Overwintering of Microcystis aeruginosa Kutz. in a shallow lake

The standing crop and photosynthetic activity of Microcystisaeruginosa Kütz. in both the plankton and sediment wereinvestigated from November 1979 to May 1982 in Lake Kasumigaura,Japan. The number of planktonic colonies of this species decreasedfrom early autumn to early spring, but increased in the sedimentduring late summer and autumn. The overwintering colonies inthe sediment were –100–1000 times greater per unitarea than those in lake water. No photoinhibition of photosynthesiscould be observed in overwintering Microcystis. The values ofthe initial slopes of photosynthesis-light (P-I) curves weresimilar to those of the summer population, although the maximumphotosynthetic rate (P_max) measured at 20°C was lower thanthat of the summer planktonic population. In winter the valuesof initial slope of the P-I curve, and the ratio of phycobilinto chlorophyll a sorted from sediment were higher than in coloniesfrom the plankton.     

Distribution and toxicity of a new colonial Microcystis aeruginosa bloom in the San Francisco Bay Estuary,California

The first distribution, biomass and toxicity study of a newly established bloom of the colonial cyanobacteria Microcystis aeruginosa was conducted on October 15, 2003 in the upper San Francisco Bay Estuary. Microcystis aeruginosa was widely distributed throughout 180 km of waterways in the upper San Francisco Bay Estuary from freshwater to brackish water environments and contained hepatotoxic microcystins at all stations. Other cyanobacteria toxins were absent or only present in trace amounts. The composition of the microcystins among stations was similar and dominated by demethyl microcystin-LR followed by microcystin-LR. In situ toxicity computed for the >75 m cell diameter size fraction was well below the 1 g l^–1 advisory level set by the World Health Organization for water quality, but the toxicity of the full population is unknown. The toxicity may have been greater earlier in the year when biomass was visibly higher. Toxicity was highest at low water temperature, water transparency and salinity. Microcystins from the bloom entered the food web and were present in both total zooplankton and clam tissue. Initial laboratory feeding tests suggested the cyanobacteria was not consumed by the adult copepod Eurytemora affinis, an important fishery food source in the estuary.     

Toxic substance from a natural bloom of Microcystis aeruginosa.

A toxic substance contained in the blue-green alga Microcystis aeruginosa was purified and partially characterized. Toxic algal cells were collected from a highly eutrophic lake in Japan, and the toxin was purified by homogenization, ultrafiltration, gel filtration, and ion-exchange chromatography. The final preparation gave a single peak on high-performance liquid chromatography. The toxicity was somewhat less than that reported for other toxins from this alga. The water extract of 6.7 mg (dry weight) of cells and 72 microgram of the purified protein was required to kill a mouse (1 mouse unit). The main amino acids of the toxin were glutamic acid, asparatic acid, alanine, glycine, arginine, and leucine. The molecular weight of the toxin was 2,950 as determined by high-performance liquid chromatography.     

Sedimentation of phytoplankton populations dominated by Microcystis in a shallow lake

The sedimentary flux of phytoplankton was measured using sedimenttraps in a shallow hypertrophic lake (Lake Kasumigaura), whereMicrocystis bloomed, from June to November 1983 The sedimenttraps were set at 0.5, 1.5 and 3.0 m depth in Takahamairi Bay(3.5 m depth). Microcystis spp. (including M.aerugmosa and M.viridis)in the traps were rare until early August, but increased thereafter.Sinking rates of Microcystis were 0.0045, 0.020 and 0.24 m day^–1in June–August, September and October respectively, whichwere far lower than those of Melosira (0.2–1.7 m day^–1)and Syncdra (0.2–1.0 m day^–1). The total sedimentaryfluxes of POC and that of algal carbon during the study periodwere 283.2 and 96.7 gC m^–2 which were 59.5% and 20.3%of the gross primary production (475.8 gC m^–2) respectively.The sedimentary flux of living algae measured by algal countswas large in June but small in August and September. On theother hand, the flux of detritus obtained by subtracting totalalgal carbon from POC was small in June and July but large inAugust and September. Therefore diatoms, which appeared mostlyin June, tended to sink as live algae, while Microcystis sankas detritus after being decomposed or consumed in the waterIt was concluded from the results of carbon budget calculationsand the respiration rate of the 1- to 20-µm fraction thatthe activity of decomposers or consumers increased greatly inthe short period at the end of the bloom of Microcystis.     

