• Journal of the Korean Society of Groundwater Environment
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• v.5 no.4
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• pp.215-222
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• 1998

The objective of this study was to investigate the effects of physico-chemical environmental factors on the changes of bacterial population from two sites used for drinking water and eight sites polluted with various pollutant in Seoul city. In all the stations except for two sites used for drinking water, the concentrations of nitrate- nitrogen and ammonia were in excess of the criteria of groundwater quality by the result of analysis of 40 variations including physicochemical environmental factors, heavy metals, and bacterial populations. The numbers of total bacteria, heterotrophic bacteria and functional groups of bacteria were ranged from 5.1 to 41.4${\times}$10$\^$5/cells/ml and from 0.01 to 29.6${\times}$10$^4$cfu/ml, respectively. The activities of extracellular enzymes showed the ranges of 0.005∼11.3${\mu}$M/l/hr and its order to lipase, phophatase, ${\beta}$-glucosidase, cellulase, chitinase, amylase. The results of correspondence and multidimensional scaling analysis between bacterial populations and its physico-chemical environmental factors were explained the effects of physico-chemical environmental factors according to site characters and separated four group, which is accord with potential pollutants at wells.

• Korean Journal of Microbiology
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• v.22 no.3
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• pp.157-165
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• 1984

Seasonal and spatial variations in propagule numbers of Trichoderma species were investigated every other month for one year in deciduous and coniferous forest soils and evaluated the relationships of Trichoderma spp. populations to soil environmental factors. The total population of Trichoderma spp. increased until summer and then declined until winter. The yearly mean frequency of Trichoderma spp. exceeded 1.4% of total fungal propagules in two sites. Decreases of absolute an relative propagule numbers of Trichoderma spp. with increasing soil depth were found and variation in Trichoderma spp. propagules caused by differences in soil depth ($0{\sim}50cm$) was greater than that caused by differences in sampling time. The most common species occurring in two sites was T. viride, followed by T. polysporum, T. koningii, and T. hamatum. Individual species of Trichoderma showed diferent abundance trend in accordance with sampling time. T. viride was dorminant from spring to autumn, while T. polysporum dominated over the other speicies in winter. Variations in propagule number of Trichoderma sppp. were principally mediated by the actions of biotic environmental factors rather than by the direct effects of abiotic factors. In multiple-regression analyses, 48% of the total vaiation in Trichoderma spp. propagules in deciduous site could be accounted for by total fungal propagules and soil CMCase actvity. In coniferous site, 65% of total variation could be accounted for by total fungal and bacterial propagules, moisture content and organic carbon content.

• Korean Journal of Soil Science and Fertilizer
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• v.37 no.4
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• pp.245-250
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• 2004

Farmers typically apply the dressed soil (coarse saprolite) for various reasons in the sloped upland with high altitude in Kangwon province. However, little researches on the impacts of application of dressed soil in uplands were conducted. Therefore, it is necessary to assess soil quality in this area and to study adverse effects on soil and water due to application of dressed soil. Coarse saprolite itself showed signiScantly poor chemical properties, Particularly P and organic matter contents were not enough for crops to grow. With respect to biological qualities such as enzyme activity and microbial population, coarse saprolite itself showed poor qualities. For example, bacterial population in coarse saprolite contains six times or ten times smaller populations. Based on survey at Jawoon-ri in Hongchon-gun, this region is susceptible for soil erosion due to massive amounts of coarse saprolite application, undesirably long slope length, etc. When weestimated soil loss, more than 40% of farming field in this region exceeded $11.2MT\;ha^{-1}\;yr^{-1}$. According to experiment by installing sediment basins. the sediment basin with up-down tillage and application with dressed soil had the highest soil loss and runofT, while the sediment basin with contour tillage and without soil dressing showed the lowest soil erosion and runoff.

