Intracellular Microcystin Content Research Articles

Changes in microcystin concentration in Lake Taihu, 13 years (2007–2020) after the 2007 drinking water crisis

Since the 2007 water crisis occurred in Lake Taihu, substantial measures have been taken to restore the lake. This study evaluates the effectiveness of these restoration activities. We examined the physicochemical parameters and the distribution of microcystin and Microcystis in both the water column and sediment during the bloom period of May 2020 to October 2020. The mean value of extracellular and intracellular microcystin content was 0.12 μg L−1 and 16.26 μg L−1, respectively. The mean value of microcystin in sediment was 172.02 ng g−1 and peaked in August. The concentration in the water and sediment was significantly lower than the historical average concentration. The abundance of toxigenic Microcystis and total Microcystis in the water column ranged from 2.61 × 102 to 2.25 × 109 copies·L−1 and 8.28 × 105 to 2.76 × 109 copies·L−1, respectively. The proportion of toxic Microcystis in the sediment ranging from 31.2% to 19.12%. The highest and lowest region was Meiliang Bay and Grass-algae type zone, respectively. The copy number of the 16S rRNA gene was 1–4 orders of magnitude higher than that of mcyA gene in populations of Microcystis, indicating that non-toxic Microcystis was the dominant form in the majority of the lake. The abundance of toxic Microcystis in the water column was positively correlated with total phosphorus, PO43--P and pH, while the water temperature played distinct role to the distribution of toxic Microcystis in sediment. Our research indicated phosphorus remains a key factor influencing the toxic Microcystis and microcystins in the water column. pH played distinct roles in the distribution of microcystins in sediment and water column. The increasing water temperature is a threat. Explicit management actions and policies, which take into account nutrient concentrations, pH, and increasing temperatures, are necessary to understand and control the distribution of microcystin and Microcystis in Lake Taihu.

Year-Round Presence of Microcystins and Toxin-Producing Microcystis in the Water Column and Ice Cover of a Eutrophic Lake Located in the Continuous Permafrost Zone (Yakutia, Russia).

This study aimed to test the hypothesis of the year-round presence of toxigenic Microcystis and cyanotoxins in the water and ice of the shallow eutrophic Lake Ytyk-Kyuyol located in the continuous permafrost zone. Three independent approaches-mass-spectrometry, molecular methods and light microscopy-were applied in the study. The cyanobacterial biomass ranged from 1.0 × 10-4 to 4.8 mg L-1. Microcystis flos-aquae and M. aeruginosa were the dominant morphospecies in plankton throughout the observation. In environmental DNA, the presence of M. aeruginosa was supported and mcy gene regions responsible for microcystin biosynthesis were detected through a BLAST (Basic Local Alignment Search Tool) search and phylogenetic estimation based on newly obtained 16S rRNA, 16S-23S ITS rRNA, mcyA and mcyE nucleotide sequences. The intracellular microcystin concentration ranged from <0.1 to 803 ng L-1, and the microcystin quota in the Microcystis biomass was extremely low. For the first time, it was shown that Microcystis cells containing mcy genes and microcystins presented permanently in the water column, both during the ice-free period and under ice, as well as inside thick ice covers within 7 months of severe winter. We hypothesized that minor pelagic and ice populations of Microcystis could participate in increasing cell density in the spring. However, further studies are needed to confirm the viability of the overwintering Microcystis colonies in the water and inside the ice of Lake Ytyk-Kyuyol.

Shotgun Metagenomic Sequencing to Assess Cyanobacterial Community Composition following Coagulation of Cyanobacterial Blooms.

