Microcystins distribution, bioaccumulation, and Microcystis genotype succession in a fish culture pond

Co-exposure of microcystin-LR and nitrite induced kidney injury through TLR4/NLRP3/GSDMD-mediated pyroptosis

The degradation of cyanobacterial blooms releases hazardous contaminants such as microcystin-LR (MC-LR) and nitrite, which may collectively exert toxicity on various bodily systems. To evaluate their individual and combined toxicity in the kidney, mice were subjected to different concentrations of MC-LR and/or nitrite over a 6-month period in this study. The results revealed that combined exposure to MC-LR and nitrite exacerbated renal pathological alterations and dysfunction compared to exposure to either compound alone. Specifically, the protein and mRNA expression of kidney injury biomarkers, such as kidney injury molecule 1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL), were notably increased in combined exposure group. Concurrently, co-exposure to MC-LR and nitrite remarkedly upregulated levels of proinflammatory cytokines TNF-α, IL-6 and IL-1β, while decreasing the anti-inflammatory cytokine IL-10. Notably, MC-LR and nitrite exhibited synergistic effects on the upregulation of renal IL-1β levels. Moreover, MC-LR combined with nitrite not only elevated mRNA levels of proinflammatory cytokines but also increased protein levels of pyroptosis biomarkers such as IL-1β, Gasdermin D (GSDMD), and Cleaved-GSDMD. Mechanistic investigations revealed that co-exposure to MC-LR and nitrite promoted pyroptosis both in vivo and in vitro, possibly through the activation of the TLR4/NLRP3/GSDMD pathway. Pretreatment with TLR4 inhibitor and NLRP3 inhibitor effectively suppressed pyroptosis induced by the co-exposure of these two toxins in HEK293T cells. These findings provide compelling evidence that MC-LR combined with nitrite synergistically induces pyroptosis in the kidney by activating the TLR4/NLRP3/GSDMD pathway. Overall, this study significantly enhances our comprehension of how environmental toxins interact and induce harm to the kidneys, offering promising avenues for identifying therapeutic targets to alleviate their toxic effects on renal health.

Blue revolution turning green? A global concern of cyanobacteria and cyanotoxins in freshwater aquaculture: A literature review

To enhance productivity, aquaculture is intensifying, with high-density fish ponds and increased feed input, contributing to nutrient load and eutrophication. Climate change further exacerbates cyanobacterial blooms and cyanotoxin production that affect aquatic organisms and consumers. A review was conducted to outline this issue from its inception - eutrophication, cyanobacterial blooms, their harmful metabolites and consequential effects (health and economic) in aquacultures. The strength of evidence regarding the relationship between cyanobacteria/cyanotoxins and potential consequences in freshwater aquacultures (fish production) globally were assessed as well, while identifying knowledge gaps and suggesting future research directions. With that aim several online databases were searched through June 2023 (from 2000), and accessible publications conducted in aquacultures with organisms for human consumption, reflecting cyanotoxin exposure, were selected. Data on cyanobacteria/cyanotoxins in aquacultures and its products worldwide were extracted and analyzed. Selected 63 papers from 22 countries were conducted in Asia (48%), Africa (22%), America (22%) and Europe (8%). Microcystis aeruginosa was most frequent, among over 150 cyanobacterial species. Cyanobacterial metabolites (mostly microcystins) were found in aquaculture water and fish from 18 countries (42 and 33 papers respectively). The most affected were small and shallow fish ponds, and omnivorous or carnivorous fish species. Cyanotoxins were detected in various fish organs, including muscles, with levels exceeding the tolerable daily intake in 60% of the studies. The majority of research was done in developing countries, employing less precise detection methods, making the obtained values estimates. To assess the risk of human exposure, the precise levels of all cyanotoxins, not just microcystins are needed, including monitoring their fate in aquatic food chains and during food processing. Epidemiological research on health consequences, setting guideline values, and continuous monitoring are necessary as well. Further efforts should focus on methods for elimination, prevention, and education.

