• 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.

• Fisheries and Aquatic Sciences
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• v.11 no.1
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• pp.15-22
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• 2008

Excessive growth of phytoplankton is a common and severe problem in intensively farmed pangasiid catfish (Pangasius hypophthalmus) culture ponds. It can lead to cyanobacterial blooms, reduced fish growth, bad-tasting fish flesh, and lower market demand. To investigate how to manage undesirable phytoplankton growth, we evaluated three stocking strategies in nine rural fishponds (0.020-0.022 ha) owned by various farmers: a pangasiid catfish mono culture (treatment 1, $T_1$), and pangasiid catfish-silver carp (Hypophthalmichthys molitrix) polycultures at two stocking ratios of 1:1 (treatment 2, $T_2$) and 2:1 (treatment 3, $T_3$). The total density of all ponds was approximately 30,000 fishes/ha. Monoculture ($T_1$) resulted in significantly higher (p < 0.05) nutrient levels (nitrate and phosphate) in ponds than did polyculture ($T_2$ and $T_3$). Nutrient loads increased with culture time, resulting in increased growth of phytoplankton, including Cyanophyceae (9 genera), Chlorophyceae (15 genera), Bacillariophyceae (8 genera), and Euglenophyceae (3 genera). The introduction of silver carp as a co-species helped to regulate phytoplankton growth and to improve the water quality of pangasiid catfish culture ponds.

• BMB Reports
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• v.39 no.6
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• pp.717-721
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• 2006

In vitro analyses of type I signal peptidase activities require protein precursors as substrates. Usually, these pre-proteins are expressed in vitro and cleavage of the signal sequence is followed by SDS polyacrylamide gel electrophoresis coupled with autoradiography. Radioactive amino acids have to be incorporated in the expressed protein, since the amount of the in vitro expressed protein is usually very low and processing of the signal peptide cannot be followed by SDS polyacrylamide gel electrophoresis alone. Here we describe a rapid and simple method to express large amounts of a protein precursor in E. coli. We have analyzed the effect of ionophors as well as of azide on the accumulation of expressed protein precursors. Azide blocks the function of SecA and the ionophors dissipate the electrochemical gradient across the cytoplasmic membrane of E. coli. Addition of azide ions resulted in the formation of inclusion bodies, highly enriched with pre-apo-plastocyanine. Plastocyanine is a soluble copper protein, which can be found in the periplasmic space of cyanobacteria as well as in the thylakoid lumen of cyanobacteria and chloroplasts, and the pre-protein contains a cleavable signal sequence at its N-terminus. After purification of cyanobacterial pre-apo-plastocyanine, its signal sequence can be cleaved off by the E. coli signal peptidase, and protein processing was followed on Coomassie stained SDS polyacrylamide gels. We are optimistic that the presented method can be further developed and applied.

• Mycobiology
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• v.34 no.3
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• pp.138-142
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• 2006

Soil cyanobacteria isolated from the rice paddy fields of 10 different locations across Korea were evaluated by agar plate diffusion test for antifungal activity. Aqueous, petroleum ether, and methanol extracts from one hundred and forty two cyanobacterial strains belonging to the 14 genera were examined for antifungal properties against seven phytopathogenic fungi causing diseases in hot pepper (Capsicum annuum L). Of total cyanobacteria, nine cyanobacteria (6.34%) exhibited antifungal effects. The nine cyanobacteria selected with positive antifungal activities were two species of Oscillatoria, two of Anabaena, three of Nostoc, one of Nodularia, and one of Calothrix. Alternaria alternata and Botrytis cinerea were inhibited by nine and eight species of cyanobacteria, respectively. Rhizopus stolonifer was suppressed by only methanol extract of Nostoc commune FK-103. In particular, Nostoc commune FK-103 and Oscillatoria tenuis FK-109 showed strong antifungal activities against Phytophthora capsici. Their antifungal activity at the late exponential growth phase is related to the growth temperature and not associated with the growth parameters such as cell biomass and $chlorophyll-{\alpha}$ concentration. The high inhibition levels of antibiotics were 22.5 and 31.8 mm for N. commune FK-103 and O. tenuis FK-109, respectively. The optimal temperature for antibiotic productivity was $35^{\circ}C$.

• Korean Journal of Environmental Biology
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• v.20 no.1
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• pp.20-24
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• 2002

We have from water samples of Kwalim, Dochang, and Mulwang reservoirs in Kyonggi-Do, where cyanobacteria blooming occurred. Isolated microbes which have lytic activity for cyanobacteria. Water samples were smeared on the Anabaena cylindrica lawn and incubated in light chamber at $28^\circ{C}$, under 3000 lux for 13 days. A fungus having cyanobacterial lytic activity was isolated from the samples of Dochang reservoir. The isolate was identified as Cryptococcus laurentii by Vitek system. From the culture of the isolate, four major extracellular protein bands (29, 35.2, 40.9, 51.1 kDa) have been detected and the 29 kDa protein band was more thickly appeared in the culture with cyanobacteria.

