Phytotoxicity, bioaccumulation and potential risks of plant irrigations using cyanobloom-loading freshwater

Microcystin-degrading bacteria reduce bioaccumulation in Fragaria vulgaris and enhance fruit yield and quality

In Morocco, red fruit production has thrived, primarily utilizing hydroponic methods to control crops, increase fruit yield and quality, and avoid soil-related problems. However, the irrigation of these expansive hydroponic farms relies heavily on water sourced from dams, many of which are contaminated with Microcystins (MCs). To address this contamination issue, ongoing research is focused on discovering effective and cost-efficient biological solutions for eliminating MCs. In this study, we isolate and identify bacterial strains capable of degrading MCs, evaluate the rate of degradation, and investigate how soil inoculated with these bacteria affects the accumulation of MCs in plant tissue. The partial 16S rRNA analyses of three bacterial sequences were conducted, identifying them through NCBI as follows: Ensifer sp. (B1) isolated from soil, Shinella sp. (B2) from a cyanobacterial bloom, and Stutzerimonas sp. (B3) from water. These bacteria exhibited the ability to degrade MCs, with approximately 34.75%, 73.75%, and 30.1% of the initial concentration (20 µg/L) being removed after a 6-day period for B1, B2, and B3, respectively. Moreover, strawberry plants were cultivated hydroponically in a greenhouse for a duration of 90 days. These plants were subjected to extracts of cyanobacteria containing 10 and 20 µg/L of Microcystins (MC), as well as water from an artificial lake contaminated with MC, both with and without the presence of isolated bacterial strains. Among these strains, Shinella sp. exhibited the highest efficacy in mitigating MC accumulation. Specifically, it resulted in a reduction of approximately 1.159 µg of MC per kilogram of root dry weight, leading to complete elimination in the leaves and fruits. The findings also indicated that the inoculation of perlite with the three MC-degrading bacterial strains significantly enhanced growth, photosynthetic pigments, yield, biochemical constituents, and quality attributes of strawberries (p ≤ 0.05). These promising outcomes suggest the potential of this approach for addressing the adverse impacts of crops irrigated with MC-contaminated water in future agricultural practices.

Single and combined toxicity of polystyrene nanoplastics and PCB-52 to the aquatic duckweed Spirodela polyrhiza

As nanoplastics and persistent organic pollutants are broadly distributed in aquatic ecosystems and pose a potential threat to ecosystem, most pertinent studies have focused on aquatic animals, while studies on freshwater plants have been rarely reported. Therefore, we analyzed the single and combined toxicological impacts of various concentrations of 80 nm polystyrene nanoplastics (PS-NPs) including 0.5, 5, 10, and 20 mg/L and polychlorinated biphenyl-52 (PCB-52, 2,2',5,5'- tetrachlorobiphenyl) at 0.1 mg/L on the aquatic plant Spirodela polyrhiza (S. polyrhiza) after a 10-day hydroponic experiment. Laser confocal scanning microscopy (LCSM) showed the accumulation of PS-NPs mainly in the root surface and the lower epidermis of leaves, and the enrichment of PS-NPs was aggravated by the presence of PCB-52. PS-NPs at 10 mg/L and 20 mg/L alone or in combination with PCB-52 notably inhibited the growth of S. polyrhiza, reduced the synthesis of chlorophylls a and b, and increased the activities of superoxide dismutase (SOD) and peroxidase (POD) as well as malondialdehyde (MDA) levels, and induced osmotic imbalance (soluble protein and soluble sugar contents) (p < 0.05). However, a single treatment with low levels of PS-NPs had positive effects on the growth (0.5 mg/L) and photosynthetic systems (0.5, 5 mg/L) of S. polyrhiza, while co-exposure exacerbated the damaging impacts of PS-NPs on the antioxidant defense system of S. polyrhiza, which was more pronounced in the roots. Furthermore, correlation analysis revealed that plant growth parameters were positively correlated with chlorophyll a and b content and negatively correlated with soluble sugars, antioxidant enzymes, lipid peroxidation, and carotenoid content (p < 0.05). These results provide data to improve the understanding of the single and combined ecotoxicological effects of nanoplastics and polychlorinated biphenyls (PCBs) in aquatic plants and their application in phytoremediation measures.

