Insights into the interaction mechanisms between Microcystin-degrading bacteria and Microcystis aeruginosa.

Interactions between bacteria and cyanobacteria influence the occurrence and development of harmful cyanobacterial blooms (HCBs). Bloom-forming cyanobacteria and cyanotoxin-degrading bacteria are essential in HCBs, nonetheless, their interactions and the underlying mechanisms remain unclear. To address this gap, a typical microcystin-LR (MC-LR)-degrading bacterium and a toxic Microcystis aeruginosa strain were co-cultivated to investigate their interactions. The cyanobacterial growth was enhanced by 24.8 %-44.3 % in the presence of the bacterium in the first 7 days, and the cyanobacterium enhanced the bacterial growth by 59.2 %-117.5 % throughout the growth phases, suggesting a mutualistic relationship between them. The presence of the bacterium increased cyanobacterial intracellular MC-LR content on days 4, 8, and 10 while reducing the extracellular MC-LR concentration, revealing the dual roles of the bacterium in enhancing cyanotoxin production and degrading cyanotoxins. The bacterium alleviated the oxidative stress, which may be crucial in promoting cyanobacterial growth. Critical functional genes related to cyanobacterial photosynthesis and MC-LR synthesis, and bacterial MC-LR degradation were up-regulated in the presence of the bacterium and cyanobacterium, respectively. Moreover, extracellular polymeric substances (EPS) were produced at the cell interface, implying EPS play a role in cyanobacterial-bacterial interactions. This study is the first to unveil the interaction mechanisms between cyanotoxin-degrading bacteria and bloom-forming cyanobacteria, shedding light on the dynamics of HCBs.

Enhanced inhibitory efficiency against toxic bloom forming Raphidiopsis raciborskii by Streptomyces sp. HY through triple algicidal modes: Direct and indirect attacks combined with bioflocculation.

Raphidiopsis raciborskii (R. raciborskii) forms harmful cyanobacterial blooms globally, and poses a great threat to the safety of drinking water and public health. There is a great need to develop eco-friendly biological alternative measures to mitigate mass blooms of R. raciborskii. However, previous rare studies on algicidal microorganisms against R. raciborskii restricted this aim. Recently, an algicidal bacterium Streptomyces sp. HY (designated HY) was identified with flavones producing ability, and could remove up to 98.73 % of R. raciborskii biomass within 48 h by directly attacking the cyanobacterium and release of algicidal substances (i.e., flavonoids) with a inoculum ratio of 5 %. Algicidal rate of HY was enhanced by 88.05 %, 89.33 % under dark and light, and full-light conditions respectively, when compared with the dark condition. Its algicidal substances were stable in a broad range of temperature (-80-55 °C) and pH (3-11) conditions, and all treated groups exhibited ≈ 100 % algicidal rate at day 3. HY treatment disrupted the photosynthesis system and triggered serious oxidative stress resulting in severe morphological injury. Thereby, HY treatment significantly affected expression levels of several essential genes (i.e., psbA, psaB, rbcL, ftsZ, recA, grpE), and simultaneously inhibited the biosynthesis and release of cylindrospermopsin. Yet, HY treatment didn't show any toxicity to zebrafish test embryos. Such results indicate that HY is a promising algicidal candidate strain to control global R. raciborskii blooms, and holds great promises for an effective biological measure to sustain water safety.

Cyanotoxin cylindrospermopsin disrupts lipid homeostasis and metabolism in a 3D in vitro model of the human liver.