The excessive proliferation of cyanobacteria in surface waters is a widespread problem worldwide, leading to the contamination of drinking water sources. Short- and long-term solutions for managing cyanobacterial blooms are needed for drinking water supplies. The goal of this research was to investigate the cyanobacteria community composition using shotgun metagenomics in a short term, in situ mesocosm experiment of two lakes following their coagulation with ferric sulfate (Fe2(SO4)3) as an option for source water treatment. Among the nutrient paramenters, dissolved nitrogen was related to Microcystis in both Missisquoi Bay and Petit Lac St. François, while the presence of Synechococcus was related to total nitrogen, dissolved nitrogen, dissolved organic carbon, and dissolved phosphorus. Results from the shotgun metagenomic sequencing showed that Dolichospermum and Microcystis were the dominant genera in all of the mesocosms in the beginning of the sampling period in Missisquoi Bay and Petit Lac St. François, respectively. Potentially toxigenic genera such as Microcystis were correlated with intracellular microcystin concentrations. A principal component analysis showed that there was a change of the cyanobacterial composition at the genus level in the mesocosms after two days, which varied across the studied sites and sampling time. The cyanobacterial community richness and diversity did not change significantly after its coagulation by Fe2(SO4)3 in all of the mesocosms at either site. The use of Fe2(SO4)3 for an onsite source water treatment should consider its impact on cyanobacterial community structure and the reduction of toxin concentrations.

Compounds to mitigate cyanobacterial blooms affect growth and toxicity of Microcystis aeruginosa

Numerous products and techniques are used to combat harmful cyanobacterial blooms in lakes. In this study, we tested nine products, the phosphate binders Phoslock® and Aqual-PTM, the coagulant chitosan, the phosphorus binder and coagulant aluminum salts (aluminum sulphate and sodium aluminate), the copper-based algicides SeClear, Captain® XTR and CuSO4·5H2O, the antibiotic Streptomycin and the oxidant hydrogen peroxide (H2O2) on their efficiency to manage the cyanobacterium Microcystis aeruginosa (M. aeruginosa). To this end, 7 days of laboratory experiments were conducted and effects were determined on chlorophyll-a, photosystem II efficiency (PSII), soluble reactive phosphorus (SRP) and intracellular and extracellular microcystin (MC) concentrations. The algicides, chitosan and H2O2 were the most powerful in reducing cyanobacteria biomass. Biomass reductions compared to the controls yielded: Chitosan (99.8%) > Hydrogen peroxide (99.6%) > Captain XTR (98.2%) > SeClear (98.1%) > CuSO4·5H2O (97.8%) > Streptomycin (86.6%) > Phoslock® (42.6%) > Aqual-PTM (28.4%) > alum (5.5%). Compounds that caused the largest reductions in biomass also strongly lowered photosystem II efficiency, while the other compounds (Phoslock®, Aqual-PTM, aluminum salts) had no effect on PSII, but strongly reduced SRP. Intracellular MC concentration followed the biomass patterns, extracellular MC was generally lower at higher doses of algicides, chitosan and H2O2 after one week. Recovery of PSII was observed in most algicides and chitosan, but not at the highest doses of SeClear and in all streptomycin treatments. Our results revealed that M. aeruginosa can be killed rapidly using several compounds, that in some treatments already signs of recovery occurred within one week. P fixatives are efficient in reducing SRP, and thus acting via resource suppression, which potentially may provide an addition to fast-acting algicides that kill most of the cells, but allow rapid regrowth as sufficient nutrients remain.

Fate of hepatotoxin microcystin during infection of cyanobacteria by fungal chytrid parasites

Chytrid parasites are increasingly recognized as ubiquitous and potent control agents of phytoplankton, including bloom-forming toxigenic cyanobacteria. In order to explore the fate of the cyanobacterial toxin microcystins (MCs) and assess potential upregulation of their production under parasite attack, a laboratory experiment was conducted to evaluate short- and long-term variation in extracellular and intracellular MC in the cyanobacteria Planktothrix agardhii and P. rubescens, both under chytrid infection and in the presence of lysates of previously infected cyanobacteria. MCs release under parasite infection was limited and not different to uninfected cyanobacteria, with extracellular toxin shares never exceeding 10%, substantially below those caused by mechanical lysis induced by a cold-shock. Intracellular MC contents in P. rubescens under infection were not significantly different from uninfected controls, whereas infected P. agardhii showed a 1.5-fold increase in intracellular MC concentrations, but this was detected within the first 48 hours after parasite inoculation and not later, indicating no substantial MC upregulation in cells being infected. The presence of lysates of previously infected cyanobacteria did not elicit higher intracellular MC contents in exposed cyanobacteria, speaking against a putative upregulation of toxin production induced via quorum sensing in response to parasite attack. These results indicate that chytrid epidemics can constitute a bloom decay mechanism that is not accompanied by massive release of toxins into the medium.

