A novel hierarchical network-based approach to unveil the complexity of functional microbial genome.

Biological networks serve a crucial role in elucidating intricate biological processes. While interspecies environmental interactions have been extensively studied, the exploration of gene interactions within species, particularly among individual microorganisms, is less developed. The increasing amount of microbiome genomic data necessitates a more nuanced analysis of microbial genome structures and functions. In this context, we introduce a complex structure using higher-order network theory, "Solid Motif Structures (SMS)", via a hierarchical biological network analysis of genomes within the same genus, effectively linking microbial genome structure with its function. Leveraging 162 high-quality genomes of Microcystis, a key freshwater cyanobacterium within microbial ecosystems, we established a genome structure network. Employing deep learning techniques, such as adaptive graph encoder, we uncovered 27 critical functional subnetworks and their associated SMSs. Incorporating metagenomic data from seven geographically distinct lakes, we conducted an investigation into Microcystis' functional stability under varying environmental conditions, unveiling unique functional interaction models for each lake. Our work compiles these insights into an extensive resource repository, providing novel perspectives on the functional dynamics within Microcystis. This research offers a hierarchical network analysis framework for understanding interactions between microbial genome structures and functions within the same genus.

Inhibition of Fusarium graminearum growth and spore germination by a Streptomyces amritsarensis strain capable of killing and growing on Microcystis scum.

AIMS: Developing energy-saving and ecofriendly strategies for treating harvested Microcystis biomass. METHODS AND RESULTS: Streptomyces amritsarensis HG-16 was first reported to effectively kill various morphotypes of natural Microcystis colonies at very high cell densities. Concurrently, HG-16 grown on lysed Microcystis maintained its antagonistic activity against plant pathogenic fungus Fusarium graminearum. It could completely inhibit spore germination and destroy mycelial structure of F. graminearum. Transcriptomic analysis revealed that HG-16 attacked F. graminearum in a comprehensive way: interfering with replication, transcription, and translation processes, inhibiting primary metabolisms, hindering energy production and simultaneously destroying stress-resistant systems of F. graminearum. CONCLUSIONS: The findings of this study provide a sustainable and economical option for resource reclamation from Microcystis biomass: utilizing Microcystis slurry to propagate HG-16, which can subsequently be employed as a biocontrol agent for managing F. graminearum.

Microcystis aeruginosa aggravated arsenic accumulation in silver carp during silver carp controlling algal bloom in arsenic-contaminated water.

Silver carp mediated biological control techniques are often advocated for controlling cyanobacteria blooms in eutrophic water, which are often enriched with arsenic (As). However, the transfer and fate of As during the biological control of cyanobacteria blooms by silver carp in As-rich eutrophic water remain unclear. Based on the simulated ecosystem experiment, the accumulation of As in silver carp and the transfer and fate of As in the water-algae-silver carp system during Microcystis aeruginosa blooms controlled by silver carp were investigated. Microcystis aeruginosa showed high tolerance to As(V). The accumulation of As in different tissues of silver carp was different, as follows: intestine > liver > gill > skin > muscle. After silver carp ingested As-rich Microcystis aeruginosa, As accumulation in the intestine, liver, gill, and skin of silver carp was enhanced under the action of digestion and skin contact. Compared with the system without algal, As accumulation in the intestine, liver, gill, and skin of silver carp increased by 1.1, 3.3, 3.3, and 9.6 times, respectively, after incubation for 30 days in the system with Microcystis aeruginosa, while the accumulation of As in the muscle was only slightly increased by 0.56 mg/kg. This work revealed the transfer and fate of As during algal control by silver carp, elucidated the accumulation mechanism of As in water-algae-silver carp system, enriched our understanding of As bioaccumulation and transformation in As-rich eutrophication water, and provided a scientific basis for assessing and predicting As migration and enrichment in water-algae-silver carp system.

A synthetic and transparent clay removes Microcystis aeruginosa efficiently.