One-pot preparation of supramolecularly functionalized silver nanoparticles for surface plasmon resonance based dual-modal sensing of phytotoxic polychlorinated biphenyl

Polychlorinated biphenyls (PCBs), as a member of persistent organic pollutants (POPs), have posed a risk to humans and the environment until today. The monitoring of phytotoxic PCB which is toxic to plants, is especially important for ecological early warning and pollution management. In this work, β-cyclodextrin modified silver nanoparticles are prepared in a one-pot method, integrating the synthesis and surface modification in one step. The nanoparticles can supramolecularly immobilize 2,4,4'-trichlorobiphenyl (PCB 28) on their surface and construct a surface plasmon resonance-based nanosensor. Surface plasmon-resonance light scattering and surface-enhanced Raman scattering sensing of PCB 28 are realized using the nanosensor. The dual-modal sensing shows excellent performance for the potential practical monitoring of phytotoxic POPs in the plant and its growing environment.

Health risk assessment of lake water contaminated with microcystins for fruit crop irrigation and farm animal drinking

The health risks linked to the consumption of microcystin-accumulating crops have been increasing worldwide in toxic cyanobloom-occurring regions. The bioaccumulation of microcystins (MCs) in agricultural produce at environmentally realistic concentrations is poorly investigated. In this field study, we assessed the health risks of MCs in raw water used for irrigating fruit crops (bioaccumulation) and watering farm animals in the Lalla Takerkoust agricultural region (Marrakesh, Morocco). Thus, MCs were extracted from water and fruit samples and quantified by enzyme-linked immunosorbent assay in order to calculate the health risk indicators. MCs posed a high health-risk level to poultry and horses, with estimated daily intakes (EDI) being 14- and 19-fold higher than the recommended limits (3.1 and 2.3 μg MC-LR L-1), respectively. Furthermore, pomegranate posed the same level of risk, with EDI being 22- and 53-fold higher than the limit dose (0.04 μg MC-LR kg-1) for adults and children, respectively. There was an urgent need for guidelines regarding water use and management in MC-polluted areas, besides the setup of nature-based tools for toxin removal from raw water used in farming practices. Moreover, MCs could contaminate the human food chain, which implies further investigations of their potential accumulation in livestock- and poultry-based food.

Microcystin-LR Combined with Cadmium Exposures and the Risk of Chronic Kidney Disease: A Case-Control Study in Central China

Increasing evidence indicates that exposure to microcystin-LR (MC-LR) can cause kidney damage. However, the association between MC-LR exposure and chronic kidney disease (CKD) risk in humans has not been studied. Therefore, we conducted a population-based case-control study involving 135 CKD cases and 135 matched controls in central China and analyzed the effects of MC-LR alone as well as combined with the known risk factor cadmium (Cd). Compared to the lowest quartile of MC-LR exposure, the highest quartile had a 6.56-fold (95% confidence interval [CI]: 2.46, 17.51) significantly increased risk for CKD, displaying a dose-response relationship (p_trend < 0.001). Our animal study also showed that MC-LR exposure induced kidney injury via the PI3K/AKT/mTOR signaling pathway. Comparing the highest Cd quartile to the lowest, the adjusted odds ratio for CKD was 3.88 (95% CI: 1.47, 10.28), exhibiting a dose-response relationship (p_trend < 0.006). Furthermore, a positive additive interaction was observed between MC-LR and Cd (relative excess risk due to interaction = 1.81, 95% CI: 0.42, 3.20; attributable proportion of interaction = 0.70, 95% CI: 0.35, 1.05). Our study firstly revealed that MC-LR exposure is an independent risk factor for CKD and has a synergistic relationship with Cd. MC-LR and Cd exposures are associated with CKD risk in a dose-response manner.

