• Journal of the Mineralogical Society of Korea
• /
• v.20 no.4
• /
• pp.357-366
• /
• 2007

Microorganisms participate in a variety of geochemical processes such as weathering and formation of minerals, leaching of precious metals from minerals, and cycling of organic matter The objective of this study was to investigate biogeochemical processes of iron leaching from magnetite ore by iron-reducing bacteria isolated from intertidal flat sediments, southwestern part of Korea. Microbial iron leaching experiments were performed using magnetite ore, Shinyemi magnetite ore, in well-defined media with and without bacteria at room temperature for a month. Water soluble Fe and Mn during the leaching experiments were determined by ICP analysis of bioleached samples, and the resulting precipitated solids were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The extent of iron leaching from magnetite in the aerobic conditions (Fe = 15 mg/L and Mn = 3.41 mg/L) was lower than that in the anaerobic environments (Fe = 32.8 mg/L and Mn = 5.23 mg/L). The medium pH typically decreased from 8.3 to 7.2 during a month incubation. The Eh of the initial medium decreased from +144.9 mV to -331.7 mV in aerobic environments and from -2.3 mV to -494.6 mV in anaerobic environments upon incubation with the metal reducing microorganisms. The decrease in pH is due to glucose fermentation producing organic acids and $CO_2$. The ability of bacteria to leach soluble iron from crystalline magnetite could have significant implications for biogeochemical processes in sediments where Fe(III) in magnetite represents the largest pool of electron acceptor as well as to use as a novel biotechnology for leaching precious and heavy metals from raw materials.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.40 no.2
• /
• pp.156-162
• /
• 2011

The objective of this study is to evaluate antioxidant activities of black ginseng prepared by nine repeated steaming-drying cycles. Ethanol extracts from each cycle of ginseng showed 33.5~41.0% of yields, 36.2~44.5% of moisture content and $64\sim66^{\circ}Brix$ of soluble solids. As the number of steaming-drying cycles increased, pH decreased, while the absorbance at 420 nm increased remarkably after the 4th cycle. Although the amounts of Rg1 and Rb1 contents quite decreased, the total phenol content of black ginseng (the final cycle of ginseng) was increased to 126%, compared with that of white ginseng. Antioxidant activities, determined by ferric-reducing antioxidant potential (FRAP), 2,2'-azinobis(3 ethybenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging activity, 1,1-diphenyl-2-picrydrazyl (DPPH) and hydroxyl radical scavenging activities, increased remarkably as the number of steaming-drying cycles increased. Especially, FRAP value increased 155.6%. Also, $IC_{50}$ values for DPPH and hydroxyl radical scavenging activities of the final 9th-cycling product, decreased 4.5 folds and 9.7 folds, respectively, compared with those of white ginseng. Based on these results, it was suggested that antioxidant activities of black ginseng improve according to the increasing number of steaming-drying cycles, which was derived from increase of total phenol content.

• Korean Journal of Microbiology
• /
• v.51 no.2
• /
• pp.97-107
• /
• 2015

Wetlands constitute a transitional zone between terrestrial and aquatic ecosystems and have unique characteristics such as frequent inundation, inflow of nutrients from terrestrial ecosystems, presence of plants adapted to grow in water, and soil that is occasionally oxygen deficient due to saturation. These characteristics and the presence of vegetation determine physical and chemical properties that affect decomposition rates of organic matter (OM). Decomposition of OM is associated with activities of various extracellular enzymes (EE) produced by bacteria and fungi. Extracellular enzymes convert macromolecules to simple compounds such as labile organic carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) that can be easily taken up by microbes and plants. Therefore, the enzymatic approach is helpful to understand the decomposition rates of OM and nutrient cycling in wetland soils. This paper reviews the physical and biogeochemical factors that regulate extracellular enzyme activities (EEa) in wetland soils, including those of ${\beta}$-glucosidase, ${\beta}$-N-acetylglucosaminidase, phosphatase, arylsulfatase, and phenol oxidase that decompose organic matter and release C, N, P, and S nutrients for microbial and plant growths. Effects of pH, water table, and particle size of OM on EEa were not significantly different among sites, whereas the influence of temperature on EEa varied depending on microbial acclimation to extreme temperatures. Addition of C, N, or P affected EEa differently depending on the nutrient state, C:N ratio, limiting factors, and types of enzymes of wetland soils. Substrate quality influenced EEa more significantly than did other factors. Also, drainage of wetland and increased temperature due to global climate change can stimulate phenol oxidase activity, and anthropogenic N deposition can enhance the hydrolytic EEa; these effects increase OM decomposition rates and emissions of $CO_2$ and $CH_4$ from wetland systems. The researches on the relationship between microbial structures and EE functions, and environmental factors controlling EEa can be helpful to manipulate wetland ecosystems for treating pollutants and to monitor wetland ecosystem services.