Clay-algae flocculation is a promising method to remove harmful algal blooms (HABs) in aquatic ecosystems. Many HAB-generating species, such as Microcystis aeruginosa (M. aeruginosa), a common species in lakes, produce toxins and harm the environment, human health, and the economy. Natural clays, such as bentonite and kaolinite, and modification of these clays have been applied to mitigate HABs by forming large aggregates and settling down. In this study, we aim to examine the impact of laponite, a commercially available smectite clay that is synthetic, transparent, compatible with human tissues, and degradable, on removing HABs. We compare the cell removal efficiencies (RE) of laponite, two natural clays, and their polyaluminum chloride (PAC)-modified versions through clay-algae flocculation experiments. Our results show that the optimum concentrations of laponite, bentonite, kaolinite, PAC-modified bentonite, and PAC-modified kaolinite to remove 80 % of the M. aeruginosa cells from the water column are 0.05 g/L, 2 g/L, 4 g/L, 2 g/L and 0.3 g/L respectively. Therefore, to achieve the same cell removal efficiency, the amount of laponite needed is 40 to 80 times less than bentonite and kaolinite, and 6 times less than PAC-modified kaolinite. We demonstrate that the superior performance of laponite clay is because of its smaller particle size, which increases the encounter rate between cells and clay particles. Furthermore, experiments using water samples from Powderhorn Lake confirmed laponite's effectiveness in mitigating HABs. Our price analysis also suggests that this commercially-available clay, laponite, can be used in the field at a relatively low cost.

Alleviation of H2O2 toxicity by extracellular catalases in the phycosphere of Microcystis aeruginosa.

High levels of environmental H2O2 represent a threat to many freshwater bacterial species, including toxic-bloom-forming Microcystis aeruginosa, particularly under high-intensity light conditions. The highest extracellular catalase activity-possessing Pseudoduganella aquatica HC52 was chosen among 36 culturable symbiotic isolates from the phycosphere in freshly collected M. aeruginosa cells. A zymogram for catalase activity revealed the presence of only one extracellular catalase despite the four putative catalase genes (katA1, katA2, katE, and srpA) identified in the newly sequenced genome (∼6.8 Mb) of P. aquatica HC52. Analysis of secreted catalase using liquid chromatography-tandem mass spectrometry was identified as KatA1, which lacks a typical signal peptide, although the underlying mechanism for its secretion is unknown. The expression of secreted KatA1 appeared to be induced in the presence of H2O2. Proteomic analysis also confirmed the presence of KatA1 inside the outer membrane vesicles secreted by P. aquatica HC52 following exposure to H2O2. High light intensities (> 100 µmol m-2 s-1) are known to kill catalase-less axenic M. aeruginosa cells, but the present study found that the presence of P. aquatica cells supported the growth of M. aeruginosa, while the extracellular catalases in supernatant or purified form also sustained the growth of M. aeruginosa under the same conditions. Our results suggest that the extracellular catalase secreted by P. aquatica HC52 enhances the tolerance of M. aeruginosa to H2O2, thus promoting the formation of M. aeruginosa blooms under high light intensities.

Physiological and transcriptome level responses of Microcystis aeruginosa and M. viridis to environmental concentrations of triclosan.

The toxicity of triclosan (TCS) to various aquatic organisms has been demonstrated at environmental concentrations. However, the effects and mechanisms of TCS on toxic cyanobacteria remains largely unexplored. This study investigated the physiological and molecular variations in two representative toxic Microcystis species (M. aeruginosa and M. viridis) under exposure to TCS for 12 d. Our findings demonstrated that the median effective concentration (EC50) of TCS for both Microcystis species were close to the levels detected in the environment (M. aeruginosa: 9.62 µg L-1; M. viridis: 27.56 µg L-1). An increased level of reactive oxygen species (ROS) was observed in Microcystis, resulting in oxidative damage when exposed to TCS at concentrations ranging from 10 µg L-1 to 50 µg L-1. The photosynthetic activity of Microcystis had a certain degree of recovery capability at low concentrations of TCS. Compared to M. aeruginosa, the higher recovery capability of the photosynthetic system in M. viridis would be mainly attributed to the increased ability for PSII repair and phycobilisome synthesis. Additionally, the synthesis of microcystins in the two species and the release rate in M. viridis significantly increased under 10-50 µg L-1 TCS. At the molecular level, exposure to TCS at EC50 for 12 d induced the dysregulation of genes associated with photosynthesis and antioxidant system. The upregulation of genes associated with microcystin synthesis and nitrogen metabolism further increased the potential risk of microcystin release. Our results revealed the aquatic toxicity and secondary ecological risks of TCS at environmental concentrations, and provided theoretical data with practical reference value for TCS monitoring.