Cyanotoxins in food: Exposure assessment and health impact

The intricate nature of cyanotoxin exposure through food reveals a complex web of risks and uncertainties in our dietary choices. With the aim of starting to unravel this intricate nexus, a comprehensive review of 111 papers from the past two decades investigating cyanotoxin contamination in food was undertaken. It revealed a widespread occurrence of cyanotoxins in diverse food sources across 31 countries. Notably, 68% of the studies reported microcystin concentrations exceeding established Tolerable Daily Intake levels. Cyanotoxins were detected in muscles of many fish species, and while herbivorous fish exhibited the highest recorded concentration, omnivorous species displayed a higher propensity for cyanotoxin accumulation, exemplified by Oreochromis niloticus. Beyond fish, crustaceans and bivalves emerged as potent cyanotoxin accumulators. Gaps persist regarding contamination of terrestrial and exotic animals and their products, necessitating further exploration. Plant contamination under natural conditions remains underreported, yet evidence underscores irrigation-driven cyanotoxin accumulation, particularly affecting leafy vegetables. Finally, cyanobacterial-based food supplements often harbored cyanotoxins (57 % of samples were positive) warranting heightened scrutiny, especially for Aphanizomenon flos-aquae-based products. Uncertainties surround precise concentrations due to methodological variations (chemical and biochemical) and extraction limitations, along with the enigmatic fate of toxins during storage, processing, and digestion. Nonetheless, potential health consequences of cyanotoxin exposure via contaminated food include gastrointestinal and neurological disorders, organ damage (e.g. liver, kidneys, muscles), and even elevated cancer risks. While microcystins received significant attention, knowledge gaps persist regarding other cyanotoxins' accumulation, exposure, and effects, as well as combined exposure via multiple pathways. Intriguing and complex, cyanotoxin exposure through food beckons further research for our safer and healthier diets.

Degradation performance and mechanism of microcystins in aquaculture water using low-temperature plasma technology

The eutrophication of aquaculture water bodies seriously restricts the healthy development of the aquaculture industry. Among them, microcystins are particularly harmful. Therefore, the development of technologies for degrading microcystins is of great significance for maintaining the healthy development of the aquaculture industry. The feasibility and mechanism of removing microcystins-LR by dielectric barrier discharge (DBD) plasma were studied. DBD discharge power of 49.6 W and a treatment time of 40 min were selected as the more suitable DBD parameters, resulting in microcystin-LR removal efficiency of 90.4%. Meanwhile, the effects of initial microcystin-LR concentration, initial pH value, turbidity, anions on the degradation effect of microcystin-LR were investigated. The removal efficiency of microcystin-LR decreased with the increase of initial microcystin-LR concentration and turbidity. The degradation efficiency of microcystin-LR at pH 4.5 and 6.5 is significantly higher than that at pH 8.5 and 3.5. HCO3- can inhibit the removal efficiency of microcystin-LR. Furthermore, five intermediates products (m/z = 1029.5, 835.3, 829.3, 815.4, 642.1) were identified in this study, and the toxicity analysis of these degradation intermediates indicated that DBD treatment can reduce the toxicity of microcystin-LR. e－aq, •OH, H2O2, and O3 have been shown to play a major role in the degradation of microcystin-LR, and the contribution ranking of these active species is e－aq > •OH > H2O2 > O3. The application of DBD plasma technology in microcystin-LR removal and detoxification has certain development potential.

The osmotic stress of Vallisneria natans (Lour.) Hara leaves originating from the disruption of calcium and potassium homeostasis caused by MC-LR

Aquatic plants are potentially impacted by microcystins (MCs) in lakes experiencing harmful algal blooms. However, how these plants respond, and possibly adapt to osmotic stress caused by MCs is unclear. Vallisneria natans is a pioneer taxon with a global distribution in eutrophic lakes. In this study, we investigated the effect of MC-LR on morphological structure, water retention, osmoregulatory ability, and homeostasis of calcium (Ca2+) and potassium (K+) ions in V. natans leaves. Results showed that the morphological changes caused by MC-LR included increased volumes of epidermal and mesophyll cells, changes in their lignification level, and the degradation of chloroplast structure and dissolution of starch granules. The increased moisture content and water potential with MC-LR concentration were consistent with the occurrence of osmotic stress, and the decreased osmotic potential implied the activation of osmoregulation. Soluble sugar and free amino acid concentrations increased at MC-LR treatments ≥10 μg/L, while inorganic ion K+ content increased in all MC-LR treatments. Although instantaneous K+inflow and Ca2+outflow occurred at 10 μg/L and 100 μg/L MC-LR, respectively, ≥1 μg/L MC-LR resulted in continuous K+ inflow and Ca2+ outflow within 24 h. Moreover, plasma membrane hyperpolarization was caused by MC-LR, especially at 1 and 10 μg/L. We suggest that Ca2+ efflux served as a signal molecule from the cytoplasmic matrix via Ca2+-ATPase, and the uptake of K+ was activated passively through transporters in response to MC-LR-induced plasma membrane hyperpolarization. Therefore, the uptake of K+ was a part of the response but not an adaptation to MC-LR stress, and is considered the cause for the uptake of water in leaves. Ca2+ and K+ homeostasis of V. natans leaves was disrupted by MC-LR concentrations as low as 1 μg/L, suggesting that aquatic plants in most eutrophic lakes may experience negative impacts such as Ca2+ loss, impacts to cell water balance, and alteration in cellular morphology, due to osmotic stress caused by MC-LR.

