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

From winter dormancy to spring bloom: Regulatory mechanisms in Microcystis aeruginosa post-overwintering recovery

Cyanobacterial blooms pose a significant environmental threat in freshwater ecosystems. These cyanobacteria exhibit resilience to cold and dark conditions during winter and flourish as temperature rise in warmer seasons. However, there is a limited understanding of the dynamic growth recovery process and regulatory signaling mechanisms in cyanobacteria after overwintering. In this study, we employed Microcystis aeruginosa (M. aeruginosa) as a model to simulate its growth recovery when subjected to increasing temperature after overwintering under low temperature (4 °C) and dark conditions. We investigated changes in cell growth, microcystin levels, and signaling pathways throughout this recovery phase. Our results indicated that compared to the non-overwintering treatment (T1), the overwintered treatment (T2) experienced a 55.6 % decrease in algae density and a significant reduction in microcystin-LR (MC-LR) levels within the 15-20 °C temperature range (p < 0.05). Overwintering suppressed photosynthetic efficiency during the recovery phase of M. aeruginosa, activated the antioxidant system, and impaired cellular ultrastructure, making algal cells more vulnerable to death. At the transcriptional level, overwintering down-regulated pathways such as photosynthesis, ribosome, the Calvin cycle, and oxidative phosphorylation, hindering the growth and metabolic capacity of M. aeruginosa. In conclusion, this study highlights the inhibitory impacts of overwintering on growth and metabolism of cyanobacteria during the recovery process. It provides insights into the mechanistic foundations of seasonal cyanobacterial blooms and the crucial role of signaling regulation in these processes.

The use of a benign fast-growing cyanobacterial species to control microcystin synthesis from Microcystis aeruginosa

Introduction

Microcystis aeruginosa (M. aeruginosa), one of the most prevalent blue-green algae in aquatic environments, produces microcystin by causing harmful algal blooms (HAB). This study investigated the combined effects of nutrients and cyanobacterial subpopulation competition on synthesizing microcystin-LR.

Method

In varied nitrogen and phosphorus concentrations, cyanobacterial coculture, and algicidal DCMU presence, the growth was monitored by optical density analysis or microscopic counting, and the microcystin production was analyzed using high-performance liquid chromatography-UV. Furthermore, growth and toxin production were predicted using MATLAB.

Results and discussion

First, coculturing with a fast-growing cyanobacterium Synechococcus elongatus UTEX 2973 (S. elongatus) reduced M. aeruginosa biomass and microcystin production at 30oC. Under high nitrogen and low phosphorus conditions, S. elongatus is mostly effective, with up to 94.7% and 92.4% limitation of M. aeruginosa growth and toxin synthesis, respectively. Second, this biological strategy became less effective at 23oC, where S. elongatus grew slower. Third, photosynthesis inhibitor DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) hindered M. aeruginosa growth (at 0.1 mg/L) and microcystin production (at 0.02 mg/L). DCMU was also effective for controlling microcystin production in S. elongatus-M. aeruginosa cocultures. Based on experimental results, a multi-substrate, multi-species kinetic model was built to describe coculture growth and population interactions.

Conclusion

Future research should examine more complex models to further develop and refine to facilitate the derivation of more effective recommendations for health prevention programs, particularly for mothers and girls.

Release of algal organic matter from cyanobacteria following application of USEPA-registered chemical algaecides

Increased occurrence of harmful algal blooms significantly impedes uses of freshwater resources, especially as potable water supply. Rapid mitigation using algaecides is common; however, the potential release of algal organic matter (AOM) and cyanotoxins poses challenges due to the difficulty of removal with conventional water treatment and negative health impacts. This study evaluated four USEPA-registered algaecides for their efficacy against Microcystis aeruginosa growth and AOM and cyanotoxin release. Successful inhibition of cell growth was achieved in both unialgal and mixed culture samples at concentrations of 0.2 mg Cu/L for copper-based algaecides and 6 mg H2O2/L for peroxide-based algaecides. At 12 h after treatment (HAT), a significant increase in dissolved phycocyanin was observed, which was more pronounced with copper-based algaecides. Microbial byproduct-related and simple aromatic proteins were measured in the unialgal culture, while microbial byproduct-related proteins and humic-like substances were dominant in the mixed culture samples. In both unialgal and mixed-culture experiments, 0.2 mg Cu/L application of copper-based algaecides was the minimum dosage for cyanobacterial cell inhibition and the lowest release of AOM and cyanotoxins, with Oximycin P5 at 6 mg H2O2/L yielding similar results among peroxide-based algaecides. These results help inform water supply managers on algaecide use toward maintaining integrity of drinking water quality.

