• Geomechanics and Engineering
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• 제17권5호
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• pp.485-496
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• 2019

Sealing of leakage in waterfront or water-retaining structures is one of the major issues in geotechnical engineering practices. With demands for biological methods as sustainable ground improvement techniques, bioclogging, defined as the reduction in hydraulic conductivity of soils caused by microbial activities, has been considered as an alternative to the chemical grout techniques for its economic advantages and eco-friendliness of microbial by-products. This study investigated the feasibility of bioaugmentation and biostimulation methods to induce fermentation-based bioclogging effect in coarse sands. In the bioaugmentation experiments, effects of various parameters and conditions, including grain size, pH, and biogenic gas generation, on hydraulic conductivity reduction were examined through a series of column experiments while Leuconostoc mesenteroides, which produce an insoluble biopolymer called dextran, was used as the model bacteria. The column test results demonstrate that the accumulation of bacterial biopolymer can readily reduce the hydraulic conductivity by three-to-four orders of magnitudes or by 99.9-99.99% in well-controlled environments. In the biostimulation experiments, two inoculums of indigenous soil bacteria sampled from waterfront embankments were prepared and their bioclogging efficiency was examined. With one inoculum containing species capable of fermentation and biopolymer production, the hydraulic conductivity reduction by two orders of magnitude was achieved, however, no clogging was found with the other inoculum. This implies that presence of indigenous species capable of biopolymer production and their population, if any, play a key role in causing bioclogging, because of competition with other indigenous bacteria. The presented results provide fundamental insights into the bacterial biopolymer formation mechanism, its effect on soil permeability, and potential of engineering bacterial clogging in subsurface.

• Geomechanics and Engineering
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• 제12권5호
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• pp.849-862
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• 2017

With growing interests in using bacterial biopolymers in geotechnical practices, identifying mechanical properties of soft gel-like biopolymers is important in predicting their efficacy in soil modification and treatment. As one of the promising candidates, dextran was found to be produced by Leuconostoc mesenteroides. The model bacteria utilize sucrose as working material and synthesize both soluble and insoluble dextran which forms a complex and inhomogeneous polymer network. However, the traditional rheometer has a limitation to capture in situ properties of inherently porous and inhomogeneous biopolymers. Therefore, we used the particle tracking microrheology to characterize the material properties of the dextran polymer. TEM images revealed a range of pore size mostly less than $20{\mu}m$, showing large pores > $2{\mu}m$ and small pores within the solid matrix whose sizes are less than $1{\mu}m$. Microrheology data showed two distinct regimes in the bacterial dextran, purely viscous pore region of soluble dextran and viscoelastic region of the solid part of insoluble dextran matrix. Diffusive beads represented the soluble dextran dissolved in an aqueous phase, of which viscosity was three times higher than the growth medium viscosity. The local properties of the insoluble dextran were extracted from the results of the minimally moving beads embedded in the dextran matrix or trapped in small pores. At high frequency (${\omega}>0.2Hz$), the insoluble dextran showed the elastic behavior with the storage modulus of ~0.1 Pa. As frequency decreased, the insoluble dextran matrix exhibited the viscoelastic behavior with the decreasing storage modulus in the range of ${\sim}0.1-10^{-3}Pa$ and the increasing loss modulus in the range of ${\sim}10^{-4}-1\;Pa$. The obtained results provide a compilation of frequency-dependent rheological or viscoelastic properties of soft gel-like porous biopolymers at the particular conditions where soil bacteria produce bacterial biopolymers in subsurface.

• 한국미생물·생명공학회지
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• 제24권1호
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• pp.111-118
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• 1996

For the screening and the development of the new bio-material, cultural conditions for the exo-biopolymer (EBP) production throught the submerged cultivation of Ganoderma lucidum mycelium were investigated. Also, the fractionations and the purifications of the exo-biopolymer were carried out and the chemical compositions of the exo-biopolymer were examined. The optimal culture conditions for the exo-biopolymer production were pH 5.0, 30$^{\circ}C$ and 100 rpm of agitation speed in the medium containing of 5% (w/v) glucose, 0.5%(w/v) yeast extract, 0.1% (w/v) ($(NH_4)_2HPO_4$, and 0.05% (w/v) $KH_2PO_4$. In the flask cultivation for 7 days under these conditions, the concentration of the maximum exo-biopolymer and the cell mass were 15.4g/l and 18.8g/l, respectively. The specific growth rate was 0.039 $hr^{-1}$. In addition, the substrate consumption rate, and the exo-biopolymer production rate were 0.043$gg^{-1}$$hr^{-1}$ and 0.025$gg^{-1}$$hr^{-1}$, respectively. The exo-biopolymer was fractionated into BWS (water soluble exo-biopolymer) and BWI (water insoluble exo-biopolymer) by the water extraction, and the sugar contents of two fractions were higher than 97% (based on dry basis). The components sugar of BWS and BWI fractions were glucose, galactose, mannose, xylose, and fucose. Their molar ratios were 3.6:1.5:2.1:0.5: trace and 2.9:3.1:2.0:1.6:0.3, respectively.