New insights into the production of fucoxanthin by mixotrophic cultivation of Ochromonas and Microcystis aeruginosa

Fucoxanthin (Fx) has attracted great interest due to its remarkable biological activities such as antioxidant and anti-obesity, and its increasing demands in biopharmaceutical and cosmetic fields. However, its commercial production is limited by low yield and high cost. In this study, we isolated and identified a species of golden algae (Ochromonas sp.) capable of engulfing Microcystis aeruginosa (M. aeruginosa) and accumulating Fx. After 72 h mixotrophic cultivation of Ochromonas sp. and M. aeruginosa, the algal culture changed from green to yellow-brown, and the content of Fx and the daily production rate were up to 11.58 mg g^-1, and 1.315 mg L^-1 d^-1, respectively. The utilization rate of M. aeruginosa was 527.27 fg cell^-1. This study will not only provide a new thought to produce Fx in an efficient, low-cost, and sustainable way but an innovative method for the control and treatment of harmful cyanobacterial blooms from eutrophic freshwaters as well.

Microcystin pollution in lakes and reservoirs: A nationwide meta-analysis and assessment in China

The frequent occurrence of microcystins (MCs) has caused a series of water security issues worldwide. Although MC pollution in natural waters of China has been reported, a systematic analysis of the risk of MCs in Chinese lakes and reservoirs is still lacking. In this study, the distribution, trend, and risk of MCs in Chinese lakes and reservoirs were comprehensively revealed through meta-analysis for the first time. The results showed that MC pollution occurrence in numerous lakes and reservoirs have been reported, with MC pollution being distributed in the waters of 15 provinces in China. For lakes, the maximum mean total MC (TMC) and dissolved MC (DMC) concentrations occurred in Lake Dianchi (23.06 μg/L) and Lake Taihu (1.00 μg/L), respectively. For reservoirs, the maximum mean TMC and DMC concentrations were detected in Guanting (4.31 μg/L) and Yanghe reservoirs (0.98 μg/L), respectively. The TMC concentrations in lakes were significantly higher than those in the reservoirs (p < 0.05), but no difference was observed in the DMC between the two water bodies (p > 0.05). Correlation analysis showed that the total phosphorus concentrations, pH, transparency, chlorophyll a, and dissolved oxygen were significantly related to the DMC in lakes and reservoirs. The ecological risks of DMC in Chinese lakes and reservoirs were generally at low levels, but high or moderate ecological risks of TMC had occurred in several waters, which were not negligible. Direct drinking water and consumption of aquatic products in several MC-polluted lakes and reservoirs may pose human health risks. This study systematically analyzed the pollution and risk of MCs in lakes and reservoirs nationwide in China and pointed out the need for further MC research and management in waters.

Selection and characterization of plant-derived alkaloids with strong antialgal inhibition: growth inhibition selectivity and inhibitory mechanism

In recent years, researches on microalgae inhibition with plant-derived active substances have attracted much attention. In this study, the inhibition of six plant-derived alkaloids (neferine, isoliensinine, linensinine, nuciferine, capsaicin, and hordenine) on bloom-forming cyanobacteria Microcystis aeruginosa were investigated. The results showed that neferine and nuciferine had stronger inhibition on the growth of M. aeruginosa compared with the other four alkaloids, and the relative inhibition rate reached 91.27% and 88.70% at the concentration of 4.5 mg/L after 7 d of exposure, respectively. Different from neferine, nuciferine has no inhibition on Chlorella sp. and Tetradesmus obliquus. It also increased the diversity and species homogeneity of phytoplankton in the environmental water samples. Nuciferine decreased the contents of chlorophyll a and β-carotene in M. aeruginosa with the extension of treatment time, which was 59.40% and 31.90% of the control at the concentration of 1.04 mg/L after 48 h, respectively. After 48 h of nuciferine exposure, the values of fluorescence parameters including maximum quantum yield (Fv/Fm), actual quantum yield of PSII (Yield), non-photochemical quenching (qN and NPQ), and electron transport rates (ETR) of M. aeruginosa cells were significantly decreased and photosynthetic capacity was weakened. The superoxide dismutase (SOD), catalase (CAT), ascorbic acid (ASA), and glutathione (GSH) in the cells were significantly reduced, and the hydrogen peroxide (H₂O₂) and malonaldehyde (MDA) contents continued to accumulate, causing severe oxidative damage. Therefore, the good biological safety and strong specific inhibition of nuciferine makes it have great application prospects in the inhibition of cyanobacteria blooms.