A newly identified algicidal bacterium of Pseudomonas fragi YB2: Algicidal compounds and effects

Harmful algal bloom (HAB) is an unresolved existing problem worldwide. Here, we reported a novel algicidal bacterium, Pseudomonas fragi YB2, capable of lysing multiple algal species. To Chlorella vulgaris, YB2 exhibited a maximum algicidal rate of 95.02 % at 120 h. The uniqueness of YB2 lies in its ability to self-produce three algicidal compounds: 2-methyl-1, 3-cyclohexanedione (2-MECHD), N-phenyl-2-naphthylamine, and cyclo (Pro-Leu). The algicidal properties of 2-MECHD have not been previously reported. YB2 significantly affected the chloroplast and mitochondrion, thus decreasing in chlorophyll a by 4.74 times for 120 h and succinate dehydrogenase activity by 103 times for 36 h. These physiological damages disrupted reactive oxygen species and Ca2+ homeostasis at the cellular level, increasing cytosolic superoxide dismutase (23 %), catalase (35 %), and Ca2+ influx. Additionally, the disruption of Ca2+ homeostasis rarely reported in algicidal bacteria-algae interaction was observed using the non-invasive micro-test technology. We proposed a putative algicidal mechanism based on the algicidal outcomes and physiological algicidal effects and explored the potential of YB2 through an algicidal simulation test. Overall, this study is the first to report the algicidal bacterium P. fragi and identify a novel algicidal compound, 2-MECHD, providing new insights and a potent microbial resource for the biocontrol of HAB.

Impact of copper sulphate treatment on cyanobacterial blooms and subsequent water quality risks

Control of algal blooms and associated biologically-induced water quality risks in drinking reservoirs is problematic. Copper sulphate (CuSO4) treatment is one intervention that has been utilised for >100 years. Evidence indicates a favourable short-term reduction in Cyanobacterial biomass (e.g. bloom termination), but here we indicate that it may also increase longer-term water quality risk. In 2022, we investigated the impacts of CuSO4 spraying on Cyanobacterial communities and nutrient levels within a drinking water supply reservoir using environmental DNA (eDNA) to assess community shifts, alongside monitoring nutrient fractions, orthophosphate (OP) and total phosphate (TP), post-treatment. CuSO4 application successfully reduced Cyanobacterial abundance, however elimination of Cyanobacteria resulted in a shift in bacterial dominance favouring Planctomycetota throughout the summer and a combination of Actinobacteriota and Verrucomicrobiota, throughout autumn. As Cyanobacterial abundance recovered post-treatment, Cyanobacterial genera demonstrated greater diversity compared to only three Cyanobacterial genera present across samples pre-treatment, and included taxa associated with water quality risk (e.g. taste and odour (T&O) metabolite and toxin producers). The increase in Cyanobacteria post-treatment was attributed to an increase in biologically available nutrients, primarily a significant increase in OP. Overall, findings suggest that the significant shift in biodiversity likely induces a less stable ecosystem with greater plasticity of response to changing environmental and biogeochemical variables. Legacy implications of CuSO4 spraying, in terms of shifts in ecosystem and nutrient balance over time, may have implications for drinking water quality, but importantly also for reservoir management options. As such, the effects of CuSO4 spraying should be considered carefully before consideration as a contender for in-reservoir biological control.

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

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

Compensatory growth of Microcystis aeruginosa after copper stress and the characteristics of algal extracellular organic matter (EOM)

Cyanobacterial blooms can impair drinking water quality due to the concomitant extracellular organic matter (EOM). As copper is often applied as an algicide, cyanobacteria may experience copper stress. However, it remains uncertain whether algal growth compensation occurs and how EOM characteristics change in response to copper stress. This study investigated the changes in growth conditions, photosynthetic capacity, and EOM characteristics of M. aeruginosa under copper stress. In all copper treatments, M. aeruginosa experienced a growth inhibition stage followed by a growth compensation stage. Notably, although chlorophyll-a fluorescence parameters dropped to zero immediately following high-intensity copper stress (0.2 and 0.5 mg/L), they later recovered to levels exceeding those of the control, indicating that photosystem II was not destroyed by copper stress. Copper stress influenced the dissolved organic carbon (DOC) content, polysaccharides, proteins, excitation-emission matrix spectra, hydrophobicity, and molecular weight (MW) distribution of EOM, with the effects varying based on stress intensity and growth stage. Principal component analysis revealed a correlation between the chlorophyll-a fluorescence parameters and EOM characteristics. These results imply that copper may not be an ideal algicide. Further research is needed to explore the dynamic response of EOM characteristics to environmental stress.