• Korean Journal of Soil Science and Fertilizer
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• v.49 no.4
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• pp.381-387
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• 2016

The scientific information on the microbial differentiation according to the changes in chemical properties of paddy soil in reclaimed tidal lands is not enough to understand the reclamation processes. The changes in microflora based on the chemical properties of paddy soils at the same sites of reclaimed tidal lands (21 samples from Nampo, Ewon, Sukmoon and Shihwa sites) were investigated in 2013 and 2015. In general, organic matter in paddy soils increased whereas pH decreased with the reclamation time. The electrical conductivities (EC) of soil samples were closely related to the exchangeable $Na^+$. With an increases in EC of paddy soils from 0.39 to $48.9dS\;m^{-1}$, the ratios (%) of halotolerant and halophilic bacteria to mesophilic bacteria proportionally increased from 0.2% to 102,000%. The population of halotolerant and halophilic bacteria in total microflora was also differentiated with the changes in EC of the same sites from reclaimed tidal soils within 2 years. The population of mesophilic bacteria decreased with an increase in EC above $5dS\;m^{-1}$. The microflora including halotolerant and halophilic bacteria could be a candidate as a biological parameter in evaluating the reclamation processes in addition to the chemical index of EC.

• KSBB Journal
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• v.21 no.3
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• pp.175-180
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• 2006

In this study, it could be found that the microbial movement in soil under electric field mainly occurred by electrophoresis and electroosmosis. The contribution of electrophoresis on the microbial mobility and flux was generally higher than that of electroosmosis. In the electrokinetic(EK) bioremediation of a pentadecane-contaminated soil, the microbial population increased simultaneously at anode and cathode regions of the soil specimen because both electrophoresis and electroosmosis affected on the microbial movement. After initial operation, the microbial population was high in order of anode, middle, and cathode regions due to their negatively-charged surface and oxygen generation at anode. However, the uniform contaminant removal was achieved by the microbial movement with two-directionality.

• The Plant Pathology Journal
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• v.32 no.2
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• pp.136-144
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• 2016

Pseudomonas fluorescens pc78 is an effective biocontrol agent for soil-borne fungal diseases. We previously constructed a P43-gfp tagged biocontrol bacteria P. fluorescens pc78-48 to investigate bacterial traits in natural ecosystem and the environmental risk of genetically modified biocontrol bacteria in tomato rhizosphere. Fluctuation of culturable bacteria profile, microbial community structure, and potential horizontal gene transfer was investigated over time after the bacteria treatment to the tomato rhizosphere. Tagged gene transfer to other organisms such as tomato plants and bacteria cultured on various media was examined by polymerase chain reaction, using gene specific primers. Transfer of chromosomally integrated P43-gfp from pc78 to other organisms was not apparent. Population and colony types of culturable bacteria were not significantly affected by the introduction of P. fluorescens pc78 or pc78-48 into tomato rhizosphere. Additionally, terminal restriction fragment length polymorphism profiles were investigated to estimate the influence on the microbial community structure in tomato rhizosphere between non-treated and pc78-48-treated samples. Interestingly, rhizosphere soil treated with strain pc78-48 exhibited a significantly different bacterial community structure compared to that of non-treated rhizosphere soil. Our results suggest that biocontrol bacteria treatment influences microbial community in tomato rhizosphere, while the chromosomally modified biocontrol bacteria may not pose any specific environmental risk in terms of gene transfer.

• Korean Journal of Soil Science and Fertilizer
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• v.44 no.4
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• pp.650-656
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• 2011

Lysobacter antibioticus HS124 isolated from pepper rhizosphere soil produced catechol type siderophore. Purified siderophore by Diaion HP-20 and silica gel column chromatography showed several hydroxyl functional groups adjacent to benzene rings by analysis of $^1H$ NMR spectroscopy. The strain HS124 showed different activities to suppress Phytophthora capsici with different concentrations of exogenous Fe (III) in minimal medium where antifungal activity with $100{\mu}M$ Fe (III) was approximately 1.5 times higher than in absence of Fe (III). Bacterial population in this Fe (III)-amended medium was also highest with $8.9{\times}10^8\;CFU\;ml^{-1}$ which also corresponded to the strongest siderophore activity. When grown in rich medium (minimal medium with N, $P_2O_5K_2O$ and glucose), HS124 exhibited approximately 2 times stronger antifungal activity compared to minimal medium. In pot trials, treatments of bacterial culture grown in rich medium with (C1) or without (C2) $100{\mu}M$ Fe (III) exhibited a high protection of pepper plants from disease, compared to medium only with (M1) or without (M2) $100{\mu}M$ Fe (III). Especially, treatment C1 showed the best disease control effect of about 70 %. Thus, the strain HS124 should be recommended as a potential biocontrol agent against P. capsici in pepper.

