• Korean Journal of Microbiology
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• v.39 no.3
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• pp.181-186
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• 2003

This study was performed to analyze quantitatively the number of living bacteria in forest soil samples collected from Mt. Keryong using improved direct viable count (DVC) and plate count (PC) methods. The number of living bacteria by DVC comprised 18～44% of the total direct count (TDC), whereas the number of living bacteria by PC was less than 1% of TDC. These results showed that viable but non-culturable (VBNC) bacteria existed in the soil with high percentages. Besides, DVC was proved to make it possible to make a quantitative detection of the VBNC bacteria. On the other hand, upon measuring the value from the conventional nutrient broth (NB) and $10^{-2}$ folded diluted nutrient broth (DNB), the values from the DNB showed 5 to 10 times higher than those from the conventional NB medium. These results indicate that oligotrophic bacterial groups, which could multiply in the low nutrient broth, abundantly exist in the soil ecosystem. It would also be possible to apply this kind of method to other substrate to make a quantitative detection of soil bacterial groups.

• Microbiology and Biotechnology Letters
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• v.39 no.3
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• pp.210-217
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• 2011

In an effort to isolate novel bacteria for the bioremediation of over-fertilized soils, we identified 135 denitrifying cells out of 3,471 oligotrophic bacteria pools (3.9%) using a denitrification medium supplemented with potassium nitrate as the sole nitrogen source. Soil samples were taken from ecologically well-conserved areas, including a mountain swamp around the demilitarized zone (Yongneup), two ecoparks (Upo and the Mujechi bog), and ten representative islands around the Korean peninsula (Jejudo, Daecheongdo, Socheongdo, Baekryeongdo, Ulrungdo, Dokdo, Geomundo, Hongdo, Huksando and Yeonpyeongdo). All of the 135 bacteria produced nitrogen gas from the denitrification medium, and were proved to be nitrate reductase positive by API-BioLog tests. Phylogenetic analysis using 16S rDNA sequences revealed that the 135 bacteria consisted of 44 different genera. Along with the most prominent, Proteobacteria (87.4%), we identified denitrifying bacteria from Firmicutes (9.4%), Actinobacteria (2.4%), and Bacteroidetes (0.8%). Physiological analyses of the 44 representative denitrifying bacteria, under various pH levels, growth temperatures and salt stresses, revealed 12 favorable denitrifying strains for soil bioremediation.

• Korean Journal of Microbiology
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• v.44 no.4
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• pp.352-357
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• 2008

We evaluated cultivation methods to obtain pure cultures of previously uncultivated bacteria from soil. Soil bacteria (suspensions) were inoculated onto various oligotrophic media with one of the following additives: 1) soil extract; 2) anthraquinone disulfonate (humic acid analogue); 3) acyl homoserine lactones (quorum-signaling compounds); 4) catalase (for the protection of bacteria from exogenous peroxides). After the relatively long period (60 days) of incubation with elevated concentrations of $CO_2$ (5%, v/v), the media containing catalase showed the highest colony count. We purified 147 randomly selected colonies from the media and the isolates were subjected to the phylogenetic analyses of their 16S rRNA gene sequences. Phylogenetic analysis revealed that approximately 30% of the isolates might belong to novel species or novel family, suggesting that the media and incubation conditions used could be useful for the cultivation of as-yet-uncultured bacteria. Especially, bacteria belonging to the phylum Acidobacteria, ubiquitous bacterial taxon known as an uncultured bacterial group (at least difficult to culture from environmental samples), were successfully cultured in this study.

• The Plant Pathology Journal
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• v.28 no.1
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• pp.68-74
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• 2012

Biocontrol microbes have mainly been screened among large collections of microorganisms $via.$ nutrient-rich $in$ $vitro$ assays to identify novel and effective isolates. However, thus far, isolates from only a few genera, mainly spore-forming bacilli, have been commercially developed. In order to isolate field-effective biocontrol microbes, we screened for more than 200 oligotrophic bacterial strains, isolated from rhizospheres of various soil samples in Korea, which induced systemic resistance against the soft-rot disease caused by $Pectobacterium$ $carotovorum$ SCC1; we subsequently conducted in $planta$ bioassay screening. Two oligotrophic bacterial strains were selected for induced systemic disease resistance against the $Tobacco$ $Mosaic$ $Virus$ and the gray mold disease caused by $Botrytis$ $cinerea$. The oligotrophic bacterial strains were identified as $Pseudomonas$ $manteilii$ B001 and $Bacillus$ $cereus$ C003 by biochemical analysis and the phylogenetic analysis of the 16S rRNA sequence. These bacterial strains did not exhibit any antifungal activities against plant pathogenic fungi but evidenced several other beneficial biocontrol traits, including phosphate solubilization and gelatin utilization. Collectively, our results indicate that the isolated oligotrophic bacterial strains possessing induced systemic disease resistance could provide useful tools as effective biopesticides and might be successfully used as cost-effective and preventive biocontrol agents in the field.