Unleashing the power of acetylacetone: Effective control of harmful cyanobacterial blooms with ecological safety

Harmful algal blooms resulting from eutrophication pose a severe threat to human health. Acetylacetone (AA) has emerged as a potential chemical for combatting cyanobacterial blooms, but its real-world application remains limited. In this study, we conducted a 42-day evaluation of AA's effectiveness in controlling blooms in river water, with a focus on the interplay between ecological community structure, organism functional traits, and water quality. At a concentration of 0.2 mM, AA effectively suppressed the growth of Cyanobacteria (88 %), Bacteroidia (49 %), and Alphaproteobacteria (52 %), while promoting the abundance of Gammaproteobacteria (5.0 times) and Actinobacteria (7.2 times) that are associated with the degradation of organic matter. Notably, after dosing of AA, the OD680 (0.07 ± 0.02) and turbidity (8.6 ± 2.1) remained at a satisfactory level. AA induced significant disruptions in two photosynthesis and two biosynthesis pathways (P < 0.05), while simultaneously enriching eight pathways of xenobiotics biodegradation and metabolism. This enrichment facilitated the reduction of organic pollutants and supported improved water quality. Importantly, AA treatment decreased the abundance of two macrolide-related antibiotic resistance genes (ARGs), ereA and vatE, while slightly increased the abundance of two aminoglycoside-related ARGs, aacA and strB. Overall, our findings establish AA as an efficient and durable algicide with favorable ecological safety. Moreover, this work contributes to the development of effective strategies for maintaining and restoring the health and resilience of aquatic ecosystems impacted by harmful algal blooms.

Metabolomic analysis reveals the toxicity mechanisms of bisphenol A on the Microcystis aeruginosa under different phosphorus levels

Harmful cyanobacterial blooms have been a global environmental problem. Discharge of anthropogenic pollutants and excess nutrient import into the freshwater bodies may be the biggest drivers of bloom. Bisphenol A (BPA), a typical endocrine-disrupting compound, is frequently detected in different natural waters, which was a threat to the balance of aquatic ecosystem. Yet mechanistic understanding of the bloom and microcystin generation under combined pollution conditions is still a mystery. Herein, the cellular and metabolomic responses to BPA exposure and phosphorus (P) levels in Microcystis aeruginosa were investigated throughout its growth period. The results showed that the stress response of M. aeruginosa to BPA was characterized by a decrease in growth density, an increase in P utilization, an increase in ATPase activity, a disruption of the photosynthetic system, and an increase in the production and release of microcystins (MCs). However, these effects are highly dependent on the growth stage of the cyanobacterial cell and the magnitude of the added P concentration. In addition, exposure to a high concentration (10 μM) of BPA significantly stimulated the production of 20.7% more and the release of 29.2% more MCs from M. aeruginosa cells at a low P level. The responses of reactive oxygen species (ROS), superoxide dismutase (SOD) and malondialdehyde (MDA) suggested that exposure to BPA exposure at a low P level can lead to oxidative stress in M. aeruginosa. In addition, the differentially expressed 63 metabolites showed that cell growth, energy generation and photosynthesis were mainly regulated by the metabolic network of 3-phosphoglyceric acid (3-PGA), D-glucose 6-phosphate, UDP-α-D-galactose and UDP-N-acetyl-D-galactosamine (UDP-GalNAc) metabolism. Amino acids and lipid metabolism collectively mediated MCs production and release. These findings will provide important references for the control of harmful cyanobacterial blooms under combined pollution.

Inactivation of harmful cyanobacteria Microcystis aeruginosa by Cu2+ doped corn stalk biochar treated with different pyrolysis temperatures

In this study, biochars (BCs) derived from corn stalk treated at various pyrolysis temperatures (350-950 °C) were prepared and then loaded with Cu2+ to form highly efficient algaecide, i.e. Cu2+-doped BC composites (Cu-BCs). The results showed BCs pyrolyzed at higher temperatures suppressed the growth of Microcystis aeruginosa in the order of BC550 ≫ BC750 > BC950, while BC350 accelerated cell growth due to the release of inorganic nutrients. The difference could be attributed to the physicochemical characteristics, including specific surface area, adsorption capacity of nutrients and the presence of particularly persistent free radicals. Furthermore, Cu-BCs exhibited the improved inactivation performance, but the 72 h growth inhibition rates and reaction activities of Cu-BCs were still influenced by the Cu2+ loading ratio and pyrolysis temperature. These results, reported for the first time, demonstrated the algae inactivation efficiency of pristine BCs, and Cu-BCs were principally manipulated by the biochar pyrolysis temperature.

