• Korean journal of applied entomology
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• v.51 no.1
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• pp.47-58
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• 2012

Effect of a new crop protectant 'Bt-Plus' on natural enemies was analyzed in this study. Tested natural enemies included two parasitic species of $Aphidius$ $colemani$ and $Eretmocerus$ $eremicus$, and four predatory species of $Harmonia$ $axyridis$, $Orius$ $laevigatus$, $Amblyseius$ $swirskii$, and $Phytoseiulus$ $persimilis$. 'Bt-Plus' was formulated by combination of three entomopathogenic bacteria ($Xenorhabdus$ $nematophila$ (Xn), $Photorhabdus$ $temperata$ subsp. $temperata$ (Ptt), $Bacillus$ $thuringiensis$ (Bt)) and bacterial metabolite (BM). All three types of 'Bt-Plus' showed significantly higher toxicities against fourth instar $Plutella$ $xylostella$ larvae than Bt single treatment. Two types of bacterial mixtures ('Xn+Bt' and 'Ptt+Bt') showed little toxicity to all natural enemies in both contact and oral feeding assays. However, 'BM+Bt' showed significant toxicities especially to two predatory mites of $A.$ $swirskii$ and $P.$ $persimilis$. The acaricidal effects of different bacterial metabolites were evaluated against two spotted spider mite, $Tetranychus$ $urticae$. All six BM chemicals showed significant acaricidal effects. The BM mixture used to prepare 'Bt-Plus' showed a high acaricidal activity with a median lethal concentration at 218.7 ppm (95% confidence interval: 163.2 - 262.3). These toxic effects of bacterial metabolites were also proved by cytotoxicity test against Sf9 cells. Especially, benzylideneacetone, which was used as a main ingredient of 'BM+Bt', showed high cytotoxicity at its low micromolar concentration.

• Journal of Applied Biological Chemistry
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• v.51 no.6
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• pp.253-261
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• 2008

Isoflavone daidzein is a phytoestrogen widely distributed in Leguminosae and is especially rich in the soybean. The C6-C3 (rings B and C) unit of isoflavones is derived from the phenylpropanoid pathway and the remaining C6 (ring A) unit is from the polyketide pathway. This unique carbon skeleton is the result of isomerization of the flavone catalyzed by the isoflavone synthase, a cytochrome P450 enzyme. The isoflavones daidzein and genistein are present in the plant mostly in the glucosylated forms. However, in the human intestine, the glycosidic linkage is broken, and the free form is uptaked into blood stream. The free form is further metabolized into various reduction products to end up at the equol, which is known to have the most potent estrogenic effect among the metabolites. Several human intestinal bacteria that can convert daidzein into equol have been described, and the study into the chemistry and biochemistry of the daizein reduction would be rewarding to the improvement of the human health.

• Journal of Microbiology and Biotechnology
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• v.26 no.3
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• pp.488-492
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• 2016

Rhodococcus species have become increasingly important owing to their ability to degrade a wide range of toxic chemicals and produce bioactive compounds. Here, we report isolation of the Rhodococcus sp. KB6, which is a new leaf-inhabiting endophytic bacterium that suppresses black rot disease in sweet potato leaves. We determined the 7.0 Mb draft genome sequence of KB6 and have predicted 19 biosynthetic gene clusters for secondary metabolites, including heterobactins, which are a new class of siderophores. Notably, we showed the first internal colonization of host plants with Rhodococcus sp. KB6 and discuss its potential as a biocontrol agent for sustainable agriculture.

