Inhibitory effect and mechanism of linoleic acid sustained-release microspheres on Microcystis aeruginosa at different growth phases

Warfare under the waves: a review of bacteria-derived algaecidal natural products

Covering: 1960s to 2024Harmful algal blooms pose a major threat to aquatic ecosystems and can impact human health. The frequency and intensity of these blooms has increased over recent decades, driven primarily by climate change and an increase in nutrient runoff. Algal blooms often produce toxins that contaminate water sources, disrupt fisheries, and harm human health. These blooms may also result in oxygen-deprived environments leading to mass fish deaths that threaten the survival of other aquatic life. In freshwater and estuarine ecosystems, traditional chemical strategies to mitigate algal blooms include the use of herbicides, metal salts, or oxidants. Though effective, these agents are non-selective, toxic to other species, and cause loss of biodiversity. They can persist in ecosystems, contaminating the food web and providing an impetus for cost-effective, targeted algal-control methods that protect ecosystems. In marine ecosystems, harmful algal blooms are even more challenging to treat due to the lack of scalable solutions and the challenge of dispersal of algal control agents in open ocean settings. Natural products derived from algae-bacteria interactions have led to the evolution of diverse bacteria-derived algaecidal natural products, which are highly potent, species specific and have potential for combating harmful algal blooms. They provide valuable starting points for the development of eco-friendly algae control methods. This review provides a comprehensive overview of all bacterial algaecides and their activities, categorized into two major groups: (1) algaecides produced in ecologically significant associations between bacteria and algae, and (2) algaecides with potentially coincidental activity but without an ecological role in specific bacteria-algae interactions. This review contributes to a better understanding of the chemical ecology of parasitic algal-bacterial interactions, "the warfare under the waves", and highlights the potential applications of bacteria-derived algaecides to provide solutions to harmful algal blooms.

Prolonged Microcystis restraint through allelochemicals sustained-release microspheres regulated by carbon material (CM-AC@SM): Optimal formulation, characterization, effects and synergistic inhibition mechanisms

The Microcystis blooms have caused serious damage to aquatic ecosystems. Microspheres containing allelochemicals with sustained-release properties have the potential to function as a cost-effective and environmentally friendly algaecide against M. aeruginosa. In the current investigation, we successfully optimized the synthesis of allelochemicals sustained-release microspheres regulated by carbon material (CM-AC@SM), which demonstrated a high embedding rate (90.17 %) and loading rate (0.65 %), with an accumulative release rate of 53.27 % on day 30. To investigate the sustained-release mechanism of CM-AC@SM, the sustained-release process of allelochemicals was determined using the Folin-Phenol method and the immersion behavior of the CM-AC@SM was characterized through SEM and XPS. Results showed that allelochemicals were released in the delayed-dissolution mode. In addition, to elucidate the synergistic mechanism of CM-AC@SM towards the inhibition of M. aeruginosa, this study comprehensively assessed the effects of allelochemicals, carbon material and CM-AC@SM on the morphology, antioxidant system activity and photosynthetic activity of M. aeruginosa. The findings indicated that allelochemicals and carbon material induced intracellular protein and nucleic acid leakage by increasing cell membrane permeability, disrupted the extracellular and intracellular morphology of algae, triggered peroxidative damage and restrained antioxidant system activity by stimulating the generation of reactive oxygen species. Simultaneously, the activity of photosystem II was inhibited by allelochemicals and carbon material, substantiated by the reduction in Fv/Fo and Fv/Fm ratios. Hence, CM-AC@SM shows promise in inhibiting M. aeruginosa, offering an efficient approach for the future large-scale control of harmful algal blooms (HABs).

Differential allelopathic effects of mangrove plants Kandelia obovata and Aegiceras corniculatum on harmful algal species: Potential applications in algal bloom control

This study examined effects of mangrove plants Kandelia obovata and Aegiceras corniculatum on harmful algal species. While A. corniculatum leaf extract had no inhibitory effect, K. obovata leaf extract significantly inhibited the growth of two harmful algal species Alexandrium tamarense and Karenia mikimotoi. The inhibitory effect was concentration-dependent, with over 90 % inhibition at the highest concentration. Morphological changes and cell size reduction were observed in both microalgae. Excessive production of reactive oxygen species and damage to algal photosynthetic system were found. The allelopathic effect of K. obovata on K. mikimotoi with low-concentration repeated exposure was more effective than high-concentration single exposure. The EC50 of K. obovata (0.33 g L-1) was lower than reported values on other coastal plants. Higher inhibitory effects of K. obovata were found on naked algal species than the armoured ones. These findings suggest potential applications of K. obovata leaf extract in controlling harmful algal blooms.

Ecotoxicological assessment, in freshwater environment, of wastewater sludge coupled and uncoupled with micro-polyvinyl chloride on algae and water fleas

In the frame of bioeconomy and circular economy, wastewater sludge (WS) could be a good candidate for its use in agriculture as fertilizer, due to its high content of organic matter, N and P, but on the other hand, it is full of toxicants such as heavy metal, microplastics, detergent, antibiotics, and so on that can reach groundwater and water bodies in leachate form. In this study, we have investigated different sludge concentrations in the eluate form, combined and not with PVC on two different freshwater organisms Selenastrum capricornutum and Daphnia magna, using ecotoxicity tests. At the endpoint, we have evaluated inhibition growth rate, oxidative stress, and pigments production for S. capricornutum, while in case of D. magna, we have assessed organism immobilization and development. From our results, it emerged that at the higher WS concentration, there was not inhibition growth rate, while at oxidative stress, it was higher in algae treated with WS and PVC. Higher Chl-a production was shown for algae treated with 0.3 g/L of sludge coupled with PVC, where higher phaeopigments production were recorded for algae treated with 0.3 g/L of WS. D. magna has shown an opposite trend when compared with algae, where at the highest WS concentrations supplied was corresponding to an increased mortality explaned as the highest immobility percentage. PRACTITIONER POINTS: Wastewater sludge is used in agriculture as fertilizer. PVC microplastic presence and associate ecotoxicity was tested. PVC presence increased oxidative stress in S. capricornutum. D. magna was significantly affected by sludge concentrations supplied.

Control of Microcystis aeruginosa by Daphnia: Experimental evidence and identification of involved infochemicals

Infochemicals refer to chemicals responsible for information exchange between organisms. We evaluated the effects of Daphnia magna and Daphnia galeata infochemicals on Microcystis aeruginosa for 15d. The Daphnia infochemicals were obtained from spent medium after culturing Daphnia in Elendt M4 medium for 48 h. Both Daphnia infochemicals significantly increased (p < 0.05) the intracellular reactive oxygen species level and microcystin-LR concentration in M. aeruginosa. This cellular effect increased colony formation of M. aeruginosa, thereby inhibiting the growth of M. aeruginosa. D. galeata infochemicals provoked significantly greater (p < 0.05) adverse effects on M. aeruginosa than those of D. magna infochemicals, which were further exaggerated by pre-exposure of Daphnia to M. aeruginosa. This result seems to be related to the different compositions and concentrations of Daphnia infochemicals. Several Daphnia infochemicals, such as methyl ferulate, cyclohexanone, 3, 5-dimethyl, hexanedioic acid, and bis(2-ethylhexyl) ester, showed a high correlation with M. aeruginosa cell concentration (|r | >0.6), suggesting that they may play a key role in controlling harmful cyanobacteria. Additionally, pre-exposure of D. magna and D. galeata to M. aeruginosa produced oleic acid, methyl ester, and n-hexadecanoic acid, with a highly correlation with M. aeruginosa cell concentration (|r | >0.6). p-tolyl acetate and linoleic acid were detected only in the pre-exposed D. galeata infochemicals. These findings suggest that some of Daphnia infochemicals identified in this study can be a promising tool to control M. aeruginosa growth. However, further studies are required to verify the specific actions of these infochemicals against cyanobacteria.