Duplex Real-Time Fluorescent Quantitative PCR Assays for the Detection of Toxigenic Microcystis Genotypes Based on SNP/InDel Variation in mcy Gene Cluster.

In this study, the toxigenic characteristics of 14 strains of Microcystis were analyzed, and single nucleotide polymorphism (SNP) and insertion/deletion (InDel) loci in microcystin synthetase (mcy) gene clusters were screened. Based on SNP and InDel loci associated with the toxigenic characteristics, primers and TaqMan or Cycling fluorescent probes were designed to develop duplex real-time fluorescent quantitative PCR (FQ-PCR) assays. After evaluating specificity and sensitivity, these assays were applied to detect the toxigenic Microcystis genotypes in a shrimp pond where Microcystis blooms occurred. The results showed a total of 2155 SNP loci and 66 InDel loci were obtained, of which 12 SNP loci and 5 InDel loci were associated with the toxigenic characteristics. Three duplex real-time FQ-PCR assays were developed, each of which could quantify two genotypes of toxigenic Microcystis. These FQ-PCR assays were highly specific, and two Cycling assays were more sensitive than TaqMan assay. In the shrimp pond, six genotypes of toxigenic Microcystis were detected using the developed FQ-PCR assays, indicating that above genotyping assays have the potential for quantitative analysis of the toxigenic Microcystis genotypes in natural water.

Seasonal dynamics of toxigenic Microcystis in a large, shallow Lake Peipsi (Estonia) using microcystin mcyE gene abundance.

Large and temperate Lake Peipsi is the fourth largest lake in Europe, where the massive cyanobacterial blooms are composed mostly of Microcystis spp., which have been common for several decades now. The seasonal dynamics of potentially toxic Microcystis were studied using microscopy and quantitative polymerase chain reaction (qPCR) by assessing the microcystin-encoding microcystin synthetase gene E (mcyE) abundances. Water samples were analyzed over the lake areas, varying in depth, trophic level, and cyanobacterial composition during the growing period of 2021. The Microcystis mcyE genes were detected through the growing period (May-October), forming peak abundances in September with decreasing temperatures (8.9-11.1 °C). Total phosphorus (TP) and nitrate (NO3-) were the most relevant environmental variables influencing the Microcystis biomass as well as mcyE abundances. Comparison with previous years (2011, 2012) indicated that the abundance and seasonal dynamics of toxigenic Microcystis can be highly variable between the years and lake areas, varying also in dominant Microcystis species. Contrary to expectations, based on mcyE abundances, the increased risk of toxin-producing Microcystis can occur in Peipsi through the growing period, independently of the water temperature and biomasses of Microcystis.

Sustained and enhanced inhibitory effects of allelochemicals on Microcystis Aeruginosa during its recruitment stage.