• Fisheries and Aquatic Sciences
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• v.17 no.2
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• pp.215-222
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• 2014

To explore marine microorganisms with medical potential, we isolated and identified marine bacteria from floats, marine algae, animals, and sponges collected from Jeju Island, Korea. We isolated and identified 21 different strains from the marine samples by 16S rRNA analysis, cultured them in marine broth, and extracted them with ethyl acetate (EtOAc) to collect secondary metabolite fractions. Next, we evaluated their anti-oxidative and anti-inflammatory effects. Among the 21 strains, the secondary metabolite fraction of Bacillus badius had both strong antioxidant and anti-inflammatory activity, and thus was selected for further experiments. An antioxidant compound detected from the secondary metabolite fraction of B. badius was purified by preparative centrifugal partition chromatography (n-hexane:EtOAc:methanol:water, 4:6:4:6, v/v), and identified as diolmycin A2. Additionally, diolmycin A2 strongly inhibited nitric oxide production. Thus, we successfully identified a significant bioactive compound from B. badius among the bacterial strains collected from Jeju Island.

• Journal of Environmental Science International
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• v.18 no.4
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• pp.435-443
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• 2009

A bacterial strain SY-97 that showed algicidal activity against Cochlodinium polykrikoides was isolated from coastal water of Uljin (eastern coast of Korea) in August, 2005. The isolated strain was identified as Brachybacterium sp. by morphological and biological tests, and analysis of 16S rDNA sequence. The optimal culture conditions for the growth of strain SY-97 were $30^{\circ}C$, initial pH 7.0, and salinity 2.0%. From the result of cell culture insert experiment, Brachybacterium sp. SY-97 is assumed to produce secondary metabolites which have algicidal activity. When 10% culture filtrate of this strain was applied to C. polykrikoides ($1.2{\times}10^4\;cells/m{\ell}$) cultures, 100% of C. polykrikoides cells was destroyed within 15 hours. The released algicides were heat-tolerant to $100^{\circ}C$ and stable in pH $6.0{\sim}10.0$. These results suggest that Brachybacterium sp. SY-97 is potentially useful for controlling outbreaks of C. polykrikoides.

• Journal of Microbiology and Biotechnology
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• v.22 no.1
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• pp.13-24
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• 2012

The genetic diversity of plant growth-promoting rhizobacterial (PGPR) fluorescent pseudomonads associated with the sugarcane (Saccharum officinarum L.) rhizosphere was analyzed. Selected isolates were screened for plant growthpromoting properties including production of indole acetic acid, phosphate solubilization, denitrification ability, and production of antifungal metabolites. Furthermore, 16S rDNA sequence analysis was performed to identify and differentiate these isolates. Based on 16S rDNA sequence similarity, the isolates were designated as Pseudomonas plecoglossicida, P. fluorescens, P. libaniensis, and P. aeruginosa. Differentiation of isolates belonging to the same group was achieved through different genomic DNA fingerprinting techniques, including randomly amplified polymorphic DNA (RAPD), amplified ribosomal DNA restriction analysis (ARDRA), repetitive extragenic palindromic (REP), enterobacterial repetitive intergenic consensus (ERIC), and bacterial repetitive BOX elements (BOX) analyses. The genetic diversity observed among the isolates and rep-PCR-generated fingerprinting patterns revealed that PGPR fluorescent pseudomonads are associated with the rhizosphere of sugarcane and that P. plecoglossicida is a dominant species. The knowledge obtained herein regarding the genetic and functional diversity of fluorescent pseudomonads associated with the sugarcane rhizosphere is useful for understanding their ecological role and potential utilization in sustainable agriculture.

• Journal of Microbiology and Biotechnology
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• v.14 no.4
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• pp.766-771
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• 2004

Julong 601, a Gram-positive anaerobic bacterium strain capable of cleaving the C-ring of isoflavones daidzein and genistein, was isolated from human feces. BLAST search revealed that its complete 16S rDNA gene sequence has 99% similarity to Eubacterium ramulus. Metabolites of daidzein and genistein were determined as O-desmethylangolensin (O-Dma) and 2-(4-hydroxyphenyl) propionic acid (2-HPPA), respectively, based on UV, EI-MS, and $^1H$ and ^{13}C$ NMR spectral analyses. Enantiomers of O-Dma and 2-HPPA were isolated by chiral stationary-phase HPLC (CSP HPLC). Cleavage of the C-ring of daidzein and genistein by strain Julong 601 was highly enantioselective. Specific rotation ([$\alpha]_D$) and circular dichroism (CD) spectra of the enantiomers are reported here for the first time. Biotransformation kinetics of daidzein and genistein indicated that the C-ring of genistein has a higher susceptibility to bacterial degradation than that of daidzein.

