• Economic and Environmental Geology
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• v.35 no.6
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• pp.553-565
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• 2002

Seasonal variations in vertical distributions of metals were investigated in the contaminated paddy soils around Siheung Cu-Pb-Zn and Deokeum Au-Ag mines. Geochemical behavior of metals was also evaluated with respect to redox changes during the cultivation of rice. Two microcosms simulating the rice-growing paddy field were set up in the laboratory. The raw paddy soils from two sites showed differences in mineralogy, metal concentrations and gecochemical parameters, and it is suggested that high proportions of exchangeable fractions in metals may give high dissolution rates at Deokeum. In both microcosms of Siheung and Deokeum, redox differences between surface and subsurface of paddy soils were maintained during the flooded period of 18 weeks. Siheung soil had neutral to alkaline pH conditions, while strongly acidic conditions and high Eh values were found at the surface soil of Deokeum. The concentrations of dissolved Fe and Mn were higher in the subsurface pore waters than in interface and upper waters from both microcosms, indicating reductive dissolution under reducing conditions. On the contrary, dissolved Pb and Zn had high concentrations at the surface under oxidizing conditions. From the Siheung microcosm, release of dissolved metals into upper waters was decreased. presumably by the trap effect of Fe- and Mn-rich layers at the interface. However, in the Deokeum microcosm, significant amounts of Pb and Zn were released into upper water despite the relatively lower contents in raw paddy soil, and seasonal variations in the chemical fractionation of metals were observed between flooded and drained conditions. Under acidic conditions, rice may uptake high amounts of metals from the surface of paddy soils during the flooded periods, and increases of exchangeable phases may also increase the bioavailability of heavy metals in the drained conditions.

• Proceedings of the Korean Society for Applied Microbiology Conference
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• 2004.06a
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• pp.60-61
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• 2004

Metabolic engineering is now a well established discipline, used extensively to determine and execute rational strategies of strain development to improve the performance of micro-organisms employed in industrial fermentations. The basic principle of this approach is that performance of the microbial catalyst should be adequately characterised metabolically so as to clearlyidentify the metabolic network constraints, thereby identifying the most probable targets for genetic engineering and the extent to which improvements can be realistically achieved. In order to harness correctly this potential, it is clear that the physiological analysis of each strain studied needs to be undertaken under conditions as close as possible to the physico-chemical environment in which the strain evolves within the full-scale process. Furthermore, this analysis needs to be undertaken throughoutthe entire fermentation so as to take into account the changing environment in an essentially dynamic situation in which metabolic stress is accentuated by the microbial activity itself, leading to increasingly important stress response at a metabolic level. All too often these industrial fermentation constraints are overlooked, leading to identification of targets whose validity within the industrial context is at best limited. Thus the conceptual error is linked to experimental design rather than inadequate methodology. New tools are becoming available which open up new possibilities in metabolic engineering and the characterisation of complex metabolic networks. Traditionally metabolic analysis was targeted towards pre-identified genes and their corresponding enzymatic activities within pre-selected metabolic pathways. Those pathways not included at the onset were intrinsically removed from the network giving a fundamentally localised vision of pathway functionality. New tools from genome research extend this reductive approach so as to include the global characteristics of a given biological model which can now be seen as an integrated functional unit rather than a specific sub-group of biochemical reactions, thereby facilitating the resolution of complexnetworks whose exact composition cannot be estimated at the onset. This global overview of whole cell physiology enables new targets to be identified which would classically not have been suspected previously. Of course, as with all powerful analytical tools, post-genomic technology must be used carefully so as to avoid expensive errors. This is not always the case and the data obtained need to be examined carefully to avoid embarking on the study of artefacts due to poor understanding of cell biology. These basic developments and the underlying concepts will be illustrated with examples from the author's laboratory concerning the industrial production of commodity chemicals using a number of industrially important bacteria. The different levels of possibleinvestigation and the extent to which the data can be extrapolated will be highlighted together with the extent to which realistic yield targets can be attained. Genetic engineering strategies and the performance of the resulting strains will be examined within the context of the prevailing experimental conditions encountered in the industrial fermentor. Examples used will include the production of amino acids, vitamins and polysaccharides. In each case metabolic constraints can be identified and the extent to which performance can be enhanced predicted