Environmental factors favouring the formation of Microcystis aeruginosa hyperscums in a hypertrophic lake

Hyperscums are crusted buoyant mats of densely packed cyanobacteria, often decimeters thick, that persist for periods of weeks to months at the same site. In Hartbeespoort Dam, a hypertrophic lake in South Africa, hyperscums of the cyanobacterium Microcystis aeruginosa that cover more than a hectare and contain up to 2 tons of chlorophyll a typically form in winter and persist for 2–3 months. This paper reports on the environmental conditions that favour hyperscum formation.Reynolds & Walsby (1975) postulated that cyanobacterial bloom formation depended on the coincidence of three preconditions: a pre-existing population, a significant proportion of the organisms having positive buoyancy, and turbulent mixing that is too weak to overcome the tendency of the cells to float. This model of bloom formation is evaluated in the context of hyperscums, based on a case-study from Hartbeespoort Dam. We examine the occurrence of hyperscums and the dynamics of their formation and breakdown in relation to diurnal and seasonal changes in the wind regime and in relation to the population dynamics and buoyancy of Microcystis. We conclude that Reynolds and Walsby's preconditions are essential but not sufficient to explain hyperscum formation. The additional preconditions are prolonged low speed wind regime, suitable lake morphometry, large cyanobacterial standing crops, and high insolation. The rare co-occurrence of these conditions make hyperscums an uncommon phenomenon, but with increasing eutrophication worldwide the frequency and distribution of hyperscum occurrence are likely to increase.     

The genetic and ecophysiological diversity of Microcystis

Microcystis is a cyanobacterium that forms toxic blooms in freshwater ecosystems around the world. Biological variation among taxa within the genus is apparent through genetic and phenotypic differences between strains and via the spatial and temporal distribution of strains in the environment, and this fine-scale diversity exerts strong influence over bloom toxicity. Yet we do not know how varying traits of Microcystis strains govern their environmental distribution, the tradeoffs and links between these traits, or how they are encoded at the genomic level. Here we synthesize current knowledge on the importance of diversity within Microcystis and on the genes and traits that likely underpin ecological differentiation of taxa. We briefly review spatial and environmental patterns of Microcystis diversity in the field and genetic evidence for cohesive groups within Microcystis. We then compile data on strain-level diversity regarding growth responses to environmental conditions and explore evidence for variation of community interactions across Microcystis strains. Potential links and tradeoffs between traits are identified and discussed. The resulting picture, while incomplete, highlights key knowledge gaps that need to be filled to enable new models for predicting strain-level dynamics, which influence the development, toxicity and cosmopolitan nature of Microcystis blooms.     

Molecular characterization of cyanobacterial diversity in a shallow eutrophic lake

