microcystin-RR Research Articles

Removal of Microcystins by Highly Efficient Photo-catalyst Bi2WO6-Activated Carbon Under Simulated Light

The photo-catalytic activities of several Bi2WO6 with various activated carbon (AC) contents were studied for the photo-catalytic degradation of microcystin-LR (MC-LR) and microcystin-RR (MC-RR) under simulated light. Some characterizations of the materials were carried out. Activated carbon increased the reaction rates in the degradation of MC-LR. A significant improvement in the photo-catalytic activity under simulated light was achieved with the 5 wt% activated carbon content when compared with pristine Bi2WO6 or with materials with other content activated carbon additions. Factors besides adsorption capability and surface areas effects may also contribute to the improvement. The kinetics of photo-catalytic degradation of MC-LR and MC-RR by Bi2WO6-activated carbon were explored. The application of the catalyst under sunlight was proven to be better than under simulated light.

Adsorption of two microcystins onto activated carbon: equilibrium, kinetic, and influential factors

Microcystins (MCs) are very stable toxins in water bodies and can be poorly removed by traditional drinking water treatment processes. Powder-activated carbon (PAC) was employed in the present study for removal of two commonly and widely occurring algal toxins, microcystin-LR (MC-LR), and microcystin-RR (MC-RR), which were obtained from cyanobacterial blooms. Results indicated that wood PAC has better adsorption capacity on MCs compared with shell and coal PAC. The Freundlich adsorption model can better describe the adsorption behavior of MCs onto PAC. And the pseudo-second-order kinetic model can better fit the adsorption process of MCs onto PAC. Moreover, the adsorption of MCs onto wood PAC was affected by temperature, pH, and anions. The adsorption rates increased with the decreasing temperature. And the adsorption capacity of wood PAC for MCs decreased with the increasing pH. Four kinds of anion hindered the adsorption and reduced the removal rate by 14–24%. Therefore, our study provides valuable information to address the water quality issues caused by microcystins, including selection of the most efficient PAC.

Changes in muscle biochemistry, myoglobin and cytoglobin in goldfishCarassius auratusexposed to hypoxia-reoxygenation and microcystin RR

AbstractCyanobacterial toxins and oxygen depletion pose serious challenges to aquatic organisms. In this study, the goldfish Carassius auratus was exposed to hypoxia-reoxygenation episodes as well as a cyanobacterial toxin microcystin arginine arginine (MCRR) with an aim of assessing the toxicity of the stressors to muscle biochemistry, cytoglobin mRNA and myoglobin mRNA. The result showed that MCRR and hypoxia-reoxygenation synergistically reduced the total antioxidant capacity of the muscle by over 90%; glutathione peroxidase activity was also significantly reduced in the groups exposed to MCRR and hypoxia (p < 0.05). Sodium ATPase (Na-ATPase) and total ATPase (tATPase) varied from 14.68 ± 2.2 to 27.87 ± 2.0 U/mg protein and were significantly reduced by MCRR (p < 0.005) only. Glucose and protein (sources of energy) were elevated in the muscles of goldfish exposed to MCRR, especially during reoxygenation, although only the latter was significant. Myoglobin and cytoglobin mRNA were not significantly infl...

Calibration of a passive, in situ, integrative sampler for monitoring of microbial biotoxins in aquatic environments

In this work, an integrative passive sampler based on a silicone membrane filled with a suspension of γ-Fe2O3 at pH 3.5 was developed. The novel device was calibrated for the measurement of microcystin concentrations in water. Laboratory calibration studies of the passive sampling devises under controlled conditions of temperature, water turbulence, and analyte concentration were conducted in order to establish how variable environmental conditions affect the novel sampler's performance. The chemical uptake of microcystin (MC)-RR, -LR, and -YR into the passive sampler remained linear and integrative throughout the 28-day exposure. The relative standard deviations of mean concentrations obtained using silicone-based sampler ranged from 1.42 to 3.74% for microcystin-LR, -RR, and -YR. The values for reproducibility from triplicate samplers ranged from 3.5 to 7.1% for microcystin-LR, -RR, and -YR. The detection limits on high performance liquid chromatography (HPLC) with PDA detection for microcystins LR, RR, and YR were 24.7, 17.2, and 23.8 μg L−1 respectively, calculated as three times the signal to noise ratio. The rate of accumulation of most of the MC compounds tested was dependent on temperature and flow velocity. Furthermore, the sample matrix, e.g. humic substances, had no significant effect on the concentration of compounds trapped in the acceptor solution and once these MC compounds were trapped in the acceptor phase they did not diffuse back during the deployment period.

