L = L-E) < (M = M-E) < H < H-E (P < 0.05). In addition, Nitzschia cells were aggregates attached to Microcystis colonies in all the treatments. The results showed that the initial biomass of colonial Microcystis affected the algal shift from Microcystis dominance to Nitzschia dominance. However, the enriched inorganic nitrogen and phosphorus was beneficial for the Nitzschia increase in the high biomass treatment alone. The shift from Microcystis dominance to diatom dominance under continuous aeration mixing may be caused by low light conditions as well as the nutrients released from Microcystis decay. Moreover, the aerobic condition caused by aeration mixing maintained the colonial mucilaginous sheath to support the growth of Nitzschia cells in aggregation. This study found for the first time that Microcystis blooms could shift to diatom Nitzschia dominance in aggregates. It provided a method to control and manipulate Microcystis blooms to diatom dominance through continuous aeration mixing to proper biomass of Microcystis colonies. The shift to diatoms dominance would provide more high quality food organisms for aquaculture and be beneficial to the materialcycling and energy flowing in food web dynamics.

Prediction of algal bloom using a combination of sparse modeling and a machine learning algorithm: Automatic relevance determination and support vector machine

Algae can produce odor substances and toxins that make the smell and taste of water unpleasant and impair the quality of human and aquatic life. Appropriate countermeasures can be implemented in advance in water purification processes to prevent algal disorders if the occurrence of algal blooms is accurately predicted. Several models have been developed to predict algal blooms. However, a comprehensive model that can be universally applied under various conditions is lacking. In this study, automatic relevance determination, a sparse modeling algorithm, and support vector machine were combined to construct prediction models for algal blooms in four Japanese dam reservoirs to predict their occurrence over 7 days. Automatic relevance determination was applied to a dataset consisting of monthly water quality data and daily hydraulic and meteorological data to identify variables relevant to the concentrations of Microcystis spp. and Dolichospermum spp., which are bloom-forming cyanobacteria and are dominant in freshwater ecosystems. A dataset of selected variables was used to train and validate the support vector machine models. The results of variable selection by automatic relevance determination revealed that the average concentration of total nitrogen in the past year and the average maximum temperature in the past 7 days may have an association with the algal concentration. Support vector machine models resulted in 92.3% accuracy and 86.4% precision for Microcystis spp. and 71.4% accuracy and 77.5% precision for Dolichospermum spp. on average in binary classification. The competitive relationship between Microcystis spp. and Dolichospermum spp., which differs according to the nutrient level and temperature, probably affects the prediction performance of the models. Our study suggests that the combination of sparse modeling and machine learning is applicable to the construction of a prediction model for site-specific algal bloom events in dam reservoirs.

Depth-Dependent Spatiotemporal Dynamics of Overwintering Pelagic Microcystis in a Temperate Water Body.

Cyanobacteria in the genus Microcystis are dominant components of many harmful algal blooms worldwide. Their pelagic–benthic life cycle helps them survive periods of adverse conditions and contributes greatly to their ecological success. Many studies on Microcystis overwintering have focused on benthic colonies and suggest that sediment serves as the major inoculum for subsequent summer blooms. However, the contemporaneous overwintering pelagic population may be important as well but is understudied. In this study, we investigated near-surface and near-bottom pelagic population dynamics of both microcystin-producing Microcystis and total Microcystis over six weeks in winter at Dog Lake (South Frontenac, ON, Canada). We quantified relative Microcystis concentrations using real-time PCR. Our results showed that the spatiotemporal distribution of overwintering pelagic Microcystis was depth dependent. The abundance of near-bottom pelagic Microcystis declined with increased depth with no influence of depth on near-surface Microcystis abundance. In the shallow region of the lake (<10 m), most pelagic Microcystis was found near the lake bottom (>90%). However, the proportion of near-surface Microcystis rose sharply to over 60% as the depth increased to approximately 18 m. The depth-dependent distribution pattern was found to be similar in both microcystin-producing Microcystis and total Microcystis. Our results suggest the top of the water column may be a more significant contributor of Microcystis recruitment inoculum than previously thought and merits more attention in early CHAB characterization and remediation.