'Floc and Sink' Technique Removes Cyanobacteria and Microcystins from Tropical Reservoir Water.

Combining coagulants with ballast (natural soil or modified clay) to remove cyanobacteria from the water column is a promising tool to mitigate nuisance blooms. Nevertheless, the possible effects of this technique on different toxin-producing cyanobacteria species have not been thoroughly investigated. This laboratory study evaluated the potential effects of the “Floc and Sink” technique on releasing microcystins (MC) from the precipitated biomass. A combined treatment of polyaluminium chloride (PAC) with lanthanum modified bentonite (LMB) and/or local red soil (LRS) was applied to the bloom material (mainly Dolichospermum circinalis and Microcystis aeruginosa) of a tropical reservoir. Intra and extracellular MC and biomass removal were evaluated. PAC alone was not efficient to remove the biomass, while PAC + LMB + LRS was the most efficient and removed 4.3–7.5 times more biomass than other treatments. Intracellular MC concentrations ranged between 12 and 2.180 µg L−1 independent from the biomass. PAC treatment increased extracellular MC concentrations from 3.5 to 6 times. However, when combined with ballast, extracellular MC was up to 4.2 times lower in the top of the test tubes. Nevertheless, PAC + LRS and PAC + LMB + LRS treatments showed extracellular MC concentration eight times higher than controls in the bottom. Our results showed that Floc and Sink appears to be more promising in removing cyanobacteria and extracellular MC from the water column than a sole coagulant (PAC).

The dynamics and release characteristics of microcystins in the plateau Lake Erhai, Southwest China.

Microcystins (MCs) have seriously polluted drinking water supplies and have caused great harm to aquatic organisms and humans. Understanding the dynamics of MC concentrations and its influencing factors is necessary for drinking water safety. Many previous studies on MC pollution focused on intracellular MCs rather than on extracellular MCs, which are more difficult to remove by water treatment. So far, the release characteristics of MCs and the relationships between intracellular and extracellular MCs are still unclear. To explore these questions, a survey was conducted at 18 sites across Lake Erhai from May 2014 to April 2015 as in Lake Erhai the frequency and coverage area of cyanobacterial blooms have been increasing. Variation of extracellular MCs lagged behind that of intracellular MCs. The highest value of intracellular MCs was 1.07μgL-1 in October 2014 and the highest extracellular MC concentration was 0.035μgL-1 in November 2014. Intracellular MCs were positively influenced by MC-producing cyanobacterial biomass, water temperature (WT), pH, and conductivity (Cond). The extracellular MCs showed little correlation with cyanobacterial abundances and intracellular MC concentrations, but showed significant negative correlations with WT, pH, and Cond. These results indicated that high biomass and high intracellular MC concentrations did not quickly lead to large releases of MCs, and that when cyanobacterial cells died and blooms disappeared, MCs were intensively released into the water, posing the greatest threat to drinking water supply.