Retinoid compounds associated with water blooms dominated by Microcystis species

Retinoic acids play a critical role in vital physiological processes and vertebrate development, and their derivatives can be produced by some cyanobacterial species into surface waters. This study presents important environmentally-relevant information on total retinoid-like activity of field cyanobacterial biomasses and their surrounding waters. Intracellular and extracellular levels of total retinoid-like activity and retinoic acids have been investigated at a set of independent sites with the occurrence of water bloom dominated by widespread species Microcystis aeruginosa. Twelve samples of biomass and surrounding water from seven localities affected by blooms were studied in comparison with samples from M. aeruginosa laboratory cultures. The method for biomass extraction was optimized and final extracts and samples of surrounding water concentrated by solid phase extraction were assessed using in vitro reporter gene bioassay and chemical analyses for all-trans-retinoic acid (ATRA), 9-cis retinoic acid (9-cis RA) and microcystins RR, LR and YR. Methanol was the most efficient solvent for the extraction of compounds with retinoid-like activity. An in vitro bioassay with the P19/A15 transgenic cell line revealed retinoid-like activity in all cyanobacterial biomasses in the range of 356–2838ng of retinoid acid equivalents (REQ)/g dry mass (dm), while only three of surrounding water samples exhibited detectable retinoid-like activity, in the range of 12.8–28.7ngREQ/L. Microcystins were detected in all samples, but they elicited no detectable retinoid-like activity up to 10mg/L. Chemical analyses detected concentrations up to 340ng/gdm of all-trans-retinoic acid (ATRA) and 84ng/gdm 9-cis retinoic acid (9-cis RA) in bloom extracts, and up to 19ng/L ATRA and 2.2ng/L 9-cis RA in surrounding water. In most samples, ATRA and 9-cis RA contributed relatively little to the total REQs, which indicates the presence of significant amounts of other compounds with retinoic acid receptor-mediated modes of action. The impact of retinoid-like cyanobacterial metabolites could be of importance namely in smaller water bodies with dense water blooms and low dilution.

Rapid and sensitive analysis of microcystins using ionic liquid-based in situ dispersive liquid–liquid microextraction

Three structurally different ionic liquids (ILs), namely 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]), 1-(6-hydroxyethyl)-3-methylimidazolium chloride ([HeOHMIM][Cl]) and 1-benzyl-3-(2-hydroxyethyl)imidazolium bromide ([BeEOHIM][Br]), were applied as extraction solvents using in situ dispersive liquid–liquid microextraction (in situ DLLME) for the preconcentration of two microcystin variants, microcystin-RR (MC-RR) and microcystin-LR (MC-LR) from aqueous samples. Extraction parameters including sample solution pH, ratio of IL to metathesis reagent, sample volume, IL quantity, and salt concentration were optimized to achieve the best extraction efficiency. The [BeEOHIM][Br] IL, which contains both an aromatic moiety and a hydroxyl group within its chemical structure, exhibited superior extraction efficiency compared to the other two ILs. The analytical performance of the [BeEOHIM][Br] IL as an extraction solvent for in situ DLLME of microcystins was investigated using HPLC-UV and HPLC-MS. The limits of detection (LODs) for MC-RR and MC-LR were 0.7μgL−1 using UV detection with a linear range from 1 to 50μgL−1. The separation method was successfully adapted for ESI-MS/SIM detection, wherein the LODs for MC-RR and MC-LR were greatly improved to 0.005 and 0.003μgL−1, respectively. The accuracy of the method was demonstrated by examining the relative recovery using tap water and river water and produced recoveries ranging from 45.0 to 109.7% and from 46.3 to 103.2%, respectively.

