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Global concerns over harmful cyanobacterial blooms brought on by eutrophication are now widespread. Aquatic ecological restoration techniques that use algicidal bacteria to control toxic algae show promise. A Bacillus subtilis S4 (S4) strain with strong Microcystis aeruginosa algicidal activity and the capacity to degrade microcystins (MCs) were successfully isolated and evaluated in this study. The dynamics of internal and extracellular MC concentration as well as the physiological response and morphological properties of M. aeruginosa were investigated in the M. aeruginosa /bacteria co-culture system. The findings demonstrated that when S4 density grew from 1 × 106 cells/ml to 1 × 108 cells/ml, the release of M. aeruginosa lysis and MCs was boosted; however, MCs dropped by approximately 90% within 18 h, regardless of bacterial density. Comparing the bacterial cell incubation system to the control and bacterial cell-free filtrate systems, the assessment of extracellular and intracellular MCs revealed a 95% reduction in MCs. The findings showed that 89% of MCs were decreased by bacterial cells, while 98% of M. aeruginosa cells were algaecided by bacterial metabolites. Sustainable eradication of M. aeruginosa and MCs has been accomplished by the combined efforts of the S4 strain and its metabolites. By secreting algicidal chemicals that are resistant to proteases, acid, base, and heat, the S4 strain indirectly acts as an algaecide. The S4 strain possesses a strong ability to break down MCs and a very effective and stable algaecide function, indicating that it can potentially treat eutrophic water with hazardous algae. [ABSTRACT FROM AUTHOR]

Temperature up-shift and UV-A radiation effects on growth, lipid damage, fatty acid (FA) composition and expression of desaturase genes desA and desB were investigated in the cyanobacteria Microcystis aeruginosa. Although UV-A damaging effect has been well documented, reports on the interactive effects of UV radiation exposure and warming on cyanobacteria are scarce. Temperature and UV-A doses were selected based on the physiological responses previously obtained by studies with the same M. aeruginosa strain used in this study. Cells pre-grown at 26 °C were incubated at the same temperature or 29 °C and exposed to UV-A + PAR and only PAR for 9 days. Growth rate was significantly affected by UV-A radiation independently of the temperature throughout the experiment. High temperature produced lipid damage significantly higher throughout the experiment, decreasing at day 9 as compared to 26 °C. In addition, the cells grown at 29 °C under UV-A displayed a decrease in polyunsaturated FA (PUFA) levels, with ω3 PUFA being mostly affected at the end of exposure. Previously, we reported that UV-A-induced lipid damage affects differentially ω3 and ω6 PUFAs. We report that UV-A radiation leads to an upregulation of desA, possibly due to lipid damage. In addition, the temperature up-shift upregulates desA and desB regardless of the radiation. The lack of lipid damage for UV-A on ω3 could explain the lack of transcription induction of desB. The significant ω6 decrease at 26 °C in cells exposed to UV-A could be due to the lack of upregulation of desA. [ABSTRACT FROM AUTHOR]

Global concerns over harmful cyanobacterial blooms brought on by eutrophication are now widespread. Aquatic ecological restoration techniques that use algicidal bacteria to control toxic algae show promise. A Bacillus subtilis S4 (S4) strain with strong Microcystis aeruginosa algicidal activity and the capacity to degrade microcystins (MCs) were successfully isolated and evaluated in this study. The dynamics of internal and extracellular MC concentration as well as the physiological response and morphological properties of M. aeruginosa were investigated in the M. aeruginosa/bacteria co-culture system. The findings demonstrated that when S4 density grew from 1 × 106 cells/ml to 1 × 108 cells/ml, the release of M. aeruginosa lysis and MCs was boosted; however, MCs dropped by approximately 90% within 18 h, regardless of bacterial density. Comparing the bacterial cell incubation system to the control and bacterial cell-free filtrate systems, the assessment of extracellular and intracellular MCs revealed a 95% reduction in MCs. The findings showed that 89% of MCs were decreased by bacterial cells, while 98% of M. aeruginosa cells were algaecided by bacterial metabolites. Sustainable eradication of M. aeruginosa and MCs has been accomplished by the combined efforts of the S4 strain and its metabolites. By secreting algicidal chemicals that are resistant to proteases, acid, base, and heat, the S4 strain indirectly acts as an algaecide. The S4 strain possesses a strong ability to break down MCs and a very effective and stable algaecide function, indicating that it can potentially treat eutrophic water with hazardous algae.

Abstract Microcystis aeruginosa blooms in water bodies, evidencing a high risk of exposure to human health due to the release of toxins, which affects water quality. Implementing physical, chemical, and microbial control methods requires an integrated understanding of cyanotoxin dynamics, especially their relationship with sediments. Consequently, sediment obtained from three stations of the Riogrande II reservoir (Antioquia, Colombia) was analyzed to determine the adsorption and removal capacity of the microcystin-LR (MC-LR). For this purpose, the sediment was subjected to different treatments to select the one with the highest MC-LR removal capacity. Furthermore, the effectiveness and stability of adsorption removal process were evaluated by analyzing mechanical processes such as aeration, sonication, and agitation. The dried sediment showed the highest reduction in toxin concentration (93%) after 24 h, followed by washed sediment (91%) and sterilized sediment (81%). On the other hand, the sediment was fractionated into silts and clays; the latter was the least effective. Finally, the fine and half silts were better adsorbents of the toxin, acting similarly over time. Initially, the utilization of sediment that has been dried by sunlight could be a complementary alternative to reinforce MC-LR control methodologies in water bodies. On the one hand, MC-LR desorption assays showed that aeration of the sediment for 30 min caused a release of up to 96% of the adsorbed compound. At the same time, the effect of sonication and agitation was less intense. However, the absorption process must be fast to avoid efficiency losses due to desorption since a high percentage of the toxin was spontaneously desorbed from the sediment in two days.

Over the last decades, Aquitaine lakes have been exposed to growing biomasses of invasive macrophytes, in particular Lagarosiphon major, and to frequent blooms of the cyanobacteria Microcystis aeruginosa. Our aim was to explore the potential role of L. major in the regulation of such blooms, through allelopathic interactions. Experiments consisted of exponential growth phase cells incubated for 96 h in L. major extracts at increasing concentrations. Our approach was based on untargeted metabolomics and photosynthetic activity measurements.We demonstrated the anticyanobacterial properties of L. major extracts. In particular, we reported that L. major extracts inhibited M. aeruginosa photosynthesis, and affected the production of various metabolite classes and pathways mainly involved in the secondary metabolism of the cyanobacteria.We further provided clear evidence about the existence of metabolite classes in L. major that may be involved in allelopathic interactions with M. aeruginosa, such as caffeic acid.