We have studied the diversity of pelagic cyanobacteria in Lake Loosdrecht, The Netherlands, through recovery and analysis of small subunit ribosomal RNA gene sequences from lake samples and cyanobacterial isolates. We used an adapted protocol for specific amplification of cyanobacterial rDNA for denaturing gradient gel electrophoresis (DGGE) analysis. This protocol enabled direct comparison of cyanobacterial community profiles with overall bacterial profiles. The theoretical amplification specificity of the primers was supported by sequence analysis of DNA from excised DGGE bands. Sequences recovered from these bands, in addition to sequences obtained by polymerase chain reaction (PCR) and cloning from lake DNA as well as from cyanobacterial isolates from the lake, revealed a diverse consortium of cyanobacteria, among which are representatives of the genera Aphanizomenon, Planktothrix, Microcystis and Synechococcus. One numerically important and persistent cyanobacterium in the lake, Prochlorothrix hollandica, appeared to co-occur with an unknown but related species. However, the lake is dominated by filamentous species that originally have been termed 'Oscillatoria limnetica-like'. We show that this is a group of several related cyanobacteria, co-occurring in the lake, which belong to the Limnothrix/Pseudanabaena group. The available variation among the coexisting strains of this group can explain the persistent dominance of the group under severe viral pressure.     

Allelopathic effect of Microcystis aeruginosa on Microcystis wesenbergii: microcystin-LR as a potential allelochemical

Microcystis aeruginosa and Microcystis wesenbergii are two cyanobacteria commonly found in eutrophic shallow lakes. Previous studies reported that microcystin-producing M. aeruginosa could have an increased competitive potential on other algae and aquatic plants, and microcystin-LR (MC-LR) was regarded as an allelochemical. Based on this hypothesis, the allelopathic interaction between these two cyanobacteria was studied for the first time under laboratory conditions, and potential allelochemicals were screened. Cyanobacteria biomass and microcystin-LR (MC-LR) concentration were monitored under different culture conditions. The potential allelochemicals from M. aeruginosa were investigated by extract fractionation and GC(LC)/MS analysis. The growth of M. wesenbergii was inhibited by the addition of cell-free filtrates of M. aeruginosa whereas M. aeruginosa was promoted by the addition of cell-free filtrates of M. wesenbergii. The higher polarity the extract of M. aeruginosa is, the stronger the inhibition effect of the extract on M. wesenbergii will be. According to our results, M. aeruginosa has a significant allelopathic inhibition effect on M. wesenbergii. Allelopathic compounds from M. aeruginosa have synergistic effects on inhibition of M. wesenbergii. Besides microcystin, there may be other allelopathic compounds in M. aeruginosa.     

Contribution of grazing in phytoplankton overall losses in a shallow French lake

SUMMARY 1. Based on data for ¹⁴C-primary production and biomass changes in a small and shallow lake (Créteil Lake, France), overall phytoplankton losses were calculated through an annual cycle (November 1985-October 1986). The summer period in 1986 is compared with two other summer periods in 1985 and 1980, these two years corresponding to extreme levels of algal biomass.
2. Independent from the trophic state of the lake, phytoplankton populations were dominated by small-sized species (<20 μm); their high growth rate (maximal in May and June: 0–8 day⁻¹) was characteristic of nanoplanktonic natural populations.
3. The positive correlation between phytoplankton losses and production indicates a close coupling between growth and loss processes.
4. With a high filtering rate (0.22 day⁻¹ as an annual average), zoo-plankton impact is considerable at any time of the year but especially in late summer, when grazing losses exceeded primary production.
5. Despite the uncertainty concerning the meaning of ¹⁴C-primary production, the persistence of small algae throughout the year implies that a great part of the phytoplankton production was harvested by grazers which led to a recycling of organic matter within the water column.     

Structural, physical and chemical characteristics of Microcystis aeruginosa hyperscums from a hypertrophic lake