Electrospun polymer nanofibres as solid-phase extraction sorbents for extraction and quantification of microcystins

Electrospun polymer nanofibres were used as novel solid-phase extraction (SPE) sorbents to extract and quantify the microcystins (MCs) including microcystin-RR (MC-RR) and microcystin-LR (MC-LR) from in-suit water samples. The parameters that influenced the extraction efficiency were studied, including the amount of nanofibre, eluted solvent, eluted volume, pH, and the water sample volume. Under optimized conditions, a linear response for MC-RR and MC-LR over the range of 0.25–4 µg/L was achieved with r2 values of 0.998 and 0.997, respectively. The extraction recovery of MC-RR and MC-LR was 97–102% and 98–100%, respectively, when the MC concentration was 0.25–4 µg/L. When their concentrations ranged from 0.05 to 0.25 µg/L, the MCs could be detected with high accuracy by the nanofibre SPE sorbent combined with nitrogen gas. Due to its simplicity, environment-friendliness, high efficiency, reusability, and sensitivity, the electrospun polymer nanofibre can be applied as a novel SPE sorbent to extract and detect the MCs from in-suit water samples.

Removal of microcystin-RR, a membrane foulant using exocellular polymer from Enterobacter ludwigii: Kinetic and isotherm studies

Microcystins (MCs), produced by cyanobacteria, are one of the most common naturally occurring toxins found in water sources. In the present study, exocellular polymer (ECP) obtained from Enterobacter ludwigii was used for the removal of microcystin-RR (MC-RR) extracted from Microcystis aeruginosa under optimized conditions. The maximum ECP produced was 0.68g of dryweight/g biomass at optimized conditions such as fermentation time, 72h; pH, 7 and temperature, 30°C. The maximum removal of MC-RR (100ng/ml) by ECP was optimized using response surface methodology and optimal removal was achieved at contact time, 5h; pH, 10; temperature, 30°C; ECP concentration, 4mg/ml and agitation speed, 150rpm. The amount of MC-RR removed at optimized conditions was 23.76ng/mg of ECP. The isotherm models were validated to understand the mechanism of adsorption of MC-RR by ECP. The removal of MC-RR by ECP followed the pseudo-second order rate kinetic model. The metal ion, Cu2+ enhanced the removal of MC-RR and the amount of MC-RR removed was 26.43ng/mg of ECP. The removal of MC-RR using ECP was confirmed by FT-IR and NMR spectroscopy.

Qualitative analysis of the most toxic and abundant microcystin variants (LR, RR, and YR) by using LCMS–IT–TOF

Contamination of microcystins (a family of heptapeptide hepatotoxins), in eutrophicated water bodies is a worldwide problem. Due to their acute and chronic poisoning of animal and human health even at a low concentration of ppb scale, the accurate analysis is required of all microcystin variants present in a sample. In this study, a sensitive and selective method for the analysis of microcystin-LR (MC-LR), microcystin-RR (MC-RR), and microcystin-YR (MC-YR) using the liquid chromatograph mass spectrometry–ion trap–time of flight (LCMS–IT–TOF) technique has been developed. A new approach to quantify and distinguish microcystin variants by using LCMS–IT–TOF, a novel hybrid mass spectrometer having the multistep tandem mass spectrometry (MSn) ability, excellent resolution, and mass accuracy, could provide highly accurate analysis for evaluation of the toxicity of microcystins in a sample. In addition, chromatographic and spectrometric conditions were optimized for high peak intensity and the fine peak separation of microcystin variants. The results obtained of multistep tandem MS spectra strongly verified the presence of the studied microcystin variants in samples, and offered the lower detection limits of 5pg on a column for MC-RR, and 10pg on a column for MC-LR and MC-YR under the given analytical conditions.

