• The Korean Journal of Pesticide Science
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• v.10 no.1
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• pp.56-65
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• 2006

An antagonistic bacterial isolate, that inhibits the growth of plant pathogens, was selected and identified from 5,000 isolates screened from the rhizosphere of various crop plants. An isolate Bacillus sp. N32, tested against Colletotrichum gloeosporioides causing anthracnose disease in hot pepper, produced both a heat resistant antifungal protein and a heat sensitive antifungal protein. The heat resistant protein was partially purified by Ammonium sulfate fractionation and gel filtration chromatography. The bioautography showed that the proteins possessed high antifungal activity. The biosynthetic gene cluster responsible for the heat resistant antifungal protein was cloned from cosmid library using DNA probe obtained from PCR product with the primers targeting the conserved nucleotide sequence of the synthetic genes reported earlier, Most of the clones obtained showed higher homology to fengycin antibiotic synthetic gene family reported earlier. On the other hand, the heat sensitive protein was isolated from SDS-PAGE and electroblotting to determine the N-terminal amino acid sequences. The heat sensitive antifungal protein gene was cloned from the ${\lambda}-ZAP$ libraries using a DNA probe based on the N-terminal amino acid sequences of the heat sensitive protein. We are contemplating to clone and sequence the whole gene cluster encoding the heat sensitive protein for further analysis.

• Microbiology and Biotechnology Letters
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• v.44 no.1
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• pp.9-18
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• 2016

Two Bacillus strains, CJW15 and SSD8, with strong antibacterial activities were isolated from cheonggukjang. Both were identified as B. amyloliquefaciens strains after gene sequencing of rRNA and recA. CJW15 strongly inhibited the growth of B. cereus (ATCC14579), Listeria monocytogenes (ATCC19111), and Lactococcus lactis (ATCC11454). In comparison, SSD8 inhibited the growth of B. cereus (ATCC14579) and Enterococcus faecium (ATCC19953). The antibacterial activities of the two strains were not affected when exposed to a temperature of $100^{\circ}C$ for 15 min and were quite stable in acidic (pH 3) and alkaline (pH 12) pH conditions. Enzymatic treatments (trypsin, pepsin, proteinase K, and protease) had no effect on the activity of CJW15, but reduced the activity of SSD8 by half. Both isolates possess genes involved in the synthesis of lipopeptides (e.g. surfactin, fengycin, iturin, and iturin A), and genes encoding subtilin, a bacteriocin. Moreover, both isolates have fibrinolytic activities as well.

• The Korean Journal of Pesticide Science
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• v.20 no.3
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• pp.189-196
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• 2016

Several microorganisms in particular Bacillus subtilis group have been isolated from diverse places such as soils and the gastrointestinal tract of ruminants etc., and used as biocontrol agent against various plant pathogens and utilized as plant growth promoting agents. Among them, Bacillus is well known as one of the most useful bacteria for biocontrol and plant growth promotion. Bacterium GH1-13 was isolated from a reclaimed paddy field in Wando Island and identified as Bacillus velezensis using phylogenetic analysis on the basis of 16S rRNA and gyrB gene. It was confirmed that GH1-13 produced indole acetic acid (IAA) associated with promoted growth of rice root. GH1-13 showed characteristics of antagonization against the main pathogen of rice as well as diverse pathogenic fungi. GH1-13 had biosynthetic genes, bacillomycin, bacilycin, fengycin, iturin, and surfactin which are considered to be associated closely with inhibition of growth of pathogenic fungi and bacteria. This study showed that GH1-13 could be used as a multifunctional agent for biocontrol and growth promotion of crop.

• Research in Plant Disease
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• v.23 no.2
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• pp.177-185
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• 2017

Bacillus amyloliquefaciens LM11 was isolated from the feces of larvae of the rhino beetle and showed strong antifungal activities against various phytopathogenic fungi by producing biosurfactants. In this study, our overall goal was to determine relationship between biosurfactants produced from the LM11 strain and its role in growth inhibition of phytopathogenic fungi. Production and expression levels of B. amyloliquefaciens LM11 biosurfactants were significantly differed depending on growth phases. Transcriptional and biochemical analysis indicated that the biosurfactants of the LM11 strain were greatly enhanced in late log-phase to stationary phase. Inhibitions of phytopathogenic mycelial growth and spore germination were directly correlated (P<0.001, R=0.761) with concentrations of the LM11 cell-free culture filtrates. The minimum inhibitory surface tension of the culture filtrate of the B. amyloliquefaciens LM11 grown in stationary phase to inhibit mycelial growth of the phytopathogenic fungi was 38.5 mN/m (P<0.001, R=0.951-0.977). Our results indicated that the biosurfactants of B. amyloliquefaciens LM11 act as key antifungal metabolites in biocontrol of plant diseases, and measuring surface tension of the cell-free culture fluids can be used as an easy indicator for optimal usage of the biocontrol agents.

• The Korean Journal of Pesticide Science
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• v.20 no.4
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• pp.380-387
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• 2016

This study was performed to select potentially available biological control agent from soil bacteria for prevention of ginseng damping off. More than five hundred strains were isolated from ginseng rhizosphere soil. By testing antifungal activity, we have selected three soil bacteria strains and their ability to produce antibiotics and lytic enzymes such as cellulase, protease and pectate lyase was examined. Also, the presence of genes for biosynthesis of lipopeptide such as fengycin, bacillomycin D, surfactin, iturin A, and zwittermicin A was investigated in selected strains. All three strains produced cellulase, protease, and xylanase. Moreover, these strains had gene for biosynthesis of bacillomycin D, surfactin, and iturin A. ES1 and ES3 strains were identified Bacillus methylotrophucus and ES2 was confirmed Bacillus amyloliquefaciens using phylogenetic analysis on the basis of 16S rRNA gene sequences. In field test, control value of ES1, ES2 and ES3 treatment was 32.4%, 46.8% and 36.7%, respectively. This results indicate that antagonistic microbes with high ability of antifungal and lytic enzyme activity can be used as a useful biological control agent to control ginseng damping off.