Allelochemicals of Alexandrium tamarense and its algicidal mechanism for Prorocentrum donghaiense and Heterosigma akashiwo

The effects of culture filtrate of Alexandrium tamarense on Prorocentrum donghaiense and Heterosigma akashiwo were investigated, including determination of algal density, photosynthesis, intracellular enzyme content and activity. The filtrate of A. tamarense had a stronger inhibitory effect on P. donghaiense than H. akashiwo, and the inhibitory effect decreased with higher temperature treatment of the filtrate. Instantaneous fluorescence (Ft) and maximum quantum yield of photosystem II (Fv/Fm) values of both kinds of target algae were reduced as exposed to the filtrate of A. tamarense, which proved that allelopathy could inhibit the normal operation of photosynthetic system. The increase of Malondialdehyde (MDA) content of the two kinds of target algae indicated that the cell membrane was seriously damaged by allelochemicals released by A. tamarense. The different responses of Superoxide Dismutase (SOD) and Catalase (CAT) activity in two kinds of target algae demonstrated the complexity and diversity of allelopathic mechanism. The filtrate of A. tamarense also influenced the metabolic function (ATPases) of P. donghaiense and H. akashiwo, and the influence on P. donghaiense was greater. Liquid-liquid extraction was used to extract and isolate allelochemicals from the filtrate of A. tamarense. It was found that only component I with molecular weight of 424.2573 and 434.2857 could inhibit the growth of P. donghaiense by HPLC-MS.

Effect of surfactant's charge properties on behavior, physiology, and biochemistry and the release of microcystins of Microcystis aeruginosa

Surfactant pollution is escalatitheng in eutrophic waters, but the effect of surfactant charge properties on the physiological and biochemical properties of toxin-producing microalgae remains inadequately explored. To address this gap, this study explores the effects and mechanisms of three common surfactants-cetyltrimethylammonium bromide (CTAB, cationic), sodium dodecyl sulfate (SDS, anionic), and Triton X-100 (nonionic)-found in surface waters, on the agglomeration behavior, physiological indicators, and Microcystin-LR (MC-LR) release of Microcystis aeruginosa (M. aeruginosa) by using UV-visible spectroscope, Malvern Zetasizer, fluorescence spectrometer, etc. Results suggest that charge properties significantly affect cyanobacterial aggregation and cellular metabolism. The CTAB-treated group demonstrates a ∼5.74 and ∼9.74 times higher aggregation effect compared to Triton X-100 and SDS (300 mg/L for 180 min) due to strong electrostatic attraction. Triton X-100 outperforms CTAB and SDS in polysaccharide extraction, attributed to its higher water solubility and lower critical micelle concentration. CTAB stimulates cyanobacteria to secrete proteins, xanthohumic acid, and humic acids to maintain normal physiological cells. Additionally, the results of SEM and ion content showed that CTAB damages the cell membrane, resulting in a ∼90% increase in the release of intracellular MC-LR without cell disintegration. Ionic analyses confirm that all three surfactants alter cell membrane permeability and disrupt ionic metabolic pathways in microalgae. This study highlights the relationship between the surface charge properties of typical surfactants and the dispersion/agglomeration behavior of cyanobacteria. It provides insights into the impact mechanism of exogenous surfactants on toxic algae production in eutrophic water bodies, offering theoretical references for managing surfactant pollution and treating algae blooms.

Physiological and molecular mechanisms of the inhibitory effects of artemisinin on Microcystis aeruginosa and Chlorella pyrenoidosa

Artemisinin, a novel plant allelochemical, has attracted attention for its potential selective inhibitory effects on algae, yet to be fully explored. This study compares the sensitivity and action targets of Microcystis aeruginosa (M. aeruginosa) and Chlorella pyrenoidosa (C. pyrenoidosa) to artemisinin algaecide (AMA), highlighting their differences. Results indicate that at high concentrations, AMA displaces the natural PQ at the QB binding site within M. aeruginosa photosynthetic system, impairing the D1 protein repair function. Furthermore, AMA disrupts electron transfer from reduced ferredoxin (Fd) to NADP+ by interfering with the iron-sulfur clusters in the ferredoxin-NADP+ reductases (FNR) domain of Fd. Moreover, significant reactive oxygen species (ROS) accumulation triggers oxidative stress and interrupts the tricarboxylic acid cycle, hindering energy acquisition. Notably, AMA suppresses arginine synthesis in M. aeruginosa, leading to reduced microcystins (MCs) release. Conversely, C. pyrenoidosa counters ROS accumulation via photosynthesis protection, antioxidant defenses, and by regulating intracellular osmotic pressure, accelerating damaged protein degradation, and effectively repairing DNA for cellular detoxification. Additionally, AMA stimulates the expression of DNA replication-related genes, facilitating cell proliferation. Our finding offer a unique approach for selectively eradicating cyanobacteria while preserving beneficial algae, and shed new light on employing eco-friendly algicides with high specificity.

Changes in physiology, antioxidant system, and gene expression in Microcystis aeruginosa under fenoxaprop-p-ethyl stress

Fenoxaprop-p-ethyl (FE) is one of the typical aryloxyphenoxypropionate herbicides. FE has been widely applied in agriculture in recent years. Human health and aquatic ecosystems are threatened by the cyanobacteria blooms caused by Microcystis aeruginosa, which is one of the most common cyanobacteria responsible for freshwater blooming. Few studies have been reported on the physiological effects of FE on M. aeruginosa. This study analyzed the growth curves, the contents of chlorophyll a and protein, the oxidative stress, and the microcystin-LR (MC-LR) levels of M. aeruginosa exposed to various FE concentrations (i.e., 0, 0.5, 1, 2, and 5 mg/L). FE was observed to stimulate the cell density, chlorophyll a content, and protein content of M. aeruginosa at 0.5- and 1-mg/L FE concentrations but inhibit them at 2 and 5 mg/L FE concentrations. The superoxide dismutase and catalase activities were enhanced and the malondialdehyde concentration was increased by FE. The intracellular (intra-) and extracellular (extra-) MC-LR contents were also affected by FE. The expression levels of photosynthesis-related genes psbD1, psaB, and rbcL varied in response to FE exposure. Moreover, the expressions of microcystin synthase-related genes mcyA and mcyD and microcystin transportation-related gene mcyH were significantly inhibited by the treatment with 2 and 5 mg/L FE concentrations. These results might be helpful in evaluating the ecotoxicity of FE and guiding the rational application of herbicides in modern agriculture.

Single and combined toxic effects of nCu and nSiO2 on Dunaliella salina

There are many studies on the toxic effects of single nanoparticles on microalgae; however, many types of nanoparticles are present in the ocean, and more studies on the combined toxic effects of multiple nanoparticles on microalgae are needed. The single and combined toxic effects of nCu and nSiO2 on Dunaliella salina were investigated through changes in instantaneous fluorescence rate (Ft) and antioxidant parameters during 96-h growth inhibition tests. It was found that the toxic effect of nCu on D. salina was greater than that of nSiO2, and both showed time and were dose-dependent with the greatest growth inhibition at 96 h. A total of 0.5 mg/L nCu somewhat promoted the growth of microalgae, but 4.5 and 5.5 mg/L nCu showed negative growth effects on microalgae. The Ft of D. salina was also inhibited by increasing concentrations of nanoparticles and exposure time. nCu suppressed the synthesis of TP and elevated the MDA content of D. salina, which indicated the lipid peroxidation of algal cells. The activities of SOD and CAT showed a trend of increasing and then decreasing with the increase of nCu concentration, suggesting that the enzyme activity first increased and then decreased. The toxic effect of a high concentration of nCu was reduced after the addition of nSiO2. SEM and EDS images showed that nSiO2 could adsorb nCu in seawater. nSiO2 also adsorbed Cu2+ in the cultures, thus reducing the toxic effect of nCu on D. salina to a certain extent. TEM image was used to observe the morphology of algal cells exposed to nCu.