Co-occurrence of co-contaminants: Cyanotoxins and microplastics, in soil system and their health impacts on plant - A comprehensive review

Cyanotoxins (CTX) and micro/nanoplastics (M/NP) are ubiquitously distributed in every environmental compartment. But the distribution, abundance and associated ecological risks of CTX are still poorly understood in soil system. On the other hand, M/NP could serve as vectors for persistent organic/inorganic pollutants in the natural environment through the sorption of pollutants onto them. Thus, co-occurrence of CTX and M/NP in soils suggests the sorption of CTX onto M/NP. So, major aim of this review is to understand the relevance of CTX and M/NP in soils as co-contaminants, possible interactions between them and ecological risks of CTX in terms of phytotoxicity. In this study, we comprehensively discuss different sources and fate of CTX and the sorption of CTX onto M/NP in soil system, considering the partition coefficient of different phases of soil and mass balance. Phytotoxicity of CTX, CTX mixture and co-contaminants has also been discussed with insights on the mechanism of action. This study indicates the need for the evaluation of sorption between co-contaminants, especially CTX and M/NP, and their phytotoxicity assessment using environmentally relevant concentrations.

Toxic effects of 2,4,4'- trichlorobiphenyl (PCB-28) on growth, photosynthesis characteristics and antioxidant defense system of Lemna minor L

Polychlorinated biphenyls (PCBs) are a common category of persistent man-made organic pollutants that are widespread in the ambient environment. Although Lemna minor L. is an extensively applied plant for aquatic remediation in ecotoxicology research worldwide, little is known regarding its responses to the potentially toxic effects of PCBs. For this study, a 14-day dissolved exposure was conducted to explore the effects of 2,4,4'- trichlorobiphenyl (PCB-28) on the growth, photosynthesis characteristics and antioxidant defense system of L. minor plants. We found that 100 and 200 μg/L of PCB-28 decreased the fresh weight, chlorophyll and protein content, and activities of superoxide dismutase, peroxidase, glutathione S-transferase, and nitroreductase, whereas plasma membrane permeability, and the malondialdehyde and reactive oxygen species concentrations were increased. However, it was observed that 5 and 20 μg/L of PCB-28 had no significant effects on these physiological indices. The ultra-structure of chloroplast demonstrated that 100 and 200 μg/L PCB-28 severely damaged the chloroplast structures. Moreover, correlation analysis revealed that the content of reactive oxygen species had negative correlations with the fresh weight, chlorophyll and protein content, as well as the activities of superoxide dismutase, peroxidase, glutathione S-transferase, and nitroreductase, but had positive correlations with the malondialdehyde content and plasma membrane permeability. This work provides valuable data toward elucidating the physiology and biochemistry of PCBs induced phytotoxicity.

Role of Rhizospheric Microbiota as a Bioremediation Tool for the Protection of Soil-Plant Systems from Microcystins Phytotoxicity and Mitigating Toxin-Related Health Risk

Frequent toxic cyanoblooms in eutrophic freshwaters produce various cyanotoxins such as the monocyclic heptapeptides microcystins (MCs), known as deleterious compounds to plant growth and human health. Recently, MCs are a recurrent worldwide sanitary problem in irrigation waters and farmland soils due to their transfer and accumulation in the edible tissues of vegetable produce. In such cases, studies about the persistence and removal of MCs in soil are scarce and not fully investigated. In this study, we carried out a greenhouse trial on two crop species: faba bean (Vicia faba var. Alfia 321) and common wheat (Triticum aestivum var. Achtar) that were grown in sterile (microorganism-free soil) and non-sterile (microorganism-rich soil) soils and subjected to MC-induced stress at 100 µg equivalent MC-LR L⁻¹. The experimentation aimed to assess the prominent role of native rhizospheric microbiota in mitigating the phytotoxic impact of MCs on plant growth and reducing their accumulation in both soils and plant tissues. Moreover, we attempted to evaluate the health risk related to the consumption of MC-polluted plants for humans and cattle by determining the estimated daily intake (EDI) and health risk quotient (RQ) of MCs in these plants. Biodegradation was liable to be the main removal pathway of the toxin in the soil; and therefore, bulk soil (unplanted soil), as well as rhizospheric soil (planted soil), were used in this experiment to evaluate the accumulation of MCs in the presence and absence of microorganisms (sterile and non-sterile soils). The data obtained in this study showed that MCs had no significant effects on growth indicators of faba bean and common wheat plants in non-sterile soil as compared to the control group. In contrast, plants grown in sterile soil showed a significant decrease in growth parameters as compared to the control. These results suggest that MCs were highly bioavailable to the plants, resulting in severe growth impairments in the absence of native rhizospheric microbiota. Likewise, MCs were more accumulated in sterile soil and more bioconcentrated in root and shoot tissues of plants grown within when compared to non-sterile soil. Thereby, the EDI of MCs in plants grown in sterile soil was more beyond the tolerable daily intake recommended for both humans and cattle. The risk level was more pronounced in plants from the sterile soil than those from the non-sterile one. These findings suggest that microbial activity, eventually MC-biodegradation, is a crucial bioremediation tool to remove and prevent MCs from entering the agricultural food chain.