• Research in Plant Disease
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• v.16 no.1
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• pp.41-47
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• 2010

A total of 10,753 oligotrophic bacteria were isolated from the cultivated soils of red-pepper infected by Phytophthora blight disease in various regions of Korea (Chungju, Anmyon, Taean, Andong, Eumsung and Goesan). Seven bacteria isolates among these collected resources were selected by the first screening of in vitro antagonistic assay against major several plant pathogenic fungi including Phytophthora capsici. Finally, strain 7F was selected by pot assay for a possible biological control agent against Phytophthora blight disease of pepper seedling in the greenhouse. Strain 7F was identified as Bacillus subtilis on the basis of its 16S rDNA sequence analysis and as standardized biochemical characteristics assay kits such as API20 NE. In the experiment of P. capsici zoospore infected red-pepper on the pot test, infection rate of red-pepper with nonetreatment to Phytophthora blight disease was 87%, while the rate was only 6% in the pot treated with strain 7F. This result indicated that the Bacillus subtilis strain 7F will be useful as a potential biocontrol agent for Phytophthora blight disease of red-pepper.

• Journal of Microbiology
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• v.42 no.3
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• pp.181-187
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• 2004

Cyanobacteria are the dominant phototrophic bacteria in water environments. Here, the diversity of cyanobacteria in seven Korean reservoir waters where different levels of algal blooms were observed during the summer of 2002, was examined by T-RFLP analysis. The number of T-RF bands in the HaIII T-RFLP profiles analyzed from those water samples ranged from 20 to 44. Of these, cyanobacteria accounted for 6.1 to 27.2％ of the total bacteria. The water samples could be clustered into 2 groups according to the Dice coefficient of the T -RF profiles. The eutrophic Dunpo and oligotrophic Chungju reservoirs were selected, and several representative clones from both reservoir waters analyzed for the nucleotide sequences of their 16S rDNA. The major clones were found to belong to the Microcystis and Anabaena species in the waters from the Dunpo and Chungju reservoirs, respectively, which was in agreement with the T-RFLP result. That is, the Microcystis and Anabaena species were dominant in the eutrophic and polluted Dunpo and oligotrophic Chungju reservoir waters, respectively. These results indicated that there is a correlation between prevalence of cyanobacterial species and levels of pollution in reservoir waters.

• Korean Journal of Agricultural Science
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• v.16 no.2
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• pp.152-162
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• 1989

Oligotrophic bacteria studied in the present report were isolated on a 100-fold dilution of the nutrient broth(NB) medium and were able to grow on a 10,000-fold dilution of the NB medium. Oligotrophbic bacteria were shown to exist abundantly in all layers of a rendzina forest soil through the year. Two-hundred three oligotrophic bacteria were isolated from forest soil at different layers(L.F.H and A layers), and their morphological and physiological characteristics were examined. They were divided into 4 groups on their cell shape: (1) regular rods(Group I. 73 isolates), (2) curved/spiral rods (Group II, 29 isolates), (3) irregular rods (Group III, 56 isolateds), (4) append aged organisms (Group IV, 45 isolates), A high propoltion(95%)of the isolated oligotrophs were Gram-negative. all the isolated were aerobic, nonspore-formers. Forty isolates utilized fenolic acid such as ferulic acid or p-coumaric acid. sixty-for isolateds utilized C-1 compounds such as methanol or formic acid.

• Korean Journal of Soil Science and Fertilizer
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• v.41 no.5
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• pp.362-368
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• 2008

In order to isolate novel oligotrophic bacteria exhibiting antifungal activities, soils were collected from pepper-cultivated fields of Yeongyang, Jecheon, Nonsan, Eumsong and Goesan area in Korea. From soils in pepper cultivated area, a total of 9,354 strains were isolated as oligotrophic bacteria by the R2A dilution method. Among 9,354 oligotrohic bacteria candidates, 1A strain was selected by screening against Phytophthora capsici causing phytophthora blight of hot pepper in the greenhouse and field. The strain was identified as Bacillus vallismortis based on its 16S rDNA sequence and key characteristics as compared with those of authentic cultures of B. vallismortis(KACC 12149) and B. mojavensis(KACC 12096). The strain showed broad spectrum of antibiotic activity in vitro test, as revealed in its strong inhibitory activity to the genera Phytophthora, Collectotrichum, Botrytis and Fusarium, but not to Rhizoctonia and Magnaporthe. In pot experiments, infection rate of hot pepper in the non-treated pots was about 89%, while it was only 29% in the pots treated with 1A strain. The result indicated B. vallismortis 1A is a potential biocontrol agent for phytophthora blight of hot pepper

• Proceedings of the Zoological Society Korea Conference
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• 1996.10a
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• pp.267.2-267
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• 1996

No Abstract, See Full Text

• Proceedings of the Zoological Society Korea Conference
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• 1996.10a
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• pp.267.1-267
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• 1996

No Abstract, See Full Text