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In the paper, to better understand the dynamic relationship between Microcystis aeruginosa and filter-feeding fish, we have constructed a new aquatic ecological model to describe the aggregation effect of Microcystis aeruginosa. Mathematical theory works mainly investigated the critical threshold condition through the discovery of transcritical bifurcation, saddle–node bifurcation, Hopf bifurcation and Bogdanov–Takens bifurcation. The numerical simulation works mainly revealed that Microcystis aeruginosa aggregation effect has played an important role in the dynamic relationship with the aid of bifurcation analysis, which also in turn proved the validity of theoretical derivation. The results showed that if the Microcystis aeruginosa aggregation area became larger and larger, and exceeded a critical threshold, the filter-feeding fish would eventually go extinct. Furthermore, it should be stressed that Microcystis aeruginosa aggregation can effectively control the feeding dynamic behavior of filter-feeding fish and provide shelter from predators. Finally, all these results were expected to be useful in studying population dynamics of some aquatic ecosystems.

Secondary metabolites of cyanobacteria and algae released during algal blooms often exhibit toxic effects, but only a small number of the metabolites are the subject of routine analytical screenings. Alternatively, ecotoxicological assays offer a better representation of the overall negative effects. The aim of this work was to compare multiple assays in their sensitivity towards cellular algal organic matter (COM) of the toxin-producing cyanobacterium Microcystis aeruginosa. Multiple endpoints were investigated: mortality, growth inhibition, bioluminescence inhibition, genotoxicity, endocrine-disrupting effects, oxidative stress, and the induction of ethoxyresorufin-O-deethylase (EROD). Three rainbow trout (Oncorhynchus mykiss) cell lines as well as representatives of bacteria, yeasts, algae, vascular plants, and crustaceans were employed, and the results were expressed per mg of dissolved organic carbon (DOC) in the COM. M. aeruginosa COM was toxic to the RTgill-W1, RTG-2, and RTL-W1 cell lines (EC50 values ranging from 0.48 ± 0.02 to 1.9 ± 0.1 mgDOC/L), to the crustacean Thamnocephalus platyurus (LC50 = 20 ± 1 mgDOC/L), and to Lepidium sativum (IC50 = 241 ± 13 mgDOC/L). In contrast, no effect was observed for bacteria and yeasts, and the growth of the alga Desmodesmus subspicatus was even stimulated. No genotoxicity, endocrine-disrupting effects or increase in oxidative stress or EROD activity was detected. The content of six microcystins (MC-LR, MC-RR, MC-YR, MC-LY, MC-LW, and MC-LF), anatoxin-a, cylindrospermopsin, and nodularin in the M. aeruginosa COM was determined by liquid chromatography–tandem mass spectrometry. An artificially prepared mixture of the detected cyanotoxins in the corresponding concentrations did not induce response in the O. mykiss cell lines and T. platyurus, suggesting that other cyanobacterial metabolites are responsible for the toxicity of M. aeruginosa.

Ozonation pretreatment is typically implemented to improve algal cell coagulation. However, knowledge on the effect of ozonation on the characteristics and coagulation of associated algal organic matter, particularly cellular organic matter (COM), which is extensively released during algal bloom decay, is limited. Hence, this study aimed to elucidate the impact of ozonation applied before the coagulation of dissolved COM from the cyanobacteria Microcystis aeruginosa. Additionally, the degradation of microcystins (MCs) naturally present in the COM matrix was investigated. A range of ozone doses (0.1–1.0 mg O3/mg of dissolved organic carbon – DOC) and ozonation pH values (pH 5, 7 and 9) were tested, while aluminium and ferric sulphate coagulants were used for subsequent coagulation. Despite negligible COM removal, ozonation itself eliminated MCs, and a lower ozone dose was required when performing ozonation at acidic or neutral pH (0.4 mg O3/mg DOC at pH 5 and 7 compared to 0.8 mg O3/mg DOC at pH 9). Enhanced MC degradation and a similar pattern of pH dependence were observed after preozonation-coagulation, whereas coagulation alone did not sufficiently remove MCs. In contrast to the benefits of MC depletion, preozonation using ≥ 0.4 mg O3/mg DOC decreased the coagulation efficiency (from 42%/48% to 28%–38%/41%–44% using Al/Fe-based coagulants), which was more severe with increasing ozone dosage. Coagulation was also influenced by the preozonation pH, where pH 9 caused the lowest reduction in COM removal. The results indicate that ozonation efficiently removes MCs, but its employment before COM coagulation is disputable due to the deterioration of coagulation.

In this study, allelochemicals were extracted from pulping effluents rather than from the raw material of plants. Herein, five organic solvents (ethyl acetate (EAC), methyl tert-butyl ether (MTBE), dichloromethane (DCM), carbon tetrachloride (CTC), and petroleum (PE)) were applied to separately extracting the allelochemicals from alkaline peroxide mechanical pulp (APMP) effluents. The results from the algal density, inhibition ratio, and optical density of 446 nm (OD446nm) concluded that the extractives from the APMP effluents can act as effective allelochemicals and showed noticeable allelopathic inhibition effects on Microcystis aeruginosa growth. The results indicated that organic solvent extraction could be a practical approach to isolate the allelochemicals from the APMP effluents, which would broaden the potential application of the APMP effluents in the production of antimicrobial agents and other value-added materials.

The biomedical applications of the secondary metabolites produced by the harmful algal blooms were studied over a few decades ago. Only few research studies have been reported on the medicinal properties of the secondary metabolites produced by the cyanobacteria Microcystis aeruginosa. The present study was aimed to screen the Biological activities of GC fractionated Benzeneacetanomide and Norvaline, n-propargyloxycarbonyl mixtures of Microcystis aeruginosa secondary metabolites. The Microcystis aeruginosa samples were collected by plankton net from the blooming area at Muttukadu. The metabolites were extracted by using polar solvent as methanol. The yield percentage of Microcystis aeruginosa methanolic extract showed moderate level of 41% from the dry weight of the pre extracted Microcystis aeruginosa powder. The crude metabolites were purified through column chromatography and GC-MS analysis. The GC-MS results showed the presence of two compounds (2 major peaks), Benzeneacetamide at the retention time (RT) of 7.315 min and l-Norvaline, n-propargyloxycarbonyl (Pyrrol derivaties) at the retention time (RT) of 12.541 min. The GC-MS fractioned compounds were characterized by FT-IR and 1HNMR. The anticancer, antioxidant and antimicrobial activity of the compounds were studied. This study highlights the bioactive potential of Microcystis aeruginosa secondary metabolites that might lead to the development of cancer drug.

Phosphine (PH3) is an important factor driving the outbreak of cyanobacterial blooms that produce toxic microcystin threating human health. To clarify the physiological and biochemical responses of cyanobacteria to PH3 under elevated CO2 concentration, Microcystis aeruginosa was used in the coupling treatment of 1000 ppmv CO2 and PH3 at different concentrations respectively. The chlorophyll a (Chl-a), carotenoid, net photosynthetic rate and total protein of M. aeruginosa exhibited evidently increasing tendency under the coupling treatment of 1000 ppmv CO2 and PH3 at different concentrations (7.51 × 10−3, 2.48 × 10−2, 7.51 × 10−2 mg/L). The coupling treatments resulted in the higher concentrations of Chl-a and carotenoid of M. aeruginosa, compared to those in the control and the treatment with CO2 alone, and their enhancement increased with the increase in PH3 concentrations. The total antioxidant capacity (T-AOC) in the coupling treatment with CO2 and PH3 of 2.48 × 10−2 mg/L and 7.51 × 10−3 mg/L showed increasing tendency, compared to the treatment with PH3 alone. Additionally, the coupling treatment with 1000 ppmv CO2 and PH3 also altered the pH and DO level in the culture medium. In this regard, the coupling treatment with CO2 and PH3 at an appropriate concentration can enhance the resistance of M. aeruginosa to PH3 toxicity and is beneficial to the reproduction of M. aeruginosa, presumably resulting in potential for the outbreak of cyanobacteria bloom. Given the concern about global warming and the increase in atmospheric CO2 level, our research laid a foundation for the scientific understanding of the correlation between PH3 and cyanobacteria blooms.