Microcystis aeruginosa is the main toxic strain in cyanobacterial blooms, and the recruitment stage in its temperature-dependent seasonal succession is considered as the key to its subsequent growth. In this study, a protocol with specific temperature settings was developed as the simulated recruitment stage in order to investigate and confirm the superior inhibitory effects of allelochemicals on M. aeruginosa at that stage of recruitment. One of the most common allelochemicals, gallic acid (GA) (10 mg/L, 20 mg/L) was employed to treat M. aeruginosa under initially low temperature condition (15 °C), then intermediate (20 °C) and last normal (26 °C), which corresponds to the critical temperatures for cyanobacterial recruitment and growth. Growth, metabolism, photosynthetic activity, extracellular polysaccharides (EPS) and microcystins (MCs) release were analyzed and discussed in this study, and a more sustained and better inhibitory effect over a 20-day period was achieved. Notably, GA (10 mg/L) markedly delayed the recruitment of M. aeruginosa from low temperature, with an inhibition efficiency of 85.71 %, and suppressing Fv/Fm and photosynthetic pigments production. It is also observed that M. aeruginosa at recruitment stage exhibited higher sensitivity and poorer resistance to allelochemical treatment, with variable responses suggesting that optimal dosages may alter. The antioxidant enzyme activities remained high under prolonged stress, and the secretion of EPS was stimulated, indicating that cyanobacteria were more inclined to form colonies. While the laboratory-based inhibitory mechanism appeared to increase the release of microcystins in individual cells, the actual concentration of microcystins in natural aquatic environments requires further investigation.

Harmful planktonic Microcystis and benthic Oscillatoria-induced toxicological effects on the Asian clam (Corbicula fluminea): A survey on histopathology, behavior, oxidative stress, apoptosis and inflammation.

Cyanobacterial blooms are worldwide distributed and threaten aquatic ecosystems and public health. The current studies mainly focus on the adverse impacts of planktonic cyanobacteria or pure cyanotoxins, while the benthic cyanobacteria-induced ecotoxic effects are relatively lacking. The cyanobacterial cell-induced toxic effects on aquatic organisms might be more serious and complex than the pure cyanotoxins and crude extracts of cyanobacteria. This study explored the chronic effects of toxin-producing planktonic Microcystis aeruginosa (producing microcystin) and benthic Oscillatoria sp. (producing cylindrospermopsin) on the behaviors, tissue structures, oxidative stress, apoptosis, and inflammation of the Asian clams (Corbicula fluminea) under 28-d exposure. The data showed that both M. aeruginosa and Oscillatoria sp. can decrease the behaviors associated with the feeding activity and induce tissue damage (i.e. gill and digestive gland) in clams. Furthermore, two kinds of cyanobacteria can alter the antioxidant enzyme activities and increase antioxidant, lipid oxidation product, and neurotransmitter degrading enzyme levels in clams. Moreover, two kinds of cyanobacteria can activate apoptosis-related enzyme activities and enhance the proinflammatory cytokine levels of clams. In addition, two kinds of cyanobacteria can disturb the transcript levels of genes linked with oxidative stress, apoptosis, and inflammation. These results suggested harmful cyanobacteria can threaten the survival and health of clams, while the benthic cyanobacteria-induced adverse effects deserve more attention. Our finding also indicated that it is necessary to focus on the entire algal cell-induced ecotoxicity when concerning the ecological impacts of cyanobacterial blooms.

Microcystis viridis NIES-102 Cyanobacteria Lectin (MVL) Interacts with SARS-CoV-2 Spike Protein Receptor Binding Domains (RBDs) via Protein-Protein Interaction.

The emergence of coronavirus disease 2019 (COVID-19) posed a major challenge to healthcare systems worldwide, especially as mutations in the culprit Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) complicated the development of vaccines and antiviral drugs. Therefore, the search for natural products with broad anti-SARS-CoV-2 capabilities is an important option for the prevention and treatment of similar infectious diseases. Lectins, which are widely recognized as antiviral agents, could contribute to the development of anti-SARS-CoV-2 drugs. This study evaluated the binding affinity of six lectins (including the cyanobacterial lectin from Microcystis viridis NIES-102 (MVL), and Jacalin, a lectin from the breadfruit, Artocarpus altilis) to the receptor binding domain (RBD) of the spike protein on the original (wild) SARS-CoV-2 and three of its mutants: Alpha, Delta, and Omicron. MVL and Jacalin showed distinct binding affinity to the RBDs of the four SARS-CoV-2 strains. The remaining four lectins (DB1, ConA, PHA-M and CSL3) showed no such binding affinity. Although the glycan specificities of MVL and Jacalin were different, they showed the same affinity for the spike protein RBDs of the four SARS-CoV-2 strains, in the order of effectiveness Alpha > Delta > original > Omicron. The verification of glycan-specific inhibition revealed that both lectins bind to RBDs by glycan-specific recognition, but, in addition, MVL binds to RBDs through protein-protein interactions.

