Impact of copper sulphate, potassium permanganate, and hydrogen peroxide on Pseudanabaena galeata cell integrity, release and degradation of 2-methylisoborneol

Advances and challenges in the technologies for cyanobacterial cells removal in drinking water treatment

Harmful cyanobacteria in reservoirs pose a serious threat to drinking water safety due to the intracellular metabolites, such as toxins and unpleasant tastes & odours. Effective removal of harmful cyanobacteria with little to no cell damage is very important to ensure the safety of drinking water. This review first introduced development history of cyanobacterial removal technologies in drinking water treatment. Then, impacts of oxidation, coagulation and pre-oxidation enhanced coagulation processes on cyanobacterial removal and integrity of the cells were comprehensively evaluated and discussed. Oxidation can remove cyanobacteria, but high doses of oxidants can result in significant cell lysis and release of intracellular metabolites, especially when using chlorine or ozone. Although there is practically no cell damage during coagulation, the removal efficiency is low in many cases. Pre-oxidation may improve cyanobacterial removal by the subsequent solid-liquid separation processes, and moderate pre-oxidation with little to no cell lysis is very important. Mechanisms of interface interaction between pre-oxidants and cyanobacteria should be defined in future to ensure moderate pre-oxidation of algal cells. Fate of cyanobacterial cells in sludge is also reviewed because more and more waterworks return sludge supernatant to the inlet of plant. Damage to cyanobacterial cells in sludge depends mainly upon coagulant type and dosage, algal species, and cyanobacteria-containing sludge should be treated before cell lysis. Efficient techniques for harmless disposal of cyanobacteria-containing sludge should be developed in future. This paper will help to better understand the cyanobacterial removal processes and provide improved perspectives for future research in this field.

Algicidal activity synchronized with nitrogen removal by actinomycetes: Algicidal mechanism, stress response of algal cells, denitrification performance, and indigenous bacterial community co-occurrence

The harmful algal blooms (HABs) can damage the ecological equilibrium of aquatic ecosystems and threaten human health. The bio-degradation of algal by algicidal bacteria is an environmentally friendly and economical approach to control HABs. This study applied an aerobic denitrification synchronization algicidal strain Streptomyces sp. LJH-12-1 (L1) to control HABs. The cell-free filtrate of the strain L1 showed a great algolytic effect on bloom-forming cyanobacterium, Microcystis aeruginosa (M. aeruginosa). The optimal algicidal property of strain L1 was indirect light-dependent algicidal with an algicidal rate of 85.0%. The functional metabolism, light-trapping, light-transfer efficiency, the content of pigments, and inhibition of photosynthesis of M. aeruginosa decreased after the addition of the supernatant of the strain L1 due to oxidative stress. Moreover, 96.05% nitrate removal rate synchronized with algicidal activity was achieved with the strain L1. The relative abundance of N cycling functional genes significantly increased during the strain L1 effect on M. aeruginosa. The algicidal efficiency of the strain L1 in the raw water was 76.70% with nitrate removal efficiency of 81.4%. Overall, this study provides a novel route to apply bacterial strain with the property of denitrification coupled with algicidal activity in treating micro-polluted water bodies.

Arsenic pollution concerning surface water and sediment of Jie River: A pilot area where gold smelting enterprises are concentrated

A comprehensive monitoring and risk assessment of arsenic (As) pollution concerning surface water and sediment is performed in the Jie River basin, where gold smelting enterprises are concentrated. The study area is divide into six regions, labeled as A, B, C, D, E, and F, from sewage outlets to downstream. Results shows that with far away from the sewage outlets, the total As concentrations in water and sediment gradually decrease from regions A to F. However, in region F, the concentration of bioavailable As significantly increases in the sediment due to the higher pH, leading to the transformation of As(V) into more mobile As(III). In sediment, Paracladius sp. exhibits strong resistance to As pollution in sediment, which can potentially elevate the risk of disease transmission. In water bodies, diatoms and euglena are the main phytoplankton in the Jie River while toxic cyanobacteria exhibits lower resistance to As pollution. Overall, measures should be taken to ecologically remediate the sediment in downstream while implementing appropriate isolation methods to prevent the spread of highly contaminated sediments from regions near sewage outlets.