Microcystis aeruginosa blooms in water bodies, evidencing a high risk of exposure to human health due to the release of toxins, which affects water quality. Implementing physical, chemical, and microbial control methods requires an integrated understanding of cyanotoxin dynamics, especially their relationship with sediments. Consequently, sediment obtained from three stations of the Riogrande II reservoir (Antioquia, Colombia) was analyzed to determine the adsorption and removal capacity of the microcystin-LR (MC-LR). For this purpose, the sediment was subjected to different treatments to select the one with the highest MC-LR removal capacity. Furthermore, the effectiveness and stability of adsorption removal process were evaluated by analyzing mechanical processes such as aeration, sonication, and agitation. The dried sediment showed the highest reduction in toxin concentration (93%) after 24 h, followed by washed sediment (91%) and sterilized sediment (81%). On the other hand, the sediment was fractionated into silts and clays; the latter was the least effective. Finally, the fine and half silts were better adsorbents of the toxin, acting similarly over time. Initially, the utilization of sediment that has been dried by sunlight could be a complementary alternative to reinforce MC-LR control methodologies in water bodies. On the one hand, MC-LR desorption assays showed that aeration of the sediment for 30 min caused a release of up to 96% of the adsorbed compound. At the same time, the effect of sonication and agitation was less intense. However, the absorption process must be fast to avoid efficiency losses due to desorption since a high percentage of the toxin was spontaneously desorbed from the sediment in two days. [ABSTRACT FROM AUTHOR]

The extracts of Chara vulgaris (a green macroalgae) were tested to explore its algicidal potential on Microcystis aeruginosa growth. Firstly, the anticyanobacterial effect of both macroalgae aqueous (MAA) and macroalgae etyl acetate (MEA) extracts against M. aeruginosa was assessed using both the paper disc diffusion and microdilution methods. Minimum inhibitory concentrations (MIC) and minimum algicidal concentrations (MAC) were evaluated. Secondly, the growth of M. aeruginosa in response to the MEA extracts was investigated in an experimental bioassay. To reveal the potential allelochemicals, total phenols (TPs), total flavonoids (TFs), tannins (TTs) were analyzed in both MAA and MEA extracts. The identification of the phenolic compounds in MEA extracts was performed by high-performance liquid chromatography (HPLC). The results from the bioassay demonstrated that MEA extracts inhibit the growth of M. aeruginosa in a concentration dependent way. The highest inhibition rate (IR) exceeds 83% on day (d) 4 of experimentation, and achieved (97.98%) on 7-d. HPLC analysis revealed seven phenolic compounds known as effective allelochemicals. Overall, the obtained results demonstrate that MEA extracts might be proposed as a potential allelochemicals, and it can be considered as an ecofriendly alternative algaecide to control Microcystis blooms in the eutrophic water bodies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Piezoelectric T-BaTiO 3 /Ag 3 PO 4 composites were prepared by co-precipitation method. • The built-in electric field in T-BaTiO 3 /Ag 3 PO 4 can change its energy band structure. • The construction of T-BaTiO 3 /Ag 3 PO 4 can prolong the lifetime of electron-hole pairs. Photocatalysis has become an effective method to control harmful algal blooms, while conventional photocatalysts usually have high carrier recombination rates and low response to visible light. The coupling of the piezoelectric effect with photocatalysis is considered to be one of the most promising approaches to overcome the above inadequacies. In this study, the T-BaTiO 3 /Ag 3 PO 4 (T-BTO/AP) with piezoelectricity was constructed and applied for the first time for the removal of M. aeruginosa under visible light with ultrasound. The experimental results showed that T-BTO/AP forms a built-in electric field under ultrasound, and the photogenerated carriers transfer path was transformed from the conventional type II to type Z, which changed the band structure of T-BTO/AP and greatly improved its catalytic efficiency. The T-BTO/AP-50 exhibited the best algae removal performance under visible light with ultrasound, and the removal rate of chlorophyll a could achieve 96.1 % within 4 h under the piezophotocatalyst dosage of 50 mg/L. Meanwhile, the photosynthetic system and cell membranes of M. aeruginosa were severely damaged under the continuous attack of •OH and •O 2 –. Furthermore, T-BTO/AP-50 still reached a 90 % degradation rate for chlorophyll a after five cycles of reused experiments, indicating its great reusability. Overall, this study provided a promising approach for algae removal. [ABSTRACT FROM AUTHOR]

Cyanobacterial blooms caused by Microcystis have become a menace to public health and water quality in the global freshwater ecosystem. Alkaline phosphatases (APases) produced by microorganisms play an important role in the mineralization of dissolved organic phosphorus (DOP) into orthophosphate (Pi) to promote cyanobacterial blooms. However, the response of extracellular and intracellular alkaline phosphatase activity (APA) of Microcystis to different DOP sources is poorly understood. In this study, we compared the growth of M. aeruginosa on two DOP substrates (β-glycerol-phosphate (β-GP) and lecithin (LEC)) and monitored the changes of P fractions and the extra- and intracellular APA under different P sources and concentrations. M. aeruginosa can utilize both β-GP and LEC to sustain its growth, and the bioavailability of LEC was greater than β-GP. For the β-GP treatment, there was no significant difference in the algal growth at different concentrations (P > 0.05), while the algal growth in the LEC treatment groups was significantly affected by concentrations (P < 0.05). The results showed that intracellular APA of M. aeruginosa could be detected in all DOP treatment groups and generally higher than extracellular APA. In addition, the intracellular APA per cell increased first and then decreased in all DOP treatment groups. Compared with the β-GP treatment, M. aeruginosa in the LEC groups could secret more extracellular APA. [ABSTRACT FROM AUTHOR]

Phosphine (PH 3) 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 PH 3 under elevated CO 2 concentration, Microcystis aeruginosa was used in the coupling treatment of 1000 ppmv CO 2 and PH 3 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 CO 2 and PH 3 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 CO 2 alone, and their enhancement increased with the increase in PH 3 concentrations. The total antioxidant capacity (T-AOC) in the coupling treatment with CO 2 and PH 3 of 2.48 × 10−2 mg/L and 7.51 × 10−3 mg/L showed increasing tendency, compared to the treatment with PH 3 alone. Additionally, the coupling treatment with 1000 ppmv CO 2 and PH 3 also altered the pH and DO level in the culture medium. In this regard, the coupling treatment with CO 2 and PH 3 at an appropriate concentration can enhance the resistance of M. aeruginosa to PH 3 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 CO 2 level, our research laid a foundation for the scientific understanding of the correlation between PH 3 and cyanobacteria blooms. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Although microcystins (MCs) are the most commonly studied cyanotoxins, their significance to the producing organisms remains unclear. MCs are known as endotoxins, but they can be found in the surrounding environment due to cell lysis, designated as extracellular MCs. In the present study, the interactions between MC producing and the non-producing strains of Microcystis aeruginosa, PCC 7806 and PCC 7005, respectively, and a green alga, Desmodesmus subspicatus, were studied to better understand the probable ecological importance of MCs at the collapse phase of cyanobacterial blooms. We applied a dialysis co-cultivation system where M. aeruginosa was grown inside dialysis tubing for one month. Then, D. subspicatus was added to the culture system on the outside of the membrane. Consequently, the growth of D. subspicatus and MC contents were measured over a 14-day co-exposure period. The results showed that Microcystis negatively affected the green alga as the growth of D. subspicatus was significantly inhibited in co-cultivation with both the MC-producing and -deficient strains. However, the inhibitory effect of the MC-producing strain was greater and observed earlier compared to the MC-deficient strain. Thus, MCs might be considered as an assistant factor that, in combination with other secondary metabolites of Microcystis, reinforce the ability to outcompete co-existing species. [ABSTRACT FROM AUTHOR]