Aerobic Denitrification Promoting by Actinomycetes Coculture: Investigating Performance, Carbon Source Metabolic Characteristic, and Raw Water Restoration

The coculture theory that promotes denitrification relies on effectively utilizing the resources of low-efficiency denitrification microbes. Here, the strains Streptomyces sp. PYX97 and Streptomyces sp. TSJ96 were isolated and showed lower denitrification capacity when cultured individually. However, the coculture of strains PYX97 and TSJ96 enhanced nitrogen removal (removed 96.40% of total nitrogen) and organic carbon reduction (removed 92.13% of dissolved organic carbon) under aerobic conditions. Nitrogen balance analysis indicated that coculturing enhanced the efficiency of nitrate converted into gaseous nitrogen reaching 70.42%. Meanwhile, the coculturing promoted the cell metabolism capacity and carbon source metabolic activity. The coculture strains PYX97 and TSJ96 thrived in conditions of C/N = 10, alkalescence, and 150 rpm shaking speed. The coculturing reduced total nitrogen and CODMn in the raw water treatment by 83.32 and 84.21%, respectively. During this treatment, the cell metabolic activity and cell density increased in the coculture strains PYX97 and TSJ96 reactor. Moreover, the coculture strains could utilize aromatic protein and soluble microbial products during aerobic denitrification processes in raw water treatment. This study suggests that coculturing inefficient actinomycete strains could be a promising approach for treating polluted water bodies.

Pollutants reduction via artificial mixing in a drinking water reservoir: Insights into bacterial metabolic activity, biodiversity, interactions and co-existence of core genera

Endogenous pollution due to long periods of hypolimnetic anoxia in stratified reservoirs has become a worldwide concern, which can threaten metabolic activity, biodiversity, water quality security, and ultimately human health. In the present study, an artificial mixing system applied in a drinking water reservoir was developed to reduce pollutants, and the biological mechanism involved was explored. After approximately 44 days of system operation, the reservoir content was completely mixed resulting in the disappearance of anoxic layers. Furthermore, the metabolic activity estimated by the Biolog-ECO microplate technique and biodiversity was enhanced. 16S rRNA gene sequencing indicated a great variability on the composition of bacterial communities. Co-occurrence network analysis showed that interactions among bacteria were significantly affected by the proposed mixing system. Bacteria exhibited a more mutualistic state and >10 keystone genera were identified. Pollutants, including nitrogen, phosphorus, organic matter, iron, and manganese decreased by 30.63-80.15 %. Redundancy discriminant analysis revealed that environmental factors, especially the temperature and dissolved oxygen, were crucial drivers of the bacterial community structure. Furthermore, Spearman's correlation analysis between predominant genera and pollutants suggested that core genus played a vital role in pollutant reduction. Overall, our findings highlight the importance and provide insights on the artificial mixing systems' microbial mechanisms of reducing pollutants in drinking water reservoirs.

The role of financial markets in the energy transition: an analysis of investment trends and opportunities in renewable energy and clean technology

The crucial role that financial markets have played in accelerating the shift to clean energy and renewable sources of energy is examined in this article. Thus, we built global essential mineral trade networks from 1999 to 2020 using a complex network technique to analyze their topological properties quantitatively. The impact of crucial mineral trade patterns on the growth of renewable energy is then examined using the dynamic econometric model, along with the mediating function of technological advancement in renewable energy. It analyzes investment patterns and possibilities in various industries while underlining the critical role that financial systems play in determining the speed and scope of the change. The research uses data from reliable sources and thoroughly analyzes the body of current literature. The data shows that investments in clean technologies and renewable energy have significantly increased recently. This increase may be ascribed to several causes, including favorable governmental regulations, falling renewable energy technology prices, and rising environmental consciousness among the general people. Venture capital, private equity, public markets, and specialist funds are just a few examples of financial markets that have been instrumental in directing funding to these industries. The report also reveals a change in how money is invested in the energy industry, with conventional investments in fossil fuels declining and investments in renewable energy growing significantly. The profitability and appeal of renewable energy projects, which are now competitive with traditional energy sources, are driving this transformation. The report also identifies new investment possibilities in clean technology, including smart infrastructure, grid modernization, and energy storage. Due to their potential to improve the effectiveness, dependability, and sustainability of energy systems, these areas are expanding. The results highlight the need to establish long-term stability and incentives for investment in the clean technology and renewable energy industries. Government assistance has considerably aided investor confidence, including carbon pricing systems, tax incentives, and subsidies for renewable energy sources. This analysis emphasizes how critical financial markets are to accelerating the energy transition. Financial markets may hasten the transition to a sustainable energy system by directing investments into clean technologies and renewable energy industries. To take advantage of the investment possibilities given by the energy transition, policymakers, investors, and industry stakeholders must work together.