Field and laboratory studies of fluorescence-based technologies for real-time tracking of cyanobacterial cell lysis and potential microcystins release

Elevated levels of dissolved microcystins (MCs) in source water due to rapid cell lysis of harmful cyanobacterial blooms may pose serious challenges for drinking water treatment. Catastrophic cell lysis can result from outbreaks of naturally-occurring cyanophages - as documented in Lake Erie during the Toledo water crisis of 2014 and in 2019, or through the application of algaecides or water treatment chemicals. Real-time detection of cyanobacterial cell lysis in source water would provide a valuable tool for drinking water plant and reservoir managers. In this study we explored two real-time fluorescence-based devices, PhycoSens and PhycoLA, that can detect unbound phycocyanin (uPC) as a potential indication of cell lysis and MCs release. The PhycoSens was deployed at the Low Service pump station of the City of Toledo Lake Erie drinking water treatment plant from July 15 to October 19, 2022 during the annual cyanobacteria bloom season. It measured major algal groups and uPC in incoming lake water at 15-min intervals during cyanobacteria dominant and senescence periods. Intermittent uPC detections from the PhycoSens over a three-month period coincided with periods of increasing proportions of extracellular MCs relative to total (intracellular and extracellular) MCs, indicating potential for uPC use as an indicator of cyanobacterial cell integrity. Following exposures of laboratory-cultured MCs-producing Microcystis aeruginosa NIES-298 (120 μg chlorophyll/L) to cyanophage Ma-LMM01, copper sulfate (0.5 and 1 mg Cu/L), sodium carbonate peroxyhydrate (PAK® 27, 6.7 and 10 mg H2O2/L), and potassium permanganate (2.5 and 4 mg/L), appearance of uPC coincided with elevated fractions of extracellular MCs. The PhycoLA was used to monitor batch samples collected daily from Lake Erie water exposed to algaecides in the laboratory. Concurrence of uPC signal and surge of dissolved MCs was observed following 24-h exposures to copper sulfate and PAK 27. Overall results indicate the appearance of uPC is a useful indicator of the onset of cyanobacterial cell lysis and the release of MCs when MCs are present.

Design, Synthesis, and Mode of Action of Thioacetamide Derivatives as the Algicide Candidate Based on Active Substructure Splicing Strategy

Lakes and reservoirs worldwide are experiencing a growing problem with harmful cyanobacterial blooms (HCBs), which have significant implications for ecosystem health and water quality. Algaecide is an effective way to control HCBs effectively. In this study, we applied an active substructure splicing strategy for rapid discovery of algicides. Through this strategy, we first optimized the structure of the lead compound S5, designed and synthesized three series of thioacetamide derivatives (series A, B, C), and then evaluated their algicidal activities. Finally, compound A3 with excellent performance was found, which accelerated the process of discovering and developing new algicides. The biological activity assay data showed that A3 had a significant inhibitory effect on M. aeruginosa. FACHB905 (EC50 = 0.46 μM) and Synechocystis sp. PCC6803 (EC50 = 0.95 μM), which was better than the commercial algicide prometryn (M. aeruginosa. FACHB905, EC50 = 6.52 μM; Synechocystis sp. PCC6803, EC50 = 4.64 μM) as well as better than lead compound S5 (M. aeruginosa. FACHB905, EC50 = 8.80 μM; Synechocystis sp. PCC6803, EC50 = 7.70 μM). The relationship between the surface electrostatic potential, chemical reactivity, and global electrophilicity of the compounds and their activities was discussed by density functional theory (DFT). Physiological and biochemical studies have shown that A3 might affect the photosynthesis pathway and antioxidant system in cyanobacteria, resulting in the morphological changes of cyanobacterial cells. Our work demonstrated that A3 might be a promising candidate for the development of novel algicides and provided a new active skeleton for the development of subsequent chemical algicides.

Progress on control of harmful algae by sustained-release technology of allelochemical: A review

The outbreak of harmful algae blooms caused by water eutrophication seriously jeopardizes the aquatic ecological environment and human health. Therefore, algae control technology has attracted widespread attention between environmental scholars. Allelochemical sustained-release technology which releases the active ingredient to the target medium at a certain rate within the effective time, so that the system maintains a certain concentration, thus prolonging its influence on the target organism. Allelochemical sustained-release technology has become the focus of research due to the characteristics of high efficiency, safety, low-cost, environment friendly and no secondary pollution. This paper reviews the characteristics of allelochemical substances and the status quo of plant extraction, explains the detailed classification of allelochemical sustained-release microspheres (ASRMs) and the application of algae inhibition, summarizes the preparation method of ASRMs, elaborates on the mechanism of algae inhibition of sustained-release technology from the perspective of photosynthesis, cellular enzyme activity, algae cell structure, gene expression, and target site action. Focuses on the summary of the factors influencing the effect of algae inhibition of ASRMs, including particle size of sustained-release microspheres, selection of carrier materials, and the growth stage of algae. The future direction and prospect of algae inhibition by allelochemical sustained-release technology were prospected to provide the scientific basis for water ecological restoration.