Size-dependent toxic effects of polystyrene microplastic exposure on Microcystis aeruginosa growth and microcystin production

Due to increasingly severe microplastic pollution in freshwaters, the interaction between these contaminants and cyanobacteria warrants study. In this study, we expose the freshwater cyanobacterium Microcystis aeruginosa to different sizes (1 μm and 100 nm) of polystyrene (PS) microplastics of 5 mg/L. Results indicate 1 μm microplastics promote algal growth (12.42% ± 0.94%) at 96 h, and have greater potential to aggregate on algal cell surfaces and inhibit photosynthesis. But no significance was observed in 100 nm microplastics treatment on algal growth and photosynthetic activity after 96 h exposure. Especially, 1 μm microplastics increased the content of intracellular microcystins (MCs) (18.42% ±0.33%) after 72 h and inhibit MCs release (23.87% ±8.79%) at 72 h, while 100 nm PS microplastics promote MCs production only at 48 h (14.83% ± 7.07%). Results indicate that smaller size does not necessarily mean greater toxicity, 1 μm microplastics showing more adverse effects than 100 nm microplastics to M. aeruginosa, improving understanding of the toxicity of microplastics in freshwater ecosystems, and challenging the conventionally held belief that smaller microplastics are more toxic.

Survey of microcystins in Singapore's reservoirs using liquid chromatography–tandem mass spectrometry (LC-MS/MS)

Microcystins (MCs) are a group of toxins produced by certain cyanobacteria that occur naturally in fresh waters and can cause acute poisoning in humans and animals. Because cyanobacteria have been found in the freshwater reservoirs of Singapore, a comprehensive survey for cyanotoxins was undertaken over a 12-month period in 17 reservoirs from November 2012 to October 2013. For the quantitative analysis of the reservoir samples, an liquid chromatography–tandem mass spectrometry (LC-MS/MS) method was developed that targeted the following hepatotoxins: MC-LR, MC-RR, MC-LW, MC-LF, MC-WR and MC-LY. The most prevalent MC variants identified were MC-LR and MC-RR. Results showed that the level of intracellular MC-LR in the raw or untreated water was close to the World Health Organisation (WHO) provisional MC-LR drinking water guideline of 1μgL–1 for 1 of 200 samples tested (0.8μgL–1), and that intracellular MC concentrations were above 0.3μgL–1 in samples collected from four reservoirs. Based on random forest analysis, total monthly rainfall and total nitrogen concentrations were found to be the most important factors affecting intracellular MC concentrations for these four reservoirs. The toxin levels for the other reservoirs were relatively low compared with the WHO provisional MC-LR guideline limit of 1.0μgL–1.

Long-term exposure to antibiotic mixtures favors microcystin synthesis and release in Microcystis aeruginosa with different morphologies

The ecological risks of antibiotics in aquatic environments have raised great concerns worldwide, but the chronic effect of antibiotic contaminants on cyanotoxin production and release remains unclear. This study investigated the long-term combined effects of spiramycin (SP) and ampicillin (AMP) on microcystin (MC) production and release in both unicellular and colonial Microcystis aeruginosa (MA) through semi-continuous exposure test. At exposure concentration of 300 ng L−1, MA growth rates were stimulated till the end of exponential phase accompanied with the up-regulation of photosynthesis-related gene. The exponential growth phases of unicellular and colonial MA were prolonged for 2 and 4 days, respectively. The stimulation rate of growth rate and MC content in unicellular MA were significantly higher than that in colonial MA. The highest concentrations of intracellular MC (IMC) and extracellular MC (EMC) were observed in the binary mixture at equivalent SP/AMP ratio (1:1). The promotion of IMC concentration was in consistent with the stimulated expression of MC-synthesis-related gene and nitrogen-transport-related gene. The malondialdehyde content and activities of superoxide dismutase and catalase in unicellular MA were significantly higher than those in colonial MA. The EMC concentration and the antioxidant responses of both unicellular and colonial MA significantly increased with exposure time. Long-term exposure to mixture of SA and AMP at environmentally relevant concentrations would aggravate the disturbance to aquatic ecosystem balance through the stimulation of MA proliferation as well as the promotion of MC production and release.