Use of physiological activities to estimate the population growth of rotifer (Brachionus calyciflorus) under the stress of toxic Microcystis and nitrite

Microcystis blooms disrupt aquatic systems and adversely affect zooplankton growth. Brachionus calyciflorus Pallas (rotifer) was introduced to different combinations of toxic Microcystis aeruginosa (0, 2 × 105, 2 × 106, and 2 × 107 cells mL−1) and nitrite (0, 2, 4, and 6 mg L−1) to evaluate their physiological activities and population growth under stress. Survival rate (S), population growth rate (r), grazing rate (G), antioxidant response, and metabolic and digestive enzyme activities were determined. Results revealed that G declined with the increasing nitrite doses and grazing time upon exposure to a certain Microcystis concentration. Toxic M. aeruginosa and nitrite inhibited the S, r, glutathione content, total antioxidant capacity level, and activities of alkaline phosphatase, xanthine oxidase, lactate dehydrogenase, and cellulase (p < 0.05) but increased the reactive oxygen species level, malondialdehyde content, and amylase activity (p < 0.05). The activities of superoxide dismutase, catalase, and pepsase were also increased in single low doses of nitrite solutions (p < 0.05). Therefore, the grazing intensity of rotifers affected B. calyciflorus physiological activities, which are useful in the estimation of its population growth in eutrophic water environments.

Acoustic scattering by gas-bearing cyanobacterium Microcystis: Modeling and in situ biomass assessment

Cyanobacterial harmful algal blooms (HABs) are increasing in a growing number of aquatic ecosystems around the world due to eutrophication and climatic change over the past few decades. Quantitative monitoring of HABs remains a challenge because their distributions are spatially heterogeneous and temporally variable. Most of the standard biological sampling methods are labor intensive and time consuming. In this paper, we present an efficient acoustic method to assess the biomass (biovolume) concentration of the cyanobacterium Microcystis in aquatic ecosystems. Acoustic backscattering vertical profiles from a gas-bearing Microcystis population were measured with echosounders at three frequencies (70, 120, and 333 kHz) in Lake Kinneret (case study). Concurrently, the volume concentration of Microcystis colonies and cyanobacteria-related Chlorophyll a were evaluated. We developed a partially coherent acoustic scattering model to quantify the cyanobacterium biomass based on depth-dependent acoustic backscattering signals. We also evaluated empirical regression models to obtain the Microcystis biomass from acoustically measured volume backscattering strength, Sv. It is demonstrated that both methods can convert the Sv to Microcystis biovolume concentrations reasonably well. Pro and cons of these methods are discussed. The results suggest that the presented methods may have a potential to be used for broader applications to monitor and quantify the gas-containing plankton in large aquatic ecosystems.

Abiotic Drivers of a Deep Cyanobacteria Layer in a Stratified and Eutrophic Lake

AbstractHarmful algal blooms (HABs), in particular those consisting of the cyanobacteria Microcystis, are becoming increasingly more common across the globe. Despite the growing body of evidence that suggests vertical heterogeneity of Microcystis can be a precursor to HAB formation, the abiotic drivers of vertical distribution of Microcystis are poorly understood in the field environment. The prediction of subsurface cyanobacteria is also pertinent because subsurface concentrations are not easily recognizable to the public or lake system managers, creating a risk of exposure to harmful algal toxins. High‐frequency temporal and vertical data were collected from a research station anchored in a stratified and eutrophic lake for five months. Using a combination of dimensional analysis and machine learning approaches, data show that the magnitude of the subsurface Microcystis concentration peak and the center of gravity of the deep cyanobacteria layer are statistically significantly mediated by the thermal structure of the lake. The peak subsurface cyanobacteria biovolume is related to the thermocline depth and temperature, whereas the center of gravity of the subsurface cyanobacteria biovolume is related to the mixed layer depth and temperature. Furthermore, our data suggest there is a seasonal evolution of the subsurface cyanobacteria center of gravity that could potentially indicate timing of HAB onset. Based on easily measured parameters associated with the vertical lake temperature profile and meteorological conditions, we provide evidence of predictable trends in subsurface cyanobacteria variables.