• The Plant Pathology Journal
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• v.29 no.2
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• pp.174-181
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• 2013

The plant growth-promoting rhizobacterium Ochrobactrum lupini KUDC1013 elicited induced systemic resistance (ISR) in tobacco against soft rot disease caused by Pectobacterium carotovorum subsp. carotovorum. We investigated of its factors involved in ISR elicitation. To characterize the ISR determinants, KUDC1013 cell suspension, heat-treated cells, supernatant from a culture medium, crude bacterial lipopolysaccharide (LPS) and flagella were tested for their ISR activities. Both LPS and flagella from KUDC1013 were effective in ISR elicitation. Crude cell free supernatant elicited ISR and factors with the highest ISR activity were retained in the n-butanol fraction. Analysis of the ISR-active fraction revealed the metabolites, phenylacetic acid (PAA), 1-hexadecene and linoleic acid (LA), as elicitors of ISR. Treatment of tobacco with these compounds significantly decreased the soft rot disease symptoms. This is the first report on the ISR determinants by plant growth-promoting rhizobacteria (PGPR) KUDC1013 and identifying PAA, 1-hexadecene and LA as ISR-related compounds. This study shows that KUDC1013 has a great potential as biological control agent because of its multiple factors involved in induction of systemic resistance against phytopathogens.

• Proceedings of the Korean Society of Applied Pharmacology
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• 1998.11a
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• pp.158-158
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• 1998

The non-mevalonate pathway is a newly discovered isoprenoid biosynthetic pathway in some bacteria, cyanobacteria, algae and plants. Because isoprenoid metabolites (ubiquinone, menaquinone, undecaprenol) are essential for bacterial growth, this pathway may represent a novel target for antibacterial agents. Antibiotics with a unique mechanism of action are needed to combat the risk of antibiotic resistance that is a current worldwide problem. In order to study this pathway as viable target, it was necessary to verify use of the pathway in our model system, the bacterium Bacillus subtilis. Incubation experiments with [6,6-$^2$H$_2$]-D-glucose and [l-$^2$H$_3$]-deoxy-D-xylulose were conducted to provide labeled menaquinone-7 (MK -7), the most abundant isoprenoid in B. subtilis. $^2$H-NMR analysis of the MK-7 revealed labeling patterns that strongly support utilization of the non-mevalonate pathway. Another approach to study the pathway is by structure activity relationships of proposed inhibitors of the pathway. Fosmidomycin is a phosphonic acid with antibacterial activity known to inhibit isoprenoid biosynthesis in susceptible bacteria and may act by inhibiting the non-mevalonate pathway. Fosmidomycin and an N-methyl analog were synthesized and tested for antibacterial activity. Fosmidomycin was active against Escherichia coli and B. subtilis, while N-formyl-N-methyl-3-amino-propylphosphonic acid was inactive.

• Biomolecules & Therapeutics
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• v.16 no.4
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• pp.356-363
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• 2008

A bacterial strain with good antibacterial activities against Staphylococus aureus and Escherichia coli was isolated from a marine sponge Stelleta sp., and it was identified as a Psychrobacter sp. by comparative 16S rDNA sequence analysis. In our search for bioactive secondary metabolites from this psychrophillic and halotolerent bacterium, sixteen cyclic dipeptides (1-16) were isolated and their structures were identified on the basis of NMR analysis. In the test of the compounds for the protective effect against Vibrio vulnificusinduced cytotoxicity in human intestinal epithelial cells, cyclo-(L-Pro-L-Phe) (5) exhibited significant protective effect. Compounds 2, 6, and 11, which contain D-amino acid, were first isolated from bacteria.