Maintenance of cell integrity during hydroxyl radical rapid inactivation of Pseudanabaena sp. and simultaneous mineralization of odor compound 2-methylisoborneol

Pseudanabaena sp. and the odor compound it produces, 2-methylisoborneol (2-MIB), has been reportedly responsible for off-flavor pollution worldwide, leading to substandard drinking water sensory indicators and serious water supply crises. In this paper, the hydroxyl radical (•OH) produced by the synergistic effect of strong ionization discharge and hydrodynamic cavitation rapidly inactivated Pseudanabaena sp. and simultaneously mineralized 2-MIB to a concentration of 2.57 ng/L, which is below the odor threshold of 10 ng/L for a total reactive oxidants (TRO) concentration of 1.2 mg/L within 12 s. Crucially, the intracellular 2-MIB level was maintained in approximately 155.26- 162.29 ng/L range, indicating that 2-MIB was not released from the cells. Based on the scanning electron microscopy (SEM) results, the integrity of Pseudanabaena sp. cells was maintained with intact membranes and no intracellular organic matters (IOM) released during •OH inactivation. In contrast, ClO2 caused severe membrane rupture and massive IOM release. Based on the gas chromatograph/mass spectrometer (GC/MS) analyses and mass spectral database, the chromatogram fitted the baseline with a TRO concentration of 4 mg/L and no peaks corresponding to intermediates were detected. Moreover, •OH could mineralize 2-MIB by opening the ring structures of 1,2,3,3-tetramethyl-4-cyclopentenone, neomenthol, and 2-methylcyclohexene-1-aldehyde to produce small-molecule compounds, finally leading to CO2 and H2O formation via three reaction pathways. Therefore, the •OH not only maintained the cell integrity of Pseudanabaena sp. during inactivation but also mineralized 2-MIB simultaneously.

Acetylacetone effectively controlled the secondary metabolites of Microcystis aeruginosa under simulated sunlight irradiation

Inactivation of cyanobacterial cells and simultaneous control of secondary metabolites is of significant necessity for the treatment of cyanobacteria-laden water. Acetylacetone (AcAc) has been reported a specific algicide to inactivate Microcystis aeruginosa (M. aeruginosa) and an effective light activator to degrade pollutants. This study systematically investigated the photodegradation ability of AcAc under xenon (Xe) irradiation on the secondary metabolites of M. aeruginosa, mainly algal organic matter (AOM), especially toxic microcystin-LR (MC-LR). Results showed that AcAc outperformed H2O2 in destructing the protein-like substances, humic acid-like matters, aromatic proteins and fulvic-like substances of AOM. For MC-LR (250 µg/L), 0.05 mmol/L AcAc attained the same degradation efficiency (87.0%) as 0.1 mmol/L H2O2. The degradation mechanism of Xe/AcAc might involve photo-induced energy/electron transfer and formation of carbon center radicals. Alkaline conditions (pH > 9.0) were detrimental to the photoactivity of AcAc, corresponding to the observed degradation rate constant (k1 value) of MC-LR drastically decreasing to 0.0013 min-1 as solution pH exceeded 9.0. The PO43- and HCO3- ions had obvious inhibition effects, whereas NO3- slightly improved k1 value from 0.0277 min-1 to 0.0321 min-1. The presence of AOM did not significantly inhibit MC-LR degradation in Xe/AcAc system. In addition, the biological toxicity of MC-LR was greatly reduced after photoreaction. These results demonstrated that AcAc was an alternative algicidal agent to effectively inactivate algal cells and simultaneously control the secondary metabolites after cell lysis. Nevertheless, the concentration and irradiation conditions should be further optimized in practical application.

Enhancement of KMnO4 treatment on cyanobacteria laden-water via 1000 kHz ultrasound at a moderate intensity

1000 kHz high-frequency ultrasound at 0.12 and 0.39 W/mL intensity was used to enhance the inactivation of suspensions of Microcystis aeruginosa cells using KMnO₄. With 10 mg/L of KMnO₄, ultrasound at 0.12 W/mL intensity was found to be effective in inactivating the cyanobacteria within 10 min. A Weibull model was found to describes the inactivation well. Its concave shape shows that some cells have a certain resistance to this treatment. Cytometry and microscopic analysis confirm that the treatment damages cell integrity. Despite that the extracellular organic matter in the water was not significantly increased. The concentration of extracellular cyanobacterial toxins even decreased. The filtered suspension of inactivated cyanobacteria was used to cultivate mung beans, and the suspension did not hinder their germination. This provides a new idea for using cyanobacteria-laden wastewater. These findings suggest a technique for speeding up the oxidation of Microcystis cells using KMnO₄ with ultrasound at moderate intensity, which provide new insights into the biological effects of ultrasound.

