• 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.

• Animal Bioscience
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• 제36권12호
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• pp.1842-1852
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• 2023

Objective: Hairy vetch is considered to improve the nutritional value of corn because of its high protein and mineral levels. To better understand the mechanism underlying hairy vetch regulated whole-plant corn silage fermentation, this experiment investigated the fermentation quality and bacterial community of whole-plant corn and hairy vetch mixture. Methods: Whole-plant corn and hairy vetch were mixed at ratios of 10:0 (Mix 10:0), 8:2 (Mix 8:2), 6:4 (Mix 6:4), 4:6 (Mix 4:6), 2:8 (Mix 2:8), and 0:10 (Mix 0:10) on a fresh weight basis. After ensiling 60 days, samples were collected to examine the fermentation dynamics, ensiling characteristics, and bacterial communities. Results: Mix 0:10, Mix 2:8, and Mix 4:6 showed poor fermentation characteristics. Mix 8:2 and Mix 6:4 silages showed high quality, based on the low pH, acetic acid, and ammonia nitrogen levels and the high lactic acid, crude protein, and crude fat contents. The bacterial diversity was affected by the mixing ratio of the two forage species. The genus Lactobacillus dominated the bacterial community in Mix 10:0 silage, whereas with the addition of hairy vetch, the relative abundance of unclassified-Enterobacter increased from 7.67% to 41.84%, and the abundance of Lactobacillus decreased from 50.66% to 13.76%. Conclusion: The silage quality of whole-plant corn can be improved with inclusion levels of hairy vetch from 20% to 40%.

• Journal of Microbiology and Biotechnology
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• 제25권10호
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• pp.1653-1659
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• 2015

Epothilone, which is produced by the myxobacterium Sorangium cellulosum, contributes significant value in medicinal development. However, under submerged culture conditions, S. cellulosum will accumulate to form bacterial clumps, which hinder nutrient and metabolite transportation. Therefore, the production of epothilone by liquid fermentation is limited. In this study, diatomite-based porous ceramics were made from diatomite, paraffin, and poremaking agent (saw dust). Appropriate methods to modify the porous ceramics were also identified. After optimizing the preparation and modification conditions, we determined the optimal prescription to prepare high-performance porous ceramics. The structure of porous ceramics can provide a solid surface area where S. cellulosum can grow and metabolize to prevent the formation of bacterial clumps. S. cellulosum cells that do not form clumps will change their erratic metabolic behavior under submerged culture conditions. As a result, the unstable production of epothilone by this strain can be changed in the fermentation process, and the purpose of increasing epothilone production can be achieved. After 8 days of fermentation under optimized conditions, the epothilone yield reached 90.2 mg/l, which was increased four times compared with the fermentation without porous ceramics.

• 한국식품조리과학회지
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• 제9권2호
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• pp.61-66
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• 1993

The object of this study was to investigate the effects of blanching and lactic acid bacterial inoculation on the quality of kimchi. The pHs of the group added Leuconostoc mesenteroides were rapidly decreased, and then kept almost steady states. However, the pHs of the groups added Bifidobacterium bifidum were gradually decreased. Blanching treatment reduced the number of viable cells. At the beginning of the fermentation, the total organic acid contents of the blanched groups were lower than those of the non-blanched groups, but later on they were higher. With fermentation, the contents of malic, citric and fumaric acid were decreased in the control group, but increased in the cultured groups and all blanched groups. The cutting forces of the blanched groups were higher than those of the non-blanched groups during the whole fermentation period. The inoculation of Leu. mesenteroides was effective on the preservation of ascorbic acid. Blanching and the inoculation of Leu. mesenteroides gave good effect on the sensory acceptability. The acceptability of the groups added Bifidobacterium bifidum was low in initial fermentation period, but increased during the late fermentation period.

• 한국식품과학회지
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• 제23권2호
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• pp.161-166
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• 1991

미생물을 이용한 유용물질 생산연구의 일환으로 토양으로부터 생물고분자 생산균주를 분리하고, 이 분리균에 대한 균학적 성질 및 생성 생물고분자의 이화학적 성상을 검토하였다. 분리균주는 Bacillus속의 한 균종으로 동정 하였으며, 알칼리 내성균주의 특징을 나타내었다. 이 균주로부터 생성된 생물고분자는 성분분석, 정색반응 및 I.R. spectrum 분석결과 단백질 함량이 높고, 일부 amino sugar가 존재하나 uronic acid는 함유하지 않았다. 그러나 cetyl pyridinium chloride에는 침전되어 산성의 생물고분자인 것으로 추정되었다.

