• Korean journal of applied entomology
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• v.49 no.4
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• pp.409-416
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• 2010

An entomopathogenic bacterium, Photorhabdus temperata ssp. temperata (Ptt), suppresses insect immune responses and facilitates its symbiotic nematode development in target insects. The immunosuppressive activity of Ptt enhances pathogenicity of various microbial pesticides including Bacillus thuringiensis (Bt). This study was performed to select a cheap and efficient bacterial culture medium for large scale culturing of the bacteria. Relatively cheap industrial bacterial culture media (MY and M2) were compared to two research media, Luria-Bertani (LB) and tryptic soy broth (TSB). In all tested media, a constant initial population of Ptt multiplied and reached a stationary phase at 48 h. However, more bacterial colony densities were detected in LB and TSB at the stationary phase compared to two industrial media. All bacterial culture broth gave significant synergism to Bt pathogenicity against third instars of the diamondback moth, Plutella xylostella. Production of bacterial metabolites extracted by either hexane or ethyl acetate did not show any significant difference in total mass among four culture media. Reverse phase HPLC separated the four bacterial metabolites, which were not much different in quantities among four bacterial culture broths. This study suggests that two industrial bacterial culture media can be used to economically culture Ptt in a large scale.

• Korean journal of applied entomology
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• v.49 no.3
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• pp.251-259
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• 2010

A bacterial colony was isolated from the gut of the bean bug, Riptortus clavatus. From morphological and biochemical tests, the bacterial isolate showed the highest similarity to Staphylococcus succinus. DNA sequence of 16S rRNA gene of the bacterium supported the identification. Oral administration of penicillin G to adults of R. clavatus gave a dose-dependent mortality of adults of R. clavatus to adults along with significant decrease of the bacterial population in the gut. Similarly, three metabolites (benzylideneacetone, proline-tyrosine, and acetylated phenylalanine-glycine-valine) derived from an entomopathogenic bacterium, Xenorhabdus nematophila, also inhibited growth of the gut bacterial population and gave significant mortalities to R. clavatus. These results suggest that a gut bacterial population classified as Staphylococcus sp. is required for survival of R. clavatus and that the three bacterial metabolites had toxic effects on the bugs due to their antibacterial properties.

• Korean Journal of Microbiology
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• v.54 no.3
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• pp.175-187
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• 2018

Myxobacteria produce diverse secondary metabolites for predation, self-defense, intercellular signaling, and other unknown functions. Many secondary metabolites isolated from myxobacteria show pharmaceutically useful bioactivity such as anticancer, antibacterial, and antifungal activities with a unique mechanism of action. Therefore, a large number of myxobacterial strains have been isolated globally and many bioactive compounds have been purified from them. However, 16S rRNA database analysis indicates that there are far more types of myxobacterial species in the wild than have ever been isolated, and genome sequence analysis suggests that each myxobacterium is capable of producing much more metabolites than already known. In this article, the current status of studies on the secondary metabolites from myxobacteria, their biosynthetic genes, biological functions, and transcriptional regulatory factors governing gene expression were reviewed.

• Korean journal of applied entomology
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• v.50 no.3
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• pp.171-178
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• 2011

Bacillus thuringiensis (Bt) is a bacterial biopesticide against insect pests, mainly lepidopterans. Spodoptera exigua and Plutella xylostella exhibit significant decreases in Bt susceptibility in late larval instars. To enhance Bt pathogenicity, we used a mixture treatment of Bt and other bacterial metabolites which possessed significant immunosuppressive activities. Mixtures of Bt with culture broths of Xenorhabdus nematophila (Xn) or Photorhabdus temperata ssp. temperata (Ptt) significantly enhanced the Bt pathogenicity against late larval instars. Different ratios of Bt to bacterial culture broth had significant pathogenicities against last instar P. xylostella and S. exigua. Five compounds identified from the bacterial culture broth also enhanced Bt pathogenicity. After determining the optimal ratios, the mixture was applied to cabbage infested by late instar P. xylostella or S. exigua in greenhouse conditions. A mixture of Bt and Xn culture broth killed 100% of both insect pests when it was sprayed twice, while Bt alone killed less than 80% or 60% of P. xylostella and S. exigua, respectively. Other Bt mixtures, including Ptt culture broth or bacterial metabolites, also significantly increased pathogenicity in the semi-field assays. These results demonstrated that the Bt mixtures collectively names "Bt-Plus" can be developed into potent biopesticides to increase the efficacy of Bt.

• Korean journal of applied entomology
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• v.53 no.3
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• pp.271-280
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• 2014

Some bacterial metabolites of Xenorhabdus nematophila (Xn) inhibit phospholipase $A_2$ ($PLA_2$) activity to shutdown eicosanoid biosynthesis in target insects. However, little has been known about the target insect $PLA_2$ of these bacterial metabolites. Eight bacterial metabolites identified in Xn culture broth exhibited significant insecticidal activities against larvae of both lepidopteran species of Plutella xylostella and Spodoptera exigua. Moreover, these bacterial metabolites significantly enhanced insecticidal activities of Bacillus thuringiensis (Bt). To determine target $PLA_2$, we cloned and over-expressed cellular $PLA_2$ ($SecPLA_2$) of S. exigua. Purified $SecPLA_2$ catalyzed phospholipids derived from the fat body and released several polyunsaturated fatty acids. Most Xn metabolites significantly inhibited $SecPLA_2$ activity, but were different in their inhibitory activities. There was a positive correlation between the inhibition of $SecPLA_2$ and the enhancement of Bt insecticidal activity. These results indicate that $SecPLA_2$ is a molecular target inhibited by Xn metabolite.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2002.10a
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• pp.137-138
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• 2002

