Use of an integrated metabolomics platform for mechanistic investigations of three commonly used algaecides on cyanobacterium, Microcystis aeruginosa

Biological and Chemical Approaches for Controlling Harmful Microcystis Blooms

The proliferation of harmful cyanobacterial blooms dominated by Microcystis aeruginosa has become an increasingly serious problem in freshwater ecosystems due to climate change and eutrophication. Microcystis-blooms in freshwater generate compounds with unpleasant odors, reduce the levels of dissolved O2, and excrete microcystins into aquatic ecosystems, potentially harming various organisms, including humans. Various chemical and biological approaches have thus been developed to mitigate the impact of the blooms, though issues such as secondary pollution and high economic costs have not been adequately addressed. Red clays and H2O2 are conventional treatment methods that have been employed worldwide for the mitigation of the blooms, while novel approaches, such as the use of plant or microbial metabolites and antagonistic bacteria, have also recently been proposed. Many of these methods rely on the generation of reactive oxygen species, the inhibition of photosynthesis, and/or the disruption of cellular membranes as their mechanisms of action, which may also negatively impact other freshwater microbiota. Nevertheless, the underlying molecular mechanisms of anticyanobacterial chemicals and antagonistic bacteria remain unclear. This review thus discusses both conventional and innovative approaches for the management of M. aeruginosa in freshwater bodies.

Toxicity of the disinfectant benzalkonium chloride (C14) towards cyanobacterium Microcystis results from its impact on the photosynthetic apparatus and cell metabolism

Quaternary ammonium compounds (QACs) are commonly used in a variety of consumer and commercial products, typically as a component of disinfectants. During the COVID-19 pandemic, QACs became one of the primary agents utilized to inactivate the SARS-CoV-2 virus on surfaces. However, the ecotoxicological effects of QACs upon aquatic organisms have not been fully assessed. In this study, we examined the effects of a widely used QAC (benzalkonium chloride-C14, BAC-14) on two toxigenic Microcystis strains and one non-toxigenic freshwater Microcystis strain and carried out an analysis focused on primary, adaptive and compensatory stress responses at apical (growth and photosynthesis) and metabolic levels. This analysis revealed that the two toxic Microcystis strains were more tolerant than the non-toxic strain, with 96 hr-EC50 values of 0.70, 0.76, and 0.38 mg/L BAC-14 for toxigenic M. aeruginosa FACHB-905, toxigenic M. aeruginosa FACHB-469, and non-toxigenic M. wesenbergii FACHB-908, respectively. The photosynthetic activities of the Microcystis, assessed via Fv/Fm values, were significantly suppressed under 0.4 mg/L BAC-14. Furthermore, this analysis revealed that BAC-14 altered 14, 12, and 8 metabolic pathways in M. aeruginosa FACHB-905, M. aeruginosa FACHB-469, and M. wesenbergii FACHB-908, respectively. It is noteworthy that BAC-14 enhanced the level of extracellular microcystin production in the toxigenic Microcystis strains, although cell growth was not significantly affected. Collectively, these data show that BAC-14 disrupted the physiological and metabolic status of Microcystis cells and stimulated the production and release of microcystin, which could result in damage to aquatic systems.

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.

Cell-Targeted Metal-Phenolic Nanoalgaecide in Hydroponic Cultivation to Enhance Food Sustainability

The growing global population necessitates substantial increases in food production. Hydroponic cultivation systems afford a critical alternative for food sustainability and enable stable annual production regardless of the climatic and geographical variations. However, the overgrowth of harmful algal blooms significantly threatens the crop yield by competing with nutrition in the solution and producing contaminants. The conventional practice of algaecides fails to control algal proliferation due to the limited efficiency and food safety concerns. Nanopesticides can deliver active ingredients responsively to suppress crop diseases and offer solutions to current practical challenges and difficulties. Inspired by prospects of nanotechnology for agricultural applications, we have utilized natural polyphenols and copper ions (Cu2+ ions) to develop self-assembled nanoalgaecides referred to as CuBes. The nanoalgaecide attached to algal cells via phenolic surface interactions, enabling localized Cu2+ ion release. This cell-targeted delivery suppressed Chlorella vulgaris for over 30 days (99% inhibition). Transcriptomics revealed that the nanoalgaecide disrupted algal metabolism by downregulating photosynthesis and chlorophyll pathways. In a solar-illuminated plant factory, the nanoalgaecide showed higher algal inhibition and lettuce biosafety versus the commercial Kocide 3000. Notably, the use of nanoalgaecide can enhance the nutrient value of lettuces, which meets the daily supply of Cu for adults. By integrating smart nanotechnology design with selective delivery mechanisms, this metal-phenolic nanoalgaecide provides a nanoenabled solution for controlling harmful algal blooms in hydroponics to advance food production.