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.

"Needle" hidden in silk floss: Inactivation effect and mechanism of melamine sponge loaded bismuth oxide composite copper-metal organic framework (MS/Bi2O3@Cu-MOF) as floating photocatalyst on Microcystis aeruginosa

Photocatalytic technology showed significant potential for addressing the issue of cyanobacterial blooms resulting from eutrophication in bodies of water. However, the traditional powder materials were easy to agglomerate and settle, which led to the decrease of photocatalytic activity. The emergence of floating photocatalyst was important for the practical application of controlling harmful algal blooms. This study was based on the efficient powder photocatalyst bismuth oxide composite copper-metal organic framework (Bi2O3 @Cu-MOF), which was successfully loaded onto melamine sponge (MS) by sodium alginate immobilization to prepare a floating photocatalyst MS/Bi2O3 @Cu-MOF for the inactivation of Microcystis aeruginosa (M. aeruginosa) under visible light. When the capacity was 0.4 g (CA0.4), MS/Bi2O3 @Cu-MOF showed good photocatalytic activity, and the inactivation rate of M. aeruginosa reached 74.462% after 120 h. MS/Bi2O3 @Cu-MOF-CA0.4 showed a large specific surface area of 30.490 m2/g and an average pore size of 22.862 nm, belonging to mesoporous materials. After 120 h of treatment, the content of soluble protein in the MS/Bi2O3 @Cu-MOF-CA0.4 treatment group decreased to 0.365 mg/L, the content of chlorophyll a (chla) was 0.023 mg/L, the content of malondialdehyde (MDA) increased to 3.168 nmol/mgprot, and the contents of various antioxidant enzymes experienced drastic changes, first increasing and then decreasing. The photocatalytic process generated·OH and·O2-, which played key role in inactivating the algae cells. Additionally, the release of Cu2+ and adsorption of the material also contributed to the process.

A contrast of emerging contaminants rac- and l-menthol toxicities to Microcystis aeruginosa through biochemical, physiological, and morphological investigations

Fragrances rac- and l-menthol extracted from peppermint are widely used and considered as emerging contaminants recently, which are persistent in the environment. Menthol has always been considered as a safe chemical for humans, but its potential adverse ecological effects on aquatic organisms and the toxic mechanisms have not yet been fully understood. The present study aims to investigate the physiological response of Microcystis aeruginosa after exposure to the two menthol isomers, and to explore the toxic mechanisms and ecological risks of these two chemicals. Results showed that rac-menthol exhibited a hormesis effect on the cell growth, chlorophyll a and protein contents; while l-menthol showed an inhibition effect. Adenosine triphosphate (ATP) content increased significantly at day 3 and then decreased markedly at day 6 after exposure to the two chemicals. Compared with rac-menthol, l-menthol can cause damage to the antioxidant system and plasmalemma more severely, promote the production and release of microcystins-LR (MC-LR) more dramatically, upregulate the expression of MC-transportation-related gene mcyH, and induce higher apoptosis rates. Overall results revealed that the toxic effects of l-menthol on cyanobacteria were significantly greater than those of rac-menthol. The significant increase in the malondialdehyde (MDA) content and the ultrastructural characteristics of the cells indicated that the plasma membranes were damaged. Thus, further attention should be paid to the scientific use, ecological and environmental risk assessment of chiral menthol. This study will also provide a scientific basis for future water quality criteria establishment on emerging contaminants such as fragrances.

Aquatic plant allelochemicals inhibit the growth of microalgae and cyanobacteria in aquatic environments

Excess nitrogen and phosphorus nutrients in the aquatic environment result in the growth of algal cells and water eutrophication, which adversely affect the aquatic environment and human health. Therefore, discovering a safe and efficient algae suppression method is necessary to ensure the ecological safety of water. Recently, the allelopathic effects of aquatic plants on algae have attracted extensive attention from researchers. This review demonstrates the current research hotspot of allelopathic algal inhibition in aquatic plants and lists the common aquatic plant species and allelochemicals. In addition, the inhibition mechanism of allelochemicals from aquatic plants on algae is systematically discussed. Moreover, the key factors affecting the inhibition of allelopathy in algae, such as pH, temperature, algal cell density, and concentration of allelochemicals, are summarized. The present utilization modes of allelochemicals on algae are also presented. Finally, the problems existing in the study of allelopathic algal inhibition of aquatic plants are highlighted, and suggestions for further research are proposed.

Effects of dissolved organic matter from sediment and soil samples on the growth and physiology of four bloom-forming algal species

Algal blooms negatively impact the water quality of reservoirs; however, the role of dissolved organic matter (DOM) in bloom formation in reservoirs has not been investigated. Therefore, we assessed the compositions of sediment- and soil-derived DOM and their effects on the growth, physiology, and photosynthetic activity of Microcystis aeruginosa, Anabaena sp., Chlamydomonas sp., and Peridiniopsis sp. (bloom-forming species). Sediment DOM promoted the growth of all algal species, whereas soil DOM significantly promoted the growth of Chlamydomonas sp. and Peridiniopsis sp.; this effect was due to enhanced stress tolerance and photosynthetic efficiency exhibited by these algae under DOM treatment. However, soil DOM slightly inhibited the growth of Anabaena sp. by increasing reactive oxygen species levels and inactivating some photosystem II reaction centers. The tyrosine-like substance, humic acid-like substances, and unsaturated aliphatic compounds were the main DOM components that affected algal growth. The findings of this study will provide a theoretical foundation for the development of bloom-prevention strategies for river-type reservoirs.

Natural Algaecide Sphingosines Identified in Hybrid Straw Decomposition Driven by White-Rot Fungi

Harmful algal blooms (HABs), which are promoted by eutrophication and intensified by global warming, occur worldwide. Allelochemicals, which are natural chemicals derived from plants or microbes, are emerging weapons to eliminate these blooms. However, the cost and technical challenges have limited the discovery of novel antialgal allelochemicals. Herein, the decomposition of agricultural straws is manipulated by white-rot fungi and achieved elevated antialgal efficiency. The transcriptomic analysis reveals that nutrient limitation activated fungal decomposition. By using a comparative nontarget metabolomics approach, a new type of allelochemical sphingosines (including sphinganine, phytosphingosine, sphingosine, and N-acetylsphingosine) is identified. These novel natural algaecides exhibit superior antialgal capability, with as high as an order of magnitude lower effective concentration on blooming species than other prevalent allelochemicals. The co-expression relationship between transcriptomic and metabolomic results indicate that sphinganine is strongly correlated with the differentially expressed lignocellulose degradation unigenes. The algal growth suppression is triggered by the activation of programmed cell death, malfunction of algal photosystem and antioxidant system, the disruption on CO2 assimilation and light absorption. The sphingosines reported here are a new category of allelochemicals in addition to the well-known antialgal natural chemicals, which are potential species-specific agents for HABs control identified by multi-omics methodology.

Characterization of a Novel Artemisinin Algicidal Particle and Its Inhibitory Effect on Microcystis aeruginosa

A new artemisinin sustained-release particle (ASP) was developed that significantly inhibits Microcystis aeruginosa (M. aeruginosa) growth. The physical and chemical properties of ASPs were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), differential scanning calorimetry, and thermogravimetry (DSC-TG). The results demonstrated that ASPs are thermally stable and have sustained-release properties. On the sixth day, the ASPs (0.2 g L^-1) inhibited M. aeruginosa with an inhibition rate (IR) greater than 70%. Additionally, ASPs inhibited M. aeruginosa without increasing microcystin-LR release (MC-LR). This research offers a novel approach to the management of cyanobacterial blooms.