Microcystins are present in some aquatic organisms, but the potential transfer to and accumulation in terrestrial organisms is less understood. We measured microcystin concentrations in multiple terrestrial life stages of Hexagenia limbata to determine whether this cyanotoxin is transferred from one life stage to another and if H. limbata subimagos and imagos transport the algal toxin microcystin into terrestrial systems. Hexagenia limbata (n = 43) were hand collected from the shore of a low-nutrient lake with a history of Microcystis aeruginosa, located in Michigan’s Lower Peninsula. We quantified microcystin concentrations in H. limbata with enzyme linked immunosorbent assay (n = 39), with a subset verified with high performance liquid chromatography tandem mass spectrometry (n = 8, including duplicates). Microcystin ranged from the method limit of detection (MLOD) to 0.64 µg/g dry weight with detectable concentrations in subimagos, imagos, and spent females, indicating a potential for transport of this toxin to terrestrial systems. These data indicate that emerging aquatic insects are a potential vector for the transfer of microcystins from aquatic to terrestrial food webs and may pose a threat in and around systems with both H. limbata and more extensive blooms of M. aeruginosa.

The effects of bisulfite-activated permanganate technology (PM/BS) as a pre-oxidation process on enhancing Microcystis aeruginosa (M. aeruginosa) removal by post coagulation were investigated. The results demonstrated that pretreatment with PM/BS process effectively promoted the algae removal by coagulation with Al2(SO4)3 as the coagulant and this phenomenon was more obvious with the increase of water hardness. Compared to the sole coagulation, PM/BS pre-oxidation combing with coagulation could neutralize the zeta potential of algal cells effectively, decrease the algal cell size, and lead to the formation of more compact flocs due to the in-situ generated MnO2. The effect of oxidant dosages on algal organic matter (AOM) was also studied and no obvious release of macromolecular substances was observed with the dosage of KMnO4 increasing from 3.0 mg/L to 7.0 mg/L, suggesting the integrity of algal cells at a high KMnO4 dosage. Moreover, PM/BS pre-oxidation could lead to the decrease of most analyzed disinfection by-products (DBPs) at a Al2(SO4)3 dosage of 40.0 mg/L. The algae removal efficiency was also significantly enhanced by PM/BS pre-oxidation in the test using real algae-laden water. This study indicated that PM/BS process might be a potential assistant technology for algae removal by subsequent coagulation.

A novel headspace solid phase microextraction arrow (HS-SPME Arrow) method combined with gas chromatography-mass spectrometry (GC-MS) was developed for extraction and analysis of volatile organic compounds of Microcystis aeruginosa under simulated natural conditions. By selecting suitable extraction fibers, 210 kinds of volatile metabolites were identified by full scanning qualitative analysis from the samples of Microcystis aeruginosa in producing period. The metabolic changes of volatile molecules during the growth of Microcystis aeruginosa were analyzed by multivariate statistical analysis and clustering analysis. Chemometric analysis based on principal component analysis, partial least squares-discriminant analysis and heat map associated with hierarchical cluster analysis provided a suitable tool to differentiate volatile organic compounds in algal material. Also 10 metabolites with statistical significance were identified, including cyclohexanol, dimethyl trisulfide, benzenemethanol, camphor, 2-methoxyphenol, 3-hexene-1-ol, 2,4-decadienal, indole, citral and 1-nonanol. Parameters affecting the extraction, such as extraction temperature, time and salt contents were systematically evaluated. The analytical conditions, including desorption temperature and time as well as gas chromatographic parameters, were also optimized. The calibration curves showed a good linearity (correlation coefficient > 0.998) in the concentration range of 0.050–1000 ng/L. The detection limits of this method were 0.010–0.030 ng/L, and the recoveries at the concentration level of 100 ng/L were 76.3%–93.0%. The new method exhibited good precision, with the RSDs values of less than 12.7%. Furthermore, the method also had many advantages such as simplicity, rapidness and applicability to complex matrices, and hence it was suitable to the determination of volatile metabolites in natural water at the early stage of blue-green algae bloom.

Summary: The study aimed at measuring the influence of a wide range of oxytetracycline concentrations, with particular attention to the low levels of the antibiotic on cyanobacteria Microcystis aeruginosa and Nodularia spumigena, diatom Phaeodactylum tricornutum and the model green algae Chlorella vulgaris by conducting prolonged toxicity tests (lasting 10 days). Standard measurements (cell number, optical density, chlorophyll a concentration) were combined with photosynthetic parameters measurements. The obtained results show that concentrations of oxytetracycline present in the environment can affect tested microorganisms. It was found to decrease photosystem II efficiency and disrupt the photosynthesis process. A careful interpretation of photosynthetic parameters allowed a better understanding of the mode of action of oxytetracycline in relation to non-target photoautotrophic organisms like cyanobacteria and microalgae. In conclusion, it would appear that the use of standard chronic toxicity tests (72 h) does not allow to accurately and reliably assess the chronic impact of bioactive compounds including drugs and their metabolites on water organisms. On this basis, we recommend the application of extended duration tests. Keywords: Antibiotics, Cyanobacteria, Microalgae, Chlorophyll a fluorescence, Toxicity studies

Cyanobacteria species are sensitive to many plant allelochemicals, such as pyrogallol. However, little attention has been paid to the relative effects of these xenobiotics on co-occurring toxigenic and non-toxigenic cyanobacterial strains, despite their co-existence in blooms. Hence, the responses of one toxigenic (TS2) and two non-toxigenic (NS1, NS2) Microcystis aeruginosa strains to pyrogallol were tested under three conditions: mono-culture and co-cultured either directly or separately by dialysis membrane. The study showed that the inhibitory effects of pyrogallol on the growth and photosynthetic yield (Fv/Fm) of either toxigenic or non-toxigenic M. aeruginosa strains were lower in direct and dialysis co-culture conditions than those in mono-culture conditions. This result indicated that chemical-mediated reciprocal effects occur between the co-existing toxigenic and non-toxigenic strains. The toxigenic M. aeruginosa strain was more sensitive to pyrogallol than the non-toxigenic strains in both mono- and co-culture systems, though whether this outcome is due to the former's toxigenic status is unclear. Intracellular microcystin-LR (MC-LR) concentrations of the toxigenic strain decreased after pyrogallol addition in both mono- and co-culture systems, whereas extracellular MC-LR concentrations increased. This finding may reflect the cell damage of M. aeruginosa because of the pyrogallol. At the same initial number of cells, the extracellular MC-LR concentration released from the same amount of TS2 cells in mono-culture was slightly higher than that in dialysis co-culture conditions. Overall, this study shows that plant allelochemicals may have the potential to reduce bloom toxicity by reducing the proportion of toxigenic cyanobacterial strains, and the effects of co-existing strains must be considered when assessing the effects of plant allelochemicals on target strains.

Microcystis aeruginosa (M. aeruginosa) is a dominant species among frequent cyanobacterial blooms and is well known for its toxin-producing ability. Phosphorus (P) is a typical growth-limiting element for M. aeruginosa. Although alterations in physiological reactions have been documented in response to various P sources, the underlying molecular processes and transcriptional patterns remain poorly understood. This study evaluated the physiological and molecular responses of M. aeruginosa to different P sources. The growth of M.aeruginosa was promoted by both dissolved inorganic phosphorus (DIP) and dissolved organic phosphorus (DOP) at a concentration of 0.4 mg/L with an initial cell density of 1.50 (±0.05) × 106 cells/mL. The cell density reached 1.38 (±0.05) × 107 cells/mL in the DIP group on day 14, a value which was higher than that in the DOP group. Most photosynthesis genes had higher levels of upregulated expression in the DIP group. For instance, gene psbA was upregulated by 0.45 Log2Fold Change (Log2FC). In the DOP group, it is interesting that the Pi (PO4-P) concentration increased to 0.09 mg/L on day 14. Meanwhile, the expression of the gene encoding alkaline phosphatase-like protein was significantly upregulated, with a value of 1.56 Log2FC, and the alkaline phosphatase concentration increased in the DOP group. The intracellular microcystin (IMC) concentration decreased with time in both groups. However, the concentration of extracellular microcystins (EMCs) increased with incubation time in both groups. Phosphorus participates in the regulation of microcystin synthesis, mainly by regulating ATP synthesis. Based on the physiological and molecular investigations in this study, the results provide crucial insights into the physiological adaptations and the role of P in modulating harmful algal bloom formation, microcystin synthesis, and potential molecular responses of M. aeruginosa.