Feasibility and mechanism of recycling carbon resources from waste cyanobacteria and reducing microcystin toxicity by dielectric barrier discharge plasma

Recycling carbon resources from discarded cyanobacteria is a worthwhile research topic. This study focuses on the use of dielectric barrier discharge (DBD) plasma technology as a pretreatment for anaerobic fermentation of cyanobacteria. The DBD group (58.5 W, 45 min) accumulated the most short chain fatty acids (SCFAs) along with acetate, which were 3.0 and 3.3 times higher than the control. The DBD oxidation system can effectively collapse cyanobacteria extracellular polymer substances and cellular structure, improve the biodegradability of dissolved organic matter, enrich microorganisms produced by hydrolysis and SCFAs, reduce the abundance of SCFAs consumers, thereby promoting the accumulation of SCFAs and accelerating the fermentation process. The microcystin-LR removal rate of 39.8% was obtained in DBD group (58.5 W, 45 min) on day 6 of anaerobic fermentation. The toxicity analysis using the ECOSAR program showed that compared to microcystin-LR, the toxicity of degradation intermediates was reduced. The contribution order of functional active substances to cyanobacteria cracking was obtained as eaq- > •OH > 1O2 > •O2- > ONOO-, while the contribution order to microcystin-LR degradation was eaq- > •OH > •O2- > 1O2 > ONOO-. DBD has the potential to be a revolutionary pretreatment method for cyanobacteria anaerobic fermentation.

Transmission of Microcystins in Natural Systems and Resource Processes: A Review of Potential Risks to Humans Health

The rapid rise of microcystins (MCs) poses a serious threat to global freshwater ecosystems and has become an important issue of global public health. MCs have considerable stability and are the most widely distributed hepatotoxins. It cannot only accumulate in aquatic organisms and transfer to higher nutrients and levels, but also be degraded or transferred during the resource utilization of cyanobacteria. No matter which enrichment method, it will lead to the risk of human exposure. This review summarizes the research status of MCs, and introduces the distribution of MCs in different components of aquatic ecosystems. The distribution of MCs in different aquatic organisms was summarized, and the potential risks of MCs in the environment to human safety were summarized. MCs have polluted all areas of aquatic ecosystems. In order to protect human life from the health threats caused by MCs, this paper also proposes some future research directions to promote MCs control and reduce human exposure to MCs.

Risk assessment and identification of factors influencing the historical concentrations of microcystin in Lake Taihu, China

Understanding the history of microcystins (MCs) pollution in large lakes can help inform future lake management. We collected sediment cores from Lake Taihu to: investigate the long-term record of MCs (MC-LR, MC-YR, and MC-RR), explore the main environmental drivers of MCs, and assess their public health and ecological risks. Results showed that MCs content in all cores increased over time. The core from north Taihu had the highest MC concentrations, with an average total MCs (sum of MC-LR, MC-YR, and MC-RR = TMCs) content of (74.31±328.55) ng/g. The core from eastern Taihu showed the lowest average TMCs content of (2.91±3.95) ng/g. PCA showed that sediment MCs at the three sites were positively correlated with sediment chlorophyll-a. MC-LR and MC-YR in northern and western Taihu negatively correlated with both the sediment total organic carbon/sediment total nitrogen ratio (STOC/STN) and water nitrate (NO₃^--N) concentration, but three MC congeners at eastern Taihu showed positive correlations with water orthophosphate (PO₄^3--P), NO₃^--N, and STOC/STN. Generalized additive model analysis at each site revealed that NO₃^--N was the main TMCs driver in northern and western Taihu where phytoplankton dominated, whereas PO₄^3--P was the main TMCs driver in eastern Taihu where macrophytes dominated. At the whole lake scale, total phosphorus (TP) and PO₄^3--P were the most important environmental drivers influencing MCs; TP explained 47.4%, 44.2%, and 47.6% while orthophosphate explained 34.8%, 31.2%, and 34.7% of the deviance on TMCs, MC-LR, and MC-YR, respectively. NO₃^--N also showed a strong effect on MCs variation, especially on MC-YR. Risk assessment showed that both ecological and public health risk has increased in recent years. We conclude that while control of phosphorus and nitrogen input should be a major focus for future lake management, lake zone-specific management strategies may also be important.