Feedback regulation of surface scum formation and persistence by self-shading of Microcystis colonies: Numerical simulations and laboratory experiments

Light availability is an important driver of algal growth and for the formation of surface blooms. The formation of Microcystis surface scum decreases the transparency of the water column and influences the vertical distribution of light intensity. Only few studies analysed the interactions between the dynamics of surface blooms and the light distribution in the water column. Particularly the effect of light attenuation caused by Microcystis colonies (self-shading) on the formation of surface scum has not been explored. In the present study, we simulate the effect of variable cell concentration of Microcystis colonies on the vertical distribution of light in the water column based on experimental estimates of the extinction coefficient of Microcystis colonies. The laboratory observations indicated that higher cell concentration of Microcystis enhance the light attenuation in water column and promotes surface scum formation. We extended an existing model for the light-driven migration of Microcystis by introducing the effect of self-shading and simulated the dynamics of vertical migration for different cell concentrations and different colonial morphologies. The simulation results show that high cell concentrations of Microcystis promote surface scum formation, as well as its persistence throughout diel photoperiods. Large and tight Microcystis colonies facilitate scum formation, while small and loose colonies increase scum stability and persistence. This study reveals a positive feedback regulation of Microcystis surface scum formation and stability by self-shading and provides novel insights into the underlying mechanisms.

Comparative toxicological effects of planktonic Microcystis and benthic Oscillatoria on zebrafish embryonic development: Implications for cyanobacteria risk assessment.

Planktonic and benthic cyanobacteria blooms are increasing in frequency in recent years. Although many studies have focused on the effects of purified toxins or cyanobacteria extracts on fish developments, the more complex impacts of cyanobacteria cells on fish populations are still considered insufficient. This study compared the toxicological effects of harmful planktonic Microcystis and benthic Oscillatoria on zebrafish (Danio rerio) early stages of development. Zebrafish embryos, at 1-2h post fertilization (hpf), were exposed to 5, 10, and 20×105cells/mL Microcystis (producing microcystins) or Oscillatoria (producing cylindrospermopsins) until 96 hpf. The results indicated that the effects of benthic Oscillatoria on embryonic development of zebrafish were different from those of planktonic Microcystis. Reduced hatching rates, increased mortality, depressed heart rates and elevated malformation rates were observed following exposures to increased concentrations of Microcystis, whilst Oscillatoria exposures only caused yolk sac edemas. Exposure to a high concentration of Microcystis induced severe oxidative damage, growth inhibition and transcriptional downregulations of genes (GH, GHR1, IGF1, IGF1rb) associated with the growth hormone/insulin-like growth factor (GH/IGF) axis. Although Oscillatoria exposure did not affect the body growth, it obviously enhanced the antioxidant enzyme activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) and up-regulated the expressions of several oxidative stress-related genes. Discrepancies in the developmental toxicity caused by Microcystis and Oscillatoria may not only attributed to the different secondary metabolites they secrete, but also to the different adhesion behaviors of algal cells on embryonic chorion. These results suggested that harmful cyanobacteria cells could influence the successful recruitment of fish, while the effects of benthic cyanobacteria should not be ignored. It also highlighted that the necessity for further investigating the ecotoxicity of intact cyanobacterial samples when assessing the risk of cyanobacterial blooms.

Algal bloom inhibition through cobalt nano particles to control Oscillatoria growth in fresh water lakes

Cobalt nano particles (CoNPs) were synthesized and tested against microalgae isolated from fresh water cyanobacterial blooms by assessing the effects on growth rate, biomass concentration and biochemical parameters. Oscillatoria was identified as the predominant isolate from algal blooms and treated with varying concentrations (1, 2, 3, 4 and 5 mg L-1) of CoNPs. Steady decline in the growth rate of microalgae was observed at the end of 5 days indicating the toxicity of CoNPs on microalgal growth. At the end of cultivation period, 88% of reduction in biomass concentration of Microcystis and Oscillatoria were observed at 5 mg L-1 of CoNPs. Both protein and carbohydrate contents of the microalgae were reduced with increasing concentration of nano particles. Based on the findings, this study demonstrates the efficiency of cobalt nano particles (CoNPs) on inhibition of fresh water algal blooms thereby reducing the eutrophication problem.

Microcystis aeruginosa affects the inducible anti-predator responses of Ceriodaphnia cornuta