Promoted aerobic denitrification through denitrifying fungal communities: Co-occurrence patterns and treatment of low C/N micro-polluted water

Despite the growing interest in using mixed-culture aerobic denitrifying fungal flora (mixed-CADFF) for water remediation, there is limited research on their nitrogen removal performance in low C/N polluted water bodies. To address this knowledge gap, we isolated three mixed-CADFFs from overlying water in urban lakes to evaluate their removal performance. The total nitrogen (TN) removal efficiencies were 93.60 %, 94.64 %, and 95.18 %, while the dissolved organic carbon removal efficiencies were 96.64 %, 95.12 %, and 96.70 % for mixed-CADFF LN3, LN7, and LN15, respectively in the denitrification medium under aerobic conditions at 48 h cultivation. The three mixed-CADFFs could utilize diverse types of low molecular weight carbon sources to drive the aerobic denitrification processes efficiently. The optimal C/N ratio for the mixed-CADFFs were C/N = 10, and then C/N = 15, 7, 5, and 2. The high-throughput sequencing analysis of three mixed-CADFFs indicated that Eurotiomycetes, Cystobasidiomycetes, and Sordariomycetes were the dominant class in the communities at class level. The network analysis showed that the rare fungal species, such as Scedosporium dehoogii Saitozyma, and Candida intermedia presented positively co-occurred with the TN removal and organic matter reduction capacity. Immobilization mixed-CADFFs treatment raw water experiments indicated that three mixed-CADFFs could reduce nearly 62.73 % of TN in the low C/N micro-polluted raw water treatment. Moreover, the cell density and cell metabolism indexes were also increased during the raw water treatment. This study will provides new insight into resource utilization of the mixed-culture aerobic denitrifying fungal community in field of environment restoration.

Efficient control of cyanobacterial blooms with calcium peroxide: Threshold and mechanism

This study explored the feasibility and mechanism of cyanobacterial blooms control by calcium peroxide (CaO₂). The obtained results demonstrated a strong inhibitory effect of CaO₂ on cyanobacterial growth. The removal chlorophyll-a rate reached 31.4 %, while optimal/maximal quantum yield of PSII (Fv/Fm) decreased to 50 % after CaO₂ treatment at a concentration of 100 mg L^-1 for 96 h. Two main mechanisms were involved in the treatment of cyanobacterial bloom with CaO₂, namely oxidative damage and cyanobacterial colony formation. It was found that CaO₂ released reactive oxygen species (ROS), namely hydroxyl radicals (·OH), singlet oxygen (¹O₂), and superoxide radicals (·O₂^-), inhibiting the activity of antioxidant enzymes in cyanobacterial cells and resulting in intracellular oxidation imbalance. Cyanobacteria can resist oxidative damage by releasing extracellular polymeric substances (EPS). These EPS can combine with CaO₂-derived Ca, forming large cyanobacterial aggregates and, consequently, accelerating cell sedimentation. In addition, CaO₂ caused programmed cell death (PCD) of cyanobacteria and irreversible damage to the ultrastructure characteristic of the cyanobacterial cells. The apoptotic rate was greatly improved at 100 mg L^-1 CaO₂. On the other hand, the results obtained using qRT-PCR analysis confirmed the contribution of CaO₂ to the down-regulation of photosynthesis-related genes (rbcL and psaB), the up-regulation of microcystins (mcyA and mcyD), the up-regulation of the oxidation system: peroxiredoxin (prx) through oxidative mechanisms. The present study proposes a novel treatment method for water-containing cyanobacterial blooms using CaO₂.