Copyright of Egyptian Journal of Botany is the property of Egyptian National Agricultural Library (ENAL) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper studied the inhibitory effect of pomegranate peel (PP) extract on the growth of Microcystis aeruginosa, the model of harmful algal blooms in aquatic environment. The allelochemicals were identified by HPLC–MS/MS from PP and tested by batch experiment through measurement of algal density, chlorophyll a (Chl-a) concentration, maximum quantum yield of photosystem II (Fv/Fm), superoxide dismutase (SOD), and malondialdehyde (MDA) contents. Results showed that both PP powder and PP extract had obvious inhibitory effect on M. aeruginosa growth. Quercetin and luteolin were identified as the allelochemicals to M. aeruginosa growth. However, the inhibitory capacity of luteolin was stronger than that of quercetin. The growth inhibition ratio of luteolin can reach up to 98.7 and 99.1% of the control on day 7 at the dosages of 7 and 10 mg/L, respectively. Moreover, the changes of Chl-a, Fv/Fm, SOD, and MDA in M. aeruginosa confirmed jointly that the allelochemicals cause inhibition of photosystem and oxidative damage to M. aeruginosa cells with the antioxidant defense system being activated, which leads to the aggravation of membrane lipid peroxidation. Thus, luteolin could be used as a promising algaecide for emergency handling of M. aeruginosa blooms. This study might provide a new direction in the management of eutrophication in the future. [ABSTRACT FROM AUTHOR]

Abstract 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. Graphical abstract Image 1 Highlights • Phosphine may be a promoter of the outbreak of cyanobacteria bloom. • An appropriate amount of phosphine is beneficial to the growth of cyanobacteria. • Long-term treatment with high concentration of phosphine can result in algae death. [ABSTRACT FROM AUTHOR]

Recent advances in research on algae inhibition by using low-cost straw proposed a possible mechanism that reactive oxygen species (ROS) generated by the solar irradiation of straw-derived dissolved organic matter (DOM) might contribute to cyanobacteria inhibition. However, this process is not clearly understood. Here, DOM from three types of straw (barley, rice, and wheat) and natural organic matter (NOM) isolates were investigated in terms of their photochemical properties and ROS generating abilities. Results demonstrated that the DOM derived from the aeration decomposition of barley straw (A-DOMbs) yielded the best formation efficiencies of hydrogen peroxide (H 2 O 2 ) and hydroxyl radicals (•OH) under solar-simulated irradiation in all organic matter samples. Correlation analysis implies that optical parameters and phenolic hydroxyl group contents can signify ROS generating abilities of different DOM solutions. Bioassay results show that A-DOMbs possesses the highest inhibition performance for M. aeruginosa in all DOM samples, much higher than those of NOM isolates. The addition of catalase greatly relieves the inhibition performance, making the loss of chlorophyll a content decreased from 37.14% to 7.83% in 2 h for A-DOMbs, which implies that for cyanobacteria growth inhibition, photochemically-produced H 2 O 2 from SOM is far more important than singlet oxygen ( 1 O 2 ), •OH, and even SOM itself. Our results show that H 2 O 2 photochemically generated from straw-derived DOM is able to result in rapid inhibition of M. aeruginosa in a relatively short period, furthering the understanding of complicated mechanisms of cyanobacteria inhibition by using low-cost straw in eutrophic waters. [ABSTRACT FROM AUTHOR]

Copyright of Research of Environmental Sciences is the property of Research of Environmental Sciences Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Epigallocatechin-3-gallate (EGCG), an eco-friendly polyphenol, has a strong inhibitory effect on the bloom-forming cyanobacterium Microcystis aeruginosa. In order to reveal the molecular mechanism of algal inhibition of plant polyphenols, quantitative proteome analysis based on iTRAQ (isobaric tags for relative and absolute quantification) was applied to investigate EGCG-induced proteomic changes in M. aeruginosa. Following treatment with EGCG for 48 h, the total protein content was compared with that of untreated cells, and 88 differentially expressed proteins were identified, of which 30 were upregulated and 58 were downregulated. Proteins involved in chlorophyll biosynthesis, carbon and nitrate assimilation and cell division were among the most downregulated, which resulted in growth suppression. By contrast, anti-oxidative proteins and molecular chaperones, such as superoxide dismutase, glutaredoxin, and heat shock proteins, were distinctly upregulated. Eighteen potentially crucial proteins were selected for assessment of transcription by real-time quantitative PCR, which confirmed the results of proteomic experiment. In addition, immunoblotting confirmed downregulation of three representative proteins, magnesium-protoporphyrin IX monomethyl ester [oxidative] cyclase AcsF, glutamine synthetase GlnN, and metalloprotease FtsH, following EGCG treatment, consistent with the results of iTRAQ quantitation experiment. It is speculated that chlorophyll biosynthesis, carbon and nitrate assimilation, and cell division are the main inhibition targets of EGCG. [ABSTRACT FROM AUTHOR]

The arsenate (As(V)) biotransformation by Microcystis aeruginosa in a medium with different concentrations of nitrogen (N) and phosphorus (P) has been studied under laboratory conditions. When 15 μg/L As(V) was added, N and P in the medium showed effective regulation on arsenic (As) metabolism in M. aeruginosa , resulting in significant differences in the algal growth among different N and P treatments. Under 0.2 mg/L P treatment, increases in N concentration (4–20 mg/L) significantly stimulated the cell growth and therefore indirectly enhanced the production of dimethylarsinic acid (DMA), the main As metabolite, accounting for 71%–79% of the total As in the medium. Meanwhile, 10–20 mg/L N treatments accelerated the ability of As metabolization by M. aeruginosa , leading to higher contents of DMA per cell. However, As(V) uptake by M. aeruginosa was significantly impeded by 0.5–1.0 mg/L P treatment, resulting in smaller rates of As transformation in M. aeruginosa as well as lower contents of As metabolites in the medium. Our data demonstrated that As(V) transformation by M. aeruginosa was significantly accelerated by increasing N levels, while it was inhibited by increasing P levels. Overall, both P and N play key roles in As(V) biotransformation processes. [ABSTRACT FROM AUTHOR]