Cylindrospermopsin, a potent hepatotoxin produced by harmful cyanobacterial blooms, poses environmental and human health concerns. We used a 3D human liver in vitro model based on spheroids of HepG2 cells, in combination with molecular and biochemical assays, automated imaging, targeted LC-MS-based proteomics, and lipidomics, to explore cylindrospermopsin effects on lipid metabolism and the processes implicated in hepatic steatosis. Cylindrospermopsin (1 µM, 48 h) did not significantly affect cell viability but partially reduced albumin secretion. However, it increased neutral lipid accumulation in HepG2 spheroids while decreasing phospholipid levels. Simultaneously, cylindrospermopsin upregulated genes for lipogenesis regulation (SREBF1) and triacylglycerol synthesis (DGAT1/2) and downregulated genes for fatty acid synthesis (ACLY, ACCA, FASN, SCD1). Fatty acid uptake, oxidation, and lipid efflux genes were not significantly affected. Targeted proteomics revealed increased levels of perilipin 2 (adipophilin), a major hepatocyte lipid droplet-associated protein. Lipid profiling quantified 246 lipid species in the spheroids, with 28 significantly enriched and 15 downregulated by cylindrospermopsin. Upregulated species included neutral lipids, sphingolipids (e.g., ceramides and dihexosylceramides), and some glycerophospholipids (phosphatidylethanolamines, phosphatidylserines), while phosphatidylcholines and phosphatidylinositols were mostly reduced. It suggests that cylindrospermopsin exposures might contribute to developing and progressing towards hepatic steatosis or metabolic dysfunction-associated steatotic liver disease (MASLD).

Detection of Anatoxins in Human Urine by Liquid Chromatography Triple Quadrupole Mass Spectrometry and ELISA.

Harmful cyanobacterial blooms are becoming more common and persistent around the world. When in bloom, various cyanobacterial strains can produce anatoxins in high concentrations, which, unlike other cyanobacterial toxins, may be present in clear water. Potential human and animal exposures to anatoxins occur mainly through unintentional ingestion of contaminated algal mats and water. To address this public health threat, we developed and validated an LC-MS/MS method to detect anatoxins in human urine to confirm exposures. Pooled urine was fortified with anatoxin-a and dihydroanatoxin at concentrations from 10.0 to 500 ng/mL to create calibrators and quality control samples. Samples were diluted with isotopically labeled anatoxin and solvent prior to LC-MS/MS analysis. This method can accurately quantitate anatoxin-a with inter- and intraday accuracies ranging from 98.5 to 103% and relative standard deviations < 15%, which is within analytical guidelines for mass spectrometry methods. Additionally, this method qualitatively detects a common degradation product of anatoxin, dihydroanatoxin, above 10 ng/mL. We also evaluated a commercial anatoxin-a ELISA kit for potential diagnostic use; however, numerous false positives were detected from unexposed individual human urine samples. In conclusion, we have developed a method to detect anatoxins precisely and accurately in urine samples, addressing a public health area of concern, which can be applied to future exposure events.

Spatial and Temporal Variability of Saxitoxin-Producing Cyanobacteria in U.S. Urban Lakes.

Harmful cyanobacterial blooms (HCBs) are of growing global concern due to their production of toxic compounds, which threaten ecosystems and human health. Saxitoxins (STXs), commonly known as paralytic shellfish poison, are a neurotoxic alkaloid produced by some cyanobacteria. Although many field studies indicate a widespread distribution of STX, it is understudied relative to other cyanotoxins such as microcystins (MCs). In this study, we assessed eleven U.S. urban lakes using qPCR, sxtA gene-targeting sequencing, and 16S rRNA gene sequencing to understand the spatio-temporal variations in cyanobacteria and their potential role in STX production. During the blooms, qPCR analysis confirmed the presence of the STX-encoding gene sxtA at all lakes. In particular, the abundance of the sxtA gene had a strong positive correlation with STX concentrations in Big 11 Lake in Kansas City, which was also the site with the highest quantified STX concentration. Sequencing analysis revealed that potential STX producers, such as Aphanizomenon, Dolichospermum, and Raphidiopsis, were present. Further analysis targeting amplicons of the sxtA gene identified that Aphanizomenon and/or Dolichospermum are the primary STX producer, showing a significant correlation with sxtA gene abundances and STX concentrations. In addition, Aphanizomenon was associated with environmental factors, such as conductivity, sulfate, and orthophosphate, whereas Dolichospermum was correlated with temperature and pH. Overall, the results herein enhance our understanding of the STX-producing cyanobacteria and aid in developing strategies to control HCBs.