• Journal of Microbiology and Biotechnology
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• 제32권3호
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• pp.341-347
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• 2022

In this study, the bacterial community of galchi-baechu kimchi was determined using culture-based and culture-independent techniques (next generation sequencing:NGS), and showed discrepancies between results. Weissella koreensis and Pediococcus inopinatus were the dominant species according to the NGS results, while Bacillus species and P. inopinatus were dominant in the culture-dependent analysis. To identify safe starter candidates, sixty-five Bacillus strains isolated from galchi-baechu kimchi using culture-dependent methods were evaluated for their antibiotic resistance, presence of toxin genes, and hemolytic activity. Strains were then assessed for salt tolerance and protease and lipase activity. As a result, four strains-B. safensis GN5_10, B. subtilis GN5_19, B. velezensis GN5_25, and B. velezensis GT8-were selected as safe starter candidates for use in fermented foods.

• Journal of Microbiology and Biotechnology
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• 제32권11호
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• pp.1479-1484
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• 2022

Bacterial cellulose (BC) is gaining attention as a carbon-neutral alternative to plant cellulose, and as a means to prevent deforestation and achieve a carbon-neutral society. However, the high cost of fermentation media for BC production is a barrier to its industrialization. In this study, chestnut shell (CS) hydrolysates were used as a carbon source for the BC-producing bacteria strain, Gluconacetobacter xylinus ATCC 53524. To evaluate the suitability of the CS hydrolysates, major inhibitors in the hydrolysates were analyzed, and BC production was profiled during fermentation. CS hydrolysates (40 g glucose/l) contained 1.9 g/l acetic acid when applied directly to the main medium. As a result, the BC concentration at 96 h using the control group and CS hydrolysates was 12.5 g/l and 16.7 g/l, respectively (1.3-fold improved). In addition, the surface morphology of BC derived from CS hydrolysates revealed more densely packed nanofibrils than the control group. In the microbial BC production using CS, the hydrolysate had no inhibitory effect during fermentation, suggesting it is a suitable feedstock for a sustainable and eco-friendly biorefinery. To the best of our knowledge, this is the first study to valorize CS by utilizing it in BC production.

• 생명과학회지
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• 제11권5호
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• pp.393-399
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• 2001

우리나라의 전통 발효식품의 고추장의 관능성 및 기능성을 증가시키기 위하여 전분질 원료인 찹쌀무게에 대하여 2%, 4%, 6% 및 8%의 다시마 분말을 첨가한 후 대조구와 함께 3$0^{\circ}C$에서 120일간 숙성시키면서 세균수와 효소활성을 검토하였다. 고추장의 세균수는 숙성 초기 $10^4$ cfu/g 수준에서 출발하여 숙성 30일에는 $10^{6}$ cfu/g의 수준을 나타내었고, 60일 이후에는 $10^{8}$ cfu/g의 수준을 유지하여 후반동안 $10^{8}$ cfu/g을 유지하였는데 다시마의 첨가 구별 차이는 없었고 미생물의 생육에 큰 영향을 미치지는 않았다. 효소활성의 경우 액화효소인 $\alpha$-amylase의 활성은 서서히 감소하여 숙성 후에는 효소의 활성이 거의 실활되었고 당화효소인 $\beta$-amyase의 활성은 숙성 30일까지 큰 폭으로 증가했다가 숙성 60일에 급격히 감소하였으며, 전반적으로 대조고추장에 비하여 다시마 고추장의 $\beta$-amylase의 활성이 약간 높게 나타났다. 단백질 분해효소인 acid protease 및 neutral protease의 활성은 숙성 30일까지는 증가하였으나 그 이후에는 불규칙적인 증감현상을 보이며 120일까지 감소하였다.

• Journal of Applied Biological Chemistry
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• 제63권4호
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• pp.429-437
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• 2020

This study aimed to investigate the change in physicochemical properties and lactic acid bacterial communities during kimchi fermentation at different temperatures (8, 15, and 25 ℃) using two molecular genetics approaches, multiplex polymerase chain reaction and 16S rRNA gene sequencing. The pH during fermentation at 8, 15, and 25 ℃ decreased from 6.17 on the initial fermentation day to 3.92, 3.79, and 3.48 after 54, 30, and 24 days of fermentation, respectively, while the acidity increased from 0.24% to 1.12, 1.35, and 1.54%, respectively. In particular, the levels of lactic acid increased from 3.74 g/L on the initial day (day 0) to 14.43, 20.60, and 27.69 g/L during the fermentation after 24, 18, and 12 days at 8, 15, and 25 ℃, respectively, after that the lactic acid concentrations decreased slowly. The predominance of lactic acid bacteria (LAB) in the fermented kimchi was dependent on fermentation stage and temperature: Lactobacillus sakei appeared during the initial stage and Leuconsotoc mesenteroides was observed during the optimum-ripening stage at 8, 15, and 25 ℃. Lac. sakei and Lactobacillus plantarum grew rapidly in kimchi produced at 8, 15, and 25 ℃. In addition, Weissella koreensis first appeared at days 12, 9, and 6 at 8, 15, and 25 ℃ of fermentation, respectively. This result suggests that LAB population dynamics are rather sensitive to environmental conditions, such as pH, acidity, salinity, temperature, and chemical factors including free sugar and organic acids.