Cu2+ and Zn2+, two ubiquitous metals in water environments, can widely trigger algae blooms at favourable environmental conditions. This paper elucidates the roles of Cu2+ and Zn2+ in the proliferation of Microcystis aeruginosa (M. aeruginosa) and synthesis of Microcystins (MCs). Findings indicate significant influences of increasing Cu2+ and Zn2+ concentrations on cell proliferation at limited available phosphorus concentrations of less than 0.1 mg/L. By contrast, Cu2+ and Zn2+ notably affected MCs production at all the inoculated phosphorus concentrations. The critical concentrations of 1 μg/L and 5 μg/L for Cu2+ and Zn2+, respectively, are determined to trigger rapid cell proliferation and MCs production. Furthermore, the impacts of Cu2+ and Zn2+ on nitrogen absorption and, subsequently, on amino acids (AAs) formation in cells, is likely key in MCs synthesis. The two AAs Alanine (Ala) and glutamic acid (Glu) demonstrate the most notable variations with the concentrations of Cu2+ & Zn2+.

Here, Microcystis aeruginosa (M. aeruginosa) was studied to analyze the effects of 0.5 mg L−1 naphthalene and 0.05 mg L−1 phenanthrene on profiles of cell growth, chlorophyll-a content and Microcystin-LR (MC-LR) production at different pH values. The results indicated that for both the naphthalene and phenanthrene treatments, the specific growth rates were higher in pH 10.0 than in either pH 7.0 or pH 5.0. In the presence of low concentrations of naphthalene or phenanthrene, chlorophyll-a in medium increased significantly more in pH 10.0 than pH 5.0. chlorophyll-a in cell was significantly lowered when exposed to naphthalene in both pH 10.0 and pH 7.0, and was higher when exposed to phenanthrene in pH 10.0 than pH 5.0. HPLC analysis revealed that the extracellular MC-LR concentrations in M. aeruginosa exposed to either naphthalene or phenanthrene were lower than in control M. aeruginosa at pH 5.0. The intracellular MC-LR levels in toxic M. aeruginosa cells exposed to naphthalene or phenanthrene were higher than in the controls at pH 10.0. Our study suggests that the MC-LR production of M. aeruginosa was affected by the pH value when low concentrations of either naphthalene or phenanthrene were present in the water. These results indicate that the pH value should not be ignored when evaluating the risk of chemicals that promote MC-LR production in eutrophic waters.

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.

Photoreduction characteristics of divalent inorganic mercury (Hg2+) in the presence of specific algae species are still not well known. Laboratory experiments were conducted in the present study to identify the effects of different concentrations of living/dead algae species, including Aphanizomenon flosaquae (AF) and Microcystis aeruginosa (MA), on the photoreduction rate of Hg2+ under various light conditions. The experimental results showed that percentage reduction of Hg2+ was significantly influenced by radiation wavelengths, and dramatically decreased with the presence of algae. The highest percentage reduction of Hg2+ was induced by UV-A, followed by UV-B, visible light and dark for both living and dead AF, and the order was dark > UV-A > UV-B > visible light for both living and dead MA. There were two aspects, i.e., energy and attenuation rate of light radiation and excrementitious generated from algae metabolisms, were involved in the processes of Hg2+ photoreduction with the presence of algae under different light conditions. The percentage reduction of Hg2+ decreased from 15% to 11% when living and dead AF concentrations increased by 10 times (from 106 to 105 cells/mL), and decreased from 11% to ~ 9% in the case of living and dead MA increased. Algae can adsorb Hg2+ and decrease the concentration of free Hg2+, thus inhibiting Hg2+ photoreduction, especially under the conditions with high concentrations of algae. No significant differences were found in percentage reduction of Hg2+ between living and dead treatments of algae species. The results are of great importance for understanding the role of algae in Hg2+ photoreduction.

Sanguinarine has strong inhibitory effects against the cyanobacterium Microcystis aeruginosa. However, previous studies were mainly limited to laboratory tests. The efficacy of sanguinarine for mitigation of cyanobacterial blooms under field conditions, and its effects on aquatic microbial community structure remain unknown. To elucidate these issues, we carried out in situ cyanobacterial bloom mitigation tests. Our results showed that sanguinarine decreased population densities of the harmful cyanobacteria Microcystis and Anabaena. The inhibitory effects of sanguinarine on these cyanobacteria lasted 17 days, after which the harmful cyanobacteria recovered and again became the dominant species. Concentrations of microcystins in the sanguinarine treatments were lower than those of the untreated control except during the early stage of the field test. The results of community DNA pyrosequencing showed that sanguinarine decreased the relative abundance of the prokaryotic microorganisms Cyanobacteria, Actinobacteria, Planctomycetes and eukaryotic microorganisms of Cryptophyta, but increased the abundance of the prokaryotic phylum Proteobacteria and eukaryotic microorganisms within Ciliophora and Choanozoa. The shifting of prokaryotic microbial community in water column was directly related to the toxicity of sanguinarine, whereas eukaryotic microbial community structure was influenced by factors other than direct toxicity. Harmful cyanobacteria mitigation efficacy and microbial ecological effects of sanguinarine presented in this study will inform the broad application of sanguinarine in cyanobacteria mitigation.

Due to the climate change and human activity, the frequency and intensity of algal blooms have increased significantly. Recent studies have shown that during the bloom event, evaluated levels of cyanobacteria could infiltrate the drinking water treatment process and emerge in the filtered and disinfected water, thus threatening the safety of the drinking water supply. Among these concerned cyanobacteria, Microcystis aeruginosa is one of the most commonly detected species that cause algal bloom in a fresh water body. The present work was designed to investigate the transport and retention behaviour of Microcystis aeruginosa in a packed column to resolve the mechanisms that drive the transport behaviour of Microcystis under various operational conditions. The results showed that lab-cultured Microcystis aeruginosa could effectively break through the packed column regardless of ionic strength, media size or flow rate, as well as the presence of dissolved organic matter in the water under the conditions investigated. Such behaviour significantly contradicts those of fluorescent microspheres, which are commonly considered as ideal colloids. In addition, the combined impacts of pre-oxidation technologies and filtration on Microcystis aeruginosa removal were tested systematically. It was found that even the cells have been lysed/oxidized, no significant improvement of cell removals were observed in packed column. This paper provides a significant and comprehensive record of transport and retention behaviour of Microcystis aeruginosa in porous media. The results found herein suggest that in addition to the effort preventing toxin release/exposure during bloom events in source water, engineers and researchers should also pay attention to the transport and retention of Microcystis aeruginosa and other algal cells in filters to minimize the risk of breakthrough of cyanobacteria cells in the drinking water treatment process.

The increasing occurrence of harmful algal blooms in surface waters may increase the input of algal organic matter (AOM) to the dissolved organic matter pool. The formation of iodinated trihalomethanes (I-THMs) and noniodinated disinfection byproducts (DBPs) in synthetic waters containing AOM extracted from Microcystis aeruginosa was investigated in chloramination (preformed and in-situ formed chloramine, NH2Cl and Cl2-NH2Cl, respectively) and chlorination (Cl2) processes. AOM is much more favorable for iodine incorporation than natural organic matter (NOM). For example, the formation of I-THM from AOM is much higher than NOM isolate extracted from treated water (e.g., 3.5 times higher in the NH2Cl process), and thus higher iodine utilization and substitution factors from AOM were observed. Short contact time (2 min) chlorination in Cl2-NH2Cl process leading to the formation of halogenated intermediates favored I-THM formation, compared with NH2Cl process. However, further increasing chlorine contact time from 5 min to 24 h facilitated the conversion from iodide to iodate and thus I-THM formation decreased. Meanwhile, the formation of noniodinated THM4, haloacetonitriles (HANs), and haloacetaldehydes (HALs) increased. Factors including concentrations of AOM and bromide, pH, and chlorine/nitrogen ratios influenced the formation of I-THMs and noniodinated DBPs. To evaluate the benefit of mitigating I-THM formation over the risk of noniodinated DBP formation, measured DBPs were weighed against their mammalian cell toxicity indexes. Increasing the chlorine exposure increased the calculated cytotoxicity based on concentrations of measured I-THMs and noniodinated DBPs since unregulated HANs and HALs were the controlling agents.

Harmful algae pollution has become the most concerned environment issue as the serious eutrophication spreads in natural waters all over the world. Highly efficient TiO2 photocatalysis is considered as a promising technique to achieve the inactivation of harmful algae using light energy. Herein, we prepare TiOX (X = N and P) photocatalyst with high activity via a facile sol-gel method in an oxygen deficient environment. The results show that the oxygen deficient environment can enhance the doping process, and the N and P can be successfully doped into TiO2 crystal by controlling the calcination temperature. The as-prepared TiOX particles can be assembled to a porous structure with a high specific surface area, which is beneficial to the adsorption of algal cells. The substitution of oxygen and the oxygen containing functional groups gives rise to disorder of the TiO2 crystal, thus tuning the light absorption capacity and promoting the separation of photogenerated charge carriers. Among the TiOX photocatalysts, the TiOX prepared at 550 °C exhibits the best photocatalytic performance with an algal inactivation rate of 81.5% for Microcystis aeruginosa following 6 h visible light irradiation, which can be attributed to the good synergetic effect of adsorption and photocatalysis. The deformation in algal morphology and disorder in cellular metabolism further confirms the inactivation process. The TiOX photocatalyst is also found to be able to effectively remove cytotoxins, which demonstrate that it holds substantial promise for the remediation of harmful algae polluted water.