Progress and challenges in exploring aquatic microbial communities using non-targeted metabolomics

Advances in bioanalytical technologies are constantly expanding our insights into complex ecosystems. Here, we highlight strategies and applications that make use of non-targeted metabolomics methods in aquatic chemical ecology research and discuss opportunities and remaining challenges of mass spectrometry-based methods to broaden our understanding of environmental systems.

Metabonomics analysis of microalga Scenedesmus obliquus under ciprofloxacin stress

The wide use of antibiotics in aquaculture has triggered global ecological security issue. Microalgal bioremediation is a promising strategy for antibiotics elimination due to carbon recovery, detoxification and various ecological advantages. However, a lack of understanding with respect to the corresponding regulation mechanism towards antibiotic stress may limit its practical applicability. The microalga Scenedesmus obliquus was shown to be capable of effectively eliminating ciprofloxacin (CIP), which is a common antibiotic used in aquaculture. However, the corresponding transcriptional alterations require further investigation and verification at the metabolomic level. Thus, this study uncovered the metabolomic profiles and detailed toxic and defense mechanisms towards CIP in S. obliquus using untargeted metabolomics. The enhanced oligosaccharide/polyol/lipid transport, up-regulation of carbohydrate and arachidonic acid metabolic pathways and increased energy production via EMP metabolism were observed as defense mechanisms of microalgal cells to xenobiotic CIP. The toxic metabolic responses included: (1) down-regulation of parts of mineral and organic transporters; (2) electrons competition between antibiotic and NAD during intracellular CIP degradation; and (3) suppressed expression of the hem gene in chlorophyll biosynthesis. This study describes the metabolic profile of microalgae during CIP elimination and reveals the key pathways from the perspective of metabolism, thereby providing information on the precise regulation of antibiotic bioremediation via microalgae.

Tea polyphenols inhibit blooms caused by eukaryotic and prokaryotic algae

With changes in global climate, blooms are becoming more frequent and difficult to control. Therefore, the selection of algal suppressor agents with effective inhibition and environmental safety is of paramount importance. One of the main treatment strategies is to inhibit the release of harmful algal toxins. Tea polyphenols (TP) are natural products that have been widely used in medicine, the environment, and other fields due to their antibacterial and antioxidant properties. To investigate their potential application in the treatment of algal blooms, TP were applied to three different microalgae. TP exhibited strong inhibitory effects towards all three microalgae. They stimulate the accumulation of ROS in algal cells, leading to lipid peroxidation and subsequent damage to the cell membrane, resulting in the rupture and necrosis of Cyclotella sp. and Chlorella vulgaris cells. Remarkably, it was observed that lower concentrations of TP exhibited the ability to induce apoptosis in M. aeruginosa cells without causing any structural damage. This outcome is particularly significant as it reduces the potential risk of microcystin release resulting from cell rupture. Overall, blooms dominated by different algae can be treated by adjusting the concentration of TP, a new algal suppressor, indicating strong potential treatment applications.

Deciphering the toxicity mechanism of haloquinolines on Chlorella pyrenoidosa using QSAR and metabolomics approaches

The hazardous potential of haloquinolines (HQLs) is becoming an issue of great concern due to its wide and long-term usage in many personal care products. We examined the growth inhibition, structure-activity relationship, and toxicity mechanism of 33 HQLs on Chlorella pyrenoidosa using the 72-h algal growth inhibition assay, three-dimensional quantitative structure-activity relationship (3D-QSAR), and metabolomics. We found that the IC₅₀ (half maximal inhibitory concentration) values for 33 compounds ranged from 4.52 to > 150 mg·L^-1, most tested compounds were toxic (1 mg·L^-1 < IC₅₀ < 10 mg·L^-1) or harmful (10 mg·L^-1 < IC₅₀ < 100 mg·L^-1) for the aquatic ecosystem. Hydrophobic properties of HQLs dominate their toxicity. Halogen atoms with large volume appear at the 2, 3, 4, 5, 6, and 7-positions of the quinoline ring to significantly increase the toxicity. In algal cells, HQLs can block diverse carbohydrates, lipids, and amino acid metabolism pathways, thereby resulting in energy usage, osmotic pressure regulation, membrane integrity, oxidative stress disorder, thus fatally damaging algal cells. Therefore, our results provide insight into the toxicity mechanism and ecological risk of HQLs.

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.

The effects of extracellular algicidal compounds of Bacillus sp. B1 on Heterosigma akashiwo: a metabolomics approach

Heterosigma akashiwo (H. akashiwo), a harmful algal species, has been a global environmental problem. Extracellular algicidal compounds (EACs) extracted from Bacillus sp. B1 exhibited algicidal effects against H. akashiwo. However, little is known about the algicidal mechanism and metabolic process. In this study, metabolomics and physiological analyses were combined to investigate the cellular responses of H. akashiwo when treated with EACs. The results indicated that EACs at 10% (v_EACs/v_sample) showed more than 90% inhibition of H. akashiwo. EAC treatment resulted in excessive reactive oxygen species (ROS) production in algal cells, causing stress responses such as inhibition of photosynthetic pigment synthesis, reduction of sugar synthesis, imbalance of osmotic pressure in the cell membrane, disruption of cell size and morphology, and eventual cell death. The results reveal the underlying mechanism of the algicidal process and provide new insights into algae-bacteria interactions and the application of metabolomics to algal research.