Physiological characteristics and toxin production of Microcystis aeruginosa (Cyanobacterium) in response to DOM in anaerobic digestion effluent

The ecological implications of livestock production intensification have received sustained attention across the globe. Anaerobic digestion is the main process for livestock waste treatment. However, the ecological consequences of dissolved organic matter originating from anaerobic digestion (AD-DOM) in eutrophic water bodies remain elusive. In this study, the physiological responses of a bloom-forming cyanobacterium, Microcystis aeruginosa, to AD-DOM were investigated. Moreover, the composition of AD-DOM was identified by using thermochemolysis followed by gas chromatography–mass spectrometry (GC–MS) analysis. The growth of M. aeruginosa FACHB905 was not sensitive to low levels (0.625–1.25%, V/V) of AD-DOM but was inhibited by high levels (2.5–5%, V/V) of AD-DOM, resulting from photoinhibition damage to photosystem II (PSII). The main target of AD-DOM in PSII was the electron accepting side (ψ0) or the electron donor side (φ P0), depending on time variables. The reactive oxygen species (ROS) level showed a positive correlation with AD-DOM addition; however, it was higher than that of the control for 3.75–5% AD-DOM on the 6th day. The intracellular microcystin contents (including MC-LR and Dha7-MC-LR) decreased in response to AD-DOM addition, but extracellular microcystin increased after 6 days of exposure. In addition, GC–MS detection showed that AD-DOM is mainly composed of lignin-derived aromatic compounds, alkanes/alkene, nitrogen­containing compounds, and sterols. The results presented in this study suggested that AD-DOM released from the livestock industry may play a subtle role in affecting harmful algal blooms through level-dependent variables. In addition, the ecological consequences of microcystin released by toxin-producing species under AD-DOM stress are still worth considering.

Decline of freshwater gastropods exposed to recurrent interacting stressors implying cyanobacterial proliferations and droughts

Freshwater biota increasingly undergo multiple stressors, but we poorly understand to what extent they influence the dynamics of community structure. Here, we study the impact of combined stressor exposure on gastropods at 9-year interval, through a monthly 1-year (2013) monitoring, also providing data on the occurrence of other macroinvertebrate taxa. Previous study in 2004 showed the occurrence of cyanobacterial proliferations, drought, trematode parasites and invasive non-native pulmonate Physa acuta. During the year 2013, we always detected cyanobacterial microcystins (MCs) in gastropods, from 59 to 4149 ng g−1 fresh mass (vs. 0–246 ng g−1 in 2004), suggesting a continuous and increased MC intoxication. Environmental intracellular MC concentrations were high (8–41 µg L−1) from August to October 2013, whereas they were detected only in August 2004 (17 µg L−1). In 2013, we recorded no trematodes among the 2490 sampled gastropods, and P. acuta represented 94% of gastropods (vs. 58% in 2004). After August 2013, nearly all gastropods disappeared as most other macroinvertebrates (except Chironomidae, Ephemeroptera and Trichoptera). The whole decline of gastropods and other macroinvertebrates, and the absence of trematodes strongly suggest adverse conditions in the study site. Despite acute stressful conditions suggested above, gastropod abundance was 13-fold higher in June 2013 (vs. 2004), reflecting successful recolonization and efficient breeding. Most gastropods exposed to drought and toxic bloom were young vulnerable stages. Thus, we supposed alternation of local gastropod extinctions versus recolonization that could induce, on a long term, a loss of diversity to the detriment of the most sensitive species.

Seasonal dynamics of photosynthetic activity of Microcystis, genotype abundances and microcystin concentrations in Meiliang Bay, Lake Taihu