Zero-valent nano-iron particles (nZVI) are increasingly present in freshwater aquatic environments due to their numerous applications in environmental remediation. However, despite the broad benefits associated with the use and development of nZVI nanoparticles, the potential risks of introducing them into the aquatic environment need to be considered. Special attention should be focused on primary producer organisms, the basal trophic level, whose impact affects the rest of the food web. Although there are numerous acute studies on the acute effects of these nanoparticles on photosynthetic primary producers, few studies focus on long-term exposures. The present study aimed at assessing the effects of nZVI on growth rate, photosynthesis activity, and reactive oxygen activity (ROS) on the freshwater green algae Scenedesmus armatus and the cyanobacteria Microcystis aeruginosa. Moreover, microcystin production was also evaluated. These parameters were assessed on both organisms singly exposed to 72 h-effective nZVI concentration for 10% maximal response for 28 days. The results showed that the cell growth rate of S. armatus was initially significantly altered and progressively reached control-like values at 28 days post-exposure, while M. aeruginosa did not show any significant difference concerning control values at any time. In both strains dark respiration (R) increased, unlike net photosynthesis (Pn), while gross photosynthesis (Pg) only slightly increased at 7 days of exposure and then became equal to control values at 28 days of exposure. The nZVI nanoparticles generated ROS progressively during the 28 days of exposure in both strains, although their formation was significantly higher on green algae than on cyanobacteria. These data can provide additional information to further investigate the potential risks of nZVI and ultimately help decision-makers make better informed decisions regarding the use of nZVI for environmental remediation. [Display omitted] • Short-term exposures to nZVI decreased freshwater microalgae growth. • nZVI-IC 10 did not affect the M. aeruginosa exponential growth rate at 28-d. • The S. armatus growth recovered after nZVI-IC 10 7-d exposure. • The initial effect on photosynthetic activity decreased after 28 days of exposure. • ROS increased in both species during 28 days of exposure to nZVI-IC 10. [ABSTRACT FROM AUTHOR]

The present investigation is aimed to understand how a bloom-forming cyanobacterium Microcystis aeruginosa adapts to changing climatic conditions. The cyanobacterium was exposed to stresses of UV-B (2 Wm) radiation and temperature (45 °C) for desired time intervals. Results showed that both the stresses affect growth and photosynthetic efficiency of M. aeruginosa. More than 50% loss of survival and content of photosynthetic pigments was noted after 4 h treatment of both the above stresses. Such changes were mainly due to the generation of reactive oxygen species which cause damage to proteins, DNA, lipids, and modulation of the membrane stability. An increase in the proline accumulation was noted in the cells which probably negates the harmful effects. In addition, activity of antioxidative enzymes namely, catalase, superoxide dismutase, ascorbate peroxidase, and peroxidase was induced by 1.5-3.0-fold on 3 h of UV-B and temperature treatment indicating their possible role in protection. Interestingly, induction of photoprotective compound, mycosporine-like amino acids (MAAs) were also found under UV-B stress which might be an additional strategy of defense mechanism for the survival of the cyanobacterium. Analysis of photoprotective compound revealed shinorine as the main MAA synthesized by the cyanobacterium. [ABSTRACT FROM AUTHOR]

Leaf aqueous (LA) extracts of medicinal plants Achillea ageratum L. and Origanum compactum Benth. were tested to explore their potential algicidal effects on Microcystis aeruginosa. The growth of M. aeruginosa and cell morphology changes in response to LA extracts was investigated. The concentrations of total phenols, total flavonoids, and total tannins in LA extracts were analyzed to reveal the potential allelochemical compounds. The results demonstrate that both A. ageratum and O. compactum LA extracts inhibit M. aeruginosa growth in a concentration-dependent way. For both LA extracts, the highest inhibition rate exceeded 80% since the fifth day of exposure. The induction of inhibition effects was translated by a decrease in photosynthetic pigments (chlorophyll-a and carotenoids) and with other morphological modifications. Our results illustrate that both A. ageratum and O. Compactum LA extracts can offer an effective solution for control of Microcystis blooms, and these are recommended in the restoration of aquatic environments contaminated by these types of algal blooms. [ABSTRACT FROM AUTHOR]

Stable isotope tracers were first applied to evaluate the Microcystis cell assimilation efficiency of Sinanodonta bivalves, since the past identification method has been limited to tracking the changes of each chl-a, clearity, and nutrient. The toxicity profile and accumulation of MC-LR, -RR and -YR in different organs (foot and digestive organs) from the three filter-feeders (Sinanodonta woodiana, Sinanodonta arcaeformis, and Unio douglasiae) were assessed under the condition of toxigenic cyanobacteria (Microcystis aeruginosa) blooms through an in situ pond experiment using 13C and 15N dual isotope tracers. Chl-a concentration in the manipulated pond was dramatically decreased after the beginning of the second day, ranging from 217.5 to 15.6 μg·L-1. The highest amount of MCs was incorporated into muscle and gland tissues in U. douglasiae during the study period, at early 2 or 3 times higher than in S. woodiana and S. arcaeformis. In addition, the incorporated 13C and 15N atom % in the U. douglasiae bivalve showed lower values than in other bivalves. The results demonstrate that U. douglasiae has less capacity to assimilate toxic cyanobacteria derived from diet. However, the incorporated 13C and 15N atom % of S. arcaeformis showed a larger feeding capacity than U. douglasiae and S. woodiana. Our results therefore also indicate that S. arcaeformis can eliminate the toxin more rapidly than U. douglasiae, having a larger detoxification capacity. [ABSTRACT FROM AUTHOR]

Little information is available on how nano-Fe 2 O 3 substituted iron ions as a possible iron source impacting on algal growth and arsenate (As(V)) metabolism under dissolved organic phosphorus (DOP) (D-glucose-6-phosphate (GP)) conditions. We investigated the growth of Microcystis aeruginosa and As(V) metabolism together with their metabolites in As(V) aquatic environments with nano-Fe 2 O 3 and GP as the sole iron and P sources, respectively. Results showed that nano-Fe 2 O 3 showed inhibitory effects on M. aeruginosa growth and microcystin (MCs) release under GP conditions in As(V) polluted water. There was little influence on As species changes in GP media under different nano-Fe 2 O 3 concentrations except for obvious total As (TAs) removal in 100.0 mg L−1 nano-Fe 2 O 3 levels. As(V) metabolism dominated with As(V) biotransformation in algal cells was facilitated and arsenite (As(III)) releasing risk was relieved clearly by nano-Fe 2 O 3 under GP conditions. The dissolved organic matter (DOM) in media exhibited more fatty acid analogs containing –CO, –CH 2 =CH 2 , and –CH functional groups with increasing nano-Fe 2 O 3 concentrations, but the fluorescent analogs were relatively reduced especially for the fluorescent DOM dominated by aromatic protein-like tryptophan which was significantly inhibited by nano-Fe 2 O 3. Thus, As methylation that was facilitated in M. aeruginosa by nano-Fe 2 O 3 in GP environments also caused more organic substances to release that absorb infrared spectra while reducing the release risks of As(III) and MCs as well as protein-containing tryptophan fractions. From 1H-NMR analysis, this might be caused by the increased metabolites of aromatic compounds, organic acid/amino acid, and carbohydrates/glucose in algal cells. The findings are vital for a better understanding of nano-Fe 2 O 3 role-playing in As bioremediation by microalgae and the subsequent potential aquatic ecological risks. [Display omitted] • Nano-Fe 2 O 3 could inhibit algal Chla synthesis but enhance its photosynthetic yield. • Nano-Fe 2 O 3 enhanced As(V) metabolism in M. aeruginosa and relieved As(III) risks. • MCs release and the protein-like tryptophan-containing component was mitigated. • Increased organic metabolites from 1H-NMR analysis could facilitate As methylation. [ABSTRACT FROM AUTHOR]