Effect of three commercial algaecides on cyanobacteria and microcystin-LR: implications for drinking water treatment using activated carbon

Toxic cyanobacterial blooms in aquatic ecosystems are associated to both public health and environmental concerns worldwide. Depending on the treatment technologies used, the removal capacity of cyanotoxins by drinking water treatment plants (DWTPs) is not sufficient to reach safe levels in drinking water. Likewise, controlling these blooms with algaecide may impair the efficiency of DWTPs due to the possible lysis of cyanobacterial cells and consequent release of cyanotoxins. We investigated the effects of three commercial algaecides (cationic polymer, copper sulfate, and hydrogen peroxide) on the growth parameters of the cyanobacterium Microcystis aeruginosa and the release of microcystin-LR (MC-LR). The potential interference of each algaecide on the MC-LR removal by adsorption on activated carbon (AC) was also tested through adsorption isotherms and kinetics experiments. Most algaecides significantly decreased the cell density and biovolume of M. aeruginosa, as well as increased the release of MC-LR. Interestingly, the presence of the algaecides in binary mixtures with MC-LR affected the adsorption of the cyanotoxin. Relevant adsorption parameters (e.g., maximum adsorption capacity, adsorption intensity, and affinity between MC-LR and AC) were altered when the algaecides were present, especially in the case of the cationic polymer. Also, the algaecides influenced the kinetics (e.g., by shifting the initial adsorption and the desorption constant), which may directly affect the design and operation of DWTPs. Our study indicated that algaecides can significantly impact the fate and the removal of MC-LR in DWTPs when the adsorption process is employed, with important implications for the management and performance of such facilities.

Allelopathic inhibition effects and mechanism of phenolic acids to Microcystis aeruginosa

Allelochemicals are essential agents for the biological control of harmful blooms. It is crucial to identify efficient algal suppressors and understand their mechanisms. This study reports the inhibition of Microcystis aeruginosa growth by 6 phenolic acids derived from plants' secondary metabolites. The inhibitory effect of phenolic acids was significantly influenced by exposure dose and phenolic acid species. Caffeic acid has the most efficient algal inhibition ability (96 h-EC₅₀ of 5.8 mg/L). In contrast, the other 5 analogs (cinnamic acid, p-coumaric acid, 3-hydroxycinnamic acid, ferulic acid, and isoferulic acid) showed a weak inhibition effect or promotion effect with the exposure dose of 5-100 mg/L. ROS and chlorophyll a content tests combined with metabolomics analysis revealed that caffeic acid could induce the ROS accumulation of M. aeruginosa. They mainly disturbed nucleotide, amino acid, and fatty acid metabolism, leading to the downregulation of most metabolites, including toxins of microcystin LR and cyanopeptolin A, and the precursors of some unpleasant terpenoids. It has been suggested that caffeic acid is an effective agent for controlling M. aeruginosa blooms.

Gut microbiota: a non-target victim of pesticide-induced toxicity

The human gut microbiota can be potentially disrupted due to exposure of various environmental contaminants, including pesticides. These contaminants enter into non-target species in multiple ways and cause potential health risks. The gut microbiota-derived metabolites have a significant role in maintaining the host's health by regulating metabolic homeostasis. An imbalance in this homeostasis can result in the development of various diseases and their pathogenesis. Pesticides have hazardous effects on the host's gut microbiota, which is evident in a few recent studies. Therefore, there is an urgent need to explore the effect of pesticide on gut microbiota-mediated metabolic changes in the host, which may provide a better understanding of pesticide-induced toxicity. The present review summarizes the pesticide-induced effects on gut microbiota, which in turn, induces changes in the release of their secondary metabolites that could lead to various host health effects.

Mechanism of macroalgae Gracilaria bailiniae responding to cadmium and lanthanum

Macroalgae can accumulate a wide array of metals, leading to their appliance as biomonitors of aquatic environments. With the rapid development of industrial and agricultural-based activities, Cd pollution in aquatic environments is considered an increasingly severe problem worldwide. Although La could alleviate the Cd stress in higher terrestrial plants, the response mechanisms of macroalgae to Cd and La are unknown. Along these lines, in this work, Cd significantly affected the growth, internal cellular structure, photosynthesis, pigment content, antioxidant enzyme activity, and lipid peroxidation level of G. bailiniae. However, the presence of La alleviated these adverse effects from Cd. Furthermore, the response mechanism of G. bailiniae to Cd was attributed to the self-antioxidant ability enhancement, membrane defense, and programmed-cellular regulation. However, the presence of La mediated the biosynthesis of both flavonoids and lipids, which inhibited the Cd accumulation, modulated algal stress signalling networks, renewed the impaired chlorophyll molecule, maintained the activity of the crucial enzyme, enhanced antioxidant ability, and maintained the stabilization of redox homeostasis, alleviating the adverse impact from Cd and improve the growth of G. bailiniae. The experimental results successfully demonstrate a new detoxicant to alleviate Cd stress, promoting a more comprehensive array of macroalgal applications.