Cyanobacterial blooms are an increasing problem in a more eutrophic world. It is still a challenge to fully understand the influence of cyanobacteria on the interactions between predator and prey at higher trophic levels. The present study was mainly undertaken to understand the inducible anti-predator responses of cladocerans while using cyanobacteria as part of food. Specifically speaking, we focused on the anti-predator strategies of Ceriodaphnia cornuta in response to different predators (fish and Chaoborus larvae) under food with different proportions of Microcystis aeruginosa. The morphological (i.e., body size and the induction of horns) and life history traits (e.g., time to first reproduction, offspring number, and survival time) responses were measured under different proportions of M. aeruginosa (i.e., 0%, 20%, 40%, 60%, 80%, and 100%). Our results showed that both the life history and the inducible anti-predator responses of C. cornuta were significantly affected by different concentrations of M. aeruginosa. Specifically, lower concentrations of Microcystis (20%–60%) can significantly promote the horns induction under Chaoborus predation risks, and higher Microcystis concentrations (60%–100%) tend to enhance reproduction in response to fish predation risks, such as larger body size, decreased time to first reproduction, and increased total offspring number. Additionally, an increasing concentration of M. aeruginosa decreased the ability of C. cornuta to reverse horns when predation risks removed. Our findings indicated that cyanobacteria affecting life history traits and the subsequent indirect effects on anti-predator responses in cladocerans could impact the interactions between predator and prey at higher trophic levels and may consequently contribute to shaping the structure of the community in a cyanobacteria bloom area.

Three-dimensional numerical modeling of the cyanobacterium Microcystis transport and its population dynamics in a large freshwater reservoir

Cyanobacterial blooms pose severe ecological and economical threats in lakes and reservoirs. Understanding the complex physical transport and biological features of cyanobacteria (also known as blue-green algae) is important for predicting blooms in freshwater systems. In this study, a three-dimensional model for nonhydrostatic free surface flow and Microcystis sp. (cyanobacteria) transport and associated population dynamics is presented. The hydrodynamic model solves the Reynolds-averaged Navier-Stokes equations using a semi-implicit, fractional time-step finite difference method. The hydrodynamic model can couple Microcystis transport to a population dynamics model that simulates buoyancy, vertical migration, and effects of temperature, light, nutrients, and salinity on the concentration of Microcystis. Microcystis transport was determined by solving the convection-diffusion equation. The vertical migration of Microcystis was simulated based on buoyancy density changes of a colony at a given depth and time due to irradiance. The transient Microcystis production at a given depth was calculated based on the effects of different environmental factors such as depth, irradiance, and temperature. The model was used to analyze the transport and growth of Microcystis in Milford Lake, which is the largest man-made lake in Kansas. Transport and population dynamics of Microcystis under different environmental conditions were simulated, and the effects of different environmental factors were compared in a 20-hour test. Overall, physical processes like wind mixing most effected Microcystis distribution throughout the simulation; when wind was low, water column turbidity effected Microcystis distribution more than temperature or ambient light. This study is the first 3D nonhydrostatic free surface flow computational model that includes Microcystis transport, buoyancy regulation/vertical migration, and population dynamics. Nonhydrostatic models are needed because existing ecological models with hydrostatic approximation can be ill-posed when dealing with open boundaries, and hydrostatic approximation is not valid when dealing with flow over rapidly changing slopes. The current model is a robust and efficient way to model Microcystis transport and can be applied to studies of other surface water systems effectively.

The importance of calcium in improving resistance of Daphnia to Microcystis.

Changing environmental calcium (Ca) and rising cyanobacterial blooms in lake habitats could strongly reduce Daphnia growth and survival. Here, we assessed the effects of maternal Ca in Daphnia on transfer of resistance to their offspring against Microcystis aeruginosa PCC7806 (M. aeruginosa). Laboratory microcosm experiments were performed to examine effects in Daphnia carinata (D. carinata) and Daphnia pulex (D. pulex), and that how Ca induce responses in their offspring. The results showed that growth and survival were increased in offspring from exposed Daphnia as compared to unexposed, when raised in high Ca and increasing M. aeruginosa concentration. Among exposed Daphnia, offspring from high Ca mothers, produced more neonates with large size and higher survival as compared to offspring from low maternal Ca. Exposed D. carinata and D. pulex offspring, when reared in Ca deficient medium and increasing M. aeruginosa concentration, time to first brood increased, size become large and total offspring decreased subsequently in three alternative broods in offspring from low maternal Ca. In contrast, growth and reproduction in offspring from high Ca exposed mothers were consistent in three alternative broods. Despite species specific responses in growth, survival and variant life history traits in two Daphnia species, our results not only show maternal induction in Daphnia but also highlight that offspring response to M. aeruginosa varies with maternal Ca. This study demonstrates that Ca have role in Daphnia maternal induction against Microcystis, and recent Ca decline and increasing Microcystis concentration in lakes may decrease Daphnia growth and survival. Our data provide insights into the interactive effect of maternal Ca and Microcystis exposure on Daphnia and their outcome on offspring life history traits and survival.