• Journal of Environmental Science International
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• v.14 no.7
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• pp.649-655
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• 2005

Microcystis aeruginosa is common form of cyanobacteria (blue-green algae) capable of producing toxic heptapeptide (microcystin) that cause illness or death. The comparison of molecular genetic method with the morphological characteristics of cyanobacteria was conducted. We have designed PCR primers (JJM98F, JJM1141R) for cyanobacterial 16S rRNA and phycocyanin intergenic spacer (PC-IGS) gene domain. To confirm the production of microcystins, PCR primers for the N-methyltransferase (NMT) domain of microcystin synthetase gene mcyA were designed using 21 cyanobacteria strains Most of isolated strains from the Nakdong River was classified as Microcystis aeruginosa and the similarities were $99\%$ with M. aeruginosa AF 139292. $38.1\%$ of isolated strains contained microcystin synthesis gene. NMT (N-methyltransferase) were not detected in isolated strain in several strains, which means non-toxic. However, the NMTs of the strains were detected during the cultivation.

• Bulletin of the Korean Chemical Society
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• v.26 no.6
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• pp.939-942
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• 2005

For the detection of cyanobacterial toxin, an Enzyme-linked immunosorbent assay (ELISA) was integrated into a PDMS microchip. The conjugates of microcystin-LR (MCLR) and keyhole limpet hemocyanin (KLH) were adsorbed on the surface of polystyrene beads and these MCLR-KLH polystyrene beads were introduced into a microchamber. MCLR on the surface of polystyrene beads reacted with horseradish peroxides (HRP) conjugated anti-MCLR monoclonal antibody (mAb) which had a competitive reaction with MCLR in water sample. After the enzyme substrate 3,3,5,5-tetramethyl benzidine (TMB) was injected into the chamber and catalyzed by HRP, the color change was detected with a liquid-cord waveguide. This integration shortened the conventional ELISA analysis time from several hours to about 30 min with only 4.2 $\mu$L MCLR sample consuming which was useful for the environmental analysis. More over, troublesome operations required for ELISA could be replaced by simple operations. The microchip based detection system showed a good sensitivity of 0.05 $\mu$g/L and maintained good reliability through its quantitative range with low coefficients of variation (2.5-10.5%).

• Journal of Microbiology and Biotechnology
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• v.22 no.2
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• pp.166-169
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• 2012

In several biotechnological applications of living bacterial cells with inducible gene expression systems, the extent of overexpression and the specificity to the inducer are key elements. In the present study, we established the concentration ranges of $Zn^{2+}$, $Ni^{2+}$, $Co^{2+}$, ${AsO_2}^-$, and $Cd^{2+}$ ions that caused significant activation of the respective promoters of Synechocystis sp. without concomitant unspecific stress responses. The low expression levels can be increased up to 10-100-fold upon treatments with $Cd^{2+}$, ${AsO_2}^-$, $Zn^{2+}$, and $Co^{2+}$ ions and up to 800-fold upon $Ni^{2+}$ treatment. These results facilitate the development of conditional gene expression systems in cyanobacteria.

• Journal of Microbiology and Biotechnology
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• v.18 no.5
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• pp.918-925
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• 2008

Controlling the light energy and major nutrients is important for high cell density culture of cyanobacterial cells. The growth phase of Anabaena variabilis can be divided into an exponential growth phase and a deceleration phase. In this study, the cell growth in the deceleration phase showed a linear growth pattern. Both the period of the exponential growth phase and the average cell growth rate in the deceleration phase increased by controlling the light intensity. To control the light intensity, the specific irradiation rate was maintained above $10\;{\mu}mol/s/g$ dry cell by increasing the incident light intensity stepwise. The final cell density increased by controlling the nutrient supply. For the control of the nutrient supply, nitrate, phosphate, and sulfate were intermittently added based on the growth yield, along with the combined control of light intensity and nutrient concentration. Under these control conditions, both final cell concentration and cell productivity increased, to 8.2 g/l and 1.9 g/l/day, respectively.

• Journal of Microbiology and Biotechnology
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• v.29 no.1
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• pp.59-65
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• 2019

Fusaricidin analogs, produced by Paenibacillus polymyxa, were tested for selective control of a major bloom-forming cyanobacterium, Microcystis sp. Fusaricidin (A and B mixtures) and four analogs were isolated from P. polymyxa E681 and investigated for their inhibition of cyanobacterial cell growth. Among the four fusaricidin analogs, fraction 915 Da (designated as Fus901) showed growth inhibition activity for Microcystis aeruginosa but not for Anabaena variabilis and Scenedesmus acutus. Microcystin concentration decreased up to 70% and its content per cell also decreased over 50% after 3 days. Fusaricidin exhibited growth inhibition against Gram-positive bacteria but Fus901 did not. Molecular weights of fusaricidin A and B were 883 Da and 897 Da, whereas that of Fus901 was 915 Da. Structure analysis by a ring-opening method revealed a linear form for Fus901. Expression of the pod gene related to oxidative stress was increased 2.1-fold by Fus901 and that of mcyD decreased up to 40%. These results indicate that Fus901 exerts oxidative stress against M. aeruginosa. Thus, Fus901 can be used as a selective cyanobactericide without disturbing the ecological system and could help in decreasing the microcystin concentration.