Heavy metal content and microbial characteristics of soil plant system in Dabaoshan mining area, Guangdong Province

The disordered mining of Dabaoshan lead-zinc mineral resources in Shaoguan has brought serious harm to the regional ecological environment. In order to investigate the heavy metal pollution status and microbial characteristics of soil plant system in mining area, The distribution of heavy metals in the soil, the activity of soil microorganisms and the accumulation characteristics of heavy metals in the dominant plant Miscanthus floridulus were studied. The results indicated that metal element contents of Miscanthus floridulus in sequence were: Zn>Pb>Cu> Cd. This study demonstrated that the elemental content of the Miscanthus floridulus plant showed Zn>Pb>Cu>Cd, with Zn being the most significantly correlated with soil elements, followed by Pb. Compared with the control group, the Miscanthus floridulus-soil system possessed obviously different soil microbial features: intensiver in microbial basal respiration strength, and higher microbial eco-physiological parameters Cmic/Corg and qCO2, but lower in soil microbial biomass. The results showed the soil enzymatic activities decreased significantly with increase of contamination of heavy metals, especially dehydrogenase and urease activities. With the increase of the content of heavy metals in the mining area soil, the intensity of soil biochemical action in the mining area (Q1, Q2) soil decreased significantly, and the biochemical action showed a significant negative correlation with the content of heavy metals in the soil. Compared with the non mining area (Q8) soil, the intensity of soil ammonification, nitrification, N fixation and cellulose decomposition decreased by 43.2%~71.1%, 70.1%~92.1%, 58.7%~87.8% and 55.3%~79.8% respectively. The decrease of soil microbial activity weakened the circulation rate and energy flow of C and N nutrients in the soil of the mining area.

A novel cyanolytic bacterium, Pseudomonas fluorescens BG-E as a potential biological control agent for freshwater bloom-forming cyanobacteria Pseudanabaena spp

The majority of bacterial antagonists identified to date are active against Microcystis. Therefore, this study aimed to isolate and characterize novel cyanolytic bacterial strains antagonistic against bloom-forming filamentous cyanobacteria. The bacterial strain BG-E isolated from the Bandagiriya Wewa in Sri Lanka was identified as Pseudomonas fluorescens (MZ007859) based on the 16S rRNA gene sequencing. BG-E showed 82% and 73% cyanolytic activity (CA) against Pseudanabaena sp. LW2 (MW288948) and Pseudanabaena lonchoides LW1 (MW288940), respectively, after 10 days of inoculation. The light microscopic images affirmed the complete disintegration in the filamentous structures of the tested Pseudanabaena species. The bacterial cell density of 15% v/v showed the CA with 95% and 89% cell lysis, respectively, in P. lonchoides and Pseudanabaena sp. LW2. Moreover, the results showed that >50% CA could be achieved by 0.100 and 1.00 (OD₇₃₀ ) cell densities for these same species. The highest CA of the cell-free supernatant of BG-E against P. lonchoides and bacterial culture against Pseudanabaena sp. LW2 illustrated the species-specific mode of action of BG-E. Although BG-E efficiently lysed the tested cyanobacterial species, the results of the MC-biodegradation assay confirmed its inability to degrade MC-LR cyanotoxin. Further, the BG-E strain lacks the mlrABCD gene cluster which is known to be responsible for the enzymatic degradation of MCs. The overall findings highlighted the applicability of P. fluorescens BG-E as a biological controlling agent to terminate blooms of freshwater filamentous cyanobacteria genus Pseudanabaena. The incorporation of cyanotoxin-degrading heterotrophic bacteria is recommended as a means of controlling toxic Pseudanabaena blooms.

Comparative assessment of algaecide performance on freshwater phytoplankton: Understanding differential sensitivities to frame cyanobacteria management

Cyanobacterial bloom represent a growing threat to global water security. With fast proliferation, they raise great concern due to potential health and socioeconomic concerns. Algaecides are commonly employed as a mitigative measure to suppress and manage cyanobacteria. However, recent research on algaecides has a limited phycological focus, concentrated predominately on cyanobacteria and chlorophytes. Without considering phycological diversity, generalizations crafted from these algaecide comparisons present a biased perpective. To limit the collateral impacts of algaecide interventions on phytoplankton communities it is critical to understand differential phycological sensitivities for establishing optimal dosage and tolerance thresholds. This research attempts to fill this knowledge gap and provide effective guidelines to frame cyanobacterial management. We investigate the effect of two common algaecides, copper sulfate (CuSO₄) and hydrogen peroxide (H₂O₂), on four major phycological divisions (chlorophytes, cyanobacteria, diatoms, and mixotrophs). All phycological divisions exhibited greater sensitivity to copper sulfate, except chlorophytes. Mixotrophs and cyanobacteria displayed the highest sensitivity to both algaecides with the highest to lowest sensitivity being observed as follows: mixotrophs, cyanobacteria, diatoms, and chlorophytes. Our results suggest that H₂O₂ represents a comparable alternative to CuSO₄ for cyanobacterial control. However, some eukaryotic divisions such as mixotrophs and diatoms mirrored cyanobacteria sensitivity, challenging the assumption that H₂O₂ is a selective cyanocide. Our findings suggest that optimizing algaecide treatments to suppress cyanobacteria while minimizing potential adverse effects on other phycological members is unattainable. An apparent trade-off between effective cyanobacterial management and conserving non-targeted phycological divisions is expected and should be a prime consideration of lake management.