• The Plant Pathology Journal
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• v.36 no.4
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• pp.355-363
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• 2020

Bacterial traits for virulence of Ralstonia solanacearum causing lethal wilt in plants were extensively studied but are not yet fully understood. Other than the known virulence factors of Ralstonia solanacearum, this study aimed to identify the novel gene(s) contributing to bacterial virulence of R. solanacearum. Among the transposon-inserted mutants that were previously generated, we selected mutant SL341F12 strain produced exopolysaccharide equivalent to wild type strain but showed reduced virulence compared to wild type. In this mutant, a transposon was found to disrupt the murI gene encoding glutamate racemase which converts L-glutamate to D-glutamate. SL341F12 lost its motility, and its virulence in the tomato plant was markedly diminished compared to that of the wild type. The altered phenotypes of SL341F12 were restored by introducing a full-length murI gene. The expression of genes required for flagella assembly was significantly reduced in SL341F12 compared to that of the wild type or complemented strain, indicating that the loss of bacterial motility in the mutant was due to reduced flagella assembly. A dramatic reduction of the mutant population compared to its wild type was apparent in planta (i.e., root) than its wild type but not in soil and rhizosphere. This may contribute to the impaired virulence in the mutant strain. Accordingly, we concluded that murI in R. solanacearum may be involved in controlling flagella assembly and consequently, the mutation affects bacterial motility and virulence.

• Korean Journal of Soil Science and Fertilizer
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• v.27 no.1
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• pp.48-53
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• 1994

This study was conducted to find out the influence of single and/or repeatedly combined application of cellulose and chlorotharonil(TPN) on bacterial population and dissipation of these chemicals by microorganism in the soil suspension culture. 1. The number of total bacteria and Gram-negative bacteria were rapidly increased for 1st week, after the time, decreased in the single application but maintained in repeatedly combined application for 5th week and that were higher at combined application of TPN and cellulose than at single application of these. 2. TPN-degrading bacteria were gradually increased by the repeated application of TPN, and elevated the increasing extents of those with the repeatedly combined application of cellulose with TPN. 3. Cellulose-degrading bacteria showed the peak at 1st week, and was increased in the repeated application of cellulose, but the bacteria was decreased in the repeatedly application of TPN with cellulose. 4. The dissipation of TPN were faster at the combined application of both than at the single application of TPN, wheras that was delayed by the repeatedly combined application. 5. The content of reducing sugar was rapidly increased at 1st week and after 4th week except for the TPN single application, that was higher in the combind application than the cellulose single, but there was no difference between them.

• Research in Plant Disease
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• v.7 no.1
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• pp.25-30
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• 2001

Influence of soil flooding with organic matters amendment at various temperatures on population changes of fungi, including Fusarium, and bacteria in ginseng-replanting field soils was examined to evaluate the effective flooding conditions for reducing the progress of ginseng root rot. Populations of Fusarium spp. and total fungi in flooded soils declined with days after flooding. The higher was the temperature in range of 20$\^{C}$ to 35$\^{C}$, the greater was the effect of flooding on the decrease of the fungal population. Flooding of soils with organic matters amendment had synergistic effect on the decrease of the fungal population at the same temperature; Fungal populations in flooded soils with and without organic matters amendment were reduced to 1/100 and 1/10, respectively, relative to those in non-flooded soils after 60 days of treatment at 30$\^{C}$. rice straw seemed to be more effective than greens. Population changes of total bacteria in flooded soils were similar to the trend of total fungi. However, the flooding seemed to influence less effect on the bacterial population than on the fungal population. Based on these experiments, we suggest than the progress of ginseng root rot in ginseng-replanting field soils may be significantly reduced by flooding them for longer than 3 months near at 30$\^{C}$ after amendment of organic matters.