Only limited information is available on the effects of dissolved organic phosphorus (DOP) on arsenate (As(V)) bioaccumulation and biotransformation in organisms. In this study, we examined the influence of three different DOP forms (β-sodium glycerophosphate (βP), adenosine 5′-triphosphate (ATP), and D-Glucose-6-phosphate disodium (GP) salts) and inorganic phosphate (IP) on As(V) toxicity, accumulation, and biotransformation in Microcystis aeruginosa. Results showed that M. aeruginosa utilized the three DOP forms to sustain its growth. At a subcellular level, the higher phosphorus (P) distribution in metal-sensitive fractions (MSF) observed in the IP treatments could explain the comparatively lower toxic stress of algae compared to the DOP treatments. Meanwhile, the higher MSF distribution of arsenic (As) in M. aeruginosa in the presence of DOP could explain the higher toxicity with lower 96-h half maximal effective concentration (EC50) values. Although we observed As(V) and P discrimination in M. aeruginosa under IP treatments with high intracellular P/As, we did not find this discrimination under the DOP treatments. As accumulation in algal cells was therefore greatly enhanced by DOP, especially βP, given its lower transformation rate to phosphate compared to ATP and GP in media. Additionally, As(V) reduction and, subsequently, As(III) methylation were greatly facilitated in M. aeruginosa by the presence of DOP, particularly GP, which was confirmed by the higher relative expression of its two functional genes (arsC and arsM). Our findings indicate that As(V) accumulation and its subsequent biotransformation were enhanced by organic P forms, which provides new insight into how DOP modulates As metabolism in algae.

Ultrasonic treatment has attracted much attention because of its physical and chemical effects that are distinct from those of chemical agents. In particularly, high-frequency ultrasound is known as an effective method because the theoretical resonance frequency of the gas vesicles in Microcystis aeruginosa is in the high frequency range (>100 kHz), which causes gas vesicles collapse and changes the settleability of the algal cells. In this work, the effects of the ultrasonic frequency, acoustic power density and duration on enhancing coagulation to remove turbidity in algae-laden water were studied. In order to explain the mechanism, the morphology of algae cells, the changes in extracellular organic substances, the zeta potential and the formation of hydroxyl radicals were analyzed systematically. Finally, Zeta potentials and flocs morphology after adding PAC were investigated to verify the mechanism. The results showed that the frequency exhibited fewer effects than power and duration on coagulation. SEM images showed that there were more severe cellular damages at 430 and 740 kHz than other frequencies. Sonication could cause the collapse of gas vesicle inside the cell, which was due to the instantaneous high pressure generated by the ultrasonic cavitation instead of the resonance. Furthermore, sonication would result in an increase in proteins in extracellular organic matter (EOM) with continuous ultrasonic irradiation, indicating that a small amount of proteins could promote coagulation and that the accumulation of proteins would inhibit coagulation. Free radical content testing showed that the production of excessive free radicals was often accompanied by a deterioration of the coagulation. The proper mechanical effects were the main mechanism of ultrasonic enhanced coagulation. Thus, it was recommended that the appropriate ultrasonic condition was the one that resulted in a small amount of protein leakage and little generation of free radicals, which occurred at 740 kHz and 0.02 W/mL in approximately 5 min, and would significantly enhance the turbidity removal rate in algae-containing water from approximately 80–90%.

Toxic cyanobacterial blooms are of major concern in eutrophic inland waters due to their water quality deterioration capabilities. Understanding their dynamics and driving factors is of great importance to manage bloom events and their consequences. Ecosystem models enable us to simulate, analyze and understand ecological processes in complex aquatic ecosystems. In this work, we examined the ability of the General Lake Model-Aquatic EcoDynamics (GLM-AED), an open-access one dimensional hydrodynamic-ecological model to simulate physical variables and the dynamics of two cyanobacterial species in 2016. The effect of possible hydrological and climatic scenarios on cyanobacterial blooms occurrence was also investigated. Results indicate that the model was able to accurately reproduce changes in water level (MAPE of 0.4%), water temperature profiles (MAPE of 5 to 7%) and the biomass of Microcystis aeruginosa and Chrysosporum (Aphanizomenon) ovalisporum at the study area. Dramatic changes were observed under warming trends including increase in both the length of the stratification period and in cyanobacteria bloom dynamics. Data analysis revealed that while water temperature was the primary factor determining cyanobacterial succession and occurrence, other factors such as water level fluctuations and irradiance are also important. Our findings suggest that any further increase in temperature would promote the development of potentially toxic cyanobacterial blooms at Karaoun Reservoir. The good performance of the model will provide essential insights required for deeper ecological understanding and water quality management.

Made available in DSpace on 2019-10-06T15:38:38Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-06-01 The excessive proliferation of toxin producing cyanobacteria constitutes a significant health risk to the environment and humans. This is due to the contamination of potable water and accumulation of cyanotoxins in plant and animal tissues. As a means of controlling bloom forming cyanobacteria, secondary metabolites with pro-oxidative activities from plants are used to treat water bodies contaminated with cyanobacterial blooms and their associated toxins. The objective of the present study was to evaluate the mechanism of action of extract, fractions and isolated flavonoids of Tridax procumbens L. on Microcystis aeruginosa (Kützing) Kützing. by monitoring changes in growth, oxidative stress, antioxidant response, and cyanatoxin microcystins (MCs) production. The extract, fraction 3 and the isolated flavonoids significantly reduced the cell density of the cyanobacterium. Furthermore, the extract and fraction 3 increased the production of reactive oxygen species, induced lipid peroxidation, and altered antioxidant enzyme activities of M. aeruginosa. The total MCs content of the cyanobacterium was negatively affected by the presence of the extract, fractions and isolated flavonoids. The present study show that T. procumbens has secondary metabolites that are capable of interfering with the physiology and microcystins production of M. aeruginosa. These characteristics are promising for the control of this noxious cyanobacterium in aquatic ecosystems. São Paulo State University (UNESP) School of Sciences Humanities and Languages Assis Department of Biotechnology Laboratory of Herbal Medicine and Natural Products, Avenida Dom Antônio 2100 São Paulo State University (UNESP) Institute of Chemistry, Rua Prof. Francisco Degni 55 Departamento de Ciências Biológicas Escola Superior de Agricultura Luiz de Queiroz Universidade de São Paulo Allelopathy Group Department of Organic Chemistry Institute of Biomolecules (INBIO) School of Science University of Cadiz, Campus de Excelencia Internacional 6 (ceiA3), C/República Saharaui 7 Department of Botany Ahmadu Bello University São Paulo State University (UNESP) School of Sciences Humanities and Languages Assis Department of Biotechnology Laboratory of Herbal Medicine and Natural Products, Avenida Dom Antônio 2100 São Paulo State University (UNESP) Institute of Chemistry, Rua Prof. Francisco Degni 55

In view of the world's immense dependency on non-renewable fossil fuels, the present study explores the prospect of Anabaena variabilis and Microcystis aeruginosa, which represent two distinct groups of cyanobacteria: nitrogen fixers and non fixers, for bioethanol production by analyzing the carbohydrate in their biomass, and maximizing its cellular accumulation inducing nitrate and phosphate stress. Under control condition, reducing sugar constituted 27.6% and 23.4% of the total carbohydrate, followed by glycogen exhibiting contents of 11.6% and 9.7% dry cell weight in the respective species. Cellulose, starch, and hemicellulose were obtained in lower quantities. Although phosphate starvation raised the carbohydrate content to a greater extent, its yield (mg L−1) was severely affected due to the depletion in the biomass. Hence, a biphasic phosphate-starved strategy was implemented generating a maximal carbohydrate content of 63.4% in A. variabilis and 55.1% in M. aeruginosa (compared to 46.2% and 41.4% under control) accompanied by ∼1.3-fold higher yield. Consequently, the bioethanol production in the test cyanobacteria reached 28.2% and 23.9% respectively with ∼1.3-fold higher (volumetric) yield than the control. Analysis of co-products revealed significant production of poly-β-hydroxybutyrate, C-phycocyanin, sodium copper chlorophyllin, and exopolysaccharides, wherein phosphate starvation induced effective stimulation of poly-β-hydroxybutyrate and exopolysaccharides, their yields again enhanced by respective ∼2 and ∼1.4-fold under the biphasic phosphate-starved approach. The present work stands out to be one of its kind comparing the suitability of A. variabilis and M. aeruginosa with an aim to have an overall view on cyanobacteria for bioethanol production by evaluating their carbohydrate profiles under different growth conditions, collectively with the production of various co-products, thus, supporting the bio-refinery concept.