Metabolites and metabolic pathways associated with allelochemical effects of linoleic acid on Karenia mikimotoi

Linoleic acid (LA) shows great potential in inhibiting the growth of multiple red tide microalgae by disturbing algal physio-biochemical processes. However, our knowledge on the mechanisms of algal mortality at metabolic level remains limited. Herein, the response of K. mikimotoi to LA was evaluated using metabolomics, stable isotope techniques (SIT), and physiological indicators. Results showed that 100 μg/L LA promoted the growth of K. mikimotoi, which was significantly inhibited by 500 μg/L LA, along with a significant reduction of photosynthetic pigments and a significant increase of reactive oxygen species (ROS). SIT showed that LA entered algal cells, and 56 isotopologues involved in ferroptosis, carotenoid biosynthesis, and porphyrin metabolism were identified. Non-targeted metabolomics identified 90 and 111 differential metabolites (DEMs) belonging to 11 metabolic pathways under the 500 μg/L and 100 μg/L LA exposure, respectively. Among them, 34 DEMs were detected by SIT. Metabolic pathway analysis showed that 500 μg/L LA significantly promoted ferroptosis, and significantly inhibited carotenoid biosynthesis, porphyrin metabolism, sphingolipid metabolism, and lipopolysaccharide biosynthesis, presenting changes opposite to those observed in 100 μg/L LA-treated K. mikimotoi. Overall, this study revealed the metabolic response of K. mikimotoi to LA, enriching our understanding on the allelochemical mechanism of LA on K. mikimotoi.

An innovative strategy to control Microcystis growth using tea polyphenols sustained-release particles: preparation, characterization, and inhibition mechanism

Allelochemicals have been shown to inhibit cyanobacterial blooms for several years. In view of the disadvantages of "direct-added" mode, natural and pollution-free tea polyphenolic allelochemicals with good inhibitory effect on cyanobacteria were selected to prepare sustained-release particles by microcapsule technology. Results showed that the encapsulation efficiency of tea polyphenols sustained-release particles (TPSPs) was 50.6% and the particle size ranged from 700 to 970 nm, which reached the nanoscale under optimum preparation condition. Physical and chemical properties of TPSPs were characterized to prove that tea polyphenols were well encapsulated and the particles had good thermal stability. The optimal dosage of TPSPs was determined to be 0.3 g/L, at which the inhibition rate on Microcystis aeruginosa in logarithmic growth period could be maintained above 95%. Simultaneous decrease in algal density and chlorophyll-a content indicated that the photosynthesis of algal cells was affected leading to cell death. Significant changes of antioxidant enzyme activities suggested that Microcystis aeruginosa's antioxidant systems had been disrupted. Furthermore, TPSPs increased the concentration of O^2- which led to lipid peroxidation of cell membrane and a subsequent increase in malondialdehyde (MDA) content. Meanwhile, the protein content, nucleic acid content, and electrical conductivity in culture medium rose significantly indicating the cell membrane was irreversibly damaged. This work can provide a basis for the utilization of environmentally friendly algal suppressants.

Inhibitory effect and mechanism of a compound essential oils on Cladophora glomerata

Cladophora glomerata (C. glomerata) is a typical macroalgae inducing green tide and affecting economic benefits in aquaculture. A high-efficiency, environment friendly compound essential oils (CEOs) was provided to control C. glomerata blooms. The inhibition effect of CEOs against C. glomerata was assessed through the growth, cellular morphology and the physiological and biochemical indexes of C. glomerata. Results of the Chl-a content indicated that 300 μL/L CEOs could significantly inhibited the growth (85 % ± 2 %) of C. glomerata on the 11th day; the damage degree of algal thallus can be observed based on the results of cell morphology; the results of the physiological and biochemical indicators presented the decreased photosynthetic capacity, the dysfunction of antioxidant system and the algal apoptosis gene caspase- 8, 9, 3 activated when C. glomerata exposed to CEOs. This study elucidated the effect and mechanism of CEOs control the green tide induced by C. glomerata.

Integrated transcriptomic and metabolomic analysis of Microcystis aeruginosa exposed to artemisinin sustained-release microspheres

Artemisinin sustained-release microspheres (ASMs) have been shown to inhibit Microcystis aeruginosa (M. aeruginosa) blooms. Previous studies have focused on inhibitory mechanism of ASMs on the physiological level of M. aeruginosa, but the algal inhibitory mechanism of ASMs has not been comprehensively and profoundly revealed. The study proposed to reveal the toxicity mechanism of ASMs on M. aeruginosa based on transcriptomics and metabolomics. After exposure to 0.2 g·L^-1 ASMs for 7 days, M. aeruginosa biomass was significantly inhibited, with an inhibition rate (IR) of 47 % on day 7. Transcriptomic and metabolomic results showed that: (1) 478 differentially expressed genes (DEGs) and 251 differential metabolites (DMs) were obtained; (2) ASMs inhibited photosynthesis by blocking photosynthetic pigment synthesis, destroying photoreaction centers and photosynthetic carbon reactions; (3) ASMs reduced L-glutamic acid content and blocked glutathione (GSH) synthesis, leading to an imbalance in the antioxidant system; (4) ASM disrupted nitrogen metabolism and the hindered synthesis of various amino acids; (5) ASMs inhibited glyoxylate cycle and TCA cycle. This study provides an important prerequisite for the practical application of ASMs and a new perspective for the management of harmful algal blooms (HABs).

Response of cytotoxin production ability to gene expression and cell molecular structure of Microcystis aeruginosa FACHB-905

To investigate the inhibitory mechanism of artemisinin sustained-release microspheres (ASMs) on Microcystis aeruginosa (M. aeruginosa) from the molecular level, prx, psbA, fabZ, and mcyD were studied, and the cell death mode were also explored. The results showed that expression of prx was slightly up-regulated, while the expression of psbA, fabZ, and mcyD was significantly reduced. It can infer that oxidant damage and photic damage are the main mechanisms for the algicidal effect of ASMs on M. aeruginosa. It can be seen from the changes in cell morphology and structure that microspheres stress triggers apoptosis-like cell death, and the cell membrane is intact effectively preventing the leakage of microcystin-LR (MC-LR). Moreover, the down-regulation of mcyD gene also played major role in less extracellular MC-LR than intracellular MC-LR. It was concluded that the ASMs will not cause secondary ecological hazards while killing algae cells and have good application prospects.

Toxicity effects of microplastics and nanoplastics with cadmium on the alga Microcystis aeruginosa

The extensive spread of microplastics (MPs) and nanoplastics (NPs) in the aquatic environment has attracted widespread attention. The toxicity of cadmium (Cd) combined with microplastics (MPs) and nanoplastics (NPs) toward freshwater algae Microcystis aeruginosa (M. aeruginosa) was investigated to evaluate the environmental behavior of the Cd complexation in fresh water. Cd alone has the highest toxicity to algae. Both MPs and NPs also have a negative effect on the growth of algae as individual components due to their adsorption of nutrients and disruption of the alga's activity in a single MPs/NPs system. Compared with the single system, the toxicity of compound pollution including MPs + Cd and NPs + Cd becomes stronger, which presents a synergistic effect. In the presence of NPs, more extracellular polymeric substances (EPS) appeared, which helped to reduce the toxic effect on the algal cells. Moreover, MPs/NPs + Cd stimulate the production of microcystin-LR (MC-LR) under different treatments. Overall, the aquatic environmental assessment shows potentially elevated risks associated with combined MPs/NPs with Cd, which should be considered.

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.