Phytotoxicity and bioconcentration of microcystins in agricultural plants: Meta-analysis and risk assessment

Microcystins are cyanotoxins produced by many species of cyanobacteria. They are specific inhibitors of serine/threonine protein phosphatases and are phytotoxic to agricultural plants. This study used a formal meta-analysis to estimate the phytotoxicity and bioconcentration rates of agricultural plants exposed to microcystins, and the human health risk from consuming microcystin-contaminated plants. Among the 35 agricultural plants investigated, microcystins were most phytotoxic to durum wheat, corn, white mustard and garden cress. Leafy vegetables such as dill, parsley and cabbage could bioconcentrate ∼3 times more microcystins in their edible parts than other agricultural plants. Although the human health risk from ingesting microcystins could be greater for leafy vegetables than other agricultural plants, further work is needed to confirm bioconcentration of microcystins in realistic water-soil-plant environments. Still, we should avoid growing leafy vegetables, durum wheat and corn on agricultural land that is irrigated with microcystins-contaminated water and be attentive to the risk of microcystins contamination in the agricultural food supply.

The Role of Serine-Threonine Protein Phosphatase PP2A in Plant Oxidative Stress Signaling-Facts and Hypotheses

Abiotic and biotic factors induce oxidative stress involving the production and scavenging of reactive oxygen species (ROS). This review is a survey of well-known and possible roles of serine-threonine protein phosphatases in plant oxidative stress signaling, with special emphasis on PP2A. ROS mediated signaling involves three interrelated pathways: (i) perception of extracellular ROS triggers signal transduction pathways, leading to DNA damage and/or the production of antioxidants; (ii) external signals induce intracellular ROS generation that triggers the relevant signaling pathways and (iii) external signals mediate protein phosphorylation dependent signaling pathway(s), leading to the expression of ROS producing enzymes like NADPH oxidases. All pathways involve inactivation of serine-threonine protein phosphatases. The metal dependent phosphatase PP2C has a negative regulatory function during ABA mediated ROS signaling. PP2A is the most abundant protein phosphatase in eukaryotic cells. Inhibitors of PP2A exert a ROS inducing activity as well and we suggest that there is a direct relationship between these two effects of drugs. We present current findings and hypotheses regarding PP2A-ROS signaling connections related to all three ROS signaling pathways and anticipate future research directions for this field. These mechanisms have implications in the understanding of stress tolerance of vascular plants, having applications regarding crop improvement.

Toxicological and ecotoxicological evaluation of the water quality in a large and eutrophic freshwater lake of China