• Journal of Soil and Groundwater Environment
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• v.13 no.6
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• pp.93-102
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• 2008

Experimental studies were conducted to characterize the synthesized nanoscale zero-valent iron (NZVI) which is resistant to oxidation in the atmospheric environment. XRD, XPS, and TEM analyses revealed that the oxidation-resistant NZVI particles formed under various controlled air contact conditions (4, 8 and 12 mL/min) have shells with ${\sim}$5 nm thickness. The shells consist of magnetite (${Fe_3}{O_4}$) and maghemite (${\gamma}-{Fe_2}{O_3}$), predominantly. No substantial differences were found in the shell components and thickness among NZVI particles formed under the various air flow rates. On the other hand, shell was not detected in the TEM image of rapidly oxidized NZVI particles. NZVI particles synthesized under the various air flow rates showed similar TCE degradation performances ($k_{obs}$= 0.111, 0.102, and 0.086 $hr^{-1}$), which are equivalent to approximately 80% of those obtained by the fresh NZVI particles. TCE degradation efficiencies of the NZVI particles(fresh, controlled air contact and rapidly oxidized) were improved after equilibrating with water for one day, indicating that depassivation of the shells occurred. The performances of NZVI particles decreased to 90% and 50% of those of the fresh NZVI particles, when they were equilibrated with the atmosphere for a week and two months, respectively. The NZVI particles synthesized under the controlled air contact would have advantages over traditional NZVI particles in terms of practical application into the site, because of their inertness toward atmospheric oxygen.

• Proceedings of the Korean Society for Applied Microbiology Conference
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• 2002.10a
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• pp.18-25
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• 2002

The pikromycin biosynthetic system in Streptomyces venezuleae is unique for its ability to produce two groups of antibiotics that include the 12-membered ring macrolides methymycin and neomethymycin, and the 14-membered ring macrolides narbomycin and pikromycin. The metabolic pathway also contains two post polyketide-modification enzymes, a glycosyltransferase and P450 hydroxylase that have unusually broad substrate specificities. In order to explore further the substrate flexibility of these enzymes a series of hybrid polyketide synthases were constructed and their metabolic products characterized. The plasmid-based replacement of the multifunctional protein subunits of the pikromycin PKS in S. venezuelae by the corresponding subunits from heterologous modular PKSs resulted in recombinant strains that produce both 12- and 14-membered ring macrolactones with predicted structural alterations. In all cases, novel macrolactones were produced and further modified by the DesVII glycosyltransferase and PikC hydroxylase leading to biologically active macrolide structures. These results demonstrate that hybrid PKSs in S. venezuelae can produce a multiplicity of new macrolactones that are modified further by the highly flexible DesVII glycosyltransferase and PikC hydroxylase tailoring enzymes. This work demonstrates the unique capacity of the S. venezuelae pikromycin pathway to expand the toolbox of combinatorial biosynthesis and to accelerate the creation of novel biologically active natural products. The polyketide backbone of rifamycin B is assembled through successive condensation and ${\beta}$-carbonyl processing of the extender units by the modular rifamycin PKS. The eighth module, in the RifD protein, contains nonfunctional DH domain and functional KR domain, which specify the reduction of the ${\beta}$-carbonyl group resulting in the C-21 bydroxyl of rifamycin B. A four amino acid substitution and one amino acid deletion were introduced in the putative NADPH binding motif in the proposed KR domain encoded by rifD. This strategy of mutation was based on the amino acid sequences of the corresponding motif of the KR domain of module 3 in the RifA protein, which is believed dysfunctional, so as to introduce a minimum alteration and retain the reading frame intact, yet ensure loss of function. The resulting strain produces linear polyketides, from tetraketide to octaketide, which are also produced by a rifD disrupted mutant as a consequence of premature termination of polyketide assembly. Much of the structural diversity within the polyketide superfamily of natural products is due to the ability of PKSs to vary the reduction level of every other alternate carbon atom in the backbone. Thus, the ability to introduce heterologous reductive segments such as ketoreductase (KR), dehydratase (DH), and enoylreductase (ER) into modules that naturally lack these activities would increase the power of the combinatorial biosynthetic toolbox. The dehydratase domain of module 7 of the rifamycin PKS, which is predicted to be nonfunctional in view of the sequence of the apparent active site, was replaced with its functional homolog from module 7 of rapamycin-producing polyketide synthase. The resulting mutant strain behaved like a rifC disrupted mutant, i.e., it accumulated the heptaketide intermediate and its precursors. This result points out a major difficulty we have encountered with all the Amycolatopsis mediterranei strain containing hybrid polyketide synthases: all the engineered strains prepared so far accumulate a plethora of products derived from the polyketide chain assembly intermediates as major products instead of just analogs of rifamycin B or its ansamycin precursors.