Stringent Response of Cyanobacteria and Other Bacterioplankton during Different Stages of a Harmful Cyanobacterial Bloom.

We conducted a field study to investigate the role of stringent response in cyanobacteria and coexisting bacterioplankton during nutrient-deprived periods at various stages of bloom in a freshwater lake (Utah Lake) for the first time. Using metagenomics and metatranscriptomics analyses, we examined the cyanobacterial ecology and expression of important functional genes related to stringent response, N and P metabolism, and regulation. Our findings mark a significant advancement in understanding the mechanisms by which toxic cyanobacteria survive and proliferate during nitrogen (N) and phosphorus (P) limitations. We successfully identified and analyzed the metagenome-assembled genomes (MAGs) of the dominant bloom-forming cyanobacteria, namely, Dolichospermum circinale, Aphanizomenon flos-aquae UKL13-PB, Planktothrix agardhii, and Microcystis aeruginosa. By mapping RNA-seq data to the coding sequences of the MAGs, we observed that these four prevalent cyanobacteria species activated multiple functions to adapt to the depletion of inorganic nutrients. During and after the blooms, the four dominant cyanobacteria species expressed high levels of transcripts related to toxin production, such as microcystins (mcy), anatoxins (ana), and cylindrospermopsins (cyr). Additionally, genes associated with polyphosphate (poly-P) storage and the stringent response alarmone (p)ppGpp synthesis/hydrolysis, including ppk, relA, and spoT, were highly activated in both cyanobacteria and bacterioplankton. Under N deficiency, the main N pathways shifted from denitrification and dissimilatory nitrate reduction in bacterioplankton toward N2-fixing and assimilatory nitrate reduction in certain cyanobacteria with a corresponding shift in the community composition. P deprivation triggered a stringent response mediated by spoT-dependent (p)ppGpp accumulation and activation of the Pho regulon in both cyanobacteria and bacterioplankton, facilitating inorganic and organic P uptake. The dominant cyanobacterial MAGs exhibited the presence of multiple alkaline phosphatase (APase) transcripts (e.g., phoA in Dolichospermum, phoX in Planktothrix, and Microcystis), suggesting their ability to synthesize and release APase enzymes to convert ambient organic P into bioavailable forms. Conversely, transcripts associated with bacterioplankton-dominated pathways like denitrification were low and did not align with the occurrence of intense cyanoHABs. The strong correlations observed among N, P, stringent response metabolisms and the succession of blooms caused by dominant cyanobacterial species provide evidence that the stringent response, induced by nutrient limitation, may activate unique N and P functions in toxin-producing cyanobacteria, thereby sustaining cyanoHABs.

Designing a cercosporin-bioinspired bifunctional algicide with flocculation and photocatalysis for efficiently controlling harmful cyanobacterial blooms.

Harmful cyanobacterial blooms (HCBs) are spreading in freshwater ecosystems worldwide, adversely affecting drinking water supplies, aquatic production, recreational and tourism activities. Therefore, the efficient and environmentally friendly method is still of interest to be developed to effectively control HCBs. Inspired by the excellent algicidal activity of cercosporin (CP), a novel metal-free algaecide SiO2@EDU@CP (EDU, N-ethyl-N'-(3-dimethylaminopropyl)urea) with flocculation and photoremoval functions, was successfully designed and prepared in one-step to simultaneously introduce CP and EDU on SiO2 nanoparticles. It could rapidly form algae flocs in 20 min with 97.1% flocculation rate, and remove Microcystis aeruginosa within 12 h with 91.0% algicidal rate under 23 W compact fluorescent light irradiation without any leaked CP detected. Additionally, odorant ß-cyclocitral and toxin microcystin-LR were both photodegraded after treatment of SiO2@EDU@CP. Further mechanistic studies showed that the introduction of EDU significantly reversed the zeta potential of SiO2-COOH to achieve the flocculation through neutral charge, and the photophysical characterization of SiO2@EDU@CP revealed the improved charge separation ability to generate reactive oxygen species. More importantly, the utility of SiO2@EDU@CP was well demonstrated by its effectiveness for algae from Taihu Lake under natural sunlight and inability to regrow after treatment. This study not only establishes a bifunctional algicide SiO2@EDU@CP to efficiently control HCBs, but also provides design possibilities to develop more novel and efficient algicides for the better control of practical HCBs.