Efficient inhibition of cyanobacteria M. aeruginosa growth using commercial food-grade fumaric acid

The control of cyanobacteria blooms is a global challenge. Here, we reported the efficient inhibition of M. aeruginosa by fumaric acid (FA), an intermediate metabolite of the tricarboxylic acid cycle. FA showed strong algicidal activity with an inhibition rate of 90.5% on the 8th day at a dose of 40 mg/L. The presence of FA caused severe membrane damage, as suggested by the fluorescence flow cytometry and morphology analysis. FA inhibited the formation of chlorophyll a, interrupting the photosynthesis system. It also induced oxidative stress in cells. Principal component analysis of the indicators suggested that the FA-treated sample had a significantly different inhibitory pattern than the acid-treated sample. Thus, the inhibitory effect was not solely caused by the pH effect. Untargeted metabolomic analysis revealed that 31 metabolites were differentially expressed in response to FA stress, which were mainly involved in the metabolite processes and the membranes. A commercial food-grade FA was able to inhibit the growth of M. aeruginosa similar to the analytical-grade FA. Our results suggest that FA can be potentially an efficient and low-risk chemical for inhibiting M. aeruginosa growth, which may find future applications in cyanobacteria bloom control.

Differential response of copper nanoparticles and ionic copper on growth, chlorophyll fluorescence, oxidative stress, and antioxidant machinery of two paddy field cyanobacteria

The current study explored the role of ionic copper (CuCl₂; 0.2 µM and 1 µM) and synthesized copper nanoparticles (CuNPs; 0.2 mM and 1 mM) in the two paddy field cyanobacteria (Nostoc muscorum ATCC 27893 and Anabaena sp. PCC 7120) with respect to growth, photosynthetic pigments, photosynthetic efficiency (O₂ evolution and photochemistry of photosystem II; PS II), oxidative stress biomarkers, and antioxidant system. The low doses of ionic Cu (0.2 µM) and CuNPs (0.2 mM) showed stimulating effects on growth, pigment content (chlorophyll a, phycobiliproteins, and carotenoids), oxygen evolution, and PS II photochemistry. High doses of Cu/CuNPs (1 µM Cu and 1 mM CuNPs) caused a decline in the above-mentioned parameters. The values of fluorescence kinetics parameters: ϕP₀, F_V/F₀, ϕE₀, Ψ₀, and PI_ABS, except for F₀/F_V, associated with PS II photochemistry in tested cyanobacteria and subjected to the high doses of ionic Cu and CuNPs, were decreased, while energy fluxes, ABS/RC, TR₀/RC, ET₀/RC, and DI₀/RC, were increased. Conversely, treatment with low doses of Cu and CuNPs caused a reverse trend, indicating normalization of PS II performance. Although the activity of enzymatic antioxidants (superoxide dismutase SOD; peroxidase POD; catalase CAT and glutathione-S-transferase GST) in both cyanobacteria exposed to high doses of ionic Cu and CuNPs was accelerated considerably, the oxidative stress remained high. Conversely, at low doses of ionic Cu and CuNPs, a significant enhancement in the activities of enzymatic antioxidants decreased the levels of oxidative stress biomarkers. Nevertheless, in Anabaena sp., the levels of biomarkers were greater than those of the control. The current study concluded that compared to synthesized CuNPs, ionic Cu at elevated concentration had a damaging effect on growth, photosynthetic pigments, and PS II photochemistry via increased oxidative stress, and this effect was enhanced in Anabaena sp. than N. muscorum.

Multiple inhibitory effects of succinic acid on Microcystis aeruginosa: morphology, metabolomics, and gene expression

The cell membrane permeability, morphology, metabolomics, and gene expression of Microcystis aeruginosa under various concentrations of succinic acid (SA) were evaluated to clarify the mechanism of SA inhibition of M. aeruginosa. The results showed that SA caused intracellular protein and nucleic acid extravasation by increasing the cell membrane permeability. Scanning electron microscopy suggested that a high dose of SA (60 mg L^-1) could damage the cell membrane and even cause lysis in some cells. Metabolomics result demonstrated that change in intracellular lipids content was the main reason for the increase of cell membrane permeability. In addition, SA could negatively affect amino acids metabolism, inhibit the biosynthesis of nucleotides, and interfere with the tricarboxylic acid (TCA) cycle of algal cells. Furthermore, SA also affected N assimilation and caused oxidative damage to Microcystis. In conclusion, SA inhibits the growth of M. aeruginosa through multisite action.