Lake Taihu is the third largest freshwater lake (surface area: 2338km2, mean depth: 1.9m) in eastern China, and it is also the primary drinking water source for 30 million residents in the lake basin. In recent decades, Lake Taihu has annually experienced lake-wide cyanobacterial blooms. However, the seasonal changes of photosynthetic activity of Micricystis, genotype abundances and microcystin and their relationship with environmental factors are still poorly understood. In the present study, surface water samples in Meiliang Bay were collected monthly from January to December in the year of 2014, at the same time, we investigated the photosynthetic activity of Micricystis, the abundances of total and toxic Microcystis genotypes, and microcystins (MCs) concentrations using pulse amplitude modulation (PAM), quantitative real-time PCR (qPCR), and high performance liquid chromatography (HPLC) techniques, respectively. It was found that the maximum and effective quantum yields both had an obvious seasonal patterns. In winter season, photosynthetic activity were not detectable, Then, it increased fast from spring to summer, at the last, it gradually decreased from fall to winter. The level of non-photochemical quenching (NPQ) increased from March to August, when it showed a maximum, decreasing thereafter toward December. The abundances of total and toxic Microcystis genotypes ranged from 1.91±0.15×105 to 8.64±0.56×107, from 2.38±0.25×104 to 5.67±0.43×106copies/mL, respectively, meanwhile, the toxic proportion ranged from 12.5±1.3 to 65.6±3.8%, and they all showed similar change patterns with increasing first and then decreasing later. The extacellular and intracellular MCs concentrations varied from 0.17±0.05 to 1.82±0.35μg/L, from 0.59±0.18 to 14.36±1.62μg/L, respectively. The correlation analysis suggested that photosynthetic capacity and NPQ of Microcystis had positive correlation with water temperature. Meanwhile, there were strong positive correlation among the total and toxic Microcystis genotypes, toxic proportion and intracellular MCs, and they were significant positively correlated with water temperature. In addition, intracellular MCs also have strong positive correlation with total phosphorus. In conclusion, the photosynthetic activity of Microcystis was corresponded to the dynamics of Microcystis bloom, and water temperature may be a key environmental factor which determined Microcystis photosynthetic activity, total and toxic Microcystis genotypes abundances as well as intracellular MCs in Lake Taihu.

Response of bacterial communities to cyanobacterial harmful algal blooms in Lake Taihu, China

Cyanobacterial harmful algal blooms are prevalent around the world, influencing aquatic organisms and altering the physico-chemical properties in freshwater systems. However, the response of bacterial communities to toxic cyanobacterial blooms and associated microcystins (MC) remain poorly understood even though global concentrations of MC have increased dramatically in the past few decades. To address this issue, the dynamics of bacterial community composition (BCC) in the water column and how BCC is influenced by both harmful cyanobacterial blooms and environmental factors were investigated on a monthly basis from August 2013 to July 2014 in Lake Taihu, China. Non-metric multidimensional scaling (NMDS) revealed that seasonal variation in BCC was significant, and that the succession of BCC greatly depends on changes in environmental conditions. Redundancy analysis (RDA) results showed that the overall variation of BCC was explained mainly by dissolved oxygen (DO), nitrate nitrogen (NO3−-N), and Microcystis. The alpha biodiversity of the bacterial community was different among months with the highest diversity in February and the lowest diversity in October. Furthermore, significant negative relationships were found between alpha biodiversity indices and Microcystis abundance as well as with intracellular MC concentrations, indicating that Microcystis and associated MC may influence the bacterial community structure by reducing its biodiversity. This study shows that potential associations exist between toxic cyanobacterial blooms and bacterial communities but more investigations are needed to obtain a mechanistic understanding of their complex relationships.

Changes in N:P Supply Ratios Affect the Ecological Stoichiometry of a Toxic Cyanobacterium and Its Fungal Parasite.