Effects of &lt;i&gt;in-situ&lt;/i&gt; simulative mixing on colony size of &lt;i&gt;Micrcocystis&lt;/i&gt; in Lake Taihu

风浪扰动是影响湖泊生态系统重要的环境因素之一.为了解风浪扰动对湖泊微囊藻群体大小的影响，在野外模拟了风浪扰动对太湖微囊藻群体大小的影响.结果表明，实验组模拟风浪连续扰动24 h，扰动结束时实验组和对照组微囊藻群体大小分别为68.38和12.56 μm，实验组和对照组微囊藻群体大小呈极显著差异；扰动结束时实验组和对照组微囊藻胞外多糖含量分别为1.49×10^-6和1.26×10^-6 mg/cell，二者差异显著.表明适当强度的风浪扰动短时间内能促使微囊藻群体显著增大，有助于人们对太湖微囊藻水华暴发机理的认识.;Mixing induced by wind-wave is one of the important factors in lake ecosystems. To understand the effects of mixing induced by wind-wave on colony size of Microcystis in lake, an in-situ experiment was conducted in Lake Taihu. The results showed that the colony size of Microcystis in treatments with wind wave for 24 h and in control was 68.38 and 12.56 μm, respectively. There was a significantly difference between them. The extracellular polysaccharides concentration of Microcystis in treatment with mixing continuing for 24 h was 1.49×10^-6 mg/cell, which was significant higher than that in control(1.26×10^-6 mg/cell). The results suggested that appropriate intensity of mixing induced by wind-wave can significantly enlarge the colony size of Microcystis in a short time. It will helpful to understand the mechanism of the Microcystis blooms in Lake Taihu.

Evaluation of models generated via hybrid evolutionary algorithms for the prediction of &lt;i&gt;Microcystis concentrations&lt;/i&gt; in the Vaal Dam, South Africa

Cyanobacteria are responsible for many problems in drinking water treatment works (DWTW) because of their ability to produce cyanotoxins that potentially can have an adverse effect on consumer health. Therefore, the monitoring of cyanobacteria in source waters entering DWTW has become an essential part of drinking water treatment management. Managers of DWTW rely heavily on results from physical, chemical and biological water quality analyses, from grab samples, for their management decisions. However, results of water quality analyses may be delayed from 3 h to 14 days depending on a magnitude of factors such as sampling, distance and accessibility to laboratory, laboratory sample turnaround times, specific methods used in analyses, etc. Therefore, the benefit to managers and production chemists to be able to forecast future events of high cyanobacterial cell concentrations in the source water is evident. During this study, physical, chemical and biological water quality data from samples taken from 2000 to 2009 in the Vaal Dam, supplying South Africa’s largest bulk drinking water treatment facility, were used to develop models for the prediction of the cyanobacterium Microcystis sp. in the source water (real-time prediction together with 7, 14 and 21 days in advance). Water quality data from the Vaal Dam from 2010–2012 were used to test these models. The model showing the most promising results for incorporation into a ‘Cyanobacterial Incident Management Protocol’ is the one predicting Microcystis sp. 7 days in advance. This model showed a square correlation coefficient (R 2 ) of 0.90 when tested with the testing dataset (chosen by bootstrapping from the 2000–2009 input dataset) and a R 2 of 0.53 when tested with the 3-year ‘unseen’ dataset from 2010–2012. Keywords : cyanobacteria, drinking water treatment works, prediction models, cyanobacterial incident management protocol, water safety plan

Extracellular microcystin prediction based on toxigenic Microcystis detection in a eutrophic lake.

Existing models for predicting microcystin concentration in water body generally use chlorophyll or cyanobacteria concentration as input variables, although microcystins only originate from toxigenic strains of a few species. Moreover, the nonconcurrency between harmful algal growth and toxin release has yet to be quantified. Therefore, this study explored a new prediction method that considers these toxin production mechanisms for the eutrophic Yangcheng Lake, a large-scale drinking water source in China. The Lake was monitored weekly at six sampling sites from July to October in 2012, including the detection of toxigenic Microcystis (expressed as mcyA copy number) by qPCR. Compared with chlorophyll a, cyanobacteria, and total Microcystis abundance, toxigenic Microcystis concentration was more significant in predicting extracellular microcystin. Site-specific nonlinear regression models that link mcyA to microcystins were established. Parameters for toxin release delay (i.e., one or two weeks) were embedded in these models. Further analysis ascribed the different release timescale to NH3-N:TN and TN:TP ratios of approximately 0.015 and 9.2, respectively, which may decrease the delay in microcystin release. Model applications in determining mcyA monitoring frequency and its warning thresholds were discussed.