최근 세균을 이용한 적조 방제연구가 활발히 진행되면서 해양에서 다수의 미세조류 저해균이 분리되고 있다. 전보에서 저자들은 규조류 Chaetoceros spp.의 생육을 저해하는 해양세균 Shewanella sp. SR-14를 분리하였으며, 이 균은 대사산물을 생성하여 그 생육을 저해하는 것으로 보고한 바 있다. 그런데 Shewanella sp. SR-14에 의한 Chaetoceros calcitrans의 생육저해는 대사산물(배양여액)만을 사용한 경우보다 세균이 공존하는 경우에 그 활성이 휠씬 강하여 세균이 생성하는 저해물질에 의한 것으로만 이해하기 어려웠으며, 다른 미지의 기구가 관여하고 있을 가능성이 시사되었다. (중략)

• Korean Journal of Fisheries and Aquatic Sciences
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• v.7 no.4
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• pp.221-228
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• 1974

산란직전의 남해산 참굴(Crassostrea gigas)을 산채로 구입하여 통상조건하에서 탈각하여 얻은 굴육질을 polyethylene laminated aluminium pouch (Al+PE : 0.03+0.03mm) 속에 밀봉하여 살균선량(0.2Mrad) 및 멸균선량(2.0Mrad)의 감마선으조 조사하고, 한편, 100ppm의 염소수에 굴육질을 2분간 침지한 후 탈수하여 같은 방법으로 포장하여 35일간의 빙장기간중 세균학적 및 화학적 변화를 대조 굴(조사치 않고 염소수 처리하지 않은)의 경우와 비교하였다. 굴육질의 시초의 총균수는 g당 700-800에 달했고, 0.2 Mrad의 감마선 조사는 빙장 10일째의 저장 기간중의 총 균수를 검측할 수 있는 선 이하로 감소시켰으며 2.0 Mrad 조사는 20일째까지 거의 무균상태를 가져왔다. 감마선 조사는 또한 세균활동을 표시하는 대사물질인 TMA와 TCA soluble nitrogen의 축적을 현저히 억제시켰으며 빙장 후기부터 번식하기 시작하여 총균수가 g당 100,000을 초과케 된 35일째까지도 대조굴의 동일한 총균수 시기에 비하여 이 대사물의 축적억제가 현저했음은 감마선 조사의 효과가 총균수의 양적인 감소뿐만 아니라 동시에 TMA를 생산하고 단백질을 분해할 능력이 있는 세균제거 내지는 번식의 억제라는 선택적인 양면을 가지고 있음을 보여 준다. 염소수 처리한 굴육질의 경우 총균수의 양적인 감소효과는 현저하지 않했는데도 불구하고 감마선 조사 경우처럼 세균대사물질 축적의 철저한 억제를 가져 왔음은 주목할만 하다. 굴육질의 glycogen 함량은 사후 저장 기간 중 쉽사리 감소되지 않했으며 PH 측정으로 본 생굴의 신선도와의 관련성은 희박하며 조사와 염소수 처리굴의 경우 더욱 그러했다.

• Korean journal of applied entomology
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• v.54 no.2
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• pp.55-62
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• 2015

'Bt-Plus' has been developed by mixing spores of Bacillus thuringiensis (Bt) and culture broth of Xenorhabdus nematophila (Xn). Despite its high toxicity, it has some imitation to broaden its efficacy against diverse insect pest spectrum. This study focuses on enhancement of Bt-Plus toxicity against semi-susceptible insect, Spodoptera exitgua, by addition of Xn metabolites. Two main Xn metabolites, oxindole (OI) and benzylideneacetone (BZA), are known to enhance the Bt insecticidal activities. The addition of OI or BZA significantly increased Bt-Plus pathogenicity. However, when the freeze-dried Xn culture broth was added to Bt-Plus, much less amount was enough to enhance the toxicity compared to the amount of OI or BZA. An HPLC analysis indicated that there were more than 12 unidentifed bacterial metabolites in Xn culture broth. These suggest that there are potent biological response modifiers in Xn metabolites other than OI and BZA.

• Proceedings of the Korean Society of Applied Entomolohy Conference
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• 2002.11a
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• pp.165-165
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• 2002

• Journal of Life Science
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• v.28 no.3
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• pp.369-375
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• 2018

Mycoplasma genitalium has 367 conserved genes and the smallest genome among mono-culturable prokaryotes. Conservative metabolic pathways were examined among M. genitalium and 14 prokaryotes, one hyperthermophilic exosymbiotic archaeon Nanoarchaeum equitans and 13 intracellular eubacteria of plants or insects, with fewer conserved genes than M. genitalium. They have 11 to 71 metabolic pathways, however complete metabolic pathways ranged from 1 to 24. Totally, metabolic pathway hole is very high due to the lack of 45.8% of the enzymes required for the whole metabolic pathways and it could be suggested that the shared metabolic pathway with the host's enzyme would work or the essential substances are host dependent. The number of genes necessary for mass transfer through the cell membrane is also very low, and it may be considered that the simple diffusion or the protein of the host will function in the cell membrane of these prokaryotes. Although the tRNA charging pathway was distributed in all 15 prokaryotes, each has 5-20 tRNA charging genes. This study would give clues to the understanding of the metabolic pathways of intracellular parasitic bacteria of plant and endosymbiotic bacteria of insects, and could provide basic data for prevention of crop damage, development of insect pests and human medicines.