Ecosystem anthropogenic enrichments enhance Chroococcus abundance and suppress Anabaena during cyanobacterial-dominated spring blooms in the Pengxi River, Three Gorges Reservoir, China.

Taxa-specific responses to the increasing anthropogenic eutrophication offer promising insights for mitigating harmful algal blooms (HABs) in freshwaters. The present study evaluated the HABs species dynamics in response to the ecosystem anthropogenic enrichment during cyanobacterial-dominated spring HABs in the Pengxi River, Three Gorges Reservoir, China. Results show significant cyanobacterial dominance with a relative abundance (RA = 76.54 %). The ecosystem enrichments triggered shifts in the HABs community structure from Anabaena to Chroococcus, especially in the culture involving iron (Fe) addition (RA = 66.16 %). While P-alone enrichment caused a dramatic increase in the aggregate cell density (2.45 × 108 cells L-1), the multiple enrichment (NPFe) led to maximum biomass production (as chl-a = 39.62 ± 2.33 µgL-1), indicating that nutrient in conjunction with the HABs taxonomic characteristics e.g., tendency to possess high cell pigment contents rather than cell density can potentially determine massive biomass accumulations during HABs. The stimulation of growth as biomass production demonstrated by both P-alone and the multiple enrichments, NPFe indicates that although P exclusive control is feasible in the Pengxi ecosystem, it can only guarantee a short-term reduction in HABs magnitude and duration, thus a lasting HABs mitigation measure must consider a policy recommendation involving multiple nutrient management, especially N and P dual control strategy. The present study would adequately complement the concerted effort in developing a rational predictive framework for freshwater eutrophication management and HABs mitigations in the TGR and elsewhere with similar anthropogenic stressors.

Discovery of a High-Efficient Algicidal Bacterium against Microcystis aeruginosa Based on Examinations toward Culture Strains and Natural Bloom Samples.

Harmful cyanobacterial blooms occur worldwide and pose a great threat to aquatic ecosystems and public health. The application of algicidal bacteria represents an eco-friendly strategy for controlling harmful cyanobacterial blooms; thus, searching for a high efficiency of algicidal bacteria has been becoming an important and continuous task in science. Herein, we identified a bacterial strain coded Streptomyces sp. HY with a highly algicidal activity, and investigated its algicidal efficiency and mechanism against Microcystis aeruginosa. The strain HY displayed high algicidal activity toward Microcystis aeruginosa cells, with a removal rate of 93.04% within 2 days via indirect attack. Streptomyces sp. HY also showed the ability to lyse several genera of cyanobacterial strains, including Dolichospermum, Pseudanabaena, Anabaena, and Synechocystis, whereas it showed a minor impact on the green alga Scenedesmus obliquus, demonstrating its selectivity specially for targeting cyanobacteria. Its algicidal mechanism involved damages to the photosynthesis system, morphological injury of algal cells, oxidative stress, and dysfunction of the DNA repair system. Furthermore, HY treatment reduced the expression levels of genes (mcyB and mcyD) related to microcystin biosynthesis and decreased the total content of microcystin-leucine-arginine by 79.18%. Collectively, these findings suggested that the algicidal bacteria HY is a promising candidate for harmful cyanobacterial bloom control.

Design, synthesis and mechanism research of novel algicide based on bioactive fragments synthesis strategy.