Microcystin-RR exposure results in growth impairment by disrupting thyroid endocrine in zebrafish larvae

Recent studies have shown that cyanobacteria-derived microcystins (MCs) have the potential to disrupt endocrine systems. However, the effects of microcystin-RR (MC-RR) and their underlying mechanisms are poorly resolved in fish. In this study, MC-RR exposure through submersion caused serious developmental toxicity, such as growth delay and depressed heart rates in zebrafish larvae. We also detected decreased levels of thyroid hormones (THs), suggesting that MC-RR-triggered thyroid endocrine disruption might contribute to the growth impairment observed in developing zebrafish. To further our understanding of mechanisms of MC-RR-induced endocrine toxicity, quantitative real-time PCR (QPCR) analysis was performed on hypothalamic–pituitary–thyroid (HPT) axis related genes, i.e., corticotropin-releasing factor (CRF), thyroid-stimulating hormone (TSH), sodium/iodide symporter (NIS), thyroglobulin (TG), thyroid receptors (TRα and TRβ) and iodothyronine deiodinases (Dio1 and Dio2), of developing zebrafish embryos exposed to 0, 0.3, 1.0 or 3.0mgL−1 MC-RR until 96h post-fertilization. Our results showed that transcription pattern of HPT axis related genes were greatly changed by MC-RR exposure, except TG gene. Furthermore, western blot was used to validate the results of gene expression. The results showed protein synthesis of TG was not affected, while that of NIS was significantly up-regulated, which are in accordance with gene expression. The overall results indicated that exposure to MC-RR can induce developmental toxicity, which might be associated with thyroid endocrine disruption in developing zebrafish larvae.

Analysis of intracellular and extracellular microcystin variants in sediments and pore waters by accelerated solvent extraction and high performance liquid chromatography-tandem mass spectrometry

The fate and persistence of microcystin cyanotoxins in aquatic ecosystems remains poorly understood in part due to the lack of analytical methods for microcystins in sediments. Existing methods have been limited to the extraction of a few extracellular microcystins of similar chemistry. We developed a single analytical method, consisting of accelerated solvent extraction, hydrophilic–lipophilic balance solid phase extraction, and reversed phase high performance liquid chromatography-tandem mass spectrometry, suitable for the extraction and quantitation of both intracellular and extracellular cyanotoxins in sediments as well as pore waters. Recoveries of nine microcystins, representing the chemical diversity of microcystins, and nodularin (a marine analogue) ranged between 75 and 98% with one, microcystin-RR (MC-RR), at 50%. Chromatographic separation of these analytes was achieved within 7.5min and the method detection limits were between 1.1 and 2.5ngg−1 dry weight (dw). The robustness of the method was demonstrated on sediment cores collected from seven Canadian lakes of diverse geography and trophic states. Individual microcystin variants reached a maximum concentration of 829ngg−1 dw on sediment particles and 132ngmL−1 in pore waters and could be detected in sediments as deep as 41cm (>100 years in age). MC-LR, -RR, and -LA were more often detected while MC-YR, -LY, -LF, and -LW were less common. The analytical method enabled us to estimate sediment-pore water distribution coefficients (Kd), MC-RR had the highest affinity for sediment particles (log Kd=1.3) while MC-LA had the lowest affinity (log Kd=−0.4), partitioning mainly into pore waters. Our findings confirm that sediments serve as a reservoir for microcystins but suggest that some variants may diffuse into overlying water thereby constituting a new route of exposure following the dissipation of toxic blooms. The method is well suited to determine the fate and persistence of different microcystins in aquatic systems.