Impact of butylparaben on growth dynamics and microcystin-LR production in Microcystis aeruginosa.

The presence of butylparaben (BP), a prevalent pharmaceutical and personal care product, in surface waters has raised concerns regarding its impact on aquatic ecosystems. Despite its frequent detection, the toxicity of BP to the cyanobacterium Microcystis aeruginosa remains poorly understood. This study investigates the influence of BP on the growth and physiological responses of M. aeruginosa. Results indicate that low concentrations of BP (below 2.5 mg/L) have negligible effects on M. aeruginosa growth, whereas higher concentrations (5 mg/L and 10 mg/L) lead to significant growth inhibition. This inhibition is attributed to the severe disruption of photosynthesis, evidenced by decreased Fv/Fm values and chlorophyll a content. BP exposure also triggers the production of reactive oxygen species (ROS), resulting in elevated activity of antioxidant enzymes. Excessive ROS generation stimulates the production of microcystin-LR (MC-LR). Furthermore, lipid peroxidation and cell membrane damage indicate that high BP concentrations cause cell membrane rupture, facilitating the release of MC-LR into the environment. Transcriptome analysis reveals that BP disrupts energy metabolic processes, particularly affecting genes associated with photosynthesis, carbon fixation, electron transport, glycolysis, and the tricarboxylic acid cycle. These findings underscore the profound physiological impact of BP on M. aeruginosa and highlight its role in stimulating the production and release of MC-LR, thereby amplifying environmental risks in aquatic systems.

Ultrasonic-assisted extraction of total flavonoids from Zanthoxylum bungeanum residue and their allelopathic mechanism on Microcystis aeruginosa.

Water eutrophication has emerged as a pressing concern for massive algal blooms, and these harmful blooms can potentially generate harmful toxins, which can detrimentally impact the aquatic environment and human health. Consequently, it is imperative to identify a safe and efficient approach to combat algal blooms to safeguard the ecological safety of water. This study aimed to investigate the procedure for extracting total flavonoids from Z. bungeanum residue and assess its antioxidant properties. The most favorable parameters for extracting total flavonoids from Z. bungeanum residue were a liquid-solid ratio (LSR) of 20 mL/g, a solvent concentration of 60%, an extraction period of 55 min, and an ultrasonic temperature of 80 °C. Meanwhile, the photosynthetic inhibitory mechanism of Z. bungeanum residue extracts against M. aeruginosa was assessed with a particular focus on the concentration-dependent toxicity effect. Z. bungeanum residue extracts damaged the oxygen-evolving complex structure, influenced energy capture and distribution, and inhibited the electron transport of PSII in M. aeruginosa. Furthermore, the enhanced capacity for ROS detoxification enables treated cells to sustain their photosynthetic activity. The findings of this study hold considerable relevance for the ecological management community and offer potential avenues for the practical utilization of resources in controlling algal blooms.

Can a shift in dominant species of Microcystis alter growth and reproduction of waterfleas?