A Review of Common Cyanotoxins and Their Effects on Fish

Global warming and human-induced eutrophication drive the occurrence of various cyanotoxins in aquatic environments. These metabolites reveal diversified mechanisms of action, encompassing cyto-, neuro-, hepato-, nephro-, and neurotoxicity, and pose a threat to aquatic biota and human health. In the present paper, we review data on the occurrence of the most studied cyanotoxins, microcystins, nodularins, cylindrospermopsin, anatoxins, and saxitoxins, in the aquatic environment, as well as their potential bioaccumulation and toxicity in fish. Microcystins are the most studied among all known cyanotoxins, although other toxic cyanobacterial metabolites are also commonly identified in aquatic environments and can reveal high toxicity in fish. Except for primary toxicity signs, cyanotoxins adversely affect the antioxidant system and anti-/pro-oxidant balance. Cyanotoxins also negatively impact the mitochondrial and endoplasmic reticulum by increasing intracellular reactive oxygen species. Furthermore, fish exposed to microcystins and cylindrospermopsin exhibit various immunomodulatory, inflammatory, and endocrine responses. Even though cyanotoxins exert a complex pressure on fish, numerous aspects are yet to be the subject of in-depth investigation. Metabolites other than microcystins should be studied more thoroughly to understand the long-term effects in fish and provide a robust background for monitoring and management actions.

The disruption of calcium and hydrogen ion homeostasis of submerged macrophyte Vallisneria natans (Lour.) Hara caused by microcystin-LR

Aquatic plants play an important role in maintaining lake water status and ecosystem stability, but the effect of the cyanotoxin microcystin (MC) on ion homeostasis in aquatic plants and the resulting adverse consequences remains unclear. This study used non-invasive micro-test technology to detect the effect of MC-LR on homeostasis of calcium (Ca²⁺) and hydrogen ions (H⁺) in Vallisneria natans (Lour.) Hara, and examined the relationship between ion homeostasis and physiological indicators. Results showed that 1) MC-LR was enriched in V. natans tissues, with greater absorption in roots than in leaves, and 2) MC-LR induced a sustained and dose-dependent Ca²⁺ efflux from leaves and recoverable Ca²⁺ efflux from roots. Although H⁺-ATPase of leaves and roots was activated by MC-LR, the effluent of H⁺ from roots and influent of H⁺ into leaves was enhanced. By affecting the homeostasis of Ca²⁺ and H⁺, MC-LR directly or indirectly affected accumulation of nutrients essential for maintaining normal growth: accumulation of nitrogen, magnesium, phosphorus, calcium, iron, and zinc decreased in leaves; calcium, magnesium, and zinc decreased in roots; and potassium showed an increase in both leaves and roots. Microscopy revealed MC-LR results in leaf swelling and reduced accumulation of protein and starch, presumably due to changes in nutrient processes. In addition, efflux of Ca²⁺ and reduced accumulation of transition metals resulted in decreased ROS levels in leaves and roots. The disruption of ionic homeostasis in aquatic plants can be caused by as small a concentration as 1 μg/L MC-LR, indicating potential ecological impacts caused by microcystin need greater attention.

Mechanism of dielectric barrier plasma technology to improve the quantity and quality of short chain fatty acids in anaerobic fermentation of cyanobacteria

The recycling of high value carbon resources from cyanobacteria has become a research hotspot. This work investigated the possibility of dielectric barrier discharge (DBD) plasma pretreatment to improve the anaerobic fermentation performance of cyanobacteria. The maximum accumulations of short-chain fatty acids (SCFAs) and acetic acid in DBD group were 3.30 and 1.49 times of that in control group. The physical effects of DBD plasma and the oxidative stress response of cyanobacteria cells could improve the solubilization of cyanobacteria polymer. The destruction of humus by DBD plasma can reduce the negative impact of humus on the early stage of anaerobic fermentation, thus facilitating the rapid start of anaerobic fermentation. The contents of Bacteroidetes, Firmicutes and Chloroflexi in DBD group were higher than those in control group, while the content of Proteobacteria was on the contrary, which was conducive to the hydrolysis and acidification process. The decrease of Methanosaeta sp. and Methanosarcina sp. abundance in DBD group might be another reason for the increase of acetic acid ratio. Under the joint action of plasma chemical oxidation and microbial degradation, the degradation effect of microcystin-LR in the anaerobic fermentation supernatant of DBD group was better than that of the control group, which was conducive to the recycling of cyanobacteria anaerobic fermentation supernatant. Therefore, DBD pretreatment was conductive to recycling valuable carbon source from cyanobacteria and can be further developed as a potential new pretreatment technology.