In this study, we simulate three-dimensional transport of algal blooms in Lake Erie using a combination of remote sensing and hydrodynamic modelling. The remote sensing algorithms use data from the Sentinel-3 OLCI satellite sensor to derive chlorophyll-a concentration from cyanobacteria blooms in Lake Erie. The derived chlorophyll-a concentration initializes an algal bloom transport model driven by the lake component of the Water Cycle Prediction System for the Great Lakes, a system of coupled atmosphere-lake-hydrological models operated out of Environment and Climate Change Canada. The bloom is modelled as Microcystis aeruginosa, a buoyant species that is often dominant in harmful algal blooms in western Lake Erie. Short-term (a few days) predictions of algal bloom transport from July 27 to October 8, 2017 are modelled in both Eulerian and Lagrangian frameworks. The Eulerian framework is used to evaluate the sensitivity of model results to the initial vertical distribution of the bloom. In this work, the Lagrangian framework is limited to two-dimensional surface confined particles. We use several error metrics to evaluate model predictions. We find that results are sensitive to the buoyancy velocity for cases where the bloom was initially distributed over a large portion of the water column. An initial vertical distribution selected from modelled chlorophyll-a half depth shows the highest accuracy for the entire range of buoyancy velocities tested. We also find that the Pierce skill score is difficult to interpret, particularly in cases where bloom intensity is greatly overpredicted by the model.

Harmful algal blooms (HABs) have become a major health and environmental concern in the Great Lakes. In 2014, severe HABs prompted the State of Ohio to request NASA Glenn Research Center (GRC) to assist with monitoring algal blooms in Lake Erie. The most notable species of HAB is Microcystis aeruginosa, a hepatotoxin producing cyanobacteria that is responsible for liver complications for humans and other fauna that come in contact with these blooms. NASA GRC conducts semiweekly flights in order to gather up-to-date imagery regarding the blooms' spatial extents and concentrations. Airborne hyperspectral imagery is collected using two hyperspectral imagers, HSI-2 and HSI-3. Hyperspectral imagery is necessary in order to conduct experiments on differentiation of algal bloom types based on their spectral reflectance. In this analysis, imagery from September 19, 2016 was utilized to study the subpixel variability within the footprint of arbitrary sized pixels using several analysis techniques. This particular data set is utilized because it represents a worst case scenario where there is significant potential for public health concern due to high concentrations of microcystin toxin found in the water on this day and the concurrent observational challenges to accurately measure the algal bloom concentration variability with a remote sensing system due to the blooms high spatial variability. It has been determined that the optimal spatial resolution to monitor algal blooms in the Great Lakes is at most 50 m, and for much lower error 25 m, thus allowing for greater ease in identifying high concentration blooms near the surface. This resolution provides the best sensitivity to high concentration areas that are of significant importance in regard to human health and ecological damage.

Early detection of harmful cyanobacterial blooms allows identification of potential risk and appropriate selection of treatment techniques to prevent exposure in recreational water bodies and drinking water supplies. Here, luminescence-based adenosine triphosphate (ATP) analysis was applied to monitor and treat cultured and naturally occurring cyanobacteria cells. When evaluating lab-cultured Microcystis aeruginosa, ATP concentrations (≤252,000 pg/mL) had improved sensitivity and correlated well (R2 = 0.969) with optical density measurements at 730 nm (OD730; ≤0.297 cm−1). Following one year of monitoring of a surface water supply, ATP concentrations (≤2000 pg/mL) correlated (R2 = 0.791) with chlorophyll-a concentrations (≤50 μg/L). A preliminary early warning threshold of 175 pg ATP/mL corresponded with 5 μg/L chlorophyll-a to initiate increased monitoring (e.g., of cyanotoxins). Following oxidation processes (i.e., chlorine, chloramine, ozone, permanganate), ATP was demonstrated as an indicator of cell lysis and a threshold value of

Microcystis aeruginosa is known as a main contributor of cyanobacterial bloom. However, factors that drive its formation and dispersion remain poorly understood. The cellular-level responses to nutrient drivers of eutrophication were investigated. The results showed that growth rate of M. aeruginosa was significantly enhanced with the increasing bisphenol A (BPA) and nitrogen (N) level. Stress of BPA significantly inhibited cellular density, chlorophyll-a content across all the nutrient conditions, while Fv/Fm and rETRmax value were promoted by BPA. Responses of reactive oxygen species (ROS) value, superoxide dismutase (SOD) activity and malodialdehyde (MDA) content indicated that nitrogen deficiency and BPA caused oxidative stress to M. aeruginosa. Besides, nitrogen and BPA regulated the production and release of microcystins (MCs). M. aeruginosa exposed to BPA caused 95 up-regulated proteins, which was primarily associated with photosynthesis, nitrogen metabolism, glycolysis/glyconeogenesis and carbon fixation in photosynthetic organisms. The 91 down-regulated proteins were related to quorum sensing, longevity regulating and cell cycle-caulobacter, confirming that the driving force of regulating the change of cellular density and genes expression weakened. These findings provide important clues to elucidate the combined regulatory mechanisms of cyanobacterial blooms triggered by endocrine-disrupting compounds and environmental factors and help to effectively prevent and reduce cyanobacterial blooms.

Overproduction of toxic cyanobacteria is a type of harmful algal blooms (HABs). The heptapeptide microcystins (MCs) are one of the most common cyanotoxins. There is increasing research concerning the effects of MCs on growth and physiology of vascular plants, however there is a lack of studies on their direct effects on aquatic macrophytes in the real environment. Here we report the occurrence of a MC producing HAB in Lake Bardos, Hungary in 2012 with harmful effects on cytological, histological and biochemical parameters of Ceratophyllum submersum (soft hornwort) plants naturally growing at the blooming site. Blue-Green Sinapis Test (BGST) showed high toxicity of HAB samples. Cell-free water samples contained a significant amount of MCs (7.31 ± 0.17 μg L−1) while C. submersum plants contained 1.01 ± 0.21 μg g DW−1 MCs. Plants showed significant increases of protein content and decreases of anthocyanin content and carotenoid/chlorophyll ratio, indicating physiological stress- as compared to plants from the control (MC free) sampling site of the same water body. Histological and cytological studies showed (i) radial swelling and the abnormal formation of lateral buds at the shoot tip leading to abnormal development; (ii) the fragmentation of nuclei as well as accumulation of phenolics in the nucleus indicating that the HAB induced cell death and stress reactions at the nuclear level. The most relevant effect was the increase of histone H3 phosphorylation in metaphase chromosomes: since MCs are strong inhibitors of protein phosphatases, this alteration is related to the biochemical targets of these toxins. The HAB decreased peroxidase activity, but increased nuclease and protease activities, showing the decreased capacity of plants to face biotic stress and as the cytological changes, the induction of cell death. This study is one of the first to show the complex harmful changes in aquatic plants that co-exist with HABs.

A wide range of cyanobacterial species and their harmful metabolites are increasingly detected in water bodies worldwide, exacerbated by climate change and human activities. The resulting bloom conditions represent significant challenges to production of safe drinking water and cost effective water reuse, therefore their removal is a priority to ensure public safety. While current microscopic taxonomy identification methods provide valuable information about cell numbers during treatment, these methods are incapable of providing information about the fate of cells during treatment. The objectives of this study were to (1) identify the critical control points for breakthrough and accumulation of cells by investigating the fate of cells during treatment processes using a combination of taxonomy, cell integrity and next-generation sequencing (NGS), and (2) assess the impact of pre-treatment processes on breakthrough prevention at critical control points, and the benefits of cell integrity and NGS analysis for improved management purposes. This paper presents the results of an unprecedented cyanobacterial monitoring program conducted in four full scale water treatment plants located in three different climate zones. Cyanobacterial cell integrity and accumulation during operation process were assessed for the first time using next generation of gene sequencing methods. NGS analysis led to detection of cyanobacterial and melainabacteria orders in water samples that were not identified by microscopy. 80 ± 5% of cells were completely lysed post pre-oxidation (for both ozone and potassium permanganate). However unlike pre-ozonation, the remaining cells were undamaged cells with the potential to accumulate and grow within the plants post-KMnO4 treatment, particularly in clarifier sludge. To effectively monitor water quality, this study presents a synergistic approach coupling new and traditional analytical methods and demonstrates the importance of identifying critical points for managing accumulation of cyanobacteria within plants.