• Journal of the Korean Society for Marine Environment & Energy
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• v.2 no.1
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• pp.102-112
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• 1999

The purpose of this study is to evaluate the effects of design criteria and environmental conditions of the site of created tidal flats on the structure and function of man-made ecosystem. Seven constructed tidal flats and three natural tidal flats were studied taking the difference in the location (wave height and tidal current), inflow of river water, slope of tidal flat and age after the construction completed into consideration. Parameters studied were physico-chemical and biological characteristics of soils and rate of respiration. The natural tidal flats had higher contents of silt, nitrogen and organic matter compared with the constructed ones. The natural ones had reductive zone below 2cm, whereas the constructed ones had aerobic zone from the surface to below 20cm. The bacterial population in the soil of the constructed tidal flats was one to two orders of magnitude lower than that in the natural ones. Both biomass of macrobenthos and microbial respiration rate, however, were not different significantly between the natural and the constructed tidal flats. There was an exceptional constructed tidal flat with similar physico-chemical and biological characteristics to the natural ones. It is most probable that sufficient conditions to have similar tidal flats to natural ones are the location in enclosed bay or calm coastal area. Thus, to make man-made tidal flats with the same characteristics as those in natural ones, man-made tidal flats should be designed and/or located to enhance the accumulation of silt on tidal flat. It is important to select a place having low water motion for construction of tidal flat.

• Microbiology and Biotechnology Letters
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• v.41 no.2
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• pp.153-159
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• 2013

A mannitol dehydrogenase (MDH; EC 1.1.1.67) gene was cloned from the Sinorhizobium meliloti 1021 (KCTC 2353) genome and expressed in Escherichia coli. It was seen to have an open reading frame consisting of 1,485 bp encoding 494 amino acids (about 54 kDa), which shares approximately 35-55% of amino acid sequence identity with some known long-chain dehydrogenase/ reductase family enzymes. The recombinant S. meliloti MDH (SmMDH) showed the highest activity at $40^{\circ}C$, and pH 7.0 (D-fructose reduction) and pH 9.0 (D-mannitol oxidation), respectively. SmMDH could catalyze the oxidative/reductive reactions between D-mannitol and D-fructose in the presence of $NAD^+/NADH$ as a coenzyme, but not with NADP+/NADPH. These results indicate that SmMDH is a typical $NAD^+/NADH$-dependent mannitol dehydrogenase.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.6
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• pp.2879-2887
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• 2011

This research is aimed for the better understanding of corrosion behavior of carbon steel in ETA or $NH_3$ solution at high temperature. To minimize the corrosion it is important to select proper pH control agent(s), which also let it maintain basic or reductive environment inside the steel pipe. This work will provide the practical guideline which can be applied to the nuclear power plant for developing the life extension method of carbon steel. Experiments were carried out by measuring the corrosion rate using the potentiodynamic polarization curve of carbon steel in ETA and NH3 at different temperatures. The corrosion rate was estimated by using the Tafel curve measured under various test conditions: i) $NH_3$ is less than ETA as a pH agent. ii) the corrosion was reduced at high pH, and iii) the corrosion was maximum in the temperature range of $150\sim200^{\circ}C$.

• Magazine of the Korean Society of Agricultural Engineers
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• v.17 no.3
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• pp.3795-3814
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• 1975