Acute effects of three surface-modified nanoplastics against Microcystis aeruginosa: Growth, microcystin production, and mechanisms

As plastic pollution continues to increase and plastic waste is shredded to form smaller plastic particles, there is growing concern about the potential impact of nanoplastics (NPs) on freshwater ecosystems. In this work, the effects of three surface-modified NPs, including polystyrene (PS), PS-NH₂, and PS-COOH, on the growth, photosynthetic activity, oxidative damage, and microcystins (MCs) production/release of Microcystis aeruginosa (M. aeruginosa) were investigated. Results indicated that all three NPs significantly inhibited the growth of M. aeruginosa after a 96 h exposure, and the growth inhibition followed the order of PS-NH₂ > PS > PS-COOH (p < 0.05). Meanwhile, all three NPs at the concentration of 100 mg/L significantly increased the content of intra-MCs (115 %, 147 %, and 121 % higher than the control, respectively) and extra-MCs (142 %, 175 %, and 151 % higher than the control, respectively) after a 96 h exposure (p < 0.05). Moreover, our findings also suggested that the potential mechanisms of surface-modified PS NPs on M. aeruginosa growth and MCs production/release were associated with physical constraints, photosynthetic activity obstruct, and oxidative damage. Our findings provided direct evidence for different kinds of surface modifications of PS NPs on freshwater algae and improve the understanding of the potential risk of NPs in aquatic ecosystems.

Experimental study on effects of prometryn exposure scenarios on Microcystis aeruginosa growth and N and P concentrations

Single exposure toxicity tests of herbicides like prometryn are commonly applied in studying ecological and environmental issues, but they are more likely exposed to microalgae through multiple applications of irrigation and water flow. The toxicity of prometryn towards Microcystis aeruginosa (M. aeruginosa) at different growth stages (different exposure period) was determined by single and multiple exposures (different exposure mode) through 39-day batch-experiment comparison study. Inhibition rates showed that M. aeruginosa growth was greatly inhibited by exposure to prometryn in a final concentration of 80 and 160 μg·L^-1 (p < 0.05). Specifically, with the same prometryn exposure periods (lag or exponential phase) and concentrations, a single exposure displayed larger toxicity on M. aeruginosa than repetitive additions of prometryn in general according to inhibition rates. Moreover, with the same prometryn exposure modes and concentrations, inhibitory effect was higher with prometryn exposure in lag phase than that in exponential phase according to M. aeruginosa densities and inhibition rates. In general, variations of total dissolved phosphorus (TDP) and total dissolved nitrogen (TDN) with time responded negatively to M. aeruginosa growth, and added prometryn inhibits the utilization rate of both P and N. Logistic function was well used to describe algae densities (R² = 0.979 ~ 0.995), growth rates (R² = 0.515 ~ 0.731), specific growth rates (R² = 0.301 ~ 0.648) and inhibition rates (R² = 0.357 ~ 0.946) along with its combination with Monod function. In addition, results showed that shifts of limiting nutrients could be prompted by not only M. aeruginosa growth but also prometryn exposure scenarios. This study provides a basis for studying the potential harm of prometryn to the ecological environment.

Enantioselective effects of chiral fragrance carvone (L- and D-carvone) on the physiology, oxidative damage, synthesis, and release of microcystin-LR in Microcystis aeruginosa

Carvone is a widely used chiral fragrance with two isomers (L-carvone and D-carvone). D-carvone smells like a caraway, whereas L-carvone smells like mint. Carvone imposes a potential burden on the aquatic ecosystem. However, the enantioselective toxic effect of carvone enantiomers on cyanobacteria remains unknown. This study aims to investigate the effects of L- and D-carvone on the physiological processes and related gene transcription (phoU, rbcL, and mcyH) in M. aeruginosa. Results showed that in the presence of L- and D-carvone, the oxidative damage and inhibitory effects on growth occurred in a concentration-dependent manner. The contents of chlorophyll a and protein and the rbcL transcription level were inhibited in M. aeruginosa. In addition, intracellular adenosine triphosphate (ATP) was heavily depleted because of various biological processes, including growth, oxidation reactions, and gene regulation. Meanwhile, L- and D-carvone stimulated the production and release of MC-LR and upregulated the expression level of the MC-LR-related gene mcyH. Intracellular MC-LR likely leaked to the water body under L-carvone exposure, posing a potential threat to the water environment. This study indicated that L- and D-carvone can regulate the physiological and metabolic activity of M. aeruginosa and show enantioselective toxic effects. The findings will also provide important insights into the influence of chiral fragrance on cyanobacterial blooms. Furthermore, this study will guide the safe application of chiral fragrance as personal care products.

Mechanistic insight into the inhibitory effect of artemisinin sustained-release inhibitors with different particle sizes on Microcystis aeruginosa

Environment-friendly algaecides based on allelopathy have been widely used to control harmful algal blooms. In this research, micro and nano scale artemisinin sustained-release algal inhibitor was prepared, the optimal preparation conditions were explored, and the inhibitory mechanism of artemisinin algaecides was turned perfect. The results showed that when the particle size of artemisinin sustained-release microspheres (ASMs) was 2/10,000 of artemisinin sustained-release granules (ASGs), the inhibitory effect was more remarkable. The optimal concentration of ASMs was 0.2 g L^-1, and the inhibitory effect reached 99% on the 10th day. The algal density and chlorophyll a both showed a downward trend, indicating that ASGs and ASMs could promote the degradation of chlorophyll a. The inhibition rate of ASGs was faster than that of ASMs on the 4th day, and the inhibitory effect of ASMs was more significant after the 5th day. The activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) increased rapidly at first and then decreased, which indicated that ASGs and ASMs caused oxidative damage to Microcystis aeruginosa and inhibited the activity of antioxidant enzymes. Furthermore, the content of the oxygen free radical (O^2-) and malondialdehyde (MDA) continued to rise after the 5th day, and the protein, nucleic acid, and conductivity in the culture medium increased. These results showed that lipid peroxidation occurred in the algal cell membrane, and the permeability of the membrane increased. In summary, the ASMs had a significant sustained inhibitory effect while the ASGs had a better short-term effect. The main inhibitory mechanism of artemisinin algaecides is the irreversible damage of cell membrane.

Removal of harmful algae by Shigella sp. H3 and Alcaligenes sp. H5: algicidal pathways and characteristics

Application of algicidal bacteria is a promising technology to control harmful algal blooms (HABs). In this study, algicidal bacteria strains Shigella sp. H3 and Alcaligenes sp. H5 were obtained via two different isolation methods from the same lake water sample, with optimal algicidal efficiencies 96% and 74% against algae mixture. The Shigella sp. H3 and Alcaligenes sp. H5 lysed algae cells through cells-to-cells direct contact and secretion of algicidal metabolites, respectively. The stronger algicidal capability of Shigella sp. H3 was also attributable to its higher efficiency for triggering reactive oxygen species, which led to broken down of the antioxidant system and more severe damage to the bacterial cells. The antioxidant enzyme activities in Alcaligenes sp. H5 group were still expressed because of its relatively weaker algicidal capability and some intact algal cells were remained. The liquid carbohydrates from algal lysis in both groups increased significantly, whereas the quantities of liquid protein decreased, which might be assimilated by algicidal bacteria. Nonetheless, the whole algicidal process resulted in the increase of total released organic matters content. This study revealed the algicidal pathways of diverse bacterial strains, and the possible secondary environmental problem caused by the algal released organic matters should be considered when applying bacteria to control HABs.