Effects of copper sulfate algaecide on the cell growth, physiological characteristics, the metabolic activity of Microcystis aeruginosa and raw water application

Harmful cyanobacteria blooms (HCBs) occurred frequently and become a serious scientific challenge. Copper sulfate (CuSO₄) is a broad-spectrum chemical algaecide to control algae blooms. Herein, the Microcystis aeruginosa was exposed to different CuSO₄ (0.0, 0.2 and 0.5 mg/L) to assess the variations in algal physiological process and metabolic profiles. The results indicated that exposure to CuSO₄ of 0.5 mg/L at 72 h could significantly inhibit the cell growth and photosynthetic capacity of M. aeruginosa, including chl-a content and chlorophyll fluorescence parameters. Plasma membrane damage causing cell lysis of M. aeruginosa increased the K⁺ release. The increase of SOD and CAT suggested that CuSO₄ treatment caused oxidative stress in algal cells. Different doses of CuSO₄ modified the carbon metabolic potential, algal cells had their unique metabolic mode thereby. Moreover, the research further verified that CuSO₄ would also inhibit algal growth and change algal community structure in site-collected water application. Overall, laboratory results of M. aeruginosa to CuSO₄ and site-collected water application of algal responses to CuSO₄ might be conducive to uncovering the controlling mechanism of algae and the potential effect of carbon cycling in an ecological environment.

Impact of submerged macrophytes on growth and 2-MIB release risk of Pseudanabaena sp.: From field monitoringa to cultural experiments

The off-flavor compound 2-methylisoborneol (2-MIB) is generally associated with the proliferation and metabolism of filamentous cyanobacteria in shallow freshwater ecosystems. Here field monitoring in East Taihu Lake from July to October 2021, along with cultural experiments, was conducted to determine the impact of submerged macrophytes on the growth and 2-MIB production of filamentous cyanobacteria. Pseudanabaena sp. was identified as the 2-MIB producer with the highest detection rate (100%) and correlation coefficient (R=0.68, p < 0.001). The 2-MIB concentration and algal growth in the macrophyte-dominated zones were markedly decreased compared with those in the phytoplankton-dominated zone. Five submerged macrophytes classified into flat-leaf type (Vallisneria natans and Potamogeton crispus) and thin-leaf type (Hydrilla verticillata, Ceratophyllum demersum, and Myriophyllum spicatum) exhibited strong inhibition effects against Pseudanabaena sp.: Overall inhibition efficiencies (IEs) of 92.7% ± 6.8% and 92.7% ± 8.4% for cell growth and 2-MIB production were achieved, respectively. Moreover, the thin-leaf macrophytes exhibited significant higher IEs for cell growth (94.0% vs. 84.7%) and 2-MIB production (99.4% vs. 82.6%) than the flat-leaf macrophytes and can be selected as pioneer species in controlling odor problems. Nutrient uptake, increasing water clarity, shading effects, and allelopathic effects of the submerged macrophytes were found to be the dominant inhibition mechanisms.

The cyanobactericidal bacterium Paucibacter aquatile DH15 caused the decline of Microcystis and aquatic microbial community succession: A mesocosm study

Microcystis blooms pose a major threat to the quality of drinking water. Cyanobactericidal bacteria have attracted much attention in the research community as a vehicle for controlling Microcystis blooms because of their ecological safety. Nonetheless, most studies on cyanobactericidal bacteria have been conducted on a laboratory scale but have not been scaled-up as field experiments. Thus, our understanding of the microbial response to cyanobactericidal bacteria in natural ecosystems remains elusive. Herein, we applied Paucibacter aquatile DH15 to control Microcystis blooms in a 1000 L mesocosm experiment and demonstrated its potential with the following results: (1) DH15 reduced Microcystis cell density by 90.7% within two days; (2) microcystins released by Microcystis death decreased to the control level in four days; (3) during the cyanobactericidal processes, the physicochemical parameters of water quality remained safe for other aquatic organisms; and (4) the cyanobactericidal processes promoted the growth of eukaryotic microalgae, replacing cyanobacteria. The cyanobactericidal processes accelerated turnover rates, decreased stability, and altered the functional profile of the microbial community. Network analysis demonstrated that this process resulted in more complex interactions between microbes. Overall, our findings suggest that strain DH15 could be considered a promising candidate for controlling Microcystis blooms in an eco-friendly manner.