The frequent outbreaks of cyanobacteria bloom are often accompanied by the generation and release of reduced phosphorus species (e.g., phosphine), which raises interesting questions regarding their potential algae-related effects. To clarify the physiological and biochemical responses of cyanobacteria to phosphine, Microcystis aeruginosa was treated with different concentrations of phosphine. Net photosynthetic rate, total antioxidant capacity (T-AOC), catalase (CAT) activity, and the concentrations of chlorophyll a, carotenoid and total protein were investigated and scanning electron microscopy (SEM) was conducted to elucidate the physiological and biochemical responses of M. aeruginosa to phosphine. The results showed that phosphine was beneficial to the growth of algal cells after M. aeruginosa acclimatized to the treatment of phosphine, and treatment with 2.48 × 10−2 mg/L phosphine had a greater positive effect on the growth and reproduction of M. aeruginosa than 7.51 × 10−3 mg/L phosphine, in which most algal cells were smooth and flat on day 16. Treatment with the high concentration of phosphine (7.51 × 10−2 mg/L) for 16 d reduced T-AOC, CAT activity, net photosynthetic rate, and the concentrations of chlorophyll a, carotenoid and total protein of M. aeruginosa to the minimums, resulting in the lysis and death of M. aeruginosa cells, which indicates phosphine has a toxic effect on the growth of algal cells. However, the high concentration of phosphine (7.51 × 10−2 mg/L) had a greater positive effect on the growth of M. aeruginosa cells than the lower two (7.51 × 10−3 mg/L and 2.48 × 10−2 mg/L) from 3 d to 12 d. Our findings provide insight into how phosphine potentially affects the growth of M. aeruginosa cells and the important roles of elevated phosphine on the outbreak of cyanobacteria bloom.

Metal-organic Frameworks (MOFs) as a new type of nanomaterials are extensively used in various fields of environment pollution remediation. However, the MOFs are rarely applied in the removal of cyanobacterial blooms, and more fundamental investigation is warrant for more insights into mechanisms for algae inhibition. In this study, Cu-MOF-74 was synthesized by a simple hydrothermal method, and its inhibitory effect on the growth of Microcystis aeruginosa was studied. Furthermore, its mechanisms were explored with respect to metal ion release, agglomeration, shading and algal cell membrane breakage, production of extracellular hydroxyl radical and intracellular reactive oxygen species. The results showed that the inhibition rate of M. aeruginosa was 372% after 24-h exposure when the concentration of Cu-MOF-74 exceeded 1 mg/L. However, the addition of Cu-MOF-74 at the concentration lower than 0.1 mg/L promoted the algal growth. The inhibition of algal growth by Cu-MOF-74 was basically attributed to the presence of hydroxyl radical and intracellular reactive oxygen species, with the released Cu2+ and cell aggregation involved to some extent. Overall, nanocrystalline Cu-MOF-74 is of great potential in the control of harmful cyanobacterial blooms and the inhibition is specific to the concentration of Cu-MOF-74.

Microcystis aeruginosa frequently forms cyanobacterial blooms in eutrophic water bodies, resulting in high concentrations of extracellular polymeric substances (EPS) in the water column. The effects of M. aeruginosa EPS (MA-EPS) on the adsorption behavior of Cu(II) onto kaolinite and the possible mechanisms were investigated in this study. The results of potentiometric titration and Fourier transform infrared (FT-IR) spectroscopy determination show that carboxyl, phosphoryl and amino/hydroxyl groups were the main adsorption groups on MA-EPS. The combination of EPS with kaolinite created new adsorption sites. MA-EPS increased the adsorption of Cu(II) by kaolinite mainly through complexation. The adsorption kinetics of Cu(II) by kaolinite or kaolinite + EPS composite (Kao + EPS) was well fitted by a pseudo-second order kinetic model. The adsorption isotherm analyses show that the incorporation of MA-EPS onto kaolinite increased its surface heterogeneity. Rather than intercalating into the kaolinite interlayers, MA-EPS and/or Cu(II) were adsorbed onto the surface of this clay.

Microcystis spp., which occur as colonies of different sizes under natural conditions, have expanded in temperate and tropical freshwater ecosystems and caused seriously environmental and ecological problems. In the current study, a Bayesian network (BN) framework was developed to access the probability of microcystins (MCs) risk in large shallow eutrophic lakes in China, namely, Taihu Lake, Chaohu Lake, and Dianchi Lake. By means of a knowledge-supported way, physicochemical factors, Microcystis morphospecies, and MCs were integrated into different network structures. The sensitive analysis illustrated that Microcystis aeruginosa biomass was overall the best predictor of MCs risk, and its high biomass relied on the combined condition that water temperature exceeded 24 °C and total phosphorus was above 0.2 mg/L. Simulated scenarios suggested that the probability of hazardous MCs (≥1.0 μg/L) was higher under interactive effect of temperature increase and nutrients (nitrogen and phosphorus) imbalance than that of warming alone. Likewise, data-driven model development using a naïve Bayes classifier and equal frequency discretization resulted in a substantial technical performance (CCI = 0.83, K = 0.60), but the performance significantly decreased when model excluded species-specific biomasses from input variables (CCI = 0.76, K = 0.40). The BN framework provided a useful screening tool to evaluate cyanotoxin in three studied lakes in China, and it can also be used in other lakes suffering from cyanobacterial blooms dominated by Microcystis.

The aim of the present research was to summarize the main reasons that explain the distribution of harmful blooms of cyanobacteria in Argentina. It is a large territory with climates ranging from humid tropical to cold temperate. We performed a meta-analysis of the published data and information in technical reports published from 1945 to 2015, and included additional data from personal non-published studies. A total of 122 water bodies affected by planktonic cyanobacterial blooms were recorded and geo-referenced. The analysis showed that blooms, defined as events exceeding 5000 cells/mL, occurred in different types of water bodies, including shallow lakes, rivers, streams, reservoirs, estuaries and storage facilities. Maximum bloom abundance and species and ecological strategies (dispersive, scum-forming, nitrogen fixer) responsible for each event were related to the geographic and climatologic characteristics and type and origin of water bodies. The Puna and the Andean Patagonia eco-regions were mostly free of blooms. The most impaired aquatic systems were shallow lakes and reservoirs (46.7 and 24.6%, respectively). Deep lakes had no reports of blooms and rivers were mainly affected at the regulated reaches, with intensities generally decreasing downstream the dams. Besides, 74.3% of the blooms reported in Argentina exceeded WHO Alert Level 2 for drinking and bathing waters (100,000 cells/mL). Thirty-nine species, identified by Komárek's polyphasic approach to taxonomy, were responsible for the blooms. Microcystis aeruginosa, Dolichospermum spiroides, Dolichospermum circinale, Raphidiopsis mediterranea and Cylindrospermopsis raciborskii were frequently found participating in either mixed or single species blooms. The species distribution was associated with the eco-region and aquatic system typologies and affected by seasonality and climatological and geographic variables. The eco-strategies of cyanobacterial species showed stronger associations with the qualitative and quantitative indicators used in the meta-analysis, and appeared as useful tools for management measures.

Co-existence of cyanobacterial harmful algal blooms (CyanoHABs) and steroid estrogens (SEs) has been an increasing concern in eutrophic waters. The cellular responses and biodegradation of 17β-estradiol (E2) in cyanobacterium Microcystis aeruginosa were investigated at different nitrogen levels. During the 10-d experiment, the growth of M. aeruginosa was stimulated by 10–100 μg L−1 of E2 at the lowest nitrogen level of 0.5 mg L−1, whereas the presence of E2 inhibited the cyanobacterial growth at 5 mg L−1 of nitrogen. With nitrogen concentration increased to 50 mg L−1, the impact of E2 on levels of growth rate and chlorophyll a (Chla) alleviated. Exposure to E2 also promoted the superoxide dismutase activity of M. aeruginosa, coupled with cellular oxidative damage as indicated by the increasing malondialdehyde content. A sufficient nitrogen supply mitigated the oxidative stress of E2 through enhancing the synthesis of detoxification-related enzymes. Simultaneously, the secretion of tryptophan-like substances in loosely- and tightly-bound extracellular polymeric substances was triggered for adapting to an E2 addition in the short term. Moreover, significant biodegradation of E2 was observed, and the process followed a first-order kinetic reaction. The obtained half-lives decreased with nitrogen levels and ranged from 2.47 to 2.81 and 3.39–5.04 d, respectively, at 10 and 100 μg L−1 of E2. These results provide a better understanding of the potential effects of SEs on CyanoHABs formation, as well as the important role of CyanoHABs on SEs removal in aquatic ecosystems, which should be fully considered in the control of combined pollution.