SUMMARY. 1. This paper examines the structural, physical and chemical characteristics of cyanobacterial hyperscums (floating scums of densely packed eyanobacteria. measuring decimetres in thickness, that are covered by a dry crust of photo-oxidized cells) from hypertrophic Hartbeespoort Dam, South Africa. 2. The hyperscum community was a cyanobacterial-baclcrial association, in which the cyanobacterium Microcystis aeruginosa comprised 98% of the biovolumc, with cell concentrations exceeding 10⁹ ml^?1. 3. The buoyancy mechanism of M. aeruginosa and evaporation at the surface led to increasing compaction of the colonies with declining distance from the surface, and the formation of three distinct, but continuous layers: a 1–2 mm dry surface crust (water content: 14%, chlorophyll a concentration: 3 g l^?1), a 5–10 mm compact layer just below the crust (77% water, 1 g l^?1 chlorophyll a), and a less compact layer (96% water, 200–500 mg l^?1 chlorophyll a) from about 1 cm depth to the bottom, comprising the bulk of the hyperscum. 4. The crust attenuated all the incident light and reduced free gas exchange. Beneath it continuously dark anaerobic, highly reduced conditions prevailed. As the hyperscum aged over 3 months in 1984, at 10 cm depth the pH gradually declined from 6.6 to 5.9, interstitial water ammonia-N concentrations increased from 0.45 to 119 mg l^?1, soluble reactive phosphorus from 2.8 to 83.3 mg l^?1, and dissolved organic carbon reached a maximum of 460 mg l^?1. At any point in time these concentrations declined gradually with increasing depth within the hyperscum, and declined dramatically beneath the hyperscum. Similar patterns were recorded in another hyperscum in 1986. 5. The chemical and temperature depth profiles indicated that free water movement took place around and under the hyperscum, but within it water movement was restricted to diffusion. 6. Gas bubbles composed of 28% methane. 19% CO₂, 53% N₂, and traces of H₂ trapped within the hyperscum, and the presence of volatile fatty acids in the interstitial water were indicative of anaerobic decomposition processes mediated by fermenting and methanogenic bacteria, and N:P ratios below 1.5 in the interstitial water suggested that nitrogen was lost as gas, possibly through denitrification. 7. We hypothesize that the major sites of decay of M. aeruginosa were the crust and the compact layer beneath it, while deeper within the hyperscum this cyanobacterium could survive prolonged periods of dark anaerobic conditions. This hypothesis requires confirmation.     

Temporal evolution and vertical stratification of Microcystis toxic potential during a first bloom event

In order to study the setup of a Microcystis bloom and the evolution of its toxic potential, we studied the temporal and vertical variations in Microcystis aeruginosa abundance, microcystins (MC) concentrations (intracellular and extracellular), and the relative proportion of potentially microcystin-producing cells (MC-producing cells) in relation to physicochemical parameters in the recently setup Moroccan reservoir “Yaacoub Al Mansour.” The Microcystis bloom appeared relatively late in the season and was associated with a low proportion of MC-producing cells in the water surface layer, probably related to non-limiting nutrient concentrations. Interestingly, the setup of the bloom leads to a vertical gradient, showing a decrease in Microcystis cell abundance inversely coupled with an increase in the proportion of MC-producing cells. Thus, this can be the result of the growth where non-MC-producing cells remain in the lighted water layer easier than MC-producing ones. Nevertheless, parameters other than light intensity may influence the toxic potential of bloom as no vertical pattern was observed concerning microcystins cellular quotas. The high microcystins concentrations measured in the deep water layer have also proved the importance of considering the deep part of aquatic ecosystem in the management of health risks associated with cyanobacterial proliferations.     

Isolation, characterization and pathology of the toxin from a Microcystis aeruginosa (= Anacystis cyanea) bloom.

The nature of the toxicity of a bloom of blue-green alga, M. aeruginosa (= Anacystis cyanea), that occurred in a man-made lake was investigated. Crude algal bloom extracts were toxic to laboratory mice when injected intraperitoneally. The lethal dose (LD100) of these extracts was 15-30 mg of lyophilized algal bloom per kilogram body weight. The toxin was purified by a procedure that included ammonium sulphate fractionation, solvent extraction, acid precipitation, Sephadex G25 and DEAE-Sephadex chromatography, and high-voltage electrophoresis at pH 6.5. The preparation gave a single spot on high-voltage electrophoresis at pH 9.0, had no free amino group, and was characterized by a simple amino acid composition of equimolar quantities of L-methionine, L-tyrosine, D-alanine, D-glutamic acid, erythro beta-methyl aspartic acid and methylamine. The LD50 for the purified toxin was estimated to be 0.056 mg/kg of mice, and the approximate LD100 is 0.070 mg/kg, based on the total material found from amino acid analysis. Parenteral administration of the purified toxin to mice produced extensive liver lobular haemorrhage and death within 1-3 h. Repeated inoculation of sublethal doses daily over some weeks produced progressive hepatocyte degeneration and necrosis and the development of fine hepatic fibrosis.     