Effect-based methods (EBMs) are recommended as holistic approach for diagnosis and monitoring of water quality; however, the application of EBMs is still scare in China. In the present study, water quality of the freshwater lake Taihu (China) was investigated by EBMs. Different types of water samples were collected from three bays of the lake during 2015, 2016 and 2017. A battery of seven effect-based bioassays, including both specific and non-specific toxicity assays, was used. The bioassay battery was recently suggested based on joint activities of the EU project SOLUTIONS and the NORMAN network on emerging pollutants and is also under discussion for being implemented into monitoring activities in the context of the European Water Framework Directive (WFD). Adverse effects were observed towards the primary producer, primary consumer and fish, indicating the potential ecotoxicity of water in Taihu Lake. Mutagenic and estrogenic effects were found in the Ames fluctuation assay and ERα CALUX (Chemically Activated Luciferase Gene-eXpression) assay, respectively, highlighting the potential risks on human health. Algal growth inhibition and mutagenic effects can be observed during each of the three years. Acute toxicity towards Daphnia magna and estrogen receptor agonistic effects were found in at least one of the samples collected in 2016 and 2017, but not in 2015. The endpoints for fish toxicity in the Danio rerio fish embryo test included both lethal and additionally several sublethal effects (only for samples from 2017) and were not compared between years. Algal growth inhibition, fish embryo toxicity, mutagenic effect and estrogenicity were observed in each of the three bays, while Daphnia acute toxicity was only found in Zhushan Bay. Taking together, this study provides a big picture on the water quality of Taihu Lake. The battery of effect-based tools is promising to be a routine for water quality monitoring in China.

Structural and functional analysis of two novel somatostatin receptors identified from topmouth culter (Erythroculter ilishaeformis)

In the present study, we cloned and characterized two somatostatin (SS) receptors (SSTRs) from topmouth culter (Erythroculter ilishaeformis) designated as EISSTR6 and EISSTR7. Analysis of EISSTR6 and EISSTR7 signature motifs, 3D structures, and homology with the known members of the SSTR family indicated that the novel receptors had high similarity to the SSTRs of other vertebrates. EISSTR6 and EISSTR7 mRNA expression was detected in 17 topmouth culter tissues, and the highest level was observed in the pituitary. Luciferase reporter assay revealed that SS14 significantly inhibited forskolin-stimulated pCRE-luc promoter activity in HEK293 cells transiently expressing EISSTR6 and EISSTR7, indicating that the receptors can be activated by SS14. We also identified phosphorylation sites important for the functional activity of EISSTR6 and EISSTR7 by mutating Ser^{23, 43, 107, 196, 311} and Ser^{7, 29, 61, 222, 225} residues, respectively, to Ala, which significantly reduced the inhibitory effects of SS14 on the CRE promoter mediated by EISSTR6 and EISSTR7. Furthermore, treatment of juvenile topmouth culters with microcystin-LR or 17β-estradiol significantly affected EISSTR6 and EISSTR7 transcription in the brain, liver and spleen, suggesting that these receptors may be involved in the pathogenic mechanisms induced by endocrine disruptors. Our findings should contribute to the understanding of the structure-function relationship and evolution of the SSTR family.

Heterologous expression of mlrA in a photoautotrophic host - Engineering cyanobacteria to degrade microcystins

In this report, we establish proof-of-principle demonstrating for the first time genetic engineering of a photoautotrophic microorganism for bioremediation of naturally occurring cyanotoxins. In model cyanobacterium Synechocystis sp. PCC 6803 we have heterologously expressed Sphingopyxis sp. USTB-05 microcystinase (MlrA) bearing a 23 amino acid N-terminus secretion peptide from native Synechocystis sp. PCC 6803 PilA (sll1694). The resultant whole cell biocatalyst displayed about 3 times higher activity against microcystin-LR compared to a native MlrA host (Sphingomonas sp. ACM 3962), normalized for optical density. In addition, MlrA activity was found to be almost entirely located in the cyanobacterial cytosolic fraction, despite the presence of the secretion tag, with crude cellular extracts showing MlrA activity comparable to extracts from MlrA expressing E. coli. Furthermore, despite approximately 9.4-fold higher initial MlrA activity of a whole cell E. coli biocatalyst, utilization of a photoautotrophic chassis resulted in prolonged stability of MlrA activity when cultured under semi-natural conditions (using lake water), with the heterologous MlrA biocatalytic activity of the E. coli culture disappearing after 4 days, while the cyanobacterial host displayed activity (3% of initial activity) after 9 days. In addition, the cyanobacterial cell density was maintained over the duration of this experiment while the cell density of the E. coli culture rapidly declined. Lastly, failure to establish a stable cyanobacterial isolate expressing native MlrA (without the N-terminus tag) via the strong cpcB560 promoter draws attention to the use of peptide tags to positively modulate expression of potentially toxic proteins.