Little information is available on how nano-Fe 2 O 3 substituted iron ions as a possible iron source impacting on algal growth and arsenate (As(V)) metabolism under dissolved organic phosphorus (DOP) (D-glucose-6-phosphate (GP)) conditions. We investigated the growth of Microcystis aeruginosa and As(V) metabolism together with their metabolites in As(V) aquatic environments with nano-Fe 2 O 3 and GP as the sole iron and P sources, respectively. Results showed that nano-Fe 2 O 3 showed inhibitory effects on M. aeruginosa growth and microcystin (MCs) release under GP conditions in As(V) polluted water. There was little influence on As species changes in GP media under different nano-Fe 2 O 3 concentrations except for obvious total As (TAs) removal in 100.0 mg L -1 nano-Fe 2 O 3 levels. As(V) metabolism dominated with As(V) biotransformation in algal cells was facilitated and arsenite (As(III)) releasing risk was relieved clearly by nano-Fe 2 O 3 under GP conditions. The dissolved organic matter (DOM) in media exhibited more fatty acid analogs containing -CO, -CH 2 =CH 2 , and -CH functional groups with increasing nano-Fe 2 O 3 concentrations, but the fluorescent analogs were relatively reduced especially for the fluorescent DOM dominated by aromatic protein-like tryptophan which was significantly inhibited by nano-Fe 2 O 3. Thus, As methylation that was facilitated in M. aeruginosa by nano-Fe 2 O 3 in GP environments also caused more organic substances to release that absorb infrared spectra while reducing the release risks of As(III) and MCs as well as protein-containing tryptophan fractions. From 1 H-NMR analysis, this might be caused by the increased metabolites of aromatic compounds, organic acid/amino acid, and carbohydrates/glucose in algal cells. The findings are vital for a better understanding of nano-Fe 2 O 3 role-playing in As bioremediation by microalgae and the subsequent potential aquatic ecological risks., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

An electrochemical treatment was investigated to remove Microcystis aeruginosa from water. A fixed bed reactor in flow was tested, which was equipped with electrodes constituted by stacks of grids electrically connected in parallel, with the electric field parallel to the fluid flow. Conductive diamond were used as anodes, platinised Ti as cathode. Electrolyses were performed in continuous and in batch recirculated mode with flow rates corresponding to Re from 10 to 160, current densities in the range 10–60 A m −2 and Cl − concentrations up to 600 g m −3 . The absorbance of chlorophyll-a pigment and the concentration of products and by-products of electrolysis were measured. In continuous experiments without algae in the inlet stream, total oxidants concentrations as equivalent Cl 2 , of about 0.7 g Cl 2 m −3 were measured; the maximum values were obtained at Re = 10 and i = 25 A m −2 , with values strongly dependent on the concentration of Cl − . The highest algae inactivation was obtained under the operative conditions of maximum generation of oxidants; in the presence of microalgae the oxidants concentrations were generally below the detection limit. Results indicated that most of the bulk oxidants electrogenerated is constituted by active chlorine. The prevailing mechanism of M. aeruginosa inactivation is the disinfection by bulk oxidants. The experimental data were quantitatively interpreted through a simple plug flow model, in which the axial dispersion accounts for the non-ideal flow behaviour of the system; the model was successfully used to simulate the performances of the reactor in the single-stack configuration used for the experiments and in multi-stack configurations. [ABSTRACT FROM AUTHOR]

The effects of light, temperature, and coculture on the intracellular microcystin-LR (MC-LR) quota of Microcystis aeruginosa were evaluated based on coculture experiments with nontoxic Dolichospermum ( Anabaena) flos-aquae. The MC-LR quota and transcription of mcyB and mcyD genes encoding MC synthetases in M. aeruginosa were evaluated on the basis of cell counts, high-performance liquid chromatography, and reverse-transcription quantitative real-time PCR. The MC-LR quotas of M. aeruginosa in coculture with a 1/1 ratio of inoculum of the two species were significantly lower relative to monocultures 6-d after inoculation. Decreased MC-LR quotas under coculture conditions were enhanced by increasing the D. flos-aquae to M. aeruginosa ratio in the inoculum and by environmental factors, such as temperature and light intensity. Moreover, the transcriptional concentrations of mcyB and mcyD genes in M. aeruginosa were significantly inhibited by D. flos-aquae competition in coculture ( P <0.01), lowered to 20% of initial concentrations within 8 days. These data suggested that coculture eff ects by D. flos-aquae not only reduced M. aeruginosa's intracellular MC-LR quota via inhibition of genes encoding MC synthetases, but also that this eff ect was regulated by environmental factors, including temperature and light intensities. [ABSTRACT FROM AUTHOR]

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

The eutrophication of shallow lakes is sensitive to dynamic currents (i.e., disturbances) because of their shallow depths and high contents of nutrients in bed sediments. The relation between the sediment resuspension and the algae bloom is not well understood in the field scale because the interwoven influencing factors cannot be examined individually. By combining the laboratory experiment and the field observation, this paper proposes a sediment-water-algae concept to simulate the effects of hydrodynamic disturbances on the algae growth in the Taihu Lake located in east China. The sediments are sampled from the Taihu Lake while the Microcystis aeruginosa (M. aeruginosa) algae is cultured in the laboratory and then transplanted into the experiment cylinders. The temperature and the light intensity in the experiment are adjusted to be similar with the prevalent in situ conditions. The results indicate that the M. aeruginosa populations under the disturbance condition of the rotational speed ≤300 rad/min in the experiment (corresponding to the bottom velocity flow ≤0.059 m/s, the shear stress ≤0.069 N/m 2 , or the wind speed ≤4 m/s in the field) are higher than those under the disturbance condition of the rotational speed is 400 rad/min (corresponding to the bottom flow velocity 0.079 m/s, the shear stress 0.124 N/m 2 ). It is suggested that a low to moderate disturbance prompts the release of the nitrogen as well as the phosphate nutrients from the bed sediments, amplifying the eutrophication of the Taihu Lake. [ABSTRACT FROM AUTHOR]

Harmful cyanobacterial blooms and the released microcystins (MCs) caused serious environmental and public health concerns to drinking water safety. Photo-oxidation is an appealing treatment option and alternative to conventional flocculation and microbial antagonists, but the performances of current photosensitizers (either inorganic or organic) are unsatisfactory. Here, a polythiophene photosensitizer (PT10) with both high yield of reactive oxygen species (ROS) production (mainly 1 O 2 , Φ Δ = 0.51, > 8 h continuous generation) and moderate photostability was used as a powerful algaecide to inhibit Microcystis aeruginosa . Due to the positive charge of PT10, the algal cells were quickly flocculated, followed by efficient inactivation in 4 h under white light irradiation (96.7%, 10 mW/cm 2 ). Meanwhile, PT10 was self-immolated in about 6 h. Upon biosafety evaluation with adult zebrafish, the low toxicity of PT10 and the degradation products of PT10 and algae (early logarithmic growth stage) were confirmed. In addition, microcystin-LR (MC-LR), a toxic microcystin that will be released during the destruction of the algal cells, was also degraded. Therefore, PT10-based photoinactivation of M. aeruginosa featured both high performance and low secondary pollution. In real-world aquatic systems, PT10 was confirmed to be capable of sunlight-assisted inactivation of M. aeruginosa and prevent algal blooms, thus making it appealing for environmental remediation.