Hyperscums of the cyanobacterium Microcystis aeruginosa in a hypertrophic lake (Hartbeespoort Dam, South Africa)

It is proposed that surface scums of densely packed planktoniccyanobacteria (blue-green algae) which exist for weeks to months,measure several decimeters in thickness and are covered by acrust of photo-oxidized cells, be called hyperscums. Hyperscumsof Microcystis aeruginosa formed during prolonged periods ofcalm weather in wind-protected sites in a hypertrophic lakesubject to low wind speeds (Hart beespoort Dam, South Africa).A hyperscum that extended over 1–2 hectares and persistedfor 103 days during winter 1983 was studied. Chlorophyll a concentrationsranged from 100 to 300 mg l^–2 Microcystis cell concentrationsreached 1.76x10⁹ cells ml^–1 or 116 cm³l^–1. The hyperscumenvironment was anoxic, aphotic, with a fluctuating temperatureregime and low pH values. The densely packed Microcystis cellssurvived these conditions for more than 2 months. This was shownby comparing the potential photosynthetic capacity of Microcystisfrom the hyperscum with that of Microcystis from the main basinof the lake. However, after 3 months the hyperscum algae losttheir photosynthetic capacity and decomposition processes prevailed.The hyperscum gradually shrank in size until a storm causedits complete disintegration.     

Genetic diversity of Microcystis populations in a bloom and its relationship to the environmental factors in Qinhuai River,China

Cyanobacterial blooms, forming massive scum and various cyanotoxins, increasingly spread in a wide range of freshwater ecosystems. One heavy Microcystis bloom occurred in the entire Qinhuai River basin in 2010 summer for the first time. To determine the Microcystis populations and their spatial distributions along Qinhuai River, a molecular approach was applied by sequencing the DNA library based on the internal transcribed spacer sequences of 16-23S rRNA (ITS). The parsimony network (TCS) analysis showed that 9 groups were formed based on the main 24 genotypes, and each group was dominated by one highly represented root sequence. Marked changes in the composition and proportion of the Microcystis ITS genotype were detected from the upper to the lower reaches. The seed sources forming the bloom were probably located at 4 different locations. Furthermore, it was found that pH was the primary factor affecting the spatial distribution of the main genotype group among samples.     

Genetic diversity of Microcystis populations in a bloom and its relationship to the environmental factors in Qinhuai River, China

Cyanobacterial blooms, forming massive scum and various cyanotoxins, increasingly spread in a wide range of freshwater ecosystems. One heavy Microcystis bloom occurred in the entire Qinhuai River basin in 2010 summer for the first time. To determine the Microcystis populations and their spatial distributions along Qinhuai River, a molecular approach was applied by sequencing the DNA library based on the internal transcribed spacer sequences of 16-23S rRNA (ITS). The parsimony network (TCS) analysis showed that 9 groups were formed based on the main 24 genotypes, and each group was dominated by one highly represented root sequence. Marked changes in the composition and proportion of the Microcystis ITS genotype were detected from the upper to the lower reaches. The seed sources forming the bloom were probably located at 4 different locations. Furthermore, it was found that pH was the primary factor affecting the spatial distribution of the main genotype group among samples.     