• 대한핵의학회지
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• 제27권1호
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• pp.123-129
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• 1993

$^{85}Sr$만을 투여한 대조군에 비해 $^{85}Sr$의 오염에 앞서 3% 카이토산을 체내에 투여한 경우 $^{85}Sr$의 체내 잔존율이 서서히 낮아지는 경향을 보였다. 그 배출효과에 있어서 위장관에 의해 1일 1회 5일간의 연속투여군에서는 1회 단일투여의 경우와 유사하게 나타났으나 수용성 카이토산의 경우 1회 투여군에서는 불용성에 비해 큰 차이를 보이지 않았고, 1일 1회 5일 간의 연속 투여군에서는 약2배 이상 그 배출율이 증가하여 연속적으로 투여하였을 때 방사선 스트론튬이 체내대사에 영향을 줄 수 있음을 시사하였다. 배출물의 경우 변증으로 대부분이 배출되며 카이토산의 투여군에서는 뇨를 통한 배출은 대조군에 비해 높게 나타났고 수용성 카이토산의 투여군에 의해 방사성 스트론륨의 소화관 흡수가 저해되어 결과적으로 배출이 촉진될 뿐만 아니라 골대사 중에 작용하여 표적 기관으로부터 $^{85}Sr$을 추출시키는데도 관여할 가능성을 시사했다. 결론적으로 본 실험에서는 수용성 카이토산과 불용성 카이토산이 방사능 방호약제로 유효하게 쓰일 수 있으며 그중 3% 수용성 카이토산은 연속적으로 투여 한 경우 $^{85}Sr$의 체내 대사에 영향을 미쳐 장기간 투여시 $^{85}Sr$을 체외로 배출시 키는데 기여 할 수 있으리라 기대된다.

• 유기물자원화
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• 제2권2호
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• pp.31-37
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• 1994

퇴비화 과정의 미생물학적 연구를 위해 퇴비화 재료인 유기성 폐기물에 많이 존재하는 고분자 물질의 분해에 관여하는 미생물들과 이들이 분비하는 효소들을 손쉽게 선별, 정량하는 방법을 개발하였고 아울러 혐기적 상태에서의 퇴비화 가능성을 탐색하는 연구의 일환으로 혐기적 분해의 최종적 역할을 하는 황산 환원 균의 퇴비화 과정에서의 분포를 알아보았다. 고분자 물질의 분해 측정법 개발에 사용된 기질은 각각 다당류 및 단백질 중에서 ${\beta}-glucan$, xylan, dextran, CMC(carboxymethylcellulose), casein, collagen 등을 재료로 사용하였고 이들을 가교제를 써서 불용화시키고 색소를 결합시켜 색소기질을 제조하였다. 제조된 기질을 이용하여 실제의 퇴비에서 고분자 분해 세균을 분리할 수 있었으며 기존의 효소 정량법에 비해 민감하게 효소 활성을 정량할 수 있었다. xylan과 ${\beta}-glucan$ 색소기질의 경우 고체 배지 상에서 고분자 분해 미생물을 선별할 때 기존의 Congo red 법과는 달리 미생물 집락에 손상을 입히지 않고도 손쉽게 사용할 수 있었다. 실험에 쓰인 오니에 포함되어 있는 황산 환원 세균은 lactic acid, propionic acid, butyric acid, formic acid 등의 유기산에 대해 높은 활성을 보여 주었고, acetic acid, valeric acid도 이용할 수 있었다.

• Preventive Nutrition and Food Science
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• 제15권1호
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• pp.57-66
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• 2010

Passion fruit fiber pectin gels represent a new alternative pectin source with potential for food and non-food applications on a commercial scale. Pectic polysaccharides were extracted from passion fruit (Passiflora edulis) fiber using citric acid as a clean catalyst and autoclaved for 20 to 60 min at $121^{\circ}C$. The best condition of pectin yield with the highest molecular weight was obtained with 1.0% of citric acid (250 mg/g dry passion fruit fiber pectin) for 20 min of autoclaving. Spectroscopic analyses by Fourier transform infrared, enzymatic degradation reactions, and ion-exchange chromatography assays showed that passion fruit pectin extracted for 20 min was homogeneous high methoxylated pectin (70%). Gel permeation analysis confirmed that the pectin extract obtained by autoclaving by 20 min showed higher molecular weights than those autoclaved for 40 and 60 min. Passion fruit pectin extracted for 20 min was enzymatically modified with fungal pectinmethylesterase to create restructured gels. Short autoclave treatment (20 min) with citric acid as extractant resulted in a significant increase of gel strength, improving pectin extraction in terms of functionality. The treatment of solubilized material (pectic polysaccharides) in the presence of insoluble material (cellulose and hemicellulose) with pectinmethylesterase and calcium led to the creation of a stiffer passion fruit fiber pectin gel, while syneresis was not observed.

• 한국미생물·생명공학회지
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• 제52권2호
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• pp.152-162
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• 2024

The microbial starter used to produce kefir beverages, kefir grain, contains a microbial exopolysaccharide called kefiran. Kefir grain consisting of water-insoluble polysaccharides, proteins, and fats, which can be applied as a multi-functional biopolymer. The mass of kefir grain can increase in the fermentation process of Kefir, but it is considered very slow. The purpose of this research is to study the impact of ammonium sulfate supplementation and yeast extract on reconstituted skim milk to increase the mass kefir grain and physical properties of kefiran. Results showed that the ammonium sulfate-supplemented substrate increased the mass of kefir grain by 547% in 14 days, with the condition that the substrate must be renewed every 2 days. Refreshing the substrate is considered one of the important factors. Supplementation on substrate did not appear to affect the viability of bacterial and yeast cells. Kefir grain produced from supplemented substrate also yields better thermal stability properties and has more functional groups than without supplementation. Two Lacticaseibacillus rhamnosus (RAL27 and RAL43) and one Limosilactobacillus fermentum (RAL29) were found to produce EPS. The three isolates also showed good skim milk fermentation ability after purification from kefir grain. The kefir grain produced in this study has the potential for wider application. This study also showed that kefir grain can be adjusted in quantity and quality through fermentation substrate engineering.