We investigated seasonal variations in cyanobacterial biomass and the forms of its dominant population ( M. aeruginosa) and their correlation with environmental factors in the water source area of Chaohu City, China from December 2011 to October 2012. The results show that species belonging to the phylum Cyanophyta occupied the maximum proportion of phytoplankton biomass, and that the dominant population in the water source area of Chaohu City was M. aeruginosa. The variation in cyanobacterial biomass from March to August 2012 was well fitted to the logistic growth model. The growth rate of cyanobacteria was the highest in June, and the biomass of cyanobacteria reached a maximum in August. From February to March 2012, the main form of M. aeruginosa was the single-cell form; M. aeruginosa colonies began to appear from April, and blooms appeared on the water surface in May. The maximum diameter of the colonies was recorded in July, and then gradually decreased from August. The diameter range of M. aeruginosa colonies was 18.37-237.77 μm, and most of the colonies were distributed in the range 20-200 μm, comprising 95.5% of the total number of samples. Temperature and photosynthetically active radiation may be the most important factors that influenced the annual variation in M. aeruginosa biomass and forms. The suitable temperature for cyanobacterial growth was in the range of 15-30°C. In natural water bodies, photosynthetically active radiation had a significant positive influence on the colonial diameter of M. aeruginosa ( P <0.01). [ABSTRACT FROM AUTHOR]

The use of allelochemicals has been proved an environmentally friendly and promising method to control harmful algal blooms. This study was conducted to explore the application potential of Ailanthus altissima ( A. altissima ) extracts in Microcystis aeruginosa ( M. aeruginosa ) control for the first time. Four treatments with A. altissima extractions (25 mg L −1 , 50 mg L −1 , 100 mg L −1 , and 200 mg L −1 respectively) and a control group were built to investigate the effects of A. altissima on the growth, cellular microstructure and cell viability, physiological changes, and release of extracellular matters. Results showed that the cell density of M. aeruginosa was effectively inhibited by A. altissima extract, and the inhibition rates were dose-dependent within 5 d. Especially for the treatment with 200 mg L −1 of extract, the inhibitory rates remains above 90% after 5 d exposure. In addition, A. altissima effectively decreased the amount of extracellular cyanotoxin microcystins and destroyed the photosynthesis-related structure of algae cell during the experimental period. The results demonstrated the A. altissima extracts can be used as an effective and safe algicide to control algal blooms. However, it must be noted that specific compounds responsible for algicidal effect should be isolated and identified to explore inhibition mechanism of A. altissima in future study. [ABSTRACT FROM AUTHOR]

Blue-green algae bloom is of great concern globally since they adversely affect the water ecosystem and also drinking water treatment processes. This work investigated the removal of Microcystis aeruginosa ( M. aeruginosa) by combining the conventional coagulant polyaluminum chloride (PACl) with nano-FeO particles as a coagulant aid. The results showed that the addition of nano-FeO significantly improved the removal efficiency of M. aeruginosa by reducing the amount of PACl dosage and simultaneously hastening the sedimentation. At the M. aeruginosa density of an order of magnitude of 10, 10, and 10 pcs/mL, respectively, the corresponding PACl dose of 200, 20, and 2 mg/L and the mass ratio of PACl to nano-FeO of 4:1, the removal efficiency of M. aeruginosa could be increased by 33.0, 44.7, and 173.1 %, respectively. Compared to PACl, PACl combined with the nano-FeO as a coagulant aid had higher removal efficiency at a wider pH range. SEM images showed that nano-FeO first combined with PACl to form clusters and further generated the flocs with algae. Results from the laser particle analyzer further suggested that the floc size increased with the addition of nano-FeO. It was noted that the addition of nano-FeO led to aluminum species change after PACl hydrolyzed in the algae solution, from Al to Al and Al subsequently. As a coagulant aid, the nano-FeO, in conjunction with PACl, apparently provided nucleation sites for larger flocs to integrate with M. aeruginosa. In addition, increased floc density improved the removal of M. aeruginosa. [ABSTRACT FROM AUTHOR]

Microcystis aeruginosa (blue-green alga) commonly blooms in summer and Cyclotella meneghiniana (diatom) outbreaks in fall in the reservoirs that serve as drinking water sources in Southeast China. Herein, an evaluation of disinfection by-product formation potential (DBPFP) from them during chlorination should be conducted. Five DBPs including trichloromethane (TCM), trichloronitromethane (TCNM), dichloroacetonitrile (DCAN), 1,1-dichloropropanone (1,1-DCP) and 1,1,1-trichloropropanone (1,1,1-TCP) were monitored. The formation potential of TCM and TCNM was enhanced with the increase of reaction time and chlorine dosage, whereas that of DCAN, 1,1-DCP and 1,1,1-TCP increased first and then fell with continuing reaction time. M. aeruginosa showed higher DBPFP than C. meneghiniana , the yield of DBPs varied with components of algal cells. The DBPFP order from components of M. aeruginosa was cell suspension (CS) ≈ intracellular organic matter (IOM) > extracellular organic matter (EOM) > cell debris (CD), which indicated that IOM was the main DBP precursors for M. aeruginosa . The yields of DBPs from components of C. meneghiniana were in the order of CS > IOM ≈ CD ≈ EOM, suggesting that three components made similar contributions to the total DBP formation. The amount of IOM with higher DBPFP leaked from both algae species increased with the chlorine dosage, indicating that chlorine dosage should be considered carefully in the treatment of eutrophic water for less destroying of the cell integrity. Though fluorescence substances contained in both algae species varied significantly, the soluble microbial products (SMPs) and aromatic protein-like substances were the main cellular components that contributed to DBP formation for both algae. [ABSTRACT FROM AUTHOR]

The objective of this study was to link hydrodynamic disturbance with sediment resuspension, phosphorus release, and algal growth in Lake Tai, a typical shallow lake located in the south of the Yangtze River Delta in China. With this regard, a sediment-water-algae laboratory experiment was conducted and extrapolated to the real situation in terms of field observations. The results show that the algal growth rate synchronically increased with dissolved total phosphorus (DTP) release rate. The DTP decreased with increase of bottom flow velocity, indicating that the phosphorus release rate was lower than its transfer rate into algal biomass. While all levels of hydrodynamic disturbances could increase sediment resuspension and phosphorus release, a low to moderate disturbance was beneficial, but a strong disturbance was harmful for algal growth. Also, a low to moderate disturbance caused the dissolved alkaline phosphatase activity (DAPA) to increase with time, which provided the enzyme for hydrolyzing a variety of organic phosphorus compounds from bed sediment into algae-needed nutritional DTP. The experiment proved to be an efficient means to understanding eutrophication mechanisms of large shallow lakes such as Lake Tai. [ABSTRACT FROM AUTHOR]