Valuable ingredients and feed toxicity evaluation of Microcystis aeruginosa acidolysis product in mice

This research studied the extraction from Microcystis aeruginosa using hydrochloric acid method as a potentially valuable protein resource from eutrophic lakes. Amino acid composition, residual algal toxins, and heavy metals of the acidolysis product were studied. After 18 h of hydrochloric acid treatment, the product of M. aeruginosa contained 17 amino acids, 51.34% of total amino acid requirements, and 30.25% of the livestock and poultry essential amino acid (Eaa). The residual microcystin-LR (MC-LR) was 0.94 µg kg⁻¹, which was less than WHO drinking water limit of microcystins. The removal ratio of microcystins was higher than 99.99% during the process of hydrolysis. The concentration of heavy metals of the product was in compliance with feed standards. Furthermore, using Horn’s method, Mouse Micronucleus Test and Sperm Shape Abnormality Test were conducted to study the forage safety of the product. Half lethal dose (LD₅₀) of acidolysis product in mice was >9.09 g kg⁻¹ body weight, actually belonging to non-toxic grade. Every dose treatment did not significantly increase activities of alkaline phosphatase (ALP), lactate dehydrogenase (LDH), and γ-glutamyltransferase (γ-GT). The results of both micronucleus test and sperm shape abnormality test were negative, which suggested the product with no mutagenicity and sperm malformation effects. This study indicated that the acidolysis product of M. aeruginosa was safe to be used as a feed ingredient.     

Temporal pattern of macroinvertebrate diversity and production in a new man made shallow lake

The construction of an aquatic system to recycle the wastewater coming from an experimental aquaculture plant provided the opportunity to follow the evolution of structural and functional properties of a community in a new eutrophic shallow lake. Specific aims of this study were to describe the temporal patterns of diversity and production of the macroinvertebrate assemblage in different habitats. The benthic assemblage was sampled monthly for 3 years starting 1 month after pond filling. Each month, replicate samples of invertebrates were collected with quantitative methods from 3 habitats: unvegetated bottom, submerged vegetation and emergent vegetation of the littoral zone. We collected a total of 48 macroinvertebrate taxa belonging to 38 families. The number of taxa increased rapidly during the first phase of colonization (93% of taxa were already recorded within 14 months from pond filling) and then slowly decreased through the next 2 years. Diversity pattern through time was not consistent among habitats, being higher in the unvegetated bottom during the first year and on the submerged vegetation and the littoral vegetation in subsequent years. Slopes of rank-abundance curves showed differences among years and habitats, even though all habitats showed a trend towards the increase of the relative dominance of few taxa (e.g. diminishing of slopes). Macroinvertebrate production changed with time and was different among habitats. The development of submerged and emergent macrophytes greatly increased not only the diversity, but also the production of the whole macroinvertebrate assemblage. %

     

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.     

Size-dependent growth of Microcystis colonies in a shallow,hypertrophic lake: use of the RNA-to-total organic carbon ratio

Microcystis was cultured under standard conditions in BG-11 and M-11 media. Using results of an analysis of RNA and total organic carbon (TOC) content, a significant logarithmic relationship between Microcystis growth rate and the RNA/TOC ratio was described to measure the growth rate. Colonial Microcystis samples collected in a shallow, hypertrophic lake (Lake Taihu, China) during May–November 2012 were divided into six size classes (<75, 75–100, 100–150, 150–300, 300–500, and >500 μm), and the RNA/TOC ratio of each class was analyzed to evaluate differences in growth. The growth rate of colonies in the 150–300-μm size class was highest from May to August, but the growth rate increased along with the increase in colony size from September to November. Our results also indicated that water temperature did not change the relationship between growth rate and colony size, but the growth rate of larger colonies was higher than the growth rate of smaller colonies at conditions of low total nitrogen, low total dissolved phosphorus concentration, and high light intensity. Taken together, these results suggest that large colonial Microcystis possess an advantage that is a consequence of this faster growth at lower nutrient concentrations and high light intensities.