Microcystis aeruginosa can cause harmful algal blooms in freshwaters worldwide. It has already seriously affected human lives and prevented the use of water resources. Therefore, there is an urgent need to develop ecofriendly and effective methods to control and eliminate M. aeruginosa in aquatic environments. In this study, Halobacillus sp. strain H9, a bacterium that showed high M. aeruginosa flocculation activity, was isolated and selected to assess its potential for the removal of M. aeruginosa. The analyses of flocculation activity and mode indicated that the strain H9 induced M. aeruginosa flocculation by secreting active flocculating substance rather than by directly contacting algal cells. A 5% concentration of the H9 supernatant could efficiently flocculate M. aeruginosa cells with a density of up to 5 × 107 cells/mL. Dramatic increases in the zeta potential indicated that charge neutralization could be the mechanism of the flocculation process. The strain H9 flocculated M. aeruginosa with no damage to the algal cell membrane, and did not result in microcystin being released into the surrounding environment. The flocculated algal culture was less toxic to zebrafish larvae, suggesting an environmentally friendly benefit of the H9 supernatant. In addition to M. aeruginosa, the H9 strain was also able to flocculate two other species causing harmful algal blooms, Phaeocystis globose and Heterosigma akashiwo. Furthermore, the flocculation activity of the H9 supernatant was stable at different temperatures and over a wide pH range. These characteristics give the H9 strain great potential for mitigating the influences of harmful algal blooms.

To improve the recovery efficiency of buoyant-bead flotation (BBF), a novel compound buoyant-bead flotation technology (CBBF) using acidified fly ash cenospheres with heat-aided pre-flocculation was developed. The effects of cenospheres concentration (0.6–3 g L−1), flotation time (5–20 min) and pH values (2–10) were studied. Response Surface Methodology was utilized to optimize the CBBF process. The results showed that pH value had the greatest influence on the recovery process. When pH values were low, the Chlorella vulgaris (C. vulgaris) cells began to flocculate, which helped to form the “C. vulgaris-cenosphere” aggregates and improved the recovery efficiency. To avoid the addition of flocculants, heat-aided pretreatment was used to promote flocculation process. The maximum recovery efficiency (93.04 ± 0.60%) was obtained at cenospheres concentration of 2.83 g L−1, pH value of 2.41, flotation time of 17.05 mins and flotation temperature of 90 °C. Furthermore, it was demonstrated that this CBBF method can be also widely applied to other microalgae strains, such as Scenedesmus obliquus, Spirulina platensis, Microcystis aeruginosa and Anabaena variabilis. It can be concluded that the CBBF technology is a feasible and highly efficient (over than 90%) process for the removal of various microalgae.

A highly sensitive fluorescence resonance energy transfer (FRET)-based quantum dot (QD)-Aptasensor was developed for microcystin-LR (MC-LR) detection in eutrophic water. The FRET-based QD-Aptasensor was able to achieve an analytical limit of detection of 10−4 μg/L MC-LR with selectivity among different congeners (microcystin-YR, microcystin-LY, microcystin-LW, microcystin-RR, microcystin-LF, microcystin-LA, and Nodularin). The performance of QD-Aptasensor was demonstrated using both laboratory grown cyanobacterial culture (Microcystis aeruginosa) and environmental water samples. For the laboratory culture, the intracellular MC-LR concentrations changed according to the cyanobacterial growth curve. The QD-Aptasensor detected MC-LR up to 12.7–15.8 μg/L-cyanobacterial culture at early stationary phase. For the environmental samples, the MC-LR was measured at cell densities of 2.7 × 108 and 6.6 × 1010 cells/L-water, which correspond to 1.0 and 7.2 μg MC-LR/L-water, respectively. For comparison, the laboratory culture and environmental samples were analyzed by the conventional enzyme-linked immuno-sorbent assay (ELISA). The MC-LR concentrations of FRET-based QD-Aptasensor showed a strong positive correlation with those of ELISA (Pearson correlation coefficient, r = 0.981 and r = 0.862) for the laboratory culture and environmental samples, respectively.

Harmful algal blooms have emerged as a worldwide issue. After concentrations of herbicides entering water, herbicides in water may pose ecological effects on them. The present study investigates the toxicity and environmental behavior of the herbicides, napropamide and acetochlor as enantiomers and as racemates on Microcystis aeruginosa which is the main specie known to produce hepatotoxins. S-napropamide/acetochlor are degraded faster than their corresponding isomer R-napropamide/acetochlor, with the latter more prone to accumulate in algal cells. Moreover, all the enantiomers did not undergo measurable racemization in the medium and algal cells. S-napropamide/acetochlor exhibited much higher toxicity than R-napropamide/acetochlor, with the S-enantiomer inducing a much greater production of antioxidant defense enzymes (superoxide dismutase (SOD) and malondialdehyde (MDA)) and microcystins (MC). SOD and MC increased after treatment with the herbicides and these increases were dependent on the exposure time, whereas MDA showed no apparent change. The information provided in this work will be useful for understanding the toxicity mechanism and environmental behaviors of different amide herbicides (napropamide and acetochlor) in aquatic environments at the enantiomeric level. Additionally, analysis of chiral herbicides in aquatic system needs more attention to aide in the environmental assessment of chiral herbicides.

The freshwater cyanobacteria, Microcystis aeruginosa (M. aeruginosa), is well known to produce microcystins (MCs) and induce the formation of harmful algal blooms (HABs) in aquatic environments, but the effects that urea fertilizer has on cyanobacterial growth and toxin production from a molecular biology perspective remain poorly understood. We evaluated changes in the growth and toxicity of M. aeruginosa cultured under different conditions of nitrogen (N) starvation (NN), low nitrogen (LN), and high nitrogen (HN). Cell density and chlorophyll-a concentrations decreased in cyanobacteria exposed to N starvation and increased following the addition of urea, whereas MCs content increased to a peak and then decreased after urea addition. Transcriptomic analysis confirmed that most genes encoding MCs and genes involved in N metabolic pathways were upregulated under N starvation and LN conditions, whereas these genes were downregulated under HN conditions. Our results offer important insights into the exploring N in controlling the formation of HABs and toxin production based on both physiological and molecular response.

The occurrence of pharmaceuticals and personal care products (PPCPs) in wastewater poses huge environmental threats, even at trace concentrations, and novel approaches are urged due to the inefficiencies of conventional wastewater treatment plants, especially when processing contaminants at high concentrations. Meanwhile, another widespread problem in the aquatic domain is the occurrence of harmful algal blooms (HABs) which cause serious damage to the ecosystem, but have rarely been investigated for possible valorization. This study investigated the possibilities, mechanisms, and effects of toxin release of using a harmful cyanobacterial species, Microcystis aeruginosa (M. aeruginosa), in order to remove the widely used drug, tetracycline, at high concentration. The results were compared with the performance obtained by the use of the hitherto generally-selected chlorophyte alga Chlorella pyrenoidosa (C. pyrenoidosa) for tetracycline concentrations of 10-100 mg L−1. M. aeruginosa exhibited a much more effective and rapid tetracycline removal (over 98.0% removal in 2 days) than did C. pyrenoidosa (36.7%-93.9% in 2 days). A comprehensive kinetic investigation into probable removal pathways indicated that, theoretically, bio-remediation dominated the process by M. aeruginosa (71.6%), while only accounting for 20.5% by C. pyrenoidosa. Both microalgae promoted the hydrolysis of tetracycline under conditions of increased pH and inhibited abiotic photolytic reactions by the shading effect to the water column, when compared with control experiments. Although identical degradation by-products were identified from treatments by both microalgal species, distinct by-products were also confirmed, unique to each treatment. Moreover, the growth of M. aeruginosa biomass exhibited strong tolerance to tetracycline exposure and released significantly lower levels of microcystin-LR, compared with the control systems. This study supports the possibility of reusing HABs species for the effective remediation of antibiotics at high concentrations. We have further suggested possible mechanisms for remediation and demonstrated control of toxin release., The research was supported by the National Key R&D Program of China (2017YFA0207204). The PhD fellowship of Minmin Pan was supported by the China Scholarship Council (CSC). We also thank the Danish Innovation Foundation for support through the InWAP project.