Cercosporin-bioinspired photoinactivation of harmful cyanobacteria under natural sunlight via bifunctional mechanisms

Harmful cyanobacterial blooms (HCBs), mainly caused by eutrophication, have deleterious impacts on water resources and pose a great threat to human health and natural ecosystems. Thus, an environmentally-friendly method to inhibit HCBs is urgently needed. Learning from nature, herein, natural product cercosporin, produced by the fungi Cercospora to damage plant cells under natural sunlight, was developed as a powerful photosensitive algicidal reagent to inhibit HCBs. Microcystis aeruginosa could be severely inactivated by 20 μM cercosporin in 36 h with 95% inhibition ratio under 23 W compact fluorescent light irradiation. Further mechanism investigation showed that algal cell walls and membranes along with the antioxidant and photosynthetic systems were damaged via two mechanisms, those being, reactive oxygen species generation and cell adsorption. More importantly, the practical applicability of cercosporin was demonstrated by its effectiveness in a 2 L-scale photoinactivation experiment using cyanobacterial blooms from Taihu Lake, China under natural sunlight with a lower dosage of cercosporin (7.5 μM). This study established the bifunctional mechanisms by which cercosporin inactivates HCBs, opening design possibilities for the development of novel photosensitive algicidal reagents to control HCBs.

Metabolomic Insights of the Effects of Bacterial Algicide IRI-160AA on Dinoflagellate Karlodinium veneficum

Shewanella sp. IRI-160 is an algicidal bacterium that secretes an algicide, IRI-160AA. This algicide specifically targets dinoflagellates, while having no adverse effects on other algal species tested. Dinoflagellates exposed to IRI-160AA exhibited increased production of reactive oxygen species (ROS), DNA damage, and cell cycle arrest, implying a programmed pathway leading to cell death (PCD). Here, a metabolomic analysis was conducted on dinoflagellate Karlodinium veneficum and a control cryptophyte species Rhodomonas exposed to IRI-160AA to investigate the cellular mechanisms behind the physiological effects and the specificity of this algicide. Results of this research supported previous observations about physiological responses to the algicide. A suite of metabolites was identified that increased in the cell pellets of K. veneficum but not in Rhodomonas, including oxidative stress biomarkers, antioxidants, and compounds involved in DNA damage and PCD. Overall, the results of this study illustrated the metabolomic mechanisms underlying the algicidal effects of IRI-160AA on dinoflagellates. This research also provided insights and future directions for studies on the cellular response of dinoflagellates exposed to antagonistic bacteria in the environment.

An optimized CaO2-functionalized alginate bead for simultaneous and efficient removal of phosphorous and harmful cyanobacteria

Simultaneous removal of phosphorus (P) and algae is important to mitigate eutrophication, however, it is rather challenging in remediation of harmful algal blooms (HABs)-contaminated water. In this study, a wet alginate bead functionalized by CaO₂ particle formed layer by layer was prepared with an in-situ method and optimized to remove phosphorous and inhibit algae growth. The stable H₂O₂ release with a concentration level of 0.06 mM was observed for a period of 26 d. The content of peroxy groups (-O-O-) in the optimal bead was 0.44 mmol·g^-1 through permanganate-based titration study. For solution with an initial phosphorous concentration of 10 mg·L^-1, the removal was around 97% in pH 3.0-10.0. XRD, SEM, and XPS studies and kinetic modelings showed that removal of phosphorus was mainly due to formation of insoluble Ca-P compounds in the bead. The CaO₂-functionalized bead inhibited algae growth with an effect lasting over 170 d, which was much better than liquid H₂O₂ and Ca(OH)₂ bead; the phosphorous removal with an efficiency of about 70% was simultaneously obtained. Furthermore, the bead demonstrated to be effective in removing algae in the realistic water from a reservoir. In summary, this study shows that the CaO₂-functionalized material is promising for simultaneous removal of phosphorous and management of HABs.

Synergistic advanced oxidation process for enhanced degradation of organic pollutants in spent sulfuric acid over recoverable apricot shell-derived biochar catalyst

The sulfuric acid-based alkylation process, which leads the industrial application market, still struggles with effectively removing a large number of organic pollutants from hazardous spent sulfuric acid. A synergistic advanced oxidation process was constructed to degrade the organic pollutants with H₂O₂ and sodium persulfate as the synergistic oxidants and apricot shell-derived biochar (OBC) as the catalyst. Taking the total organic carbon (TOC) and the color scale as the indices, the effects of critical experimental factors, i.e., reaction temperature, initial oxidant concentration, catalyst dosage, and aeration rate, were optimized. The results showed that the removal rates of TOC and the color of the spent sulfuric acid reached ∼91% and 96.6%, respectively, after 150 min under the optimum conditions. Besides, the efficient and low-cost OBC catalyst developed in this study could be continuously used for at least four times with about 75% TOC removal and 80% color removal, exhibiting favorable stability and good resistance to acid corrosion. Further study confirmed that the SO₄−˙ and ˙OH radicals generated in the synergistic advanced oxidation process strengthened the degradation and elimination of organic pollutants. The synergistic advanced oxidation process could provide a feasible insight for spent sulfuric acid treatment.