Responses of submerged macrophyte Ceratophyllum demersum to the gradient concentrations of microcystin-LR (MC-LR)

The responses of Ceratophyllum demersum to gradient concentrations (0, 0.8, 3.2, and 10 µg/L) of microcystin-LR (MC-LR) were comprehensively investigated by laboratory simulation experiments. The high reduction and accumulation efficiency of MC-LR by C. demersum were verified in this study. Results showed that the reduction ratio of MC-LR in the cultivation medium was up to 99% after 14 days of exposure, and the accumulation of MC-LR in C. demersum was highest at an exposure concentration of 10 μg/L, the value of which was 0.9 ng/g fresh weight (FW). Meanwhile, a series of negative effects on C. demersum was detectable, accompanied by a significant biomass reduction of the plant and changes in microbial community composition. In particular, this study indicated that the amount of Flavobacteria was elevated under the stress of MC-LR, provoking great threats to aquatic ecosystems. Moreover, oxidative damage was evidenced by the changes in total antioxidant capacity, superoxide dismutase, and glutathione. The results also demonstrated significant increases in sugar (0.025 mg/g FW), protein (0.3 mg/g FW), and carotenoids (0.6 mg/g FW) in C. demersum stressed by 10 μg/L of MC-LR, compared with the control without microcystins, which were among the defense strategies for dealing with adverse conditions. These results verified the good potential of submerged macrophytes as an eco-friendly strategy for controlling cyanobacterial blooms. However, the negative effects of MC-LR on the macrophytes themselves were also demonstrated, which would be considered in future practice and management.

Combined effects of the pesticide spinetoram and the cyanobacterium Microcystis on the water flea Daphnia pulex

Spinetoram is one of the most worldwidely used pesticides for its high insecticidal efficacy and low human toxicity. Following the large usage of spinetoram, the ecotoxicity and environmental risks to aquatic ecosystems have call for urgent study. In the present study, we investigated the combined effects of spinetoram and the harmful alga Microcystis aeruginosa in freshwater, on survival and reproduction of Daphnia pulex. Acute toxicity test of spinetoram resulted in negative effects on survival, with a 48-h LC₅₀ value of 37.71 μg L^-1. Under the long-time exposure to environmentally relevant concentrations (0.18 and 0.35 μg L^-1) of spinetoram and a low composition of Microcystis (30%) in the diet, D. pulex showed both shorter longevity and lower fecundity; the time to first brood also increased. At population level, carrying capacity was highly decreased by spinetoram and Microcystis, whereas a significant decrease of intrinsic growth rate was observed at 0.35 μg L^-1 spinetoram with 30% Microcystis as food. The present study highlighted that pesticide spinetoram had highly toxic effects on D. pulex and could reduce the tolerance of D. pulex to M. aeruginosa, causing great effects on D. pulex population in natural waterbodies.

Acute microcystin exposure induces reversible histopathological changes in Chinook Salmon (Oncorhynchus tshawytscha) and Atlantic Salmon (Salmo salar)

Atlantic Salmon (Salmo salar) and Chinook Salmon (Oncorhynchus tshawytscha) develop a severe liver disease called net-pen liver disease (NPLD), which is characterized by hepatic lesions that include megalocytosis and loss of gross liver structure. Based on studies where salmonids have been exposed to microcystin (MC) via intraperitoneal injection, NPLD is believed to be caused by MC exposure, a hepatotoxin produced by cyanobacteria. Despite the link between MC and NPLD, it remains uncertain if environmentally relevant MC exposure is responsible for NPLD. To determine if we could produce histopathology consistent with NPLD, we compared the response of Atlantic and Chinook Salmon sub-lethal MC exposure. Salmon were orally gavaged with saline or MC containing algal paste and sampled over 2 weeks post-exposure. Liver lesions appeared by 6 h but were resolved 2-weeks post-exposure; histopathological changes observed in other tissues were not as widespread, nor was their severity as great as those in the liver. There was no evidence for NPLD due to the absence of hepatic megalocytosis. These results indicate that the development of NPLD is not due to acute MC exposure but may be associated with higher MC concentration occurring in food, long-term exposure through drinking of contaminated seawater and/or interactions with other marine toxins.