Feeding response of &lt;i&gt;Daphnia&lt;/i&gt; cf.&lt;i&gt; similis&lt;/i&gt; to different concentration gradients of &lt;i&gt;Microcystis&lt;/i&gt; and its implication for preventing algal blooming

Daphnia are important components of zooplankton communities in lakes, ponds and reservoirs. Currently freshwater ecosystems are affected worldwide by Cyanobacterial blooms through the process of eutrophication. The objective of this study was to provide experimental evidence to the response of Daphnia to various concentrations of Microcystis . The experiment contained four treatments and two controls each with three replicates. The first control contained D . cf. similis without Microcystis and the second control contained Microcystis without D .cf. similis . The remaining four treatments contained both D . cf. similis and Microcystis at different concentration of Microcystis .. The results showed a significant negative relationships between D . cf. Similis and Microcystis across the treatments (F=294.5; p<0.00). From the four Microcystis concentration gradients, we found mortality of D. cf. Similis in HMC (high Microcystis concentration) and 67% of the original HMC gradient while in the other treatments, in 43% and 22% original HMC treatment, D . cf. Similis reproduce and attain high density. Therefore, from these results it is concluded that D . cf. similis can control the growth of Microcystis if the concentration is low but they cannot reduce an already existing bloom. Keywords : Concentration gradient, D. cf. Similis, Feeding-treatment, Microcystis, Ethiopia.

English

In the last decades, large number of reported cases of illnesses in Mozambique is related to drinking water. However, only a limited number of studies have focused on aquatic pollution in this country. Cyanobacterial blooms dominated by&nbsp;Microcystis&nbsp;sp are regularly identified in freshwater bodies in Mozambique.&nbsp;Microcystis&nbsp;is known to proliferate in freshwater bodies and produce microcystins which have adverse effects on animals and humans. The aim of this study was to quantify microcystin-producingMicrocystis&nbsp;in three different freshwater bodies in Southern Mozambique. TaqMan based real time polymerase chain reaction (PCR) (Taq&nbsp;Nuclease Assay) was used to quantify populations of&nbsp;Microcystis&nbsp;in three aquatic ecosystems in Southern Mozambique. Total&nbsp;Microcystis&nbsp;spp (microcystin-producing and non-producing strains) were quantified in the three selected study areas with the determination of the copy numbers of the phycocyanin (PC) operon.&nbsp; Microcystin-producing gene copy numbers were quantified using specific primer pair, amplifying the&nbsp;mcyB gene.Microcystis mcyB copy numbers varied from&nbsp;4.2 x 106&nbsp;to&nbsp;1.6 x 109&nbsp;gene copies /L in 2008, corresponding to 2.15 to 98.55% of total&nbsp;Microcystis, and from&nbsp;9.6 x 107&nbsp;to 4.5 x 109&nbsp;gene copies /L&nbsp;in 2009, corresponding to 1.53 to 34.52% of total&nbsp;Microcystis. High copy numbers of&nbsp;mcyB occurred in Nhambavale Lake in June 2008, whereas in March 2009, high copy numbers of&nbsp;mcyB was observed in Ch&ograve;kw&eacute; Irrigation Channels. Samples from Pequenos Libombos Dam had the lowest number of&nbsp;mcyB gene copies in both sampling periods. The findings of the present study show that microcystin-producing strains are common in Southern Mozambique, and that their absolute and relative numbers varies geographically and temporarily. The highest concentration of&nbsp;Microcystis sp.&nbsp;in the sampling areas occurred in samples collected in March 2009, which corresponds to the rain season with warm temperatures. To our knowledge, this is the first report of the quantification of microcystin-producingMicrocystis&nbsp;in Mozambique using molecular techniques. Key words:&nbsp;Microcystis sp, Taq nuclease assay, phycocyanin (PC),&nbsp;mcyB, Mozambique.