Binary toxicity of polystyrene nanoplastics and polybrominated diphenyl ethers to Arctic Cyanobacteria under ambient and future climates

Cyanobacteria are the predominant biota in the Arctic. Interactive effects on Arctic cyanobacteria between climate-change-shifting parameters and anthropogenic contaminants are largely unknown. We utilized a fractional factorial experiment and Arctic cyanobacteria Pseudanabaena biceps Strain PCCC_O-153 to capture the complexity of interacting climate factors, nano-polystyrene (nano-PS) and 2,2´,4,4´-tetrabromodipenyl ether (BDE-47). The short-term binary toxicity of nano-PS and BDE-47 was then examined through experiments, toxicity units, and reference models. The toxic mechanism was further revealed through biochemical analyses and multivariate statistics. We found that BDE-47 and nano-PS had more hazardous effects than changing climate conditions. The mixture had antagonistic effects on PCCC_O-153, attributing to the aggregation of nano-PS, the adsorption of BDE-47, and the wrapping of both contaminants by released extracellular polymeric substances. Binary toxicity was caused by the chain reactions triggered by combining individual contaminants. Total protein was a sensitive target and positively correlated to chlorophyll pigment. Oxidative stress for the mixture mainly resulted from the presence of nano-PS. This is the first study to access the hazardous effects of a mixture of anthropogenic contaminants on Arctic cyanobacteria under ambient and future climates.

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.

Changes in fatty acid composition as a response to glyphosate toxicity in Pseudomonas fluorescens

Excessive use of herbicides decreases soil biodiversity and fertility. The literature on the xenobiotic response by microorganisms is focused on herbicide biodegradation as a selective event. Non-degradation systems independent of selection could allow the survival of tolerant bacteria in contaminated environments, impacting xenobiotic turnover and, consequently, bioremediation strategies. However, it is uncertain whether the response based on these systems requires selective pressure to be effective. The objective here was to analyze non-degradation phenotypes, enzymatic and structural response systems, of Pseudomonas fluorescens CMA-55 strain, already investigated the production pattern of quorum sensing molecules in response to glyphosate, not present at the isolation site. One mode of response was associated with decrease in membrane permeability and effective antioxidative response for 0–2.30 mM glyphosate, at the mid-log growing phase, with higher activities of Mn-SOD, KatA, and KatB, and presence of fatty acids as nonadecylic acid, margaric and lauric acid. The second response system was characterized by lower antioxidative enzymes activity, presence of KatC isoform, and pelargonic, capric, myristic, stearic, palmitoleic and palmitic acid as principal fatty acids, allowing the strain to face stressful conditions in 9.20–11.50 mM glyphosate at the stationary phase. Therefore, the bacterial strain could modify the fatty acid composition and the permeability of membranes in two response modes according to the herbicide concentration, even glyphosate was not previously selective for P. fluorescens, featuring a generalist system based on physiological plasticity.

Potential Use of Aquatic Vascular Plants to Control Cyanobacterial Blooms: A Review

Intense “blooming” of cyanobacteria (blue-green algae) caused by eutrophication and climate change poses a serious threat to freshwater ecosystems and drinking water safety. Preventing the proliferation of cyanobacteria and reducing water nutrient load is a priority for the restoration of eutrophic water bodies. Aquatic plants play an important role in the function and structure of aquatic ecosystems, affecting the physiochemistry of the water and bottom sediments, primary production, and biotic interactions that support a balanced ecosystem. This review examines the inhibitory effect of aquatic vascular plants on harmful blooms of cyanobacteria. Aquatic plants are able to successfully inhibit the growth of cyanobacteria through various mechanisms, including by reducing nutrient and light availability, creating favorable conditions for the development of herbivorous zooplankton, and releasing allelopathic active substances (allelochemicals) with algicidal effect. Allelopathy is species-specific and therefore acts as one of the key mechanisms by which the development of cyanobacterial populations in aquatic ecosystems is regulated. However, allelopathic activity of aquatic vascular plants depends on various factors (species characteristics of aquatic plants, area, and density of overgrowth of water bodies, physiochemical properties of allelopathically active substances, hydrological and hydrochemical regimes, temperature, light intensity, etc.), which may regulate the impact of allelochemicals on algal communities. The paper also discusses some problematic aspects of using fast-growing species of aquatic vascular plants to control cyanobacterial blooms.

Allelopathic effect of Oocystis borgei culture on Microcystis aeruginosa

This study evaluated the possibility of using Oocystis borgei to prevent and control harmful algae blooms. Firstly, Microcystis aeruginosa and O. borgei were co-cultured to assess the competition for nutrients between them. Different physiological and biochemical parameters, such as growth, cell membrane permeability and esterase activities were determined in exudate culture experiment to investigate allelopathic effects of O. borgei culture and mixed cultures (O. borgei and M. aeruginosa) at different growth phase on harmful microalgae (M. aeruginosa). Results showed that O. borgei could significantly inhibited M. aeruginosa when volume ratios were 4:1 and 1:1 (M. aeruginosa: O. borgei) in co-culture experiment. Further, it was found that the membrane system of M. aeruginosa was disintegrated by the culture filtrate of O. borgei at exponential phase. In addition, esterase activities and photorespiration were significantly inhibited. In conclusion, O. borgei exhibited different allelopathic effects at different growth phase. Its exponential phase showed a significant inhibitory effect, while no inhibitory effect was observed at the decline phase.

Effect of protopine exposure on the physiology and gene expression in the bloom-forming cyanobacterium Microcystis aeruginosa

Environment-friendly sound measures with high algal growth inhibition efficiency are required to control and eliminate CyanoHABs. This study examined the effects of protopine on growth, gene expression, and antioxidant system of the M. aeruginosa TY001 and explored possible damage mechanism. The results revealed that higher concentrations of protopine seriously inhibited the growth of M. aeruginosa. Quantitative real-time PCR analysis showed downregulated expression of stress response genes (prx and fabZ), and DNA repair gene (recA) on days 3 and 5. The activities of antioxidant enzymes were also decreased markedly, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). Additionally, protopine stress can significantly increase the malondialdehyde (MDA) level in cells. In conclusion, oxidative damage and DNA damage are the main mechanisms of protopine inhibition on M. aeruginosa TY001. Our studies provide evidence that alkaloid compounds such as protopine may have a potential use value as components of aquatic management strategies.

Succinic acid inhibits photosynthesis of Microcystis aeruginosa via damaging PSII oxygen-evolving complex and reaction center

To elucidate the mechanism of succinic acid (SA) inhibition of Microcystis aeruginosa, the chlorophyll fluorescence transients, photosynthesis, photosynthetic electron transport activity, and gene expression of M. aeruginosa were evaluated under various doses of SA. The results demonstrated that, after treatment with 60 mg L^-1 SA for 1 h, the chlorophyll fluorescence transients and related parameters changed significantly, indicating that the function and structure of photosynthetic apparatuses of Microcystis were seriously damaged. The initial quantum efficiency α, maximum net photosynthetic rate P_nmax, dark respiration rate Rd, and gross photosynthetic rate decreased to 57%, 49%, 49%, and 46%, respectively, relative to the control. Furthermore, photosystem II (PSII) activity (H₂O→p-BQ) and the electron transport activity of H₂O→MV and DPC→MV significantly decreased. Real-time PCR analysis revealed that, following incubation with 60 mg L^-1 SA for 24 h, the expression level of core protein genes (psbA, psaB, psbD, and psbO) of the photosynthesis centers photosystem I (PSI) and PSII decreased significantly. However, the transcription of gene nblA encoding phycobilisome degradation protein was elevated. The downregulation of the rbcL gene, which encodes the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), resulted in the suppression of CO₂ fixation and assimilation. High concentration (60 mg L^-1) of SA resulted in damage to oxygen-evolving complex (OEC) and reaction center of PSII, blocking photosynthetic electron transport, thereby lowering the rate photosynthesis and inhibiting the growth of Microcystis. We concluded that inhibition of photosynthesis is an important mechanism of SA inhibition in M. aeruginosa.