Colony formation is an essential stage of cyanobacterial blooms. High calcium concentration can promote Microcystis aeruginosa aggregation behavior, but the mechanism of colony formation caused by calcium has rarely been reported. In this study, high calcium-induced colony formation was identified as a shift from cell adhesion to cell division, rather than only cell adhesion as previously thought. Algae responded to this calcium-induced environmental pressure by aggregating and forming colonies. Algal cells initially secreted large quantities of extracellular polysaccharides (EPS) and rapidly aggregated by cell adhesion. The highest aggregation proportion was up to 68.93%. However, high calcium concentrations cannot completely inhibit algal cell growth, but only delay the algae into the rapid growth phase. With adaption to calcium and existing high EPS content, the daughter cells reduced EPS synthesis and the aggregation proportion decreased. The increasing growth rate was also responsible for the decreased xylose content in EPS. The mechanism of colony formation changed to cell division. The downregulation of genes related to EPS secretion also supported this hypothesis. Overall, these results can benefit for our understanding of cyanobacterial bloom formation. [Display omitted] • High calcium concentrations can only delay the algae into the rapid growth phase. • The environmental stress caused by high calcium concentrations was adaptive. • The calcium-induced aggregation shifted from cell adhesion to cell division. • This shift is due to the extracellular polysaccharides and the adaptation of algae. • The xylose content decreased because the cell growth rate increased. [ABSTRACT FROM AUTHOR]

Algicidal bacteria is considered as an efficient and environmentally friendly approach to suppress Microcystis aeruginosa (M. aeruginosa). However, algicidal bacteria in natural water is limited during the practical application due to the interference of external factors and the low reuse capability. In this study, a bio-degradation capsule for M. aeruginosa is prepared by bio-compatible sodium alginate (SA) compositing with eco-friendly ethyl cellulose (EC) to improve the property and reuse capability of algicidal bacteria. Bacterial strain HL was well immobilized and the capsule was obtained with 2% of SA, 3% of calcium chloride (CaCl 2) and 3% of EC. It has been proved that capsules immobilizing bacteria HL shows considerable advantage over traditional bio-treatment systems (free-living bacteria) and good reusable performance. A better algicidal rate of 77.67% ± 1.14% at 7th day was obtained with the use of capsule embedding 50 mL of algicidal bacteria, enhanced by 11.05% comparing with same amount of free-living bacteria. Moreover, the algicidal rate of M. aeruginosa still reached 68.57% ± 2.88% after three times repetitive use. The effect of capsules on the fluorescence and antioxidant system of M. aeruginosa indicated that the photosystems were irreversibly damaged and the antioxidant response of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were significantly induced. Overall, capsules prepared in this study can provide a desirable environment for algicidal bacteria HL and ensure algicidal bacteria to in-situ work well in inhibiting booms of algae. [Display omitted] • A high-efficient bio-degradation capsule for Microcystis aeruginosa is prepared. • Algicidal bacteria HL is well retained in capsule. • Capsules suppressed growth of Microcystis aeruginosa. • Photosynthetic activities of Microcystis aeruginosa are inhibited. [ABSTRACT FROM AUTHOR]

We report on the application of an automated and easy-to-use device to directly measure the immunoreactions between adda-specific monoclonal antibodies and microcystins. The antibodies were immobilized on a gold electrode whose surface was modified first with polytyramine and then with gold nanoparticles. The immunoreaction leads to a change in the capacitance of the system. Under optimum conditions, the sensor is capable of performing stable regeneration-assay cycles and has a low detection limit at a concentration of 0.01 pM level of microcystin-leucine-arginine (MC-LR). The surface of the biosensor can be regenerated with pH 2.5 glycine buffer which dissociates the antibody-antigen complex. The biosensor was used to monitor the production of microcystins during batch cultivation of Microcystis aeruginosa (isolated from ponds in Botswana). Liquid chromatography coupled to MS/MS detection was used to identify three variants, viz. MC-LR (995.6 Da), DmMC-LR (981.2 Da) and MC-LA (910.5 Da). [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Arsenic (As) as a major hazardous metalloid was affected by phytoplankton in many aquatic environments. The toxic dominant algae Microcystis aeruginosa was exposed to different concentrations of inorganic arsenic (arsenate or arsenite) for 15 days in BG11 culture media. Arsenic accumulation, toxicity, and speciation in M. aeruginos as well as the changes of As species in media were examined. M. aeruginosa has a general well tolerance to arsenate and a definite sensitivity to arsenite. Additionally, arsenate actively elevated As methylation by the algae but arsenite definitely inhibited it. Interestingly, the uptake of arsenite was more pronounced than that of arsenate, and it was correlated to the toxicity. Arsenate was the predominant species in both cells and their growth media after 15 days of exposure to arsenate or arsenite. However, the amount of the methylated As species in cells was limited and insignificantly affected by the external As concentrations. Upon uptake of the inorganic arsenic, significant quantities of arsenate as well as small amounts of arsenite, DMA, and MMA were produced by the algae and, in turn, released back into the growth media. Bio-oxidation was the first and primary process and methylation was the minor process for arsenite exposures, while bioreduction and the subsequent methylation were the primary metabolisms for arsenate exposures. Arsenic bioaccumulation and transformation by M. aeruginosa in aquatic environment should be paid more attention during a period of eutrophication. [ABSTRACT FROM AUTHOR]

Using new polymerase chain reaction (PCR) primers, a once known to be under-transcribed microcystin synthetase A (mcyA) gene from the only known toxigenic cyanobacterium Microcystis aeruginosa dominating the Hartbeespoort Dam was consistently amplified from genomic DNA extracted from a set of algal and cell free water samples collected across this dam. In addition to this, five more mcy genes (mcyBCDEG) were also amplified during this study. The resultant mcyA PCR products (518 bp) were purified and sequenced and gave nucleotide sequence segments of 408 bp sizes. The obtained sequence was aligned to the published mcyA gene sequence available online on the NCBI database and resulted in 100% similarity to a 408 bp mcyA gene sequence segment of M. aeruginosa UWOCC RID-1. Furthermore, it was found that the above sequence segment (408 bp) spans from a common base in M. aeruginosa PCC 7806 and M. aeruginosa PCC 7820 from 141 to 548 bp in the N-methyl transferase (NMT) region signifying their closer relatedness to M. aeruginosa UWOCC strains. This study has for the first time amplified mcyA gene consistently from both intracellular and extracellular DNA extracts obtained from algal and cell free water samples, respectively. Sequence data and the amplified mcy genes showed that M. aeruginosa is widely distributed and dominant in this dam. [ABSTRACT FROM AUTHOR]