The frequency and intensity of harmful cyanobacterial blooms (HCBs) are increasing all over the world, their prevention and control have become a great challenge. In this paper, a series of 1,3,4-thiadiazole thioacetamides (T series) were designed and synthesized as potential algaecides. Among them, the compound T3 showed its best algacidal activity against Synechocystis sp. PCC 6803 (PCC 6803, EC50 = 1.51 µM) and Microcystis aeruginosa FACHB 905 (FACHB905, EC50 = 4.88 µM), which was more effective than the lead compound L1 (PCC6803, EC50 = 7.7 µM; FACHB905, EC50 = 8.8 µM) and the commercially available herbicide prometryn (PCC6803, EC50 = 4.64 µM；FACHB905, EC50 = 6.52 µM). Meanwhile, T3 showed a lower inhibitory activity (EC50 = 12.76 µM) than prometryn (EC50 = 7.98 µM) to Chlorella FACHB1227, indicating that T3 had selective inhibition to prokaryotic algae (PCC6803, FACHB905) and eukaryotic algae (FACHB1227). Furthermore, the algacidal and anti-algae activities of T3 were significantly better than those of prometryn, while the toxicity of zebrafish and human cells was less than prometryn. Electron microscope, physiological, biochemical and metabonomic analysis showed that T3 interfered with light absorption and light conversion during photosynthesis by significantly reducing chlorophyll content, thus inhibited metabolic pathways such as the Calvin cycle and TCA cycle, and eventually led to the cell rupture of cyanobacteria. These results afforded further development of effective and safe algaecides.

An insight into algicidal characteristics of Bacillus altitudinis G3 from dysfunctional photosystem and overproduction of reactive oxygen species.

Cyanobacterial blooms negatively affect aquatic ecosystems and human health. Algicidal bacteria can efficiently kill bloom-causing cyanobacteria. Bacillus altitudinis G3 isolated from Dianchi Lake shows high algicidal activity against Microcystis aeruginosa. In this study, we investigated its algicidal characteristics including attack mode, photosynthesis responses, and source and the contribution of reactive oxygen species (ROS). The results showed that G3 efficiently and specifically killed M. aeruginosa mainly by releasing both thermolabile and thermostable algicidal substances, which exhibited the highest algicidal activity (99.8%, 72 h) in bacterial mid-logarithmic growth phase. The algicidal ratio under full-light conditions (99.5%, 60 h) was significantly higher than under dark conditions (<20%, P < 0.001). G3 filtrate caused photosystem dysfunction by decreasing photosynthetic efficiency, as indicated by significantly decreased Fv/Fm and PIABS (P < 0.001) values. It also inhibited photosynthetic electron transfer as indicated by significantly decreased rETR (P < 0.001), especially QA- downstream, as revealed by significantly decreased φEo and ψo, and increased Mo (P < 0.001). These results indicated that the algicidal activity of G3 filtrate is light-dependent, and the cyanobacterial photosystem is an important target. Cyanobacterial ROS and malondialdehyde contents greatly increased by 37.1% and 208% at 36 h, respectively. ROS levels decreased by 49.2% (9 h) when diuron (3-(3-4-dichlorophenyl)-1,1-dimethylurea) partially blocked photosynthetic electron transport from QA to QB. Therefore, excessive ROS were produced from disrupted photosynthesis, especially the inhibited electron transport area in QA- downstream, and caused severe lipid peroxidation with significantly increased MDA content and oxidative stress in cyanobacteria. The ROS scavenger N-acetyl-l-cysteine significantly decreased both cyanobacterial ROS levels (34%) and algicidal ratio (52%, P < 0.05) at 39 h. Thus, excessive ROS production due to G3 filtrate administration significantly contributed to its algicidal effect. G3 could be an excellent algicide to control M. aeruginosa blooms in waters under suitable light conditions.

Cyanophage infections reduce photosynthetic activity and expression of CO2 fixation genes in the freshwater bloom-forming cyanobacterium Aphanizomenon flos-aquae.