Coupling hydrodynamics and buoyancy regulation in Microcystis aeruginosa for its vertical distribution in lakes

In this research we introduce a coupled column model to simulate the vertical migration of Microcystis aeruginosa in natural lakes. M. aeruginosa is a unicellular cyanobacteria that form colonies. They produce toxins and therefore become a potential threat to water quality and human health. Understanding the distribution of this species in space and time is important for improving water management strategies. The model we propose includes both hydrodynamics and physiological responses including explicitly buoyancy regulation in Microcystis cells. Our model applies the Langevin–Fokker–Planck approach to simulate the total colony number concentration along the water column. This approach allows the description of sinking and rising velocities of colonies of different sizes and compositions subjected to turbulent mixing. The model is first applied to the 30m deep Lake Vlietland in the Netherlands for the summer of 2009. During this summer, the lake showed high blooms of Microcystis which eventually led to scum formation along the shore. The simulations show the preferential distribution of M. aeruginosa through the water column and their strong dependency on colony size. On a daily cycle, small colonies (50–200μm) do not remain near the surface but are highly concentrated in the middle of the epilimnion, whereas large colonies (≥800μm) are able to migrate to greater depths and concentrate only temporarily near the surface. For comparing our computer model with available measurements of Microcystis concentration distributions we applied it to Lakes IJsselmeer and Vinkeveen. The results show a good agreement with the observations of diurnal changes in buoyancy status.

Increasing Microcystis cell density enhances microcystin synthesis: a mesocosm study

An experimental protocol using mesocosms was established to study the effect of Microcystis sp. cell abundance on microcystin production. The mesocosms (55 L) were set up in a shallow eutrophic lake and received either no (control), low (to simulate a moderate surface accumulation), or high (to simulate a dense surface scum) concentrations of Microcystis sp. cells collected from the lake water adjacent to the mesocosms. In the low- and high-cell addition mesocosms (2 replicates of each), the initial addition of Microcystis sp. cells doubled the starting cell abundance from 500 000 to 1 000 000 cells mL−1, but there was no detectable effect on microcystin quotas. Two further cell additions were made to the high-cell addition mesocosms after 60 and 120 min, increasing densities to 2 900 000 and 7 000 000 cells mL−1, respectively. Both additions resulted in marked increases in microcystin quotas from 0.1 pg cell−1 to 0.60 and 1.38 pg cell−1, respectively, over the 240 min period. Extracellular microcystins accounted for <12% of the total microcystin load throughout the whole experiment. The results of this study indicate a relationship between Microcystis cell abundance and/or mutually correlated environmental parameters and microcystin synthesis.

Potential synergistic effects of microcystins and bacterial lipopolysaccharides on life history traits of Daphnia galeata raised on low and high food levels

Metastudies have found no consistent effects of the cyanobacterial toxin microcystin on Daphnia, and there are discrepancies between field observations and experiments. Confounding factors include absence or presence of alternative high quality food or the presence of bioactive compounds, other than microcystins in cyanobacteria. Of specific interest are lipopolysaccharides (LPS) on the outer cell wall. LPS may have a number of biological effects, including reduced detoxication of microcystins in plants and animals. When grazing seston in the field, filterfeeders take up heterotrophic bacteria attached to cyanobacteria, as well as free-living bacteria. The LPS produced by heterotrophic bacteria have been shown to be much more harmful than cyanobacterial LPS. We performed two experiments in which we tested for potential synergistic effects between bacterial LPS and microcystins. Full-factorial experiments separated the main effects and interactions between (i) food quantity as well as food quality (addition of the green alga Scenedesmus), (ii) presence or absence of strains that vary in amount and composition of microcystins (microcystin free strain NIVA-CYA43, moderate microcystin producing strain NIVA-CYA140 and high microcystin producing strain PCC7820), and (iii) presence or absence of bacterial LPS on different life history traits of Daphnia galeata. We measured juvenile growth rate, age and size at first reproduction, death before first reproduction and standard carbon content of Daphnia. From the experiments we conclude that microcystin-producing Microcystis had deleterious effects on the life history of D. galeata, but especially when the availability of high quality green algal food was limited in comparison to the supply of microcystin producing strain PCC7820. In the experiment in which PCC7820 was used as microcystin-producing strain, addition of LPS lowered SCC of Daphnia, but had no effects on other life history parameters. The interaction between Microcystis strain, Microcystis concentration and LPS was highly significant in case of PCC7820, but not in case of CYA-140, indicating that the effects of LPS and its interactions with microcystin on Daphnia life history were strongly context dependent.