Evidence-Based Framework to Manage Cyanobacteria and Cyanotoxins in Water and Sludge from Drinking Water Treatment Plants

Freshwater bodies and, consequently, drinking water treatment plants (DWTPs) sources are increasingly facing toxic cyanobacterial blooms. Even though conventional treatment processes including coagulation, flocculation, sedimentation, and filtration can control cyanobacteria and cell-bound cyanotoxins, these processes may encounter challenges such as inefficient removal of dissolved metabolites and cyanobacterial cell breakthrough. Furthermore, conventional treatment processes may lead to the accumulation of cyanobacteria cells and cyanotoxins in sludge. Pre-oxidation can enhance coagulation efficiency as it provides the first barrier against cyanobacteria and cyanotoxins and it decreases cell accumulation in DWTP sludge. This critical review aims to: (i) evaluate the state of the science of cyanobacteria and cyanotoxin management throughout DWTPs, as well as their associated sludge, and (ii) develop a decision framework to manage cyanobacteria and cyanotoxins in DWTPs and sludge. The review identified that lab-cultured-based pre-oxidation studies may not represent the real bloom pre-oxidation efficacy. Moreover, the application of a common exposure unit CT (residual concentration × contact time) provides a proper understanding of cyanobacteria pre-oxidation efficiency. Recently, reported challenges on cyanobacterial survival and growth in sludge alongside the cell lysis and cyanotoxin release raised health and technical concerns with regards to sludge storage and sludge supernatant recycling to the head of DWTPs. According to the review, oxidation has not been identified as a feasible option to handle cyanobacterial-laden sludge due to low cell and cyanotoxin removal efficacy. Based on the reviewed literature, a decision framework is proposed to manage cyanobacteria and cyanotoxins and their associated sludge in DWTPs.

Higher sensitivity to Cu2+ exposure of Microcystis aeruginosa in late lag phase is beneficial to its control

Cyanobacterial blooms are always treated in exponential phase, which demands high dosages of algicides (e.g., CuSO4). 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 CuSO4 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 CuSO4. The results showed that M. aeruginosa in late lag phase had a higher ratio of dividing-cells, Fv/Fm 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, Fv/Fm and membrane integrity occurred under the same dosages of CuSO4 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 CuSO4, indicating that CuSO4 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.

On the Efficacy of H2O2 or S2O82- at Promoting the Inactivation of a Consortium of Cyanobacteria and Bacteria in Algae-Laden Water

Harmful algal blooms in coastal areas can significantly impact a water source. Microorganisms such as cyanobacteria and associated pathogenic bacteria may endanger an ecosystem and human health by causing significant eco-hazards. This study assesses the efficacy of two different reagents, H2O2 and S2O82−, as (pre-)treatment options for algae-laden waters. Anabaena sp. and Vibrio alginolyticus have been selected as target microorganisms. With the objective of activating H2O2 or S2O82−, additional experiments have been performed with the presence of small amounts of iron (18 µmol/L). For the cyanobacterial case, H2O2-based processes demonstrate greater efficiency over that of S2O82−, as Anabaena sp. is particularly affected by H2O2, for which >90% of growth inhibition has been achieved with 0.088 mmol/L of H2O2 (at 72 h of exposure). The response of Anabaena sp. as a co-culture with V. alginolyticus implies the use of major H2O2 amounts for its inactivation (0.29 mmol/L of H2O2), while the effects of H2O2/Fe(II) suggests an improvement of ~60% compared to single H2O2. These H2O2 doses are not sufficient for preventing the regrowth of V. alginolyticus after 24 h. The effects of S2O82− (+ Fe(II)) are moderate, reaching maximum inhibition growth of ~50% for Anabaena sp. at seven days of exposure. Nevertheless, doses of 3 mmol/L of S2O82− can prevent the regrowth of V. alginolyticus. These findings have implications for the mitigation of HABs but also for the associated bacteria that threaten many coastal ecosystems.

Moderate pre-ozonation coupled with a post-peroxone process remove filamentous cyanobacteria and 2-MIB efficiently: From bench to pilot-scale study

The increasing frequency and intensity of taste- and odour-producing cyanobacteria in water sources is a growing global issue. Odour events caused by 2-methylisoborneol (2-MIB) mainly arising from filamentous cyanobacteria have been a very common problem in water supply. Removal rates of filamentous cyanobacteria and 2-MIB by conventional water treatment, such as coagulation, and disinfection treatment processes is low. Hence, a moderate pre-ozonation of cyanobacteria (with little cell damage) was proposed in this study as an enhanced coagulation step to remove filamentous cyanobacteria and intracellular 2-MIB effectively, while avoiding the release of intracellular 2-MIB. A post-peroxone (O₃/H₂O₂) process was applied after sand filtration to degrade the residual dissolved 2-MIB. Results show that moderate pre-ozonation (0.2 mg/L O₃ oxidation for 20 min) can substantially enhance the coagulation efficiency for algae, with low cell lysis and high cell viability. Furthermore, 2.0 mg/L O₃ combined with 2.0 mg/L H₂O₂ can degrade the residual dissolved 2-MIB nearly 100% after 20 min reaction. Based on the optimal dosages, a 0.6 m³/h pilot system, including pre-ozonation, coagulation and sedimentation, sand filtration, and post-peroxone processes, was continuously run for 14 days, and it was found that the proposed process can effectively and stably remove filamentous cyanobacteria and 2-MIB.

