• Korean Journal of Ecology and Environment
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• v.47 no.spc
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• pp.19-30
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• 2014

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 $10{\mu}gmL^{-1}$) of microcystin-LR (MC-LR) and microcystin-RR (MC-RR) exposure on Oryza sativa (rice) and Brassica oleraces var. italica (broccoli). The $EC_{50}$ of leaves and roots of rice was 0.9 and $1.1{\mu}gMC-LRmL^{-1}$, respectively. The no observed effect level (NOEL) of rice was less than $0.1{\mu}gmL^{-1}$ ($100{\mu}gL^{-1}$). The $EC_{50}$ of the stems and roots of broccoli was 8.7 and $7.2{\mu}gMC-RRmL^{-1}$, respectively. There was no difference in the germination rate of broccoli among microcystin-RR concentrations. After exposure to 0, 0.01 to $10{\mu}gmL^{-1}$ MC-RR for seven days, 14, 89 and 154 ng mg-1 (dry weight) MC-RR accumulated in B. oleracea. These $EC_{50}$ 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.

• Korean Journal of Ecology and Environment
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• v.56 no.1
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• pp.1-13
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• 2023

Targeting Microcystin (MC), which is most abundantly detected in the North-Han River water area, we analyzed the relationship between the MC biosynthesis gene (mcyA gene), cyanobacteria cell density, and MC concentration, derived an RNA-MC conversion formula, and derived the cyanobacteria. The concentration of MC present in cells was predicted. In the North-Han River waters, the mcyA gene was found mainly at downstream sites of the North-Han River after Muk-Hyeon Stream junction, and higher copy numbers were found on average than other sites. In the Uiam Lake waters upstream of the North-Han River, the mcyA gene copy number increased at the Kong-Ji Stream point, and after September, the mcyA gene copy number decreased throughout the North-Han River waters. The expression of the mcyA gene was concentrated in the short period of summer due to the spatio-temporal difference between upstream and downstream water bodies. The mcyA gene expression level was not only highly correlated with MC concentration, but also correlated with the cell density of Microcystis aeruginosa and Dolichospermum circinale, which are known to biosynthesize MC. Six conversion formulas derived based on the RNA-MC relationship showed statistical significance (p<0.05) and exhibited high correlation coefficients (r) of 0.9 or higher. The expression level of MC biosynthesis gene present in eRNA determines the synthesis of cyanotoxin substances in water, quickly quantifies gene activity, and can be fully utilized for early warning of MC development.

• Proceedings of the Microbiological Society of Korea Conference
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• 2001.11a
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• pp.113-120
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• 2001

The production of microcystins from Microcystis aeruginosa was investigated in a P-limited continuous culture and a batch culture. The microcystin content of M aeruginosa was higher at a lower $\mu$, whereas the microcystin (MC)-producing rate was linearly proportional to $\mu$. The ratios of the MC-producing rate to the C-fixation rate were higher at a lower $\mu$. Consequently, increases in the microcystin content per dry weight along with the production of the more toxic form, MC-LR, were both observed under more P-limited conditions. The microcystin content of M. aeruginosa exhibited a high correlation with the total N content regardless of N-fixed or P-fixed culture. The microcystin concentration was investigated from spring to autumn in 1999 in the Daechung Reservoir, Korea. The dominant species in the algal blooming season was Microcystis. When the microcystin concentration exceeded about 100 ng $1^{-1}$ the ratio of particulate to dissolved total nitrogen (TN) or total phosphorus (TP) interestingly converged at a value of 0.6. The microcystin concentration was lower than 50 ng $1^{-1}$ at a particulate N:P ratio below 8, whereas the microcystin concentration varied quite substantially from 50 ng $1^{-1}$ to 250 ng $1^{-1}$ at a particulate N:P ratio> 8.