The response of sediment microbial communities to temporal and site-specific variations of pollution in interconnected aquaculture pond and ditch systems

Sediment microbial communities play critical roles in the health of fish and the biogeochemical cycling of elements in aquaculture ecosystems. However, the response of microbial communities to temporal and spatial variations in interconnected aquaculture pond and ditch systems remains unclear. In this study, 61 sediment bacterial samples were collected over one year from 11 sites (including five ponds and six ditches) in a 30-year-old fish aquaculture farm. The 16S rRNA approach was used to determine the relative abundances of microbial communities in the sediment samples. The relationships among nutrients, heavy metals, and abundant microorganisms were analyzed. Our results showed that Proteobacteria, Bacteroides and Chloroflexi were the predominant phyla in the sediments of aquaculture pond, with average abundances of 36.33%, 18.60%, and 14.58%, respectively. The microbial diversity in aquaculture sediments was negatively correlated (P < 0.05) with the concentrations of total nitrogen and total phosphorus in sediments, indicating that the microbial diversity is highly associated with the remediation of nutrients in sediments. The sediment samples with high similarities were discovered by the t-distributed stochastic neighbor embedding (t-SNE) method. The site-specific correlations between specific microorganisms and heavy metals were explored. The network analysis revealed that the microbial diversities in aquaculture ponds were more stable than that in aquaculture ditches. The network analysis also illustrated that the microbial genera with low relative abundances may become key groups of microbial communities in sediment ecosystems. Our work deepens the understanding of the relationships between microbial communities and the spatiotemporal characteristics of surface water and sediments in aquaculture farms.

A Novel Freshwater Cyanophage, Mae-Yong924-1, Reveals a New Family

Cyanobacterial blooms are a worldwide ecological issue. Cyanophages are aquatic viruses specifically infecting cyanobacteria. Little is known about freshwater cyanophages. In this study, a freshwater cyanophage, Mae-Yong924-1, was isolated by the double-layer agar plate method using Microcystis aeruginosa FACHB-924 as an indicator host. Mae-Yong924-1 has several unusual characteristics: a unique shape, cross-taxonomic order infectivity and a very unique genome sequence. Mae-Yong924-1 contains a nearly spherical head of about 100 nm in diameter. The tail or tail-like structure (approximately 40 nm in length) is like the tassel of a round Chinese lantern. It could lyse six diverse cyanobacteria strains across three orders including Chroococcales, Nostocales and Oscillatoriales. The genome of the cyanophage is 40,325 bp in length, with a G + C content of 48.32%, and 59 predicted open reading frames (ORFs), only 12 (20%) of which were functionally annotated. Both BLASTn and BLASTx scanning resulted in “No significant similarity found”, i.e., the Mae-Yong924-1 genome shared extremely low homology with sequences in NCBI databases. Mae-Yong924-1 formed a root node alone and monopolized a root branch in the proteomic tree based on genome-wide sequence similarities. The results suggest that Mae-Yong924-1 may reveal a new unknown family apparently distinct from other viruses.

Cyanotoxins and Food Contamination in Developing Countries: Review of Their Types, Toxicity, Analysis, Occurrence and Mitigation Strategies

Cyanotoxins have gained global public interest due to their potential to bioaccumulate in food, which threatens human health. Bloom formation is usually enhanced under Mediterranean, subtropical and tropical climates which are the dominant climate types in developing countries. In this context, we present an up-to-date overview of cyanotoxins (types, toxic effects, analysis, occurrence, and mitigation) with a special focus on their contamination in (sea)food from all the developing countries in Africa, Asia, and Latin America as this has received less attention. A total of 65 publications have been found (from 2000 until October 2021) reporting the contamination by one or more cyanotoxins in seafood and edible plants (five papers). Only Brazil and China conducted more research on cyanotoxin contamination in food in comparison to other countries. The majority of research focused on the detection of microcystins using different analytical methods. The detected levels mostly surpassed the provisional tolerable daily intake limit set by the World Health Organization, indicating a real risk to the exposed population. Assessment of cyanotoxin contamination in foods from developing countries still requires further investigations by conducting more survey studies, especially the simultaneous detection of multiple categories of cyanotoxins in food.