Effects of hydrogen peroxide on Scenedesmus obliquus: Cell growth, antioxidant enzyme activity and intracellular protein fingerprinting

Hydrogen peroxide (H₂O₂) is an environmental-friendly algicide and it is widely used to control algal blooms in aquatic ecosystems. However, the response of algal cell metabolic characteristics and intracellular protein profile under H₂O₂ stress is still not well understood. In the present study, the green alga Scenedesmus obliquus was exposed to different concentrations of H₂O₂ (0, 2, 6, 8 and 10 mg L^-1) to evaluate the changes in algal morphological, physiological, and proteomic features to H₂O₂ exposure. The results showed that 8 mg L^-1 of H₂O₂ could effectively inhibit the cell growth and photosynthetic activity of S. obliquus including chlorophyll-a content and chlorophyll fluorescence parameters. The increased activities of superoxide dismutase (SOD) and catalase (CAT) observed in this study indicate that cells exposure to H₂O₂ caused oxidative stress. The metabolic activity of S. obliquus was significantly decreased by H₂O₂ treatment. In terms of proteomic analysis, 251 differentially expressed proteins (DEPs) were successfully identified. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed significant protein enrichment in the metabolic pathways, photosynthesis, ascorbic acid, and alginate metabolism and phenylpropane biosynthesis of S. obliquus. The analysis of protein-protein interaction system shows that the pathways of photosynthesis and metabolic pathways of S. obliquus were essential to resist oxidative stress. Taking together, these results shed new lights on exploring the cell physiological metabolism and intracellular protein mechanisms of H₂O₂ inhibition on algal blooms.

Potassium permanganate as a promising pre-oxidant to treat low-viability cyanobacteria and associated removal of cyanotoxins and extracellular organic matters

Cell-viability of cyanobacteria declines from development to decay stage during a successive bloom. Potassium permanganate (KMnO₄) has demonstrated to be a superior pre-oxidant to treat high-viability cyanobacteria compared to other common oxidants (e.g., chlorine), but whether it is feasible to treat low-viability cyanobacteria is unknown. Here, effects of KMnO₄ on membrane integrity, cyanotoxin fate and extracellular organic matters (EOMs) removal of high- and low-viability cyanobacteria were compared. Results showed that cell-viability of cyanobacteria could affect oxidant decay (k_decay), membrane damage (k_loss), and cyanotoxins release (k_i) and degradation (k_e) during KMnO₄ oxidation, similar to chlorination. However, unlike chlorination, initial low dosages of KMnO₄ (0.5 and 1 mg L^-1) minimized membrane damage for low-viability cyanobacteria (< 27%), and continuously decrease extracellular cyanotoxins, extracellular organic matters (EOMs), and aromatic compounds to some degrees (P<0.05). High dosages of KMnO₄ (> 2 mg L^-1) caused severe membrane destruction (> 89%) for low-viability cyanobacteria, leading to a fast increase of extracellular cyanotoxins within 1 h. However, total/extracellular cyanotoxins were oxidized to below the safety guideline of 1 μg L^-1 after being dosed with sufficient oxidant exposure. EOMs and aromatic compounds were also reduced by 5-18% (P<0.05). Additionally, KMnO₄-assisted coagulation significantly improved the removal of low-viability cyanobacteria (2-5 fold). Consequently, KMnO₄ could be a promising pre-oxidant to treat low-viability cyanobacteria at decay stage of a successive bloom.

Using sodium percarbonate to suppress vertically distributed filamentous cyanobacteria while maintaining the stability of microeukaryotic communities in drinking water reservoirs

The increasing frequency and intensity of blooms of toxin- and taste & odour-producing filamentous cyanobacteria in water sources is a growing global issue. Compared to the common spherical Microcystis genus, the removal of filamentous cyanobacteria is more difficult in drinking water treatment plants; hence, abatement and control of the occurrence and proliferation of harmful filamentous cyanobacteria within drinking water sources is important for water supply. In this study, the solid sodium percarbonate (SPC), Na₂CO₃·1.5H₂O₂, was used as an algaecide to eliminate the cyanobacteria distributed throughout the water column in the surface and bottom layer of a reservoir serving as a drinking water source. Results showed that although the oxidation capacity of SPC was higher in the surface water due to the higher light intensity than in the bottom water, 3.0 mg/L SPC can still suppress the harmful cyanobacteria in the bottom water after 36 h because the carbonate ion generated by SPC decomposition can act as an activator of H₂O₂ to generate many reactive oxygen species - including superoxide radicals, carbonate radical anions, and hydroxyl radicals - even in the light-limited environment. The obtained inactivation rates for the main cyanobacteria in this reservoir followed the order: Pseudanabaena limnetica > Raphidiopsis curvata > Cylindrospermopsis raciborskii. 3.0 mg/L SPC has a slight impact on microeukaryotic communities according to the 18S rRNA gene sequencing, while 6.0 mg/L SPC changed the composition of eukaryotic phytoplankton and zooplankton clearly. Eukaryotic co-occurrence networks showed that although the network of eukaryotic plankton in treated surface water was more compact and clustered, stability of microeukaryotes in the treated surface water was lower than for the treated bottom water, owing to the higher oxidation capacity of SPC in the surface water. The results above not only have important implications for full-scale control of harmful cyanobacteria in drinking water sources, especially filamentous cyanobacteria with vertical distributions, but also help to ensure the health and stability of the whole aquatic ecosystem.

