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Park, Youngjin,Kim, Younggyun,Youngkeun Yi Korean Society of Applied Entomology 1999 Journal of Asia-Pacific Entomology Vol.2 No.2
A symbiotic bacterium was idnetified from the etomopathogenic nematode, Steinernema carpocapsae, collected in Korea and its biological significance was examined for insecticidal and antibiotic effects. The symbiotic bacterium was isolated from the nematode-infected hemolymph of the fifth instar larvae of Spodoptera exigua. The intra-hemocoelic injection of the bacterial isolates killed the insect hosts within 24h. Several biochemical and morphological characters of the bacterium were identical to those of Xenorhabdus nematophilus. The bacterial growth was not showed antibacterial effects on containing 4,000 ppm of streptomycin sulfate or 2,000 ppm of penicillin. They showed antibacterial effects on Escherichia coli, Ralstonia solanacearum and Pseudomonas aeruginosa, but not on Pseudomonas putida and Pseudomonas fluorescens.
Park Youngjin,Kim Yonggyun Korean Society of Applied Entomology 2005 Journal of Asia-Pacific Entomology Vol.8 No.1
It has been suggested that an entomopathogenic bacterium, Xenorhabdus nematophila, exerts its pathogenicity against beet armyworm, Spodoptera exigua, by inhibiting phospholipase $A_2\;(PLA_2)$ to shut down release of arachidonic acid, which is the primary substrate for eicosanoid biosynthetic pathway. This research aimed to prove the inhibitory hypothesis of X. nematophila on $PLA_2$ by directly quantifying arachidonic acid released from natural biological membrane. For determining optimal membrane preparation, fatty acid compositions from different tissues (hemocyte, fat body, and gut) were analyzed using gas chromatography in S. exigua. These tissue membranes showed different compositions in fatty acids, but possessed significant levels of arachidonic acid, amounting to ${\approx}\;0.02\%$ among all fatty acids. Also, all cytosolic fractions of three tissues possessed significant and specific $PLA_2$ activity because these $PLA_2$ extracts catalyzed release of arachidonic acid from the membrane preparation into medium and were inhibited by a specific $PLA_2$ inhibitor, dexamethasone. For massive assay, we chose fat body as a tissue source of $PLA_2$ and substrate membrane because of its relative abundance. The effect of fat body $PLA_2$ extract on release of arachidonic acid increased with its concentration and incubation time. The fat body $PLA_2$ was susceptible to dexamethasone (a specific $PLA_2$ inhibitor) and p-bromophenacyl bromide (a secretory type $PLA_2$ inhibitor), but not to methylarachidonyl fluorophosphate (a cellular type $PLA_2$ inhibitor). X nematophila significantly inhibited fat body $PLA_2$ activity, but did not after heat-killing. An organic extract of X. nematophila culture broth also inhibited the fat body $PLA_2$ activity. These results indicate that S. exigua possesses arachidonic acid on the membrane and $PLA_2$ in tissues and that X. nematophila releases $PLA_2$ inhibitor(s) and inhibits $PLA_2$, which is susceptible to a secretory type $PLA_2$ inhibitor.
Cold hardiness of the palm thrips, Thrips palmi
Youngjin Park,Kwangho Kim,Yonggyun Kim 한국응용곤충학회 2013 한국응용곤충학회 학술대회논문집 Vol.2013 No.10
Cold tolerance of the palm thrips, Thrips palmi Karny, was investigated to predict its survival in field during winter. Supercooling temperatures of T. palmi ranged from -26.4 to -18.4°C. However, exposure to subzero temperatures (from -5°C to -15°C) gave significant mortality to all developmental stages of T. palmi. Thus, T. palmi was determined to be a freeze-susceptible and suffered with cold injury. A brief pre-exposure to a low temperature (4°C) for 7 h significantly increase the cold tolerance of all stages of T. palmi with respect to survival at -10°C and supercooling capacity. A pre-exposure of T. palmi at 4°C significantly increased the survival rate on all developmental stages at -10°C. The rapid cold hardiness (RCH) was dependent on the duration of the pre-exposure period at 4°C in adult stage. Cryoprotectant analysis using an HPLC showed that the pre-exposure treatment increased the adult to synthesize glycerol, trehalose, mannitol, and mannose, at which trehalose represented the highest content. This study suggests that all stages of T. palmi are able to become cold-hardy by RCH, in which several polyols may play crucial roles as cryoprotectant.
A Pathogenic Bacterium, Enterococcus faecalis, to the Beet Armyworm, Spodoptera exigua
Park, Youngjin,Kim, Kilho,Kim, Yonggyun Korean Society of Applied Entomology 2002 Journal of Asia-Pacific Entomology Vol.5 No.2
A bacterial disease was found in the beet armyworm, Spodoptera exigua (Hubner). Blackened body of the infected larvae was a typical symptom of the epizootic disease especially at the intersegmental areas. We isolated the bacteria from the hemolymph of the infected 5th instar larvae and identified the isolate as a gram-positive bacterium, Enterococcus faecalis. When the 4th instar larvae were injected with the bacteria, half lethal dose of the bacteria was estimated as 22,593 colony-forming units (cfu) per larva and half lethal time of the bacteria was estimated as 2 days at $1O^7$ cfu injection and 6 days at $1O^8$ cfu injection. The bacteria were strongly resistant to each 1,000 ppm of ampicillin, kanamycin, and streptomycin. They were, however, relatively susceptible to mixture (1,000 ppm) of different combinations of the three antibiotics.
High-modulus and strength carbon nanotube fibers using molecular cross-linking
Park, Ok-Kyung,Choi, Hoikil,Jeong, Hanbin,Jung, Yeonsu,Yu, Jaesang,Lee, Jae Kwan,Hwang, Jun Yeon,Kim, Seung Min,Jeong, Youngjin,Park, Chong Rae,Endo, Morinobu,Ku, Bon-Cheol Elsevier 2017 Carbon Vol.118 No.-
<P>We present a systematic and simple approach to produce high-strength carbon nanotube fibers (CNTFs) with electrical conductivity in the high performance range (> 1000 S/cm). We studied several critical parameters to improve the mechanical properties of CNTFs by aryl cross-linking reaction. Both the molecular dynamics (MD) simulations and experimental results showed that the mechanical properties strongly depended on the degree of cross-linking, length of cross-linkers, and CNT diameter. The monobenzene (MB) covalent bonding between CNTF with double-walled CNTs (DWCNTs) showed the highest load transfer, resulting in significantly enhanced specific tensile strength (3.7 N/tex) and Young's modulus (210 N/tex) which are superior to the strongest commercial carbon fiber (3.6 N/tex and 180 N/tex), respectively. Furthermore, the mechanical properties of aryl cross-linked CNTF exhibited no significant change in strength with sample size of CNTFs, showing uniformity of strength with increasing degree of cross-linking. The electrical conductivity of the MB cross-linked CNTFs was similar to 1400 S/cm, which is higher than the best value of commercial carbon fibers (715 S/cm). These results demonstrate that aromatic linker between CNTFs can significantly enhance mechanical properties without significant loss of electrical conductivity. These molecular