Cyanobacteria are the dominant bloom-forming species in Lake Taihu. Understanding the competition among algae is important to control strategies for bloom formation and outbreaks in freshwater ecosystems. In this study, we demonstrate that the cyanobacterium Microcystis aeruginosa PCC7820 and the green alga Quadrigula chodatii FACHB-1080 exhibit a strong competitive inhibitory relationship under co-culture conditions, with the latter strain inhibiting the former. Several factors influence the competitive relationship between the two species, including nutrition, temperature, and organic/inorganic compounds. Q. chodatii strongly inhibited M. aeruginosa growth through the inhibition of nitrogen utilization during co-culture. Temperature was also an influential determinant of the competition capacity between the two species under eutrophic conditions: at lower temperatures (15 °C), M. aeruginosa grew better than Q. chodatii, but the difference was not significant ( p > 0.05), whereas at higher temperatures (25 °C, 35 °C), Q. chodatii grew significantly better than M. aeruginosa ( p < 0.05). Furthermore, the Q. chodatii filtrate strongly inhibited the growth of M. aeruginosa. An analysis of the crude extracts of the algae culture filtrates from uni- and co-cultures using gas chromatography mass spectrometry (GC/MS) indicated that algal metabolites, such as dibutyl phthalate and beta-sitosterol, might play a key role in the competition between algae. [ABSTRACT FROM AUTHOR]

Three common polyphenol compounds Gallic Acid (GA), Pyrogallic Acid (PA) and Catechol (CA) are known to have allelochemical-exhibiting inhibitory effects on the growth of the cyanobacteriumMicrocystis aeruginosa(M. aeruginosa). Metabolism and antioxidant responses inM. aeruginosawere investigated to elucidate the mechanism by which the three polyphenols inhibit algal growth. The inhibition effects of polyphenols were in the order of CA > PA > GA. The GA and CA exposures increased protein contents, superoxide dismutase (SOD) activity, catalase (CAT) activity and soluble sugar, especially for exposure to GA of 25 mg L−1. Soluble sugar content increased significantly especially when exposed to CA for 72 h. When exposed to PA, protein content, and SOD and CAT activities initially increased but over longer treatment time the activities decreased, in contrast to sugar content. Our results suggest that PA exposure for longer periods of time may inhibit catabolism action, while CA exposure could induce more oxide stress than GA or PA. The overall study showed that polyphenol-induced oxidative damage might be responsible for polyphenol inhibition onM. aeruginosagrowth. The increases in cellular antioxidant enzymes and soluble sugar may have been to counteract the oxidative stress. [ABSTRACT FROM AUTHOR]

Abstract: There is an increasing need to describe the growth characteristics of cyanobacteria exposed to polycyclic aromatic hydrocarbons (PAHs) because the presence of PAHs in lakes is known to affect the growth of this kind of microorganisms. In this work, the effects of low concentrations of PAHs on Microcystis aeruginosa (M. aeruginosa) were investigated. M. aeruginosa were cultivated in the medium with a mixture of PAHs (0.486mgL−1 naphthalene, 0.049mgL−1 phenanthrene, and 0.0015mgL−1 pyrene) and different concentrations of nitrogen and phosphorus. During 31d of incubation, profiles of cell number and chlorophyll-a content were determined. The results indicated that when the concentration of an individual PAH was below its no observed effect concentration (NOEC), the exposure of M. aeruginosa to a mixture of PAHs markedly promoted cell density after 7d of culture. Low concentrations of nutrients in the medium improved the growth of M. aeruginosa in the presence of PAHs. When concentrations of both phosphorus and nitrogen were 50% lower than those of the control, the specific growth rate of M. aeruginosa increased by 100% when exposed to PAHs, and the generation time decreased from 10.5 to 5.3d. The chlorophyll-a content in medium also increased from 2.23 to 3.18μgmL−1, which was attributed to an increase in cell numbers. [Copyright &y& Elsevier]

Abstract: The dynamics of the bloom-forming cyanobacterium Microcystis aeruginosa (MA), total bacteria (TB), and the algicidal bacterium Pseudomonas aeruginosa R219 (PaR) in a eutrophic lake was followed from December 2007 to November 2008 by measuring the copy numbers of 16s rRNA genes (CNrG) of each species using a real-time fluorescence quantitative PCR (FQ-PCR) technique. The highest CNrG of MA was observed in July (3.4×105 copiesmL−1), while those of TB and PaR peaked in May (2.1×106 copiesmL−1) and August (3.2×104 copiesmL−1), respectively. A significant relationship was found between the CNrG of MA and biological factors such as the CNrG of PaR, TB, and the ratio of PaR to TB, as well as environmental factors including dissolved nitrogen (DN) and surface water temperature (T) (r 2 =0.955, p <0.001), suggesting that the dynamics of the algicidal bacterium PaR and TB, particularly the ratio of PaR to TB, may regulate the abundance of M. aeruginosa. Thus, we suggest that the algicidal bacterium PaR together with T and DN might play important roles in MA bloom formation and outbreaks in freshwater environments. [Copyright &y& Elsevier]

Many measures have been developed to control the harmful algal blooms that are potentially threatening potable waters. The pilot experiments showed that the unfiltered and the sterile-filtered decoctions of Radix Astragali inhibited the growth of Microcystis aeruginosa. The inhibitory effect diminished in natural pond conditions after 68 days, due to photo-degradation of the flavonoids from Radix Astragali that appear to be responsible for the action on M. aeruginosa. Four phases (assemblage, conglomeration, cell membrane destruction and decomposition) can be characterized in the process of cell death with increasing decoction dose. The quantum yields and electron transport rates of photosynthesis system II of M. aeruginosa cells markedly decreased during contact with the decoction, resulting in the disruption of M. aeruginosa photosynthesis. The results indicate that the application of Radix Astragali decoction for the inhibition of M. aeruginosa growth is feasible when the dose is less than 20mlL−1. [Copyright &y& Elsevier]

In recent years, Microcystis bloom occurs frequently and causes a wide range of social, environmental, and economic problems. In this study, dose-dependent inhibitory effect of cinnamaldehyde on the growth of Microcystis aeruginosa was investigated. It was found that cinnamaldehyde with the concentration more than 0.6 mM showed algicide activity against M. aeruginosa. When M. aeruginosa was exposed to 0.6 mM cinnamaldehyde, considerable reactive oxygen species (ROS) were generated followed by lipid peroxidation and decrease in the content of both chlorophyll a and soluble protein. Although superoxide dismutase had made response to the stress caused by cinnamaldehyde, activity increasing after a time of lag could not prevent the lysis of M. aeruginosa cells. Interestingly, the addition of antioxidants glutathione and l-ascorbic acid (Vc) could prevent the lysis of M. aeruginosa cells. All the results suggested that cinnamaldehyde induced the death of M. aeruginosa cells via inducing ROS burst. Further understanding of the mechanism of cinnamaldehyde-induced M. aeruginosa cell death would contribute to the control of cyanobacteria pollution. [ABSTRACT FROM AUTHOR]