The bloom-forming species Microcystis wesenbergii and M. aeruginosa occur in many lakes globally, and may exhibit alternating blooms both spatially and temporally. As environmental changes increase, cyanobacteria bloom in more and more lakes and are often dominated by M. wesenbergii. The adverse impact of M. aeruginosa on co-existing organisms including zooplanktonic species has been well-studied, whereas studies of M. wesenbergii are limited. To compare effects of these two species on zooplankton, we explored effects of exudates from different strains of microcystin-producing M. aeruginosa (Ma905 and Ma526) and non-microcystin-producing M. wesenbergii (Mw908 and Mw929), on reproduction by the model zooplankter Daphnia magna in both chronic and acute exposure experiments. Specifically, we tested physiological, biochemical, molecular and transcriptomic characteristics of D. magna exposed to Microcystis exudates. We observed that body length and egg and offspring number of the daphnid increased in all treatments. Among the four strains tested, Ma526 enhanced the size of the first brood, as well as total egg and offspring number. Microcystis exudates stimulated expression of specific genes that induced ecdysone, juvenile hormone, triacylglycerol and vitellogenin biosynthesis, which, in turn, enhanced egg and offspring production of D. magna. Even though all strains of Microcystis affected growth and reproduction, large numbers of downregulated genes involving many essential pathways indicated that the Ma905 strain might contemporaneously induce damage in D. magna. Our study highlights the necessity of including M. wesenbergii into the ecological risk evaluation of cyanobacteria blooms, and emphasizes that consequences to zooplankton may not be clear-cut when assessments are based upon production of microcystins alone.

Microplastics enhanced the allelopathy of pyrogallol on toxic Microcystis with additional risks: Microcystins release and greenhouse gases emissions.

Cyanobacteria blooms (CBs) caused by eutrophication pose a global concern, especially Microcystis aeruginosa (M. aeruginosa), which could release harmful microcystins (MCs). The impact of microplastics (MPs) on allelopathy in freshwater environments is not well understood. This study examined the joint effect of adding polystyrene (PS-MPs) as representative MPs and two concentrations (2 and 8 mg/L) of pyrogallol (PYR) on the allelopathy of M. aeruginosa. The results showed that the addition of PS-MPs intensified the inhibitory effect of 8 mg/L PYR on the growth and photosynthesis of M. aeruginosa. After a 7-day incubation period, the cell density decreased to 69.7 %, and the chl-a content decreased to 48 % compared to the condition without PS-MPs (p < 0.05). Although the growth and photosynthesis of toxic Microcystis decreased with the addition of PS-MPs, the addition of PS-MPs significantly resulted in a 3.49-fold increase in intracellular MCs and a 1.10-fold increase in extracellular MCs (p < 0.05). Additionally, the emission rates of greenhouse gases (GHGs) (carbon dioxide, nitrous oxide and methane) increased by 2.66, 2.23 and 2.17-fold, respectively (p < 0.05). In addition, transcriptomic analysis showed that the addition of PS-MPs led to the dysregulation of gene expression related to DNA synthesis, membrane function, enzyme activity, stimulus detection, MCs release and GHGs emissions in M. aeruginosa. PYR and PS-MPs triggered ROS-induced membrane damage and disrupted photosynthesis in algae, leading to increased MCs and GHG emissions. PS-MPs accumulation exacerbated this issue by impeding light absorption and membrane function, further heightening the release of MCs and GHGs emissions. Therefore, PS-MPs exhibited a synergistic effect with PYR in inhibiting the growth and photosynthesis of M. aeruginosa, resulting in additional risks such as MCs release and GHGs emissions. These results provide valuable insights for the ecological risk assessment and control of algae bloom in freshwater ecosystems.

Combined effects of toxic Microcystis aeruginosa and high pH on antioxidant responses, immune responses, and apoptosis of the edible freshwater bivalve Corbicula fluminea.