A synergistic advanced oxidation process was constructed to degrade the organic pollutants in spent sulfuric acid with apricot shell-derived biochar as the catalyst. It realized the effect of treating waste with waste.

Mutual impacts and interactions of antibiotic resistance genes, microcystin synthetase genes, graphene oxide, and Microcystis aeruginosa in synthetic wastewater

The physiological impacts and interactions of antibiotic resistance gene (ARG) abundance, microcystin synthetase gene expression, graphene oxide (GO), and Microcystis aeruginosa in synthetic wastewater were investigated. The results demonstrated that the absolute abundance of sul1, sul2, tetW, and tetM in synthetic wastewater dramatically increased to 365.2%, 427.1%, 375.2%, and 231.7%, respectively, when the GO concentration was 0.01 mg/L. Even more interesting is that the sum gene copy numbers of mcyA-J also increased to 243.2%. The appearance of GO made the significant correlation exist between ARGs abundance and mcyA-J expression. Furthermore, M. aeruginosa displayed better photosynthetic performance and more MCs production at 0.01 mg/L GO. There were 65 pairs of positive correlations between the intracellular differential metabolites of M. aeruginosa and the abundance of sul1, sul2, tetM, and tetW with various GO concentrations. The GO will impact the metabolites and metabolic pathway in M. aeruginosa. The metabolic changes impacted the ARGs, microcystin synthetase genes, and physiological characters in algal cells. Furthermore, there were complex correlations among sul1, sul2, tetM, tetW, mcyA-J, MCs, photosynthetic performance parameters, and ROS. The different concentration of GO will aggravate the hazards of M. aeruginosa by promoting the expression of mcyA-J, producing more MCs; simultaneously, it may cause the spread of ARGs.

Microcystis aeruginosa removal by peroxides of hydrogen peroxide, peroxymonosulfate and peroxydisulfate without additional activators

Harmful algal bloom (HAB) is one of the most globally severe challenges in ecological system and water safety. Hydrogen peroxide has been commonly used in the management/treatment. Solid oxidants (e.g., peroxymonosulfate (PMS) and peroxydisulfate (PDS)) may outperform liquid H₂O₂ due to ease in transportation, handling, and applications. However, the information on applications of PMS and PDS in algae treatment is limited. In this study, the two solid peroxides and H₂O₂ were investigated for the removal of the blue-green algae of Microcystis aeruginosa. H₂O₂ and PMS effectively removed algae in 2 d at pH 5.0, 7.0 and 9.0, while PDS was only effective at pH 5.0. The change in pH and the release of dissolved organic carbon were insignificant at 0.2 mM H₂O₂ and PMS. The PMS could degrade microcystin-LR and phycobiliproteins. The studies of phycobiliproteins degradation and scanning electron microscopy indicated that PMS might cause the cell inactivation mainly by damaging the chemical components in algae cell wall and membrane while H₂O₂ might mainly enter the cell to form oxidation pressure to kill algae. The scavenger experiments showed that radicals were not crucial in H₂O₂ and PDS applications. Similarly, the algae removal by PMS was obtained mainly by non-radical pathways; about 77% was direct PMS oxidation and no more than 3% was singlet oxygen-mediated process, while radical pathways of sulfate radical and hydroxyl radical accounted for 18% and 2%, respectively. For the realistic algae-contaminated natural water, the PMS effectively lasted for 60 d, while the H₂O₂ lasted for 12 d. This research work demonstrates that the PMS is promising in control of HAB. The findings can provide some useful design and application parameters of PMS technology for better management/treatment of algae-contaminated water.

Effect of algicidal compound Nω-acetylhistamine on physiological response and algal toxins in Heterosigma akashiwo