Cyanobacterial dominance and succession: Factors, mechanisms, predictions, and managements

Eutrophication of natural water bodies worldwide has led to cyanobacteria becoming the dominant species in phytoplankton communities, causing serious harm environmentally and economically. Cyanobacterial succession makes effective treatment of cyanobacterial blooms a challenge. Although there are many studies about cyanobacterial dominance and succession, it is still lack of relevant review summarizing the advances on this topic. To control cyanobacterial blooms and manage water quality effectively, we conducted a critical review and drew the following conclusions: (1) cyanobacterial dominance and succession occur from spring to summer, with changes of multiple environmental factors dominated by temperature and nutrients conditions; (2) the cyanobacterial dominance and succession are inherently attributed to the distinctive traits of cyanobacteria including colony formation, gas vesicles, toxin release, and nitrogen fixation; (3) given the current meta-omics explorations on mechanisms of cyanobacterial succession, how to combine the extensive data to draw general conclusions is a challenge in the future; (4) the dominant niche of high temperature-adapted cyanobacteria genera will be further reinforced with global warming and elevated carbon dioxide in the future; (5) considering the causes and future developments of cyanobacterial blooms, the management strategies for controlling cyanobacterial blooms include reducing external nutrient input and removing internal nutrient in sediment, artificial mixing waters to decrease buoyancy of cyanobacteria, and biological control using allelopathy of aquatic plants and/or enhancing zooplankton feeding.

A Novel Jumbo Phage PhiMa05 Inhibits Harmful Microcystis sp

Microcystis poses a concern because of its potential contribution to eutrophication and production of microcystins (MCs). Phage treatment has been proposed as a novel biocontrol method for Microcystis. Here, we isolated a lytic cyanophage named PhiMa05 with high efficiency against MCs-producing Microcystis strains. Its burst size was large, with approximately 127 phage particles/infected cell, a short latent period (1 day), and high stability to broad salinity, pH and temperature ranges. The PhiMa05 structure was composed of an icosahedral capsid (100 nm) and tail (120 nm), suggesting that the PhiMa05 belongs to the Myoviridae family. PhiMa05 inhibited both planktonic and aggregated forms of Microcystis in a concentration-dependent manner. The lysis of Microcystis resulted in a significant reduction of total MCs compared to the uninfected cells. A genome analysis revealed that PhiMa05 is a double-stranded DNA virus with a 273,876 bp genome, considered a jumbo phage. Out of 254 predicted open reading frames (ORFs), only 54 ORFs were assigned as putative functional proteins. These putative proteins are associated with DNA metabolisms, structural proteins, host lysis and auxiliary metabolic genes (AMGs), while no lysogenic, toxin and antibiotic resistance genes were observed in the genome. The AMGs harbored in the phage genome are known to be involved in energy metabolism [photosynthesis and tricarboxylic acid cycle (TCA)] and nucleotide biosynthesis genes. Their functions suggested boosting and redirecting host metabolism during viral infection. Comparative genome analysis with other phages in the database indicated that PhiMa05 is unique. Our study highlights the characteristics and genome analysis of a novel jumbo phage, PhiMa05. PhiMa05 is a potential phage for controlling Microcystis bloom and minimizing MC occurrence.

Source contribution to phosphorus loads from the Maumee River watershed to Lake Erie

Coastal eutrophication is a leading cause of degraded water quality around the world. Identifying the sources and their relative contributions to impaired downstream water quality is an important step in developing management plans to address water quality concerns. Recent mass-balance studies of Total Phosphorus (TP) loads of the Maumee River watershed highlight the considerable phosphorus contributions of non-point sources, including agricultural sources, degrading regional downstream water quality. This analysis builds upon these mass-balance studies by using the Soil and Water Assessment Tool to simulate the movement of phosphorus from manure, inorganic fertilizer, point sources, and soil sources, and respective loads of TP and Dissolved Reactive Phosphorus (DRP). This yields a more explicit estimation of source contribution from the watershed. Model simulations indicate that inorganic fertilizers contribute a greater proportion of TP (45% compared to 8%) and DRP (58% compared to 12%) discharged from the watershed than manure sources in the March-July period, the season driving harmful algal blooms. Although inorganic fertilizers contributed a greater mass of TP and DRP than manure sources, the two sources had similar average delivery fractions of TP (2.7% for inorganic fertilizers vs. 3.0% for manure sources) as well as DRP (0.7% for inorganic fertilizers vs. 1.2% for manure sources). Point sources contributed similar proportions of TP (5%) and DRP (12%) discharged in March-July as manure sources. Soil sources of phosphorus contributed over 40% of the March-July TP load and 20% of the March-July DRP load from the watershed to Lake Erie. Reductions of manures and inorganic fertilizers corresponded to a greater proportion of phosphorus delivered from soil sources of phosphorus, indicating that legacy phosphorus in soils may need to be a focus of management efforts to reach nutrient load reduction goals. In agricultural watersheds aground the world, including the Maumee River watershed, upstream nutrient management should not focus solely on an individual nutrient source; rather a comprehensive approach involving numerous sources should be undertaken.