Cyanobacteria play a significant role in ecosystem functioning as photosynthetic and CO2 fixing microorganisms. Whether and to what extent cyanophages alter these carbon and energy cycles in their cyanobacterial hosts is still poorly understood. In this study, we investigated changes in photosynthetic activity (PSII), expression of genes associated with the light phase of photosynthesis (psbA, petA, ndhK) and carbon metabolism (rbcL, zwf) as well as intracellular ATP and NADHP concentrations in freshwater bloom-forming filamentous cyanobacterium Aphanizomenon flos-aquae infected by cyanophage vB_AphaS-CL131. We found that PSII activity and expression level of rbcL genes, indicating potential for CO2 fixation, had decreased in response to cyanophage adsorption and DNA injection. During the period of viral DNA replication and assembly, PSII performance and gene expression remained at this decreased level and did not change significantly, indicating lack of transcriptional shutdown by the cyanophage. Combined, these observations suggest that although there is little to no interference between cyanophage DNA replication, host transcription and cellular metabolism, A. flos-aquae underwent a physiological state-shift toward lower efficiency of carbon and energy cycling. This further suggest potential cascading effect for co-occurring non-infected members of the microbial community.

Recent Advances in the Research on the Anticyanobacterial Effects and Biodegradation Mechanisms of Microcystis aeruginosa with Microorganisms.

Harmful algal blooms (HABs) have attracted great attention around the world due to the numerous negative effects such as algal organic matters and cyanobacterial toxins in drinking water treatments. As an economic and environmentally friendly technology, microorganisms have been widely used for pollution control and remediation, especially in the inhibition/biodegradation of the toxic cyanobacterium Microcystis aeruginosa in eutrophic water; moreover, some certain anticyanobacterial microorganisms can degrade microcystins at the same time. Therefore, this review aims to provide information regarding the current status of M. aeruginosa inhibition/biodegradation microorganisms and the acute toxicities of anticyanobacterial substances secreted by microorganisms. Based on the available literature, the anticyanobacterial modes and mechanisms, as well as the in situ application of anticyanobacterial microorganisms are elucidated in this review. This review aims to enhance understanding the anticyanobacterial microorganisms and provides a rational approach towards the future applications.

Genotoxicity of Natural Water during the Mass Development of Cyanobacteria Evaluated by the Allium Test Method: A Model Experiment with Microcosms.

Cyanobacteria, which develop abundantly in aquatic ecosystems, can be harmful to humans and animals not only by releasing toxins that cause poisoning but also by provoking cytogenetic effects. The influence of the mass development of cyanobacteria on the genotoxic properties of natural water has been studied in model ecosystems (microcosms) with different compositions of biotic components (zooplankton, amphipods and fish). The validated plant test system "Allium test" was used in this study. Genotoxic effects were detected at microcystin concentrations below those established by the World Health Organization (WHO) for drinking water. In all experimental treatments, cells with disorders such as polyploidy and mitotic abnormalities associated with damage to the mitotic spindle, including c-mitosis, as well as lagging chromosomes were found. Genotoxic effects were associated with the abundance of cyanobacteria, which, in turn, depended on the composition of aquatic organisms in the experimental ecosystem. Fish, to a greater extent than other aquatic animals, maintain an abundance of cyanobacteria. After one month, in microcosms with fish, mitotic abnormalities and polyploidy continued to be detected, whereas in other treatments, there were no statistically significant genotoxic effects. In microcosms with amphipods, the number and biomass of cyanobacteria decreased to the greatest extent, and only one parameter of genotoxic activity (frequency of polyploidy) significantly differed from the control.

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

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

Effective Early Treatment of Microcystis Exponential Growth and Microcystin Production with Hydrogen Peroxide and Hydroxyapatite.