Antibiotics induced alterations in cell density, photosynthesis, microcystin synthesis and proteomic expression of Microcystis aeruginosa during CuSO4 treatment

Antibiotic contaminants have the potential to interfere with the control of cyanobacterial bloom through generating hormesis in cyanobacteria at current contamination level of ng L^-1. This study investigated the influence of a mixture of four frequently detected antibiotics, amoxicillin, ciprofloxacin, sulfamethoxazole and tetracycline, during the treatment of Microcystis aeruginosa by copper sulfate (CuSO₄) algaecide. CuSO₄ significantly (p <  0.05) inhibited cell density, growth rate, F_v/F_m value, chlorophyll a content and microcystin production ability of M. aeruginosa in a dose-dependent manner at application doses of 0.01-0.05 mg L^-1. Besides, CuSO₄ inhibited oxidation-reduction process, photosynthesis and biosynthesis in M. aeruginosa at the proteomic level. Preventative application of CuSO₄ to a low density (4 × 10⁵ cells mL^-1) of M. aeruginosa effectively prevented the formation of bloom at low CuSO₄ doses, which is a possible route for eliminating the negative effects of CuSO₄ algaecide in aquatic environments. The presence of mixed antibiotics alleviated the toxicity of CuSO₄ in M. aeruginosa, through the downregulation of cation transport proteins and the upregulation of proteins related with chlorophyll a synthesis, photosynthesis, gene expression and oxidation-reduction. Mixed antibiotics also promoted microcystin synthesis in CuSO₄ treated cells through the upregulation of microcystin synthetases. Mixed antibiotics significantly (p <  0.05) increased cell density, growth rate, F_v/F_m value, chlorophyll a content and microcystin production ability in CuSO₄ treated cells at test concentrations of 80 and 200 ng L^-1. A no-impact threshold of 20 ng L^-1 for mixed antibiotics (5 ng L^-1 for each antibiotic) was suggested for eliminating the interference of antibiotic contaminants on cyanobacterial bloom control.

Structure optimization and bioactivity evaluation of ThDP analogs targeting cyanobacterial pyruvate dehydrogenase E1

Harmful cyanobacteria bloom (HCB) has occurred frequently in recent years and it is urgent to develop novel algicides to deal with this problem. In this paper, a series of novel thiamin diphosphate (ThDP) analogs 5a-5g were designed and synthesized targeting cyanobacterial pyruvate dehydrogenase complex E1 (Cy-PDHc E1). Our results showed that compounds 5a-5g have higher inhibitory activities against Cy-PDHc E1 (IC₅₀ 9.56-3.48 µM) and higher inhibitory activities against two model cyanobacteria strains Synechocystis sp PCC6803 (EC₅₀ 2.03-1.58 µM) and Microcystis aeruginosa FACHB905 (EC₅₀ 1.86-0.95 µM). Especially, compound 5b displayed highest inhibitory activities (IC₅₀ = 3.48 µM) against Cy-PDHc E1 and powerful inhibitory activities against cyanobacteria Synechocystis sp PCC6803 (EC₅₀ = 1.58 µM) and Microcystis aeruginosa FACHB905 (EC₅₀ = 1.04 µM). Moreover, the inhibitory activities of compound 5b were even higher than those of copper sulfate (EC₅₀ = 2.02 and 1.71 µM separately) which has been widely used as algicide against cyanobacteria PCC6803 and FACHB905. The more important was that compound 5b display much higher inhibitory selectivity between Cy-PDHc E1 (Inhibitory rate 97.4%) and porcine PDHc E1 (Inhibitory rate 11.8%) under the same concentration (100 μM). The inhibition kinetic experiment and molecular docking research showed that compound 5b can inhibit Cy-PDHc E1 by occupying the ThDP-binding pocket and then blocking Cy-PDHc E1 bound to ThDP as competitive inhibitor. The imagines of SEM and TEM showed that cellular microstructures were heavily destroyed under compound 5b stress. Our results demonstrated compound 5b could be taken as a potential lead compound targeting Cy-PDHc E1 to obtain environment-friendly algicide for harmful cyanobacterial blooms control.