The toxic alga Heterosigma akashiwo (Raphidophyceae) is known to form harmful algal blooms (HABs), which can have serious negative effects on the aquatic ecosystem and human life. Previous study has shown that Nω-acetylhistamine (N-AcH), an algicidal compound secreted by algicidal bacteria Bacillus sp. Strain B1, can inhibit the growth of H. akashiwo. In this study, the algicidal mechanism of N-AcH against H. akashiwo was explored, and the changes of toxicity of H. akashiwo treated with N-AcH were investigated. The algal inhibition rate was calculated by the optical density method, and the results showed that the growth inhibition rate of H. akashiwo was about 90% when treated in the medium with 40 μg/mL N-AcH at 96 h. After 72 h treatment, transmission electron microscopy (TEM) showed that the microstructure of H. akashiwo cell was seriously damaged at this concentration. The content of Chlorophyll a and Chlorophyll b decreased while malonaldehyde levels increased, and superoxide dismutase activity first increased and then decreased as well as soluble protein content. GC-MS revealed that the type and content of fatty acids cut down after 48 h and 96 h treatment. Hemolytic test, MTT assay, and micronucleus test all demonstrated the decrease in the toxicity of H. akashiwo treated with 40 μg/mL N-AcH. In brief, N-AcH mainly kills H. akashiwo cell through oxidative stress and can also reduce its toxicity, so it is a promising algicide with the dual functions of killing algae and inhibiting algal toxic effects.

Effects and possible mechanisms of sanguinarine on the competition between Raphidiopsis raciborskii (Cyanophyta) and Scenedesmus obliquus (Chlorophyta): A comparative toxicological study

The phytogenic algicide sanguinarine shows strong inhibitory effects on some bloom-forming cyanobacteria and exhibits great potential in cyanobacterial bloom mitigation. To evaluate the possible ecological effects of sanguinarine on microalgae, the effects and possible mechanisms of sanguinarine on the competition between bloom-forming cyanobacterium Raphidiopsis raciborskii (formerly named Cylindrospermopsis raciborskii) and green alga Scenedesmus obliquus were investigated through co-culture competition test and comparative toxicological study including growth characteristics, chlorophyll fluorescence transients, activities of antioxidant enzymes, and lipid peroxidation. The results of Raphidiopsis-Scenedesmus co-culture competition test showed that sanguinarine decreased the competition ability of R. raciborskii, which benefitted S. obliquus in winning the competition. Toxicological studies have shown that sanguinarine exhibited high inhibitory effects on the growth and photosynthesis of R. raciborskii but no obvious toxicity on S. obliquus at concentrations of no more than 80 μg L^-1. Oxidative damage partially contributed but was not the primary mechanism for the toxicity of sanguinarine on R. raciborskii. The results presented in this study indicate that sanguinarine may be a good algicidal candidate in mitigation of Raphidiopsis-based water bloom.

Catalytic degradation mechanism of sulfamethazine via photosynergy of monoclinic BiVO4and microalgae under visible-light irradiation

To improve the efficiency of antibiotic degradation, the photosynergistic performance of bismuth vanadate (BiVO₄) with a microalga, Dictyosphaerium sp., was demonstrated under visible-light irradiation for the first time. Sulfamethazine (SM2) was selected as a representative sulfanilamide antibiotic, and the photocatalytic degradation mechanism of SM2 was evaluated in media via the BiVO₄-algae system. The hydrothermally synthesized sample was characterized using X-ray powder diffraction, X-ray photoelectron spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, transmission electron microscopy, Brunauer-Emmett-Teller surface area, and Fourier transform infrared spectroscopy techniques. The results demonstrated that the prepared photocatalyst corresponded to phase-pure monoclinic scheelite BiVO₄. The synthesized BiVO₄ showed superior photocatalytic properties under irradiation with visible light, and more than 80% of photocatalytic degradation efficiency was obtained by the BiVO₄-algae system. Based on quenching experiments, the photocatalytic degradation of SM2 in the BiVO₄-algae system was primarily accomplished via the generation of triplet state dissolved organic matter, and hydroxyl radicals played a small role in the degradation process. The direct oxidation of holes made no contribution to the degradation. Metabolomics data showed that a total of 91 metabolites were significantly changed between the two comparison groups (algae-SM2 group vs algae group; algae-BiVO₄-SM2 group vs algae-BiVO₄ group). The glycometabolism pathways were increased and the tricarboxylic acid cycle was activated when BiVO₄ was present. The study provides a distinctive approach to remove antibiotics using visible light in the aqueous environment.

Gut Microbiota: A Key Factor in the Host Health Effects Induced by Pesticide Exposure?

In the past few decades, a large number of pesticides have been widely used for plant protection. Pesticides may enter non-target organisms through multiple ways and bring potential health risks. There is a dense and diverse microbial community in the intestines of mammals, which is called the gut microbiota. The gut microbiota and its metabolites play vital roles in maintaining the health of the host. Interestingly, many studies have shown that exposure to multiple pesticides could affect the gut microbiota of the host. However, the roles of gut microbiota and its related metabolites in the host health effects induced by pesticide exposure of non-target organisms need further study. We reviewed the relationships between pesticide exposure and host health effects as well as between the gut microbiota and host health effects. Importantly, we reviewed the latest research on the gut microbiota and its metabolites in the host health effects induced by pesticide exposure.