Effects on photosynthetic and antioxidant systems of harmful cyanobacteria by nanocrystalline Zn-MOF-FA

Metal-organic frameworks (MOFs) constitute new class of materials recently used by researchers in the field of controlling cyanobacteria. However, the use of MOFs in combination with allelochemicals for cyanobacteria inhibition had not been investigated before. The present study is aimed towards the investigation of the effect and mechanism of cyanobacteria inhibition by combining MOF with allelochemical (ferulic acid, FA) for the first time. In this study, the results showed that the synergistic effect of Zn²⁺ and FA from Zn-MOF-FA could inhibit cyanobacteria to a greater extent than the corresponding dosage of Zn²⁺ and FA. The inhibition ratio of Microcystis aeruginosa has been found to be more than 50% when the Zn-MOF-FA concentration exceeds 2 mg·L^-1 after four days exposure. Zn-MOF-FA at 1 mg·L^-1 did not completely inhibit M. aeruginosa, and the inhibition effect has been of only temporary type. The inhibitory effect of Zn-MOF-FA on algae has mainly been attributed to the hindrance of electron transfer and energy capture in the photosynthetic system and the oxidative damage caused by reactive oxygen species (ROS).

Remediation Strategies to Control Toxic Cyanobacterial Blooms: Effects of Macrophyte Aqueous Extracts on Microcystis aeruginosa (Growth, Toxin Production and Oxidative Stress Response) and on Bacterial Ectoenzymatic Activities

Increasing toxic cyanobacterial blooms in freshwater demand environmentally friendly solutions to control their growth and toxicity, especially in arid countries, where most drinking water is produced from surface reservoirs. We tested the effects of macrophyte allelochemicals on Microcystis aeruginosa and on the fundamental role of bacteria in nutrient recycling. The effects of Ranunculus aquatilis aqueous extract, the most bioactive of four Moroccan macrophyte extracts, were tested in batch systems on M. aeruginosa growth, toxin production and oxidative stress response and on the ectoenzymatic activity associated with the bacterial community. M. aeruginosa density was reduced by 82.18%, and a significant increase in oxidative stress markers was evidenced in cyanobacterial cells. Microcystin concentration significantly decreased, and they were detected only intracellularly, an important aspect in managing toxic blooms. R. aquatilis extract had no negative effects on associated bacteria. These results confirm a promising use of macrophyte extracts, but they cannot be generalized. The use of the extract on other toxic strains, such as Planktothrix rubescens, Raphidiopsis raciborskii and Chrysosporum ovalisporum, caused a reduction in growth rate but not in cyanotoxin content, increasing toxicity. The need to assess species-specific cyanobacteria responses to verify the efficacy and safety of the extracts for human health and the environment is highlighted.

Effects of mycosubtilin homolog algicides from a marine bacterium, Bacillus sp. SY-1, against the harmful algal bloom species Cochlodinium polykrikoides

The marine bacterium, Bacillus sp. SY-1, produced algicidal compounds that are notably active against the bloom-forming alga Cochlodinium polykrikoides. We isolated three algicidal compounds and identified these as mycosubtilins with molecular weights of 1056, 1070, and 1084 (designated MS 1056, 1070, and 1084, respectively), based on amino acid analyses and 1H, 13C, and two-dimensional nuclear magnetic resonance spectroscopy, including 1H-15N heteronuclear multiple bond correlation analysis. MS 1056 contains a β-amino acid residue with an alkyl side chain of C15, which has not previously been seen in known mycosubtilin families. MS 1056, 1070, and 1084 showed algicidal activities against C. polykrikoides with 6-h LC50 values of 2.3 ± 0.4, 0.8 ± 0.2, and 0.6 ± 0.1 μg/ml, respectively. These compounds also showed significant algicidal activities against other harmful algal bloom species. In contrast, MS 1084 showed no significant growth inhibitory effects against other organisms, including bacteria and microalgae, although does inhibit the growth of some fungi and yeasts. These observations imply that the algicidal bacterium Bacillus sp. SY-1 and its algicidal compounds could play an important role in regulating the onset and development of harmful algal blooms in natural environments.

Polystyrene nanoplastics affect growth and microcystin production of Microcystis aeruginosa

Nanoplastics are widely distributed in freshwater environments, but few studies have addressed their effects on freshwater algae, especially on harmful algae. In this study, the effects of polystyrene (PS) nanoplastics on Microcystis aeruginosa (M. aeruginosa) growth, as well as microcystin (MC) production and release, were investigated over the whole growth period. The results show that PS nanoplastics caused a dose-dependent inhibitory effect on M. aeruginosa growth and a dose-dependent increase in the aggregation rate peaking at 60.16% and 46.34%, respectively, when the PS nanoplastic concentration was 100 mg/L. This caused significant growth of M. aeruginosa with a specific growth rate up to 0.41 d^-1 (50 mg/L PS nanoplastics). After a brief period of rapid growth, the tested algal cells steadily grew. In addition, the increase in PS nanoplastics concentration promoted the production and release of MC. When the PS nanoplastic concentration was 100 mg/L, the content of the intracellular (intra-) and extracellular (extra-) MC increased to 199.1 and 166.5 μg/L, respectively, on day 26, which was 31.4% and 31.1% higher, respectively, than the control. Our results provide insights into the action mechanism of nanoplastics on harmful algae and the potential risks to freshwater environments.

A review: Application of allelochemicals in water ecological restoration--algal inhibition

Problems caused by harmful algal blooms have attracted worldwide attention due to their severe harm to aquatic ecosystems, prompting researchers to study applicable measures to inhibit the growth of algae. Allelochemicals, as secondary metabolites secreted by plants, have excellent biocompatibility, biodegradability, obvious algal inhibiting effect and little ecological harm, and have promising application prospect in the field of water ecological restoration. This review summarized the research progress of allelochemicals, including (i) definition, development, and classification, (ii) influencing factors and mechanism of algal inhibition, (iii) the preparation methods of algal inhibitors based on allelochemicals. The future research directions of allelochemicals sustained-released microspheres (SRMs) were also prospected. In the future, it is urgent to explore more efficient allelochemicals, to study the regulation mechanism of allelochemicals in natural water bodies, and to improve the preparation method of allelopathic algal suppressant. This paper proposed a feasible direction for the development of allelochemicals SRMs which exhibited certain guiding significance for their application in water ecological restoration.

Growth inhibition, toxin production and oxidative stress caused by three microplastics in Microcystis aeruginosa

Microplastics (MPs) have aroused widespread concern due to their extensive distribution in aquatic environments and adverse effects on aquatic organisms. However, the underlying toxicity of different kinds of MPs on freshwater microalgae has not been examined in detail. In this study, we investigated the effects of polyvinyl chloride (PVC), polystyrene (PS) and polyethylene (PE) MPs on the growth of Microcystis aeruginosa, as well as on its toxin production and oxidative stress. We found that all three kinds of MPs had an obvious inhibition effect on the growth of M. aeruginosa. Considering the results of antioxidant-related indicators, the activity of superoxide dismutase (SOD) and catalase (CAT), and cell membrane integrity were greatly affected with exposure to PVC, PS and PE MPs. Moreover, the content of intracellular (intra-) and extracellular (extra-) microcystins (MCs) had a noticeable increase due to the presence of PVC, PS, and PE MPs. Finally, according to the comprehensive stress resistance indicators, the resistance of M. aeruginosa to three MPs followed the order: PE (3.701)> PS (3.607)> PVC (2.901). Our results provide insights into the effects of different kinds of MPs on freshwater algae and provide valuable data for risk assessment of different types of MPs.

A review on control of harmful algal blooms by plant-derived allelochemicals

Harmful algal blooms (HABs) have several negative impacts on aquatic ecosystem, and even harm to humans. Utilization of allelochemicals to inhibit microalgal overgrowth is an environment-friendly approach for controlling HABs. This paper demonstrated the development of allelochemicals with algicidal effects, including the development history of allelopathy, the application methods, the reported allelopathic plants and their derived allelochemicals. Allelopathy is a promising strategy to control HABs as the effectiveness of allelochemicals on inhibiting microalgae cells has been discovered and confirmed for many years. The proposed allelopathic mechanisms and species-selective properties were expounded as well. Moreover, this paper further proposed suggestions for the further research and development of allelopathy strategy for HABs control.