Microcystin-producing and non-producing cyanobacterial blooms collected from the Central India harbor potentially pathogenic Vibrio cholerae

On the basis of relative abundance, frequency and biovolume, the important value index ranks were assigned to individual cyanobacteria in phytoplankton samples collected from fourteen water resources of Central India. The mcyABDE genes were detected in all the blooms with Microcystis (-aeruginosa, –viridis, -panniformis, –botrys) as being the major constituent morphospecies. On the other hand, blooms composed of primarily Oscillatoria (-limosa,-agardhii, -laetevirens) along with Anabaena, Nostoc, Phormidium and Spirulina as sub-dominant forms exhibited quite a patchy distribution of one or the other mcy genes. Fifty percent of Microcystis- but none of the Oscillatoria dominant blooms produced microcystins–RR and desmethyl–RR at 0.03–0.41mgg−1 bloom dry mass. Traces of dissolved microcystin was detected in lake water, which is well below the WHO guideline. Irrespective of cyanobacterial composition and microcystin production ability, during the study period 43–64% of the cyanobacterial bloom samples exhibited association of viable but nonculturable forms of Vibrio cholerae O1 and O139, as evident from amplification of the antigen genes. We believe that spread of endemic cholera is the major threat associated with harmful algal blooms.

Microcystins-LR, -YR and -RR in Six Bulgarian Water Bodies of Health and Conservational Importance (2012-2014)

This study presented the results of HPLC-DAD microcystin and nodularin analyses from five Bulgarian water bodies (reservoirs Stoudena, Pchelina and Bistritsa, and lakes Dourankoulak and Vaya) carried out in 2012-2014, as a continuation of our work from 2004 to 2005 and in 2011, and first data on microcystins in the lake Momin Brod were detected in the period 2012-2014. The total concentration of microcystins in water samples ranged from 0.1 to 1.8 μg/l and their amount in the concentrated biomasses from net samples ranged from 1.35 to 296 μg/g (d.w.). The presence of the most toxic microcystin-LR was recorded in all studied lakes and reservoirs, where also microcystins RR and YR were detected, but no microcystin-LA and nodularin were found.

Mitochondrial electron transport chain is involved in microcystin-RR induced tobacco BY-2 cells apoptosis

Microcystin-RR (MC-RR) has been suggested to induce apoptosis in tobacco BY-2 cells through mitochondrial dysfunction including the loss of mitochondrial membrane potential (ΔΨm). To further elucidate the mechanisms involved in MC-RR induced apoptosis in tobacco BY-2 cells, we have investigated the role of mitochondrial electron transport chain (ETC) as a potential source for reactive oxygen species (ROS). Tobacco BY-2 cells after exposure to MC-RR (60mg/L) displayed apoptotic changes in association with an increased production of ROS and loss of ΔΨm. All of these adverse effects were significantly attenuated by ETC inhibitors including Rotenone (2μmol/L, complex I inhibitor) and antimycin A (0.01μmol/L, complex III inhibitor), but not by thenoyltrifluoroacetone (5μmol/L, complex II inhibitor). These results suggest that mitochondrial ETC plays a key role in mediating MC-RR induced apoptosis in tobacco BY-2 cells through an increased mitochondrial production of ROS.

Quantitative liquid chromatography-tandem mass spectrometry method for determination of microcystin-RR and its glutathione and cysteine conjugates in fish plasma and bile.

A rapid and sensitive liquid chromatography-mass spectrometry (LC-MS) method was developed and validated for the simultaneous determination of microcystin-RR (MC-RR) and its glutathione and cysteine conjugates (MC-RR-GSH and MC-RR-Cys, respectively) in fish plasma and bile. The analytes were extracted using methanol, followed by an Oasis mixed-mode cation-exchange polymeric sorbent. The separation was performed on a reversed-phase Waters XBridge C18 column with the gradient mobile phase, consisting of water and acetonitrile (both acidified with 0.5‰ formic acid). Mean recoveries of MC-RR, MC-RR-GSH and MC-RR-Cys ranged from 80.7 to 93.7%, 81.1 to 93.1% and 80.3 to 93.2%, respectively, at three concentrations (0.2, 1.0 and 5.0 μg mL(-1)). Limits of detection (LODs) for MC-RR, MC-RR-GSH and MC-RR-Cys were 6, 12 and 9 ng mL(-1), respectively. Limits of quantification (LOQs) were 15, 30 and 22.5 ng mL(-1) for MC-RR, MC-RR-GSH and MC-RR-Cys, respectively. This method makes it feasible for the identification and quantification of MC-RR, MC-RR-GSH and MC-RR-Cys in limited and complex biological fluid samples (such as plasma and bile, typically 50 μL), which were previously excluded or difficult to study due to the relatively large sample volumes.