Mitigating cyanotoxin production is essential to protecting aquatic ecosystems and public health. However, current harmful cyanobacterial bloom (HCB) control strategies have significant shortcomings. Because predicting HCBs is difficult, current HCB control strategies are employed when heavy HCBs have already occurred. Our pilot study developed an effective HCB prediction approach that is employed before exponential cyanobacterial growth and massive cyanotoxin production can occur. We used a quantitative polymerase chain reaction (qPCR) assay targeting the toxin-encoding gene mcyA to signal the timing of treatment. When control measures were applied at an early growth stage or one week before the exponential growth of Microcystis aeruginosa (predicted by qPCR signals), both hydrogen peroxide (H2O2) and the adsorbent hydroxyapatite (HAP) effectively stopped M. aeruginosa growth and microcystin (MC) production. Treatment with either H2O2 (10 mg·L-1) or HAP (40 µm particles at 2.5 g·L-1) significantly reduced both mcyA gene copies and MC levels compared with the control in a dose-dependent manner. While both treatments reduced MC levels similarly, HAP showed a greater ability to reduce mcyA gene abundance. Under laboratory culture conditions, H2O2 and HAP also prevented MC production when applied at the early stages of the bloom when mcyA gene abundance was below 105 copies·mL-1.

Low-Resolution Raman Spectroscopy for the detection of contaminant species in algal bioreactors.

Fouling of aquatic systems by harmful microalgal and cyanobacterial species is an environmental and public health concern. Microalgal bioreactors are engineered ecosystems for the cultivation of algal biomass to meet the increasing demand for alternative protein sources and algae-derived products. Such bioreactors are often open or semi-open ponds or raceways that are prone to contamination by contaminant photosynthetic microorganisms, including harmful cyanobacterial species (HCBs). HCBs affect the quality of products through the accumulation of off-flavours, reducing their acceptance by consumers, and through the production of several different toxins collectively known as cyanotoxins. The density of cultured species within the bioreactor environment creates difficulty in detecting low concentrations of contaminant cells, and there is currently no technology enabling rapid monitoring of contaminations. The present study demonstrates the potential of Low-Resolution Raman Spectroscopy (LRRS) as a tool for rapid detection of low concentrations of HCBs within dense populations of the spirulina (Arthrospira platensis) cultures. An LRRS system adapted for the direct measurement of raw biomass samples was used to assemble a database of Raman spectral signatures, from eight algal and cyanobacterial strains. This dataset was used to develop both quantitative and discriminative chemometric models. The results obtained from the chemometric analyses demonstrate the ability of the LRRS to detect and quantify algal and cyanobacterial species at concentrations as low as 103 cells/mL and to robustly discriminate between species at concentrations of 104 cells/mL. The LRRS and chemometric analyses were further able to detect the presence of low concentrations (103cells/mL) of contaminating species, including the toxic cyanobacterium Microcystis aeruginosa, within dense (>107 cells/mL) spirulina cultures. The results presented provide a first demonstration of the potential of LRRS technology for real-time detection of contaminant species within microalgal bioreactors, and possibly for early detection of developing harmful algal blooms in other aquatic ecosystems.

Environmental controls of harmful cyanobacterial blooms in Chinese inland waters.

Harmful cyanobacterial blooms (CyanoHABs) are expanding world-wide, adversely affecting aquatic food production, recreational and tourism activities and safe drinking water supplies. China's inland waters have been increasingly threatened by CyanoHABs during the past several decades. The environmental factors controlling CyanoHABs are highly variable in space and time in China due to significant variations in climate, geography, geological and geochemical conditions among its many regions. Here, we synthesize diverse examples among Chinese water bodies regarding interactive effects of anthropogenic, climatic and geographic drivers influencing CyanoHAB potentials and dynamics in lakes and reservoirs; in order to provide a perspective and integrative approach to mitigating CyanoHABs. In China's many shallow water bodies, water quality is highly susceptible to human activity and to changing climatic and hydrological conditions, when compared to deeper lakes. Rapid increases in population, economic activity, and wastewater have accelerated CyanoHABs in China since 1980s, especially in the heavily urbanized, agricultural and industrial regions in the middle and lower Yangtze River basins. Climatic changes have provided an additional catalyst for expansion of CyanoHABs. In particular, rising spring temperatures have accelerated the onset and proliferation of Microcystis spp, blooms in the middle and lower reaches of Yangtze River basin. Large hydroelectric and water supply projects, like the Three Gorges Reservoir (TGR), have altered hydrological regimes, and have led to an increase of CyanoHABs in reservoirs and tributaries due to increases in water residence times. Manipulating water level fluctuations in the TGR may prove useful for controlling CyanoHAB in its tributary bays. Overall,CyanoHAB mitigation strategies will have to incorporate both N and P input reductions in these shallow systems. Furthermore, nutrient reduction strategies must consider climate change-induced increases in extreme weather events, including more intense rainfall and protracted heat waves and droughts, which can extend the magnitudes and duration of CyanoHABs. Ensuring the maintenance of natural hydrologic connectivity between lakes and rivers is of utmost importance in mitigating CyanoHABs throughout China.