Nowadays Cylindrospermopsis raciborskii (C. raciborskii) and the metabolites produced, such as cylindrospermopsin (CYN), pose a serious threat to the ecosystem. Advanced oxidation technologies have been verified as constituting a very promising means to eliminate the risk from harmful algae. But so far little research has focused on the visible-light photocatalytic destruction of C. raciborskii cells and the degradation of their metabolites. In our study, N-doped TiO2 (N-TiO2) was used to degrade C. raciborskii and the degradation was compared with that of the Microcystis aeruginosa (M. aeruginosa). Results showed that although the photodegradation of C. raciborskii was more difficult than that of M. aeruginosa, the treatment with N-TiO2 was still satisfactory. After adding 200 mg/L N-TiO2, C. raciborskii cells (5 × 106 cells/mL) were completely destroyed within 20 h under visible light irradiation, and nearly 90% of the organic matter and CYN in the suspensions were also degraded, thereby markedly improving the water quality. The photocatalytic process starts with damage to the cell membrane resulting in the leakage of internal components. Subsequently, the leaked metabolites were oxidised by the reactive oxidizing species produced by N-TiO2. Thus, the application of N-TiO2 is a promising method for the treatment of C. raciborskii.

Cyanobacterial blooms are intensifying global ecological hazards. The fine structure and dynamics of bloom community are critical to understanding bloom development but little understood. Here, the questions whether dominant bloomers have high diversity and whether dominant OTUs (operational taxonomical units) compete with one another were addressed. 16S rRNA gene amplicons from an annual bloom at five locations in Harsha Lake (Ohio, USA) showed cyanobacteria were the dominant phylum, and co-existing major bacterial phyla included Proteobacteria, Bacteroidetes, Actinoacteria, and Verrucomicrobia. On the genus level, the initial dominance by Dolichospermum in June yielded to Planktothrix in July, which were replaced by Microcystis and Cylindrospermopsis in August throughout the bloom. Based on the number of verified unique OTUs (a within-genus biodiversity metric), dominant genera tended to have high within-genus diversity. For example, Dolichospermum had 57 unique OTUs, Planktothrix had 36, Microcystis had 12, and Cylindrospermopsis had 4 unique OTUs. Interestingly, these different OTUs showed different dynamics and association with other OTUs. First, no between-OTU competitions were observed during the bloom cycle, and dominant OTUs were abundant throughout the bloom. Such biodiversity of OTUs and their dynamics were verified in Microcystis aeruginosa with two microcystin synthetase genes (mcyA and mcyG): the relative abundance of both genes varied during the bloom based on quantitative PCR. Two Dolichospermum circinale OTUs and one P. rubescens OTU were most abundant and persistently present throughout the entire bloom. Second, these OTUs differed in the OTUs they were associated with. Third, these OTUs tended to have different levels of association with the environmental factors, even they belonged to the same genera. These findings suggest the structure and dynamics of a cyanobacterial bloom community is complex, with only few OTUs dominating the bloom. Thus, high-resolution molecular characterization will be necessary to understand bloom development.

Although toxic cyanobacterial blooms and their toxins threaten drinking water and ecology and are promoted by nutrient loading, the precise nutrient regime that increases cyanobacterial populations and toxin production is poorly understood. Here, the influences of arginine (Arg), as a common amino acid with high nitrogen content, on the growth and microcystins (MCs) production of Microcystis aeruginosa (M. aeruginosa) were investigated by an isotope method (15N). The results showed that the biomass and production of microcystin-LR (MC-LR) increased with an increase in initial Arg concentrations in the range of 0.3–1.4 mmol-N L−1, whereas a higher Arg concentration (3.6 mmol-N L−1) inhibited the growth. MC-LR on different days (days 0, 6, 12, and 18) was detected by liquid chromatography with tandem mass spectrometry (LC-MS/MS) after incubation with 15N-Arg. The MC-LR molecular weight increased from 995 to 1004 with 100% relative abundance with 10 15N atoms bound by the Adda, Arg (4 15N), Glu, Mdha, Ala, Leu, and MeAsp residues on day 18. It seems that there was a sequential order when M. aeruginosa assimilated Arg to synthesize MC-LR. The Arg residue in the molecule of MC-LR was the last one to be labeled by 15N from 15N-arginine. This study not only presents a deeper insight into the biosynthesis of free amino acids that are incorporated into MCs but also reminds us of the potential risk caused by Arg, which should arouse concerns.

Single and co-culture systems of Microcystis aeruginosa and Scenedesmus obliquus were prepared with different initial algal densities and treated with different concentrations of aqueous extracts from the rhizome of Pontederia cordata to study its inhibitory effect on algal growth and the competitive relationship between these two algal species. The results showed that aqueous extracts could inhibit the growth of M. aeruginosa and S. obliquus, and the inhibition rate of aqueous extracts on the growth of M. aeruginosa was always higher than that of S. obliquus. A Lotka–Volterra competition model revealed that these two algal species can co-exist without the addition of aqueous extracts, and S. obliquus exhibited a stronger ability to compete than that of M. aeruginosa. Meanwhile, the dominant algal species changed with the addition of aqueous extracts regardless of the initial ratios of the two algae. The species ratio of mixed cultures had a strong effect on the interspecific interaction between the two algae. The higher proportion of S. obliquus in the initial proportion of two algae, the stronger competitive ability of S. obliquus when compared with that of M. aeruginosa.

As aquatic ecosystems become increasingly affected by hydrologic alterations, drought and sea level rise a need exists to better understand the biological effects of elevated salinity on toxigenic cyanobacteria such as Microcystis aeruginosa. This study investigated the impacts of oligohaline/low mesohaline conditions and exposure time on selected physiological and biochemical responses in M. aeruginosa including cell viability, oxidative stress, antioxidant responses, in addition to microcystin synthesis and release into the surrounding environment. M. aeruginosa was able to grow in most test salinity treatments (1.4-10 ppt), as supported by cell abundance data and chlorophyll-a (chl-a) concentrations. Physiological data showed that after certain salinity thresholds (∼7ppt) were surpassed, salt stress had cascading effects, such as increased ROS production and lipid peroxidation, potentiating the decline in cellular viability. Furthermore, elevated salinity induced oxidative stress which was concomitant with a decrease in cell abundance, chl-a concentration and photochemical efficiency in the 7-10 ppt treatments. M. aeruginosa did not synthesize microcystins (MCs) in response to increased saline conditions, and mcy-D expression was not correlated with either salinity treatment or extracellular MC concentrations, indicating that salinity stress could inhibit toxin production and that released toxins were likely synthesized prior to exposure. Additionally, extracellular MC concentrations were not correlated with decreased cellular integrity, as evidenced by SYTOX analyses, suggesting that toxins may be released through mechanisms other than cellular lysis. Results from this study support that M. aeruginosa can survive with limited negative impacts to cellular structure and function up to a certain threshold between 7-10 ppt. However, after these thresholds are surpassed, there is radical decline in cell health and viability leading to toxin release. This work underscores the importance of understanding the balance between ROS production and antioxidant capacities when assessing the fate of M. aeruginosa under mesohaline conditions.

We determined the potential interference of extracellular algal organic matter (EAOM) and intracellular algal organic matter (IAOM) extracted from Microcystis aeruginosa on MS2 bacteriophage inactivation under UV irradiation at two wavelengths (220 and 254 nm). UV irradiation at 220 nm doubled the inactivation rate of MS2 in water containing EAOM than in organic-free phosphate buffered solution. In contrast, EAOM did not change MS2 inactivation by exposure to UV 254 nm. The presence of IAOM did not significantly influence MS2 inactivation by exposure to either UV 254 or UV 220 nm. To achieve 3 log10 inactivation of MS2, UV254 nm required more than double the dose of UV220 nm (45 mJ/cm2 vs. 20 mJ/cm2). Linear correlations between the reduction in infectivity and the reduction in genome copies detected by reverse transcription quantitative polymerase chain reaction suggested that genomic damage is the main mechanism responsible for MS2 inactivation in water containing algal organic matter (AOM) by exposure to UV irradiation. These findings suggest that the presence of AOM did not negatively influence MS2 inactivation by either 220 or 254 nm irradiation, and that a lower UV dose of 220 nm irradiation can be used to achieve the same level of inactivation in water containing AOM.