Full-scale thermophilic aerobic co-composting of blue-green algae sludge with livestock faeces and straw

A high incidence of harmful algal bloom in eutrophic surface waters causes many environmental problems. Thermophilic aerobic composting enables effective treatment and disposal of algal sludge that remains after the dewatering of algae slurries, and provides a value-added organic fertiliser. Previous studies have either only dealt with the composting of a single waste component or were conducted at a lab-/pilot-scale; however, this work is a comprehensive assessment of full-scale mechanized thermophilic aerobic co-composting of algal sludge and other typical biomass-based wastes, including chicken faeces and rice straw, in a water-rich rural area in the Tai lake basin, China. With the optimised feedstock material mass ratio (6.0:1.8:1.0 for straw:algae:faeces; initial C/N ratio of 20; and initial moisture of 60 wt%), the co-composting process effectively achieved the reduction, harmlessness, and reuse of waste. The moisture content (28.36 wt% of wet weight), organic matter content (57.91 wt% of dried weight), total nutrient content (6.59 wt% for TN + TP + TK of dried weight), and heavy metal contents as well as the pH of the final product fully met the Chinese National Agricultural Organic Fertiliser Standard requirements. The reduction rates of microcystin and toxic volatile fatty acid contents were higher than 99.5%, and the seed germination index of the product was 114.5%. A notable economic benefit with a gross profit margin of 167-434% of the process was highlighted. Investigation of the associated mechanisms, including statistical analysis, spectral characterisation, micro-morphological observation, and microbial community analysis, revealed that a decreased particle sizes with a looser structure and an efficient humification effect, resulting from the work of several identified dominant microbial species, contributed to the high product quality. The current study provided a demonstration of the promising full-scale co-composting technology for comprehensive management of the environment in water-rich rural areas and the construction of a sustainable watershed.

A Review of Nephrotoxicity of Microcystins

Cyanobacterial blooms triggered by eutrophication and climate change have become a global public health issue. The toxic metabolites microcystins (MCs) generated by cyanobacteria can accumulate in food chain and contaminate water, thus posing a potential threat to human and animals health. Studies have suggested that aside liver, the kidney may be another target organ of MCs intoxication. Therefore, this review provides various evidences on the nephrotoxicity of MCs. The review concludes that nephrotoxicity of MCs may be related to inhibition of protein phosphatases and excessive production of reactive oxygen species, cytoskeleton disruption, endoplasmic reticulum stress, DNA damage and cell apoptosis. To protect human from MCs toxic consequences, this paper also puts forward some directions for further research.

The behaviors of Microcystis aeruginosa and microcystins during the Fe2+/persulfate (PS) preoxidation-coagulation and flocs storage period

The frequent occurrence of toxin-producing cyanobacteria blooms driven by anthropogenic eutrophication has become a major threat to aquaculture ecosystems worldwide. In this study, the behavior of M. aeruginosa cells during flocs storage period of 6 days was first investigated after pre-oxidation and coagulation of Fe²⁺/PS. Fe²⁺/PS achieved a superior removal efficiency of 90.7% for OD₆₈₀ and 90.4% for chl-a. The contents of extracellular MCs in the pre-oxidation and coagulation system were significantly (P < 0.05) lower than those in the control. A significant (P < 0.05) difference in intracellular protein between the control and the coagulated systems was observed. Three-dimensional fluorescence excitation emission matrix (EEM) was employed to investigate the variations in extracellular organic matter (EOM) during flocs storage. The results indicated the presence of four peaks, representing protein-like substances, intermediate dissolved microbial metabolites, fulvic and humic-like compounds in the Fe²⁺/PS process. And the intensities of four peaks were all decreased in the Fe²⁺/PS system compared to those in the control. A low level of accumulated residual Fe of 0.28 mg/L was observed without posing potential environmental risk. The results showed that the M. aeruginosa cells were under stressful conditions after 3-d storage due to the decomposition of extracellular polymeric substances (EPSs) and the insufficient supply of nutrients. However, SEM results indicated that no significant alteration in cell morphology was observed. Therefore, with high removal of M. aeruginosa, low MCs concentrations, and trivial cell damage, the Fe²⁺/PS preoxidation-coagulation was proved to be an environmental-friendly method for cyanobacteria removal without yielding serious secondary pollution. This work will contribute to better understanding and managing the cyanobacteria-laden aquaculture water after pre-oxidation and coagulation.