Deciphering the mechanism of carbon sources inhibiting recolorization in the removal of refractory dye: Based on an untargeted LC-MS metabolomics approach

In this study, the biological decolorization of reactive black 5 (RB5) by Klebsiella sp. KL-1 in yeast extract (YE) medium was captured the recolorization after exposure to O₂, which induced a 15.82% reduction in decolorization efficiency. Similar result was also observed in YE + lactose medium, but not in YE + glucose/xylose media (groups YE + Glu/Xyl). Through biodegradation studies, several degradation intermediates without quinoid structure were produced in groups YE + Glu/Xyl and differential degradation pathways were deduced in diverse groups. Metabolomics analysis revealed significant variations in up-/down-regulated metabolites using RB5 and different carbon sources. Moreover, the underlying mechanism of recolorization inhibition was proposed. Elevated reducing power associated with variable metabolites (2-hydroxyhexadecanoic acid, 9(R)-HODE cholesteryl ester, linoleamide, oleamide) rendered additional reductive cleavage of C-N bond on naphthalene ring. This study provided a new orientation to inhibit recolorization and deepened the understanding of the molecular mechanism of carbon sources inhibiting recolorization in the removal of refractory dyes.

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.

Lomatogonium Rotatum for Treatment of Acute Liver Injury in Mice: A Metabolomics Study

Lomatogonium rotatum (L.) Fries ex Nym (LR) is used as a traditional Mongolian medicine to treat liver and bile diseases. This study aimed to investigate the hepatoprotective effect of LR on mice with CCl₄-induced acute liver injury through conventional assays and metabolomics analysis. This study consisted of male mice (n = 23) in four groups (i.e., control, model, positive control, and LR). The extract of whole plant of LR was used to treat mice in the LR group. Biochemical and histological assays (i.e., serum levels of alanine transaminase (ALT) and aspartate transaminase (AST), and histological changes of liver tissue) were used to evaluate LR efficacy, and metabolomics analysis based on GC-MS and LC-MS was conducted to reveal metabolic changes. The conventional analysis and metabolomic profiles both suggested that LR treatment could protect mice against CCl₄-induced acute liver injury. The affected metabolic pathways included linoleic acid metabolism, α-linolenic acid metabolism, arachidonic acid metabolism, CoA biosynthesis, glycerophospholipid metabolism, the TCA cycle, and purine metabolism. This study identified eight metabolites, including phosphopantothenic acid, succinic acid, AMP, choline, glycerol 3-phosphate, linoleic acid, arachidonic acid, and DHA, as potential biomarkers for evaluating hepatoprotective effect of LR. This metabolomics study may shed light on possible mechanisms of hepatoprotective effect of LR.

The response of Microcystis aeruginosa strain MGK to a single or two consecutive H2 O2 applications

Various approaches have been proposed to control/eliminate toxic Microcystis sp. blooms including H₂ O₂ treatments. Earlier studies showed that pre-exposure of various algae to oxidative stress induced massive cell death when cultures were exposed to an additional H₂ O₂ treatment. We examined the vulnerability of exponential and stationary-phase Microcystis sp. strain MGK cultures to single and double H₂ O₂ applications. Stationary cultures show a much higher ability to decompose H₂ O₂ than younger cultures. Nevertheless, they are more sensitive to an additional H₂ O₂ dose given 1-6 h after the first one. Transcript analyses following H₂ O₂ application showed a fast rise in glutathione peroxidase abundance (227-fold within an hour) followed by a steep decline thereafter. Other genes potentially engaged in oxidative stress were far less affected. Metabolic-related genes were downregulated after H₂ O₂ treatments. Among those examined, the transcript level of prk (encoding phosphoribulose kinase) was the slowest to recover in agreement with the decline in photosynthetic rate revealed by fluorescence measurements. Our findings shed light on the response of Microcystis MGK to oxidative stress suggesting that two consecutive H₂ O₂ applications of low concentrations are far more effective in controlling Microcystis sp. population than a single dose of a higher concentration.

Comparing effects of berberine on the growth and photosynthetic activities of Microcystis aeruginosa and Chlorella pyrenoidosa

Berberine is a potent algicidal allelochemical of Microcystis aeruginosa. To optimize its application in the control of Microcystis blooms, the effects of berberine on the growth and photosynthetic activities of M. aeruginosa and a non-target green alga, Chlorella pyrenoidosa, were compared. The results showed that the algicidal activity of berberine on M. aeruginosa was light dependent. Berberine had no algicidal effects on C. pyrenoidosa with or without light exposure. Under light-dark conditions, berberine significantly decreased the chlorophyll fluorescence parameters in M. aeruginosa while no significant berberine-induced changes were observed under constant darkness. Significant reductions of photosystem II (PSII) and whole chain electron transport activities in M. aeruginosa exposed to berberine suggested that PSII was the important target site attacked by berberine. Contrary to M. aeruginosa, no berberine-induced inhibition in photosynthesis activities were observed in C. pyrenoidosa. The differences in photosynthetic apparatuses of these two algae might be responsible for their different sensitivities to berberine.