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Over the years, algae have proved to be a water pollutant due to global warming, climate change, and the unregulated addition of organic compounds in water bodies from diffused resources. Harmful algal blooms (HABs) are severely affecting the health of humans and aquatic ecosystems. Among available anti-blooming technologies, semiconductor photocatalysis has come forth as an effective alternative. In the recent past, literature has been modified extensively with a decisive knowledge regarding algal invasion, desired preparation of nanomaterials with enhanced visible light absorption capacity and mechanisms for algal cell denaturation. The motivation behind this review article was to gather algal inactivation data in a systematic way based on various research studies, including the construction of nanoparticles and purposely to test their anti-algal activities under visible irradiation. Additionally, this article mentions variety of starting materials employed for preparation of various nano-powders with focus on their synthesis routes, analytical techniques as well as proposed mechanisms for lost cellular integrity in context of reduced chlorophyll' a' level, cell rapture, cell leakage and damages to other physiological constituents; credited to oxidative damage initiated by reactive oxidation species (ROS). Various floating and recyclable composited catalysts Ag 2 CO 3 -N: GO, Ag/AgCl@ZIF-8, Ag 2 CrO 4 -g-C 3 N 4 -TiO 2 /mEP proved to be game-changers owing to their enhanced VL absorption, adsorption, stability, separation and reusability. An outlook for the generalized limitations of published reports, cost estimations for practical implementation, issues and challenges faced by nano-photocatalysts and possible opportunities for future studies are also proposed. This review will be able to provide vast insights for coherent fabrication of catalysts, breakthroughs in experimental methodologies and help in elaboration of damage mechanisms., 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 © 2024 Elsevier Inc. All rights reserved.)

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., 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 The Authors. Published by Elsevier Ltd.. All rights reserved.)

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.

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., 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 © 2022 Elsevier Ltd. All rights reserved.)

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.

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]

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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]

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]

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]

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]

• M. aeruginosa in late lag phase held higher metabolic activity than that in exponential phase. • M. aeruginosa in late lag phase could be more effective inactivated by CuSO 4. • This effective inactivation was partially due to its higher sensitivity to CuSO 4 exposure. • The higher sensitivity was the inherent characteristic of M. aeruginosa in late lag phase. • M. aeruginosa control in late lag phase can reduce the risk of cyanotoxin release. Cyanobacterial blooms are always treated in exponential phase, which demands high dosages of algicides (e.g., CuSO 4). Actually, cyanobacterial blooms in late lag phase exhibit low cell-density and specific physiological/biochemical characteristics, implying the possibility of controlling blooms in a more efficient and economical way with CuSO 4 treatment if cyanobacterial cells in late lag phase can be treated. In this study, the outbreakof a Microcystis bloom was simulated, and Microcystis samples in late lag and exponential phases were treated with CuSO 4. The results showed that M. aeruginosa in late lag phase had a higher ratio of dividing-cells, F v /F m and intracellular total organic carbon content (TOC) than that in exponential phase, indicating that its metabolic activity was vigorous. M. aeruginosa in late lag phase could more easily be blocked, since a higher decrease in chlorophyll-a, F v /F m and membrane integrity occurred under the same dosages of CuSO 4 exposure compared to M. aeruginosa in exponential phase. Meanwhile, microcystin release in late lag phase was less than that in exponential phase. Moreover, higher sensitivity in late lag phase was confirmed at the individual level, as the photosynthesis related genes psaB and rbcL were more down-regulated than those in exponential phase. In general, cyanobacteria in late lag phase exhibited higher sensitivity to CuSO 4 , indicating that CuSO 4 treatments in late lag phase can achieve a higher control efficiency and fewer release of microcystin with low-dosages algicide. Hence, it is a more environmentally friendly strategy to control cyanobacterial blooms than the traditional strategy applied in exponential phase. [Display omitted] [ABSTRACT FROM AUTHOR]

Recently, cyanobacteria blooms (or water blooms) occurred on the surface of water bodies frequently and extensively due to eutrophia of the water. That has posed more and more serious environmental problems worldwide. In this paper, the effects of pulsed streamerlike discharge on M. aeruginosa cells are reported, which are one genus of cyanobacteria and ease to form water blooms. A stainless needle with a diameter of 30 μm was employed as a point discharge electrode, which is 15-cm apart from the cylinder cathode, and a 2-μs 160-kV pulse was applied. A pulsed streamerlike discharge was obtained in the water filled with cyanobacteria cells (named as sample water in this paper). From the experimental result, it can be found that the discharge collapsed the intracellular-structure gas vesicles in the M. aeruginosa cells, and the colonies of the cells sank to the bottom of the discharge chamber and rotten gradually. [ABSTRACT FROM AUTHOR]

The increasing presence of toxic cyanobacteria in drinking and recreational water bodies, and their potential to impact on human and animal health is cause for concern. Recent work suggests that apoptosis plays a major role in the toxic effects induced by microcystin-LR (MCLR) in the gastrointestinal tract; however, the biochemical pathway remains elusive. Exposure of CaCo2, a human colon carcinoma cell line, and MCF-7, a cell line deficient in pro-caspase-3, cells to 50 μM MCLR induced similar reductions in cell viability as measured by MTT and LDH leakage. The role of MCLR induced oxidative stress in the initiation of apoptosis was investigated over a 2-hr period, and it was found that there was an increase in the release of H2O2 in the first 30 min of exposure for both cell lines. Both cell lines exhibited a dose-dependent increase in both micro- and millicalpain after 24 h exposure to MCLR suggesting a role for protease activation in MCLR-induced apoptosis in non-hepatic human derived cell lines. [Copyright &y& Elsevier]

Harmful algal and cyanobacterial blooms pose threats to human and ecological health due to their release of hazardous toxins. Microcystin-LR (MC-LR), a potent hepatotoxin, is the most prevalent cyanotoxin found in freshwater blooms. Although produced by many species of cyanobacteria, Microcystis aeruginosa is most commonly associated with MC-LR production. These blooms are increasing in occurrence in lakes, ponds, and other surface waters and, therefore, require efficient treatment methods to be removed from water supplies. Ionizing radiation technologies offer promising approaches for the removal of organic pollutants in water, including cyanotoxins and cyanobacteria. Gamma irradiation for the degradation of cyano-bacteria and toxins is effective for overall MC-LR degradation as well as reducing cell concentrations. However, gamma irradiation technology involves use of radioactive isotopes and, therefore, may not feasible commercially from a security perspective. Electron beam (eBeam) irradiation technology, which relies on regular electricity to generate highly energetic electrons, is able to achieve the same results without the confounding challenges of radioactive isotopes and related security issues. In this critical review, the current state of the science concerning the remediation of MC-LR and M. aeruginosa with ionizing radiation technologies is presented and future necessary research is discussed. Image 1 • Cyanotoxins are a global environmental problem. • Ionizing radiation is a possible remediation technology for cyanotoxins. • Cellular effects of ionizing radiation on cyanobacteria need further investigation. • E-beam technology is suitable for cyanotoxin removal from aqueous samples. • Technology requires further optimization for commercialization. [ABSTRACT FROM AUTHOR]