Human activities have dramatically altered nutrient fluxes from the landscape into receiving waters. As a result, not only the concentration of nutrients in surface waters has increased, but also their elemental ratios have changed. Such shifts in resource supply ratios will alter autotroph stoichiometry, which may in turn have consequences for higher trophic levels, including parasites. Here, we hypothesize that parasite elemental composition will follow changes in the stoichiometry of its host, and that its reproductive success will decrease with host nutrient limitation. We tested this hypothesis by following the response of a host–parasite system to changes in nitrogen (N) and phosphorus (P) supply in a controlled laboratory experiment. To this end, we exposed a fungal parasite (the chytrid Rhizophydium megarrhizum) to its host (the freshwater cyanobacterium Planktothrix rubescens) under control, low N:P and high N:P conditions. Host N:P followed treatment conditions, with a decreased N:P ratio under low N:P supply, and an increased N:P ratio under high N:P supply, as compared to the control. Shifts in host N:P stoichiometry were reflected in the parasite stoichiometry. Furthermore, at low N:P supply, host intracellular microcystin concentration was lowered as compared to high N:P supply. In contrast to our hypothesis, zoospore production decreased at low N:P and increased at high N:P ratio as compared to the control. These findings suggest that fungal parasites have a relatively high N, but low P requirement. Furthermore, zoospore elemental content, and thereby presumably their size, decreased at high N:P ratios. From these results we hypothesize that fungal parasites may exhibit a trade-off between zoospore size and production. Since zooplankton can graze on chytrid zoospores, changes in parasite production, stoichiometry and cell size may have implications for aquatic food web dynamics.

Dynamic variation of toxic and non-toxic Microcystis proportion in the eutrophic Daechung Reservoir in Korea.

This study was conducted to determine the environmental factors affecting the level of potentially toxic Microcystis. The long-term tendencies of temperature, precipitation, and water quality factors were analyzed to determine the environmental characteristics of the Daechung Reservoir in Korea, and water samples were directly collected to analyze the dynamics of toxic and non-toxic Microcystis at weekly intervals from May to October 2012. Microcystis was the dominant genus during the study period, and it was composed of potentially toxic and non-toxic Microcystis. The fraction of potentially toxic Microcystis ranged from 6.0% to 61.1%. The amount of toxic Microcystis was highly related to the intracellular microcystin concentration (r = 0.760, P < 0.01). Therefore, the fraction of potentially toxic Microcystis is an important concern in Microcystis blooming because the intracellular microcystin concentration may reflect microcystin levels in the water. The prevalence of potentially toxic Microcystis was highly related to water temperature in Daechung Reservoir (r = 0.585, P < 0.01). Thus, temperature increase during Microcystis blooming may lead to more frequent toxic Microcystis blooms in eutrophic water bodies.

Effects of laser irradiation on a bloom forming cyanobacterium Microcystis aeruginosa.

Effects of laser irradiation on photosystem II (PS II) photochemical efficiencies, growth, and other physiological responses of Microcystis aeruginosa were investigated in this study. Results indicate that laser irradiation (wavelengths 405, 450, 532, and 650nm) could effectively inhibit maximal PS II quantum yield (Fv/Fm) and maximal electron transport rates (ETRmax) of M. aeruginosa, while saturating light levels (Ek) of M. aeruginosa did not change significantly. Among the four tested wavelengths, 650nm laser (red light) showed the highest inhibitory efficiency. Following 650nm laser irradiation, the growth of M. aeruginosa was significantly suppressed, and contents of cellular photosynthetic pigments (chlorophyll a, carotenoid, phycocyanin, and allophycocyanin) decreased as irradiation dose increased. Meanwhile, laser irradiation enhanced the enzyme activities of superoxide dismutase (SOD) and peroxidase (POD) in M. aeruginosa cells. Lower irradiation doses did not change the intracellular microcystin contents, but higher dose irradiation (>1284Jcm-2) caused the release of microcystin into the culture medium. Transmission electron microscope examination showed that the ultrastructure of M. aeruginosa cells was destructed progressively following laser irradiation. Effects of laser irradiation on M. aeruginosa may be a combination of photochemical, electromagnetic, and thermal effects.