Due to increasing anthropogenic perturbation and water eutrophication, cyanobacterial blooms (CYBs) have become a global ecological and environmental problem. Toxic CYBs and elevated pH are considered to be the two key stressors associated with eutrophication in natural waters, particularly in the event of CO2 depletion induced by dense blooms. However, previous research has been focused on investigating the impacts of toxic CYBs or pH changes in isolation, whereas the interactive effects of such stressors on edible bivalves that inhabit CYB waters still lack information. In this study, the combined effects of toxic Microcystis aeruginosa and pH shifts on the antioxidant responses, immune responses, and apoptosis of the edible freshwater bivalve Corbicula fluminea were explored. The results showed that the activity of antioxidant enzymes was significantly impacted by the interactive effects between toxic M. aeruginosa exposure and time course, yet pH shifts showed no significant effects on the activities of these antioxidant enzymes, implying that the antioxidant response in C. fluminea was mainly triggered by toxic M. aeruginosa exposure. Toxic M. aeruginosa also induced an increased production of reactive oxygen species and malondialdehyde in treated clams, particularly under high pH settings. The elevated lysosomal enzyme activity helped C. fluminea defend against toxic M. aeruginosa exposure under high pH conditions. The principal component analysis (PCA) and the integrated biomarker response (IBR) results suggested that the treated clams were subjected to the elevated toxicity of toxic M. aeruginosa in conditions of high pH. The heat shock proteins-related genes might be triggered to resist the oxidative damage in treated clams. Moreover, the upregulation of TNF and casp8 genes indicated the potential activation of the caspase8-mediated apoptotic pathway through TNF receptor interaction, potentially resulting in apoptosis. The TUNEL assay results further confirmed that apoptosis appeared in treated clams. These findings improve our understanding of the combined toxicological effects of harmful algae and pH shifts on bivalves, which will provide insights into a comprehensive ecological risk assessment of toxic CYBs to edible bivalve species.

Harvesting of cyanobacteria and phosphorus by electrocoagulation-flocculation-flotation: Role of phosphorus precipitation in cell separations and organics destabilization.

A high level of phosphate triggers the excretion of algogenic organic matter (AOM) during algae blooming, leading to disinfection by-products (DBPs) formation. The presence of phosphate could impact cyanobacteria harvesting and AOM separations by electrocoagulation. This study aims to investigate the role of phosphate in cell separations and AOM destabilization by Al-based electrocoagulation-flocculation-flotation (EFF) for harvesting of cyanobacteria and phosphate. The Al-based EFF was conducted to harvest Microcystis aeruginosa (MA) with varied phosphate (0-10 mg/L) at 5 mA/cm2 and pH 8. Fluorescent organic fractions, molecular weight distributions, the properties of flocs and DBPs formation potential were fully investigated. The results showed that the EFF at a low level of phosphate (1 mg/L) effectively improves the harvesting of MA cells, phosphate and the reduction in dissolved organic matter (DOC) up to 99.5 %, 95 % and 50 %, respectively. However, the presence of concentrated phosphate (10 mg/L) alleviates cell harvesting and worsens AOM separations due to ineffective floc formation induced by the fast formation of inactive AlPO4 precipitates along with limited Al(OH)3. At such a condition, it worsens DBPs precursors minimization owing to AOM release from MA cells. The increase in the current density during EFF can compensate for cell harvesting efficiency even though at concentrated phosphate, but it further induces AOM release. It is concluded that Al-based EFF demonstrates an efficient harvesting of cyanobacteria, phosphorus and AOM separations from algae-laden water under phosphate impact.

Exudates of Microcystis aeruginosa on oxidative stress and inflammatory responses in gills of Sinocyclocheilus grahami.

Early cyanobacterial blooms studies observed that exposure to blue-green algae led to fish gills impairment. The objective of this work was to evaluate the toxic mechanisms of exudates of Microcystis aeruginosa (MaE) on fish gills. In this study, the toxic mechanism of MaE (2×106 cells/mL) and one of its main components phytosphingosine (PHS) with two concentrations 2.9 ng/mL and 145 ng/mL were conducted by integrating histopathology, biochemical biomarkers, and transcriptomics techniques in Sinocyclocheilus grahami (S. grahami) for 96 h exposure. Damaged gill tissue with epithelial hyperplasia and hypertrophy, remarkable Na+/K+-ATPase (NKA) enzyme activity, disrupted the redox homeostats including lipid peroxidation and inflammatory responses were observed in the fish of MaE exposure group. Compare to MaE exposure, two concentrations of PHS exposure appeared to be a trend of lower degree of tissue damage, NKA activity and oxidative stress, but induced obviously lipid metabolism disorder with higher triglycerides, total cholesterol and total bile acid, which might be responsible for inflammation responses in fish gill. By transcriptome analysis, MaE exposure were primarily enriched in pathways related to gill function and immune response. PHS exposure, with higher number of differentially expressed genes (DEGs), were enriched in Toll-like receptor (TLR), Mitogen-Activated Protein Kinase (MAPK) and NOD-like receptor protein 3 (NLRP3) pathways. We concluded that MaE and PHS were induced the inflammatory responses, with oxidative stress-induced inflammation for MaE exposure but lipid metabolism disorder-induced inflammation for PHS exposure. The present study provided two toxin-induced gill inflammation response pathways under cyanobacterial blooms, which could be a scientific basis for the ecological and health risk assessment in the aquatic environment.