• Korean Journal of Ecology and Environment
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• v.40 no.2
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• pp.294-302
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• 2007

This study was to evaluate microcystin production by Microcystis aeruginosa in response to three different levels of indirect (0, 10, 50% of fish cultured media filtrate; control, FCMF1 and FCMF2) exposures to omnivorous and planktivorous fish (Carassius gibelio langsdorfi and Hypophthalmichthys molitrix, CCMF and HCMF, repectively). The cell biomass, intracellular microcystin (MC) and extracellular MC were measured everyday. The intracellular MC contents of all treatments were significantly increased than the controls (CCMF1, P=0.015; CCMF2, P<0.001; HCMF1, P<0.001; HCMF2, P<0.001). The intracellular MC contents of M. aeruginosa were significantly higher in CCMF2 than in CCMF1 (P=(0.023), Those of M, aeruginosa in HCMF2 were significantly higher than that in HCMF1 (P<0.001). The extracellular MC contents were not significantly different between control and CCMFs but those of M, aeruginosa in HCMF1 and HCMF2 were significantly higher than that in control (HCMF1, P=0.003; HCMF2, P<0.001). This study strongly supports that induced-defensive MC production (intra and extracellular MC) of potentially toxic cyanobacteria in response to kairomone concentration and this results can consider the biomanipulation of eutrophic waters as well as an information concerning strategies for recovering eutrophic waters.

• Korean Journal of Ecology and Environment
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• v.34 no.3 s.95
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• pp.175-184
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• 2001

The temporal and diel changes of cyanobacterial cell density, species composition, and cyanobacterial toxins (microcystin-RR, -YR, -LR) were examined for the outflow water of Lake Suwa in Japan from May to October, 1998. The highest total cell densities of Microcystis were observed in July and September, when the dominant phytoplankton was Microcystis ichthyoblabe and M. viridis, respectively. Both the species composition and total cell density of Microcystis affected the variation of the concentration of three microcystin variants. Only microcystin-RR(MC-RR) and -LR (MC-LR) were detected in July when Microcystis ichthyoblabe dominated, while microcystin-RR, -YR (MC-YR) and -LR were detected in August and October when Microcystis viridis dominated. The microcystin concentration and the cell density of Microcystis in the outflow water showed diel variations; the ratio of maximum to minimum value was $3{\sim}20$ fold far microcystin concentration, and $5{\sim}31$ fold for cell density. The diel variations of toxin concentration as well as Microcystis cell density was closely related to the diel variation of wind. During the windy period, when higher speeds occurred in the afternoon hours than morning hours, both the cell density of Microcystis and microcystin concentration tended to increase in the morning and decrease in the afternoon. The results of this study suggest that controlling the timing of lake discharge at the floodgate or intake tower can be useful for water resource management with respect to decreasing cyanobacteria biomass within intake water.

• Korean Journal of Ecology and Environment
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• v.39 no.2 s.116
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• pp.209-218
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• 2006

This study was to evaluate microcystin production by two strains of cyanobacteria (Microcystis aeruginosa and Planktothrix agardhii) in response to three different levels of direct (0,4,8 inds.) or indirect (0,25, 50% of zooplankton culture media filtrate) exposures to zooplankton (Daphnia magna and Moina macrocopa). The cell biomass and intracellular microcystin (MC) were measured everyday. The survival rates of zooplankton were evaluated for daily intervals for the direct exposure. The intracellular MC produced peaked on the day 3 or 4, and then decreased over the both exposure experiment. In the direct experiment, the MC values were significantly different among the control and zooplankton treatments (ZT; repeated measures-ANOVA: P< 0.039). The MC contents of P. agardhii strain (No.204) were significantly higher (Tukey test, P< 0.082) in ZT2 (8 inds.) than in ZT2 (4 inds.). On the peak day, the intracellular MC exposed to both zooplanktons was significantly higher than the control (One-way ANOVA, P< 0.021). Higher zooplankton survivals were observed in the M. aeruginosa strain (No. 111) rather than in high toxic P. agardhii strain. In the indirect experiment, the intracellular MC of the M. aeruginosa strain was significantly different among the control and zooplankton culture media filtrate (ZCMF)treatments (rm-ANOVA: P<0.004), The MC exposed ZCMF2 (50%) were significantly higher than in ZCMFI (25%: Tukey test, P< 0.025) for both strains. This study strongly supports the induced-defensive MC production of potentially toxic cyanobacteria in response to the presence of zooplankton.