Effect of the toxin (microcystin) content of Microcystis on copepod grazing

Although phytoplankton chemical defense may regulate plankton dynamics, demonstrating an ecologically relevant anti-grazer cue is challenging. Presented here is a novel approach to evaluate the quantitative effect of microcystin (MC), the most studied group of cyanobacterial metabolites, on grazing by the common copepod Eudiaptomus gracilis. A temperature-induced gradient in the intracellular MC concentration of three different Microcystis strains enabled the comparison of grazing pressure on cells of the same cyanobacterial strain producing different amounts of MC, in a diet with alternative food (Chlamydomonas). In all treatments, grazing pressure on Microcystis was inversely related to its MC-LR content, while selection for alternative prey was positively related to the MC-LR content of Microcystis. Moreover, grazing on Chlamydomonas also declined with increasing Microcystis MC-LR content, suggesting toxicity related inhibition of E. gracilis. The negative relation between cellular MC-LR concentration and feeding responses supported the anti-grazer hypothesis. Not all MC variants responded to temperature, and some were therefore not associated to grazing responses. Using an induced gradient in the concentration of a suspected phytoplankton defense metabolite to evaluate its quantitative relationship with grazing pressure offers an improved inference on the ecological roles of toxins. Results suggest that either MC-LR or a correlating trait may be inversely linked to the grazer pressure on Microcystis.

Microcystin production in Microcystis aeruginosa: effect of type of strain, environmental factors, nutrient concentrations, and N:P ratio on mcyA gene expression

Blooms affect water quality mainly due to the release of microcystins (MCs) by cyanobacteria. The synthesis of MCs is influenced by factors such as nutrient concentration, temperature, pH, light intensity, salinity, turbidity, and the presence of xenobiotics. In this study, we evaluated the effect of environmental factors (temperature and light intensity), the concentration of three nutrients (NaNO3, K2HPO4, and FeCl3), and the N:P ratio on the growth of two Microcystis aeruginosa strains (Ch10 and UTEX LB2385), as well as on mcyA gene expression and intracellular MC concentration. Under similar conditions, the population growth and chlorophyll a concentration per cell of both strains were different. The mcyA gene was significantly up-regulated from the early growth phase (5 days) to the stationary phase (15 days) in most cases, whereas intracellular MC concentrations varied depending on the assessed factor. The N:P ratio affected the development of both strains and MCs production differently. High concentration of intracellular MCs was recorded at low nitrogen and iron concentrations, low temperature, and high light intensity. The response in mcyA gene expression, related to the incubation time, of both strains was different, because strain Ch10 responded in most cases starting at 5 days of growth, whereas UTEX LB2385 responded until 10 and 15 days. This difference reflects physiological plasticity that could help to understand the permanence and dominance of Microcystis genus blooms in eutrophic freshwaters. The variability in response to the tested environmental factors confirms that population growth, genetic expression, and microcystin production are not related to a single factor but to an array of conditions that, when combined, stimulate MCs production. These conditions can be both stress-causing and favorable; hence, monitoring of environmental factors aimed at alerting against health risks provoked by cyanotoxins is a very complex task.

Effects of benzene and several pharmaceuticals on the growth and microcystin production in Microcystis aeruginosa PCC 7806

Ef fects of benzene and several pharmaceuticals on the growth and microcystin production in Microcystis aeruginosa PCC 7806 Currently, the presence of several pharmaceuticals and other organic compounds called ‘emerging’ contaminants has increased in water bodies. These compounds do not need to persist in the environment to cause negative effects because they are continuously introduced. Hence, assessing the effects of these compounds on aquatic ecosystems is essential. Therefore, the aim of the present study was to analyse the effects of several emerging contaminants (ibuprofen, atenolol, diclofenac and paracetamol) and benzene on Microcystis aeruginosa PCC 7806 growth and toxicity. For this purpose, the growth and intracellular microcystin concentration in M. aeruginosa PCC 7806 were measured in presence of the four emerging contaminants and benzene. The growth rate was estimated by chlorophyll a concentration, and no relevant changes were found. Changes in the expression of the operon mcy were examined by semi-quantitative RT-PCR. Intracellular microcystin production was determined using a MicroCystest R kit, and no changes were observed compared to control cells. Thus, the tested concentrations of the contaminants analysed in this study do not have a significant effect on microcystin production in this strain under laboratory conditions.