Toxigenic Microcystis aeruginosa (Cyanobacteria) affects the population growth of two common green microalgae: Evidence of other allelopathic metabolites different to cyanotoxins.

Agriculture runoffs and discharge of wastewaters are the major causes of eutrophication. Although eutrophication could promote the thriving of any phytoplankter, harmful algal blooms (HABs) are dominated frequently by cyanobacteria. Currently, HABs dominated by the toxigenic cyanobacterium Microcystis aeruginosa in lakes and reservoirs are the main environmental concerns worldwide. This study aimed to determine how M. aeruginosa (Ma) modifies the population growth of Pseudokirchneriella subcapitata (Ps) and Ankistrodesmus falcatus (Af). Growth kinetics were determined for each species and in the combinations: Ps-Ma, Af-Ma, Af-Ps, and Ps-Af-Ma. At the end of experiments, photosynthetic pigments, phycobiliproteins, and microcystins were quantified. A logistic equation significantly described the growth trend for all of the tested species, enabling the identification of negative effects on early stages in the population growth of co-cultures with the cyanobacterium; in addition, the interaction effects on the growth rate and in the maximum attainable population density were determined. The biomasses of A. falcatus and P. subcapitata were significantly higher when cultured individually than in all of the combinations with the cyanobacterium. The concentrations of chlorophyll a and b, as well as carotenoids, were lower in combined cultures, but phycobiliprotein content in the cultures with M. aeruginosa was not significantly affected. Microcystis aeruginosa negatively affected the growth of the microalgae, but A. falcatus was significantly more inhibited than P. subcapitata; however, microcystin concentrations were significantly reduced in the co-cultures with microalgae. These results could help to explain the displacements of microalgae when cyanobacteria are present, giving rise to cyanobacterial blooms in eutrophic freshwaters.

Potentially Toxic Planktic and Benthic Cyanobacteria in Slovenian Freshwater Bodies: Detection by Quantitative PCR.

Due to increased frequency of cyanobacterial blooms and emerging evidence of cyanotoxicity in biofilm, reliable methods for early cyanotoxin threat detection are of major importance for protection of human, animal and environmental health. To complement the current methods of risk assessment, this study aimed to evaluate selected qPCR assays for detection of potentially toxic cyanobacteria in environmental samples. In the course of one year, 25 plankton and 23 biofilm samples were collected from 15 water bodies in Slovenia. Three different analyses were performed and compared to each other; qPCR targeting mcyE, cyrJ and sxtA genes involved in cyanotoxin production, LC-MS/MS quantifying microcystin, cylindrospermopsin and saxitoxin concentration, and microscopic analyses identifying potentially toxic cyanobacterial taxa. qPCR analyses detected potentially toxic Microcystis in 10 lake plankton samples, and potentially toxic Planktothrix cells in 12 lake plankton and one lake biofilm sample. A positive correlation was observed between numbers of mcyE gene copies and microcystin concentrations. Potential cylindrospermopsin- and saxitoxin-producers were detected in three and seven lake biofilm samples, respectively. The study demonstrated a potential for cyanotoxin production that was left undetected by traditional methods in both plankton and biofilm samples. Thus, the qPCR method could be useful in regular monitoring of water bodies to improve risk assessment and enable timely measures.