• Korean Journal of Ecology and Environment
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• v.34 no.1 s.93
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• pp.45-53
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• 2001

Transport of cyanobacterial toxins (microcystin-LR, -RR, -YR) were assessed from a eutrophic lake, Lake Suwa, through the outflowing river, the Tenryu River, and its irrigation channel branch. Temporal variation of phytoplankton species composition in the river coincided with those of the lake; Microcystis ichthyoblabe dominated from June to July, and M. viridis dominated from August to September. When cyanobacterial bloom occurred, microcystins were continuously detected at the concentration of $0.3{\sim}3.2\;{\mu}g/l$ even at 32 km downstream. The change of the content of three microcystin variants were related both with the total cell density of Microcystis and with the change of Microcystis species composition. When Microcystis ichthyoblabe dominated during July, only microcystin-RR (MC-RR) and -LR (MC-LR) were detected, while when Microcystis viridis dominated between August and October, microcystin-RR,-YR (MC -YR) and -LR were detected. Along 29 km flowing distance (flow time 11 hours) between site 2 and site 5 in the Tenryu River, cyanobacterial density and microcystin concentration were reduced by 73% and 72%, respectively, which is mostly contributed by the dilution effect of tributary waters (61% and 57%, respectively) . In the artificial irrigation channel microcystins and cyanobacterial cells were decreased less than in the natural river. The results indicate that cyanobacterial toxins can be transported far downstream without much removal and give hazards to water usage in downstream of eutrophic lakes with cyanobacterial blooms.

• Toxicological Research
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• v.22 no.3
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• pp.301-306
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• 2006

Microcystin-LR(MC-LR), a cyanobacterial toxin produced by Microcystis aeruginosa, causes severe hepatotoxicity. Here we investigated the morphologic changes of rat hepatocyte spheroid induced by exposure of MC-LR($10^{-6}M$) in vitro. In addition, to determine the effects of such toxin in the process of hepatocyte spheroid formation, primarily isolated hepatocytes were incubated with MC-LR and the process of spheroid formation was observed. In both hepatocyte spheroid and suspension culture systems, the morphologic changes caused by MC-LR were noticible at 5 min post exposure and were characterized by the loss of microvilli, cytoplasmic vacuolation, the accumulation of lipid droplets, and blob formation. Especially, the size and numbers of blob on the cell surface were increased as the incubation time prolonged and the appearance of electron dense bodies were observed in the cytoplasm of hepatocyte at 20 min post exposure. Furthermore, bile canaliculi-like structures in the hepatocyte spheroids were slightly widened and the process of spheroids formation was inhibited in the isolated hepatocytes incubated with MC-LR. These results indicate that morphologic changes in. the hepatocyte membrane and organelles seem to be typical events in showing the MC-LR induced hepatotoxic effects and the spheroid culture method might be a useful experimental tool to evaluate hepatoxicity since it reflects the in vivo status of hepatocytes.

• Applied Chemistry for Engineering
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• v.24 no.5
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• pp.518-524
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• 2013

This study investigated the degradation of taste-and-odor compounds and toxins using dielectric barrier discharge plasma. The degradation of taste-and-odor compounds was conducted on geosmin and 2-methyl isoborneol (2-MIB), and the toxins investigated were microcystin-LR (MC-LR), microcystin-RR (MC-RR), microcystin-YR (MC-YR) and anatoxin-a. Largely depending on the type of gas fed to the plasma reactor, the degradation efficiencies of the taste-and-odor compounds decreased in order of oxygen (100%) > dry air (96%) > nitrogen (5%) for geosmin and in order of oxygen (100%) > dry air (94%) > nitrogen (2%) for 2-MIB on the basis of 150 s reaction time. This result suggests that the oxidative reactive species generated during plasma treatment, especially long-lived ozone, are mainly responsible for the degradation of these compounds. When using oxygen as the feed gas, geosmin and 2-MIB were totally degraded within 150 s, microcystins within 10 s, and anatoxin-a within 30 s. It was found that the taste-and-odor compounds and toxins were degraded more rapidly in real lake water than in distilled water.

• Journal of Korean Society on Water Environment
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• v.16 no.4
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• pp.479-490
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• 2000

This study investigated the removal characteristics, Microcystin decomposition and generation of by-products when aqueous Microcystis sp. is oxidized by ozone. The concentration of Microcystin (MC) in aqueous solution has been found by HPLC analysis to decrease continuously by ozonation after the initial, abrupt increase. The kinetic constant of the decomposition of MC-RR and -LR were 0.0596 and 0.0243, respectively. This means that removal efficiency of MC-RR by its oxidative decomposition is preferable compared with that of MC-LR. On the other hand, it has been found that the decomposition product, TOC, exhibits the continuous decrease in the concentration by further ozonation, while DOC and UV-254 increase temporarily until 10 minutes before the decrease. Furthermore, the GC/MSD analysis has revealed that the ozonation of Microcystis sp. for 100minutes affords five kinds of aldehydes, six kinds of alcohols, and trans-1, 2-dimethyl-cyclopropane.