Enhancement of adsorption of cyanobacteria, Microcystisa aeruginosaby bacterial-based compounds.

In the present study, algicidal bacteria cultivated in an aqueous medium were utilized as a surface modification agent to develop an efficient adsorbent for the removal of Microcystis aeruginosa. The modification considerably enhanced M. aeruginosa cell removal efficiency. Moreover, the introduction of bio-compounds ensured specificity in the removal of M. aeruginosa. Additionally, the cyanotoxin release and acute toxicity tests demonstrated that the adsorption process using the developed adsorbent is environmentally safe. Furthermore, the practical feasibility of the adsorptive removal of M. aeruginosa was confirmed through cell removal tests performed using the developed adsorbent in a scaled-up reactor (50 L and 10 tons). In these tests, the effects of the adsorbent application type, water temperature, and initial cell concentration on the M. aeruginosa removal efficiency were evaluated. The results of this study provide novel insights into the valorization strategy of biological algicides repurposed as adsorbents, and provide practical operational data for effective M. aeruginosa removal in scaled-up conditions.

Metabologenomics reveals strain-level genetic and chemical diversity of Microcystis secondary metabolism.

Microcystis spp. are renowned for producing the hepatotoxin microcystin in freshwater cyanobacterial harmful algal blooms around the world, threatening drinking water supplies and public and environmental health. However, Microcystis genomes also harbor numerous biosynthetic gene clusters (BGCs) encoding the biosynthesis of other secondary metabolites, including many with toxic properties. Most of these BGCs are uncharacterized and currently lack links to biosynthesis products. However, recent field studies show that many of these BGCs are abundant and transcriptionally active in natural communities, suggesting potentially important yet unknown roles in bloom ecology and water quality. Here, we analyzed 21 xenic Microcystis cultures isolated from western Lake Erie to investigate the diversity of the biosynthetic potential of this genus. Through metabologenomic and in silico approaches, we show that these Microcystis strains contain variable BGCs, previously observed in natural populations, and encode distinct metabolomes across cultures. Additionally, we find that the majority of metabolites and gene clusters are uncharacterized, highlighting our limited understanding of the chemical repertoire of Microcystis spp. Due to the complex metabolomes observed in culture, which contain a wealth of diverse congeners as well as unknown metabolites, these results underscore the need to deeply explore and identify secondary metabolites produced by Microcystis beyond microcystins to assess their impacts on human and environmental health.IMPORTANCEThe genus Microcystis forms dense cyanobacterial harmful algal blooms (cyanoHABs) and can produce the toxin microcystin, which has been responsible for drinking water crises around the world. While microcystins are of great concern, Microcystis also produces an abundance of other secondary metabolites that may be of interest due to their potential for toxicity, ecological importance, or pharmaceutical applications. In this study, we combine genomic and metabolomic approaches to study the genes responsible for the biosynthesis of secondary metabolites as well as the chemical diversity of produced metabolites in Microcystis strains from the Western Lake Erie Culture Collection. This unique collection comprises Microcystis strains that were directly isolated from western Lake Erie, which experiences substantial cyanoHAB events annually and has had negative impacts on drinking water, tourism, and industry.