Variation of Microcystis and microcystins coupling nitrogen and phosphorus nutrients in Lake Erhai, a drinking-water source in Southwest Plateau, China

Lake Erhai is the second largest lake of Southwest China and an important drinking water source. The lake is currently defined as the preliminary stage of eutrophic states, but facing a serious threat with transfer into intensive eutrophication. The present study examined the dynamics of Microcystis blooms and toxic Microcystis in Lake Erhai during 2010, based on quantitative real-time PCR method using 16S rRNA gene specific for Microcystis and microcystin systhesis gene (mcy), and chemical analysis on microcystin (MC) concentrations. Total Microcystis cell abundance at 16 sampling sites were shown as an average of 1.7 × 10(7) cells l(-1) (1.3 × 10(2)-3.8 × 10(9) cells l(-1)). Microcystin LR (MC-LR) and microcystin RR (MC-RR) were the main variants. The strong southwesterly winds, anticlockwise circular flows and geographical characteristics of lake and phytoplankton community succession impacted the distribution patterns of Chl a and MC in the lake. The concentration of Chl a and MC and abundances of total Microsytis and MC-producing Microsystis (MCM) were shown to be positively correlated with pH, DO and TP, negatively correlated with SD, NO₃-N, TN/Chl a and TN/TP, and not correlated with NH₄-N, TN, dissolved total nitrogen (DTN) and water temperatures. When TN/TP decrease, Microcystis tended to dominate and MC concentrations tended to increase, suggesting that the "TN/TP rule" can be partially applied to explain the correlation between the cyanobacterial blooms and nutrients N and P only within a certain nutrient level. It is speculated that N and P nutrients and the associated genes (e.g., mcy) may jointly drive MC concentration and toxigenicity of Microcystis in Lake Erhai.

Characterization of the second and third steps in the enzymatic pathway for microcystin-RR biodegradation by Sphingopyxis sp. USTB-05

Microcystin-RR (MC-RR) is a dominant variant of microcystin (MC) worldwide. We previously isolated Sphingopyxis sp. USTB-05, which can efficiently biodegrade MC-RR. At least three enzymes encoded by MC-degrading genes are involved. Based on the successful expression of the first gene USTB-05-A, the second (USTB-05-B, KC513423) and third (USTB-05-C, KC573527) genes involved in the biodegradation of MC-RR were further cloned from Sphingopyxis sp. USTB-05 and expressed in Escherichia coli BL21 (DE3). After purification, the MC-degrading enzymes encoded by these genes were used for the catalytic degradation of MC-RR. The results demonstrated that the second enzyme encoded by USTB-05-B could convert linear MC-RR to a tetrapeptide by breaking the Ala–Arg bond. The third enzyme encoded by USTB-05-C could cleave Adda-Glu peptide bonds of both linear MC-RR and the tetrapeptide of Adda-Glu-Mdha-Ala, producing Adda as their common product. These findings will help better understand the biodegradation mechanism of MCs by Sphingopyxis sp. USTB-05.

Vertical distribution of cyanobacteria biomass and cyanotoxin production in the polymictic Siemianówka Dam Reservoir (eastern Poland)

Abstract The summer-autumn dominance of the toxic cyanobacterium Planktothrix agardhii was described in the lowland polymictic Siemianowka Dam Reservoir (SDR) in 2010 and 2011. The study was conducted at a station located in the deepest part of the reservoir. The species composition of phytoplankton was very similar at the four depths analyzed. Microcystins were continually present in the cyanobacterial biomass. Demethylated microcystin-RR (dmMC-RR) and microcystin-RR (MC-RR) were identified as the major microcystin variants in most samples, while demethylated microcystin-LR (dmMC-LR) and microcystin-LR (MC-LR) were each recorded only once. The concentration of microcystin-RR correlated strongly with the biomass of P. agardhii. The effect of environmental factors on cyanobacterial biomass the production of microcystins by cyanobacteria was minor, but increased water temperatures and pH favored the production of microcystins. Phytoplankton biomass was also influenced by how water outflow from the reservoir was regulated; the biomas increased with depth when the upper flaps were opened, but it was very similar throughout the water column when they were closed. According to the Polish phytoplankton-based index (IFPL), the ecological potential of the reservoir was determined to be poor.