Highlighting of the antialgal activity of organic extracts of Moroccan macrophytes: potential use in cyanobacteria blooms control

Many studies have demonstrated the effectiveness of algicidal compounds produced by macrophytes against microalgae. The aim of this study was to assess the algicidal activity of seven Moroccan macrophyte ethyl acetate extracts (MEA) to control harmful algal blooms (HABs). The response and sensitivity of prokaryotic toxic cyanobacteria (Microcystis aeruginosa) and eukaryotic microalgae (Chlorella sp.) were highlighted. The algicidal effect of MEA extracts against the two microalgae was assessed using both the paper disc diffusion and microdilution methods. This last was used in order to evaluate the minimum inhibitory concentrations (MIC) and minimum algicidal concentrations (MAC). Results showed that the growth of both microalgae was significantly inhibited by all MEA extracts. Myriophyllum spicatum organic extract shows the highest growth inhibition activity against M. aeruginosa (35.33 ± 1.53) and Chlorella sp. (30.33 ± 1.15 mm). This stronger inhibitory activity was confirmed by the low MIC (6.25, 12.5 mg/L) and MAC (6.25, 12.5 mg/L) values. Furthermore, results showed different sensitivity between the prokaryotic and eukaryotic microalgae into MEA extracts. Based on the MIC and MAC values, we can distinguish two groups of plants. The first one, including M. spicatum, Ranunculus aquatilis, and Enteromorpha sp., can be considered as a preferable anti-prokaryotic group with a stronger inhibitory activity on M. aeruginosa growth. The second group, constituted by Potamogeton natans, Nasturtium officinale, Elodea sp., and Ceratophyllum sp., has a preferable and stronger inhibitory effect against eukaryotic algae (Chlorella sp.). Overall the results reveal the potential algicidal activity of macrophytes and suggested that MEA extracts could play an important role in biocontrol of HABs.

Algal toxicity induced by effluents from textile-dyeing wastewater treatment plants

This research aimed to evaluate the alga Scenedesmus obliquus toxicity induced by textile-dyeing effluents (TDE). The toxicity indicator of TDE in alga at the physiological (algal growth), biochemical (chlorophyll-a (Chl-a) synthesis and superoxide dismutase (SOD) activity) and structural (cell membrane integrity) level were investigated. Then we further study the relationship among toxicity indicators at physiological and biochemical level, and supplemented by research on algal biomacromolecules. According to the analysis of various endpoints of the alga, the general sensitivity sequence of toxicity endpoints of Scenedesmus obliquus was: SOD activity > Chl-a synthesis > algal growth. The stimulation rate of SOD activity increased from day 3 (57.25%~83.02%) to day 6 (57.25%~103.81%), and then decreased on day 15 (-4.23%~-32.96%), which indicated that the antioxidant balance system of the algal cells was destroyed. The rate of Chl-a synthesis inhibition increased gradually, reaching 19.70%~79.39% on day 15, while the rate of growth inhibition increased from day 3 (-12.90%~10.16%) to day 15 (-21.27%~72.46%). Moreover, the algal growth inhibition rate was positively correlated with the inhibition rate of SOD activity or Chl-a synthesis, with the correlation coefficients were 0.6713 and 0.5217, respectively. Algal cells would be stimulating to produce excessive reactive oxygen species, which would cause peroxidation in the cells, thereby destroying chloroplasts, inhibiting chlorophyll synthesis and reducing photosynthesis. With increasing exposure time, irreversible damage to algae can lead to death. This study is expected to enhance our understanding of the ecological risks through algal tests caused by TDE.

Synthesis and fouling resistance of capsaicin derivatives containing amide groups

Capsaicin, which inhibits the attachment and growth of fouling organisms, is a bioactive substance that is generally recognized as a highly active environmental algaecide agent. Its derivatives are simple in structure and have been proven to have low toxicity and be environmentally friendly. Six capsaicin derivatives were synthesized via Friedel-Crafts alkylation and characterized using melting point (MP) analysis, infrared (IR) spectroscopy, nuclear magnetic resonance (¹H NMR) spectroscopy and high-resolution mass spectrometry (HRMS). The inhibition effect and toxicity of these compounds towards Phaeodactylum tricornutum (P. tricornutum), Skeletonema costatum (S. costatum) and Chaetoceros curvisetus (C. curvisetus) were tested. The capsaicin derivatives all showed inhibitory effects. In particular, compound E with over 95% (3 mg·L^-1) inhibition and intermediate toxicity was superior to the other compounds, reflecting an environmentally friendly effect. This finding indicates that capsaicin derivatives possess the potential to become environmentally friendly algaecide agents. The fouling resistance of capsaicin derivatives incorporated into the coatings as antifouling agents was measured in the marine environment. The results showed that capsaicin derivatives possess excellent fouling resistance, with only a small amount of algae and muck attached to the tested panel at 90 days. The above results provide a scientific basis for the application of capsaicin derivatives as environmentally friendly antifouling agents.

Formation mechanism of the Microcystis aeruginosa bloom in the water with low dissolved phosphorus

The utilization of phosphorus by algae in the low-phosphorus state has drawn wide concerns due to the high risk of forming algal blooms. The cyanobacteria Microcystis aeruginosa (M. aeruginosa) grew well under low-phosphorus condition by hydrolyzing dissolved organic phosphorus (DOP) to dissolved inorganic phosphorus (DIP) through alkaline phosphatase (AP). There was a negative correlation between DIP concentration and AP activity of algae. AP activity significantly increased at 0-3 d (p < 0.05), and reached the peak values of 43.06 and 49.11 King unit/gprot on day 5 for DIP (0.1 mg/L) and DOP (4.0 mg/L), respectively. The relative expression of phosphate transporter gene increased with decreasing phosphorus concentrations. The catalase activity under low-phosphorus condition increased significantly (p < 0.05) after one week, and was generally higher than 0.15 U/mgprot on day 14. Understanding the utilization efficiency and mechanism of DIP and DOP in the low-phosphorus state would help to inhibit the formation of algal blooms.

Effect of Phenyl-Acyl Compounds on the Growth, Morphology, and Toxin Production of Microcystis aeruginosa Kützing

The proliferation of cyanobacteria and, consequently, the production of cyanotoxins is a serious public health concern; for their control, several alternatives have been proposed, including physical, chemical, and biological methods. In the search for new alternatives and a greater understanding of the biochemical process involved in the blooms’ formation, we report here the effect of eight phenyl-acyl compounds in the growth of Microcystis aeruginosa Kützing (assesed as cell density/count and Chl a fluorescence concentration) morphology, and production of the toxin microcystin-LR (MC-LR). Caffeic acid and eugenol decreased the growth of M. aeruginosa Kützing and the levels of Chl a. However, 3,5-dimethoxybenzoic acid and syringic acid caused the opposite effect in the growth; 2′and 4′only affected the Chl a. A reduction in the concentration of the MC-LR toxin was detected after treatment with syringic acid, caffeic acid, and eugenol. According to HPLC/MS (High Performance Liquid Chromatography coupled to Mass Spectrometry), a redox process possibly occurs between caffeic acid and MC-LR. The optical microscopy and Scanning Electron Microscopy analyses revealed morphological changes that had been exposed to caffeic acid and vanillin, specifically in the cell division and presence of mucilage. Finally, assays in Daphnia pulex De Geer neonates indicated that caffeic acid had a non-toxic effect at concentrations as high as 100 mg/L at 48 h.