The purpoes of this thesis is to study the effect of the variation of the beginning date of the suspension of irrigation and the length of intermittent suspension period of irrigation in the paddy field on the growth and yield of rice, so as the provide a critical limit of saving irrigation water and an irrigation method to prevent drough damage in rice cultivation. In this experiment, the rice variety adopted was NONGRIM No.29. There were seven main test plot, each test plot having a different beginning date of the suspension of irrigation. A main test plot was susdivided into five small test plots, each having a different length of the suspension period of irrigation. The results obtained in this experiment are summarized as follows: 1. The number of tillers is controlled by the treatment of the suspension of irrigation, its beginning date being early of late. The reductive effects of beginning dates of suspension upon the number of tillers. investigated on July 30, are about 84% for the treatment suspended on July 8, 87% on July 12, and 92% on July 19, respectively, in comparison with the standard plot. However. the suspenion treatments after the foregoing dates does not affect the control of their numbers. On the other hand, the lengths of intermittent suspension periods influence highly on the number of tillers to be restrained considerably, the decrease ratio ranging from 91% to 80% Both treatments on dates and periods are so intermingled that the restraining effects of suspension periods become greater as the dates of its beginning are earlier. 2. The elongation of plant hieghts also restrained considerably by the longer periods and earlier dates of suspension treatments of irrigation. Especially, the effects of the lengths of suspension periods become more serious. 3. Heading dates are delayed by two to five days through the suspension treatments of irrigation. However, the heading stage ends almost on the same day without relation to the differences between the irrigation suspension treatments. In the test plot where the suspension date of irrigation comes after the young panicle forming stage, the heading stage ends one or two days later than in the standard test plot. 4. Both culm lengths and panicle lengths show significant differences in their values, i.e., their lengths are shorter, as the begining dates of irrigation suspension are earlier and the suspension periods are longer. 5. The earlier the beginning date and the longer the period of irrigation suspension, the less is the number of panicles per hill in comparison with the standard plot. 6. The earlier the beginning date and the longer the period of irrigation suspension, the higher is the significant difference in the number of kernels per panicle in comparison with that in the standard test plot, i.e., the less is the number of kernels per panicle. 7. The earlier the beginning date and the longer the period of irrigation suspension, the lighter are the weights of rough rice and straws per hill in comparison with those in the standard plot.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.9
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• pp.521-527
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• 2016

Nanoscale zero valent iron (nZVI) has been intensively studied for the treatment of a plethora of pollutants through reductive reaction, however, the nano size should be of concern when nZVI is considered for water treatment, due to difficulties in recovery. The loss of nZVI causes not only economical loss, but also potential risk to human health and environment. Thus, the immobilization onto coarse or structured support is essential. In this study, two representative processes for nZVI immobilization on granular activated carbon (GAC) were evaluated, and optimized conditions for synthesizing Fe/GAC composite were suggested. Both total iron content and $Fe_0$ content can be significantly affected by preparation processes, therefore, it was important to avoid oxidation during preparation to achieve higher reduction capacity. Synthesis conditions such as reduction time and existence of intermediate drying step were investigated to improve $Fe_0$ content of Fe/GAC composites. The optimal condition was two hours of $NaBH_4$ reduction without intermediate drying process. The prepared Fe/GAC composite showed synergistic effect of the adsorption capability of the GAC and the degradation capability of the nZVI, which make this composite a very effective material for environmental remediation.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.26 no.2
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• pp.91-101
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• 1993

To investigate the effects on pigmentation and carotenoid metabolism of red sea breams Pagrus major and flounders Paralichithys olivaceus by the supplemented carotenoids, fishes wire fed the diet each containing ${\beta}$-carotene, lutein ester, astaxanthin, astaxanthin monoester, astaxanthin diester and ${\beta}$-apo-8'-carotenal for 8 weeks. Carotenoids in the integuments were analyzed. In cultured red sea breams with supplemented carotenoids, carotenoid deposition and pigmentation were higher in order of astaxanthin diester group, ${\beta}$-apo-8'-carotenal group and astaxanthin monoester group. The main carotenoids of red sea breams were astaxanthin diester, tunaxanthin and ${\beta}$-carotene. Difference in the content of astaxanthin diester and ${\beta}$-carotene was observed from natural and cultured red sea breams. In cultured flounders with supplemented carotenoids, carotenoid deposition and pigmentation were higher in order of ${\beta}$-carotene group and lutein ester group. The main carotenoids of flounders were zeaxanthin and lutein. Difference in lutein and ${\beta}$-carotene contents was observed from the natural and cultured flounders. Based on the contents and composition of carotenoids in each group after feeding experimental diet, carotenoid metabolism in red sea breams were presumed the reductive metabolic pathway, astaxanthin to tunaxanthin, and likewise, in flounders, lutein to tunaxanthin.