Accumulation and Inhibitory Effects of Microcystin on the Growth of Rice and Broccoli

Microcystins (MCs) produced by cyanobacteria are severe hepatotoxins for mammalian and protein phosphatase inhibitors. Irrigation water for grain and vegetables is often contaminated with cyanobacteria and microcystin during warm seasons. We assessed the effects of various concentrations (0, 0.01 to 10 μg mL-1) of microcystin-LR (MC-LR) and microcystin-RR (MC-RR) exposure on Oryza sativa (rice) and Brassica oleraces var. italica (broccoli). The EC50 of leaves and roots of rice was 0.9 and 1.1 μg MC-LRmL-1, respectively. The no observed effect level (NOEL) of rice was less than 0.1 μg mL-1 (100 μg L-1). The EC50 of the stems and roots of broccoli was 8.7 and 7.2 μg MC-RR mL-1, respectively. There was no difference in the germination rate of broccoli among microcystin-RR concentrations. After exposure to 0, 0.01 to 10 μg mL-1 MC-RR for seven days, 14, 89 and 154 ng mg-1 (dry weight) MC-RR accumulated in B. oleracea. These EC50 values showed that microcystin-LR and -RR affected the growth of rice and broccoli. These findings suggest that MC is carried into terrestrial ecosystems via irrigation, and that the biota of higher ecological niches can be influenced by MC through bioaccumulation. Therefore, a guideline for MC concentrations in irrigation water should be set using the NOEL.

Microcystin-Degrading Activity of an Indigenous Bacterial Strain Stenotrophomonas acidaminiphila MC-LTH2 Isolated from Lake Taihu

Microcystin-LR (MC-LR) and microcystin-RR (MC-RR) produced by harmful cyanobacterial blooms (HCBs) pose substantial threats to the ecosystem and public health due to their potential hepatotoxicity. Degradation of microcystins (MCs) by indigenous bacteria represents a promising method for removing MCs from fresh water without harming the aquatic environment, but only a few microcystin (MC)-degrading bacteria have been isolated and had their mechanisms reported. This study aimed to isolate indigenous bacteria from Lake Taihu, and investigate the capability and mechanism of MC degradation by these bacteria. During a Microcystis bloom, an indigenous MC-degrading bacterium designated MC-LTH2 was successfully isolated from Lake Taihu, and identified as Stenotrophomonas acidaminiphila based on phylogenetic analysis. In the presence of MC-LR together with MC-RR, the strain MC-LTH2 was capable of totally degrading both simultaneously in 8 days, at rates of 3.0 mg/(L⋅d) and 5.6 mg/(L⋅d), respectively. The degradation rates of MCs were dependent on temperature, pH, and initial MC concentration. Adda (3-amino-9-methoxy-2, 6, 8-trimethyl-10-phenyldeca-4, 6-dienoic acid) was detected as an intermediate degradation product of MCs using high performance liquid chromatography coupled with time-of-flight mass spectrometry (HPLC-TOF-MS). To the best of our knowledge, this is the first report of Stenotrophomonas acidaminiphila capable of degrading two MC analogues and other compounds containing Adda residue completely under various conditions, although the mlrA gene in the strain was not detected. These results indicate the Stenotrophomonas acidaminiphila strain MC-LTH2 possesses a significant potential to be used in bioremediation of water bodies contaminated by MC-LR and MC-RR, and is potentially involved in the degradation of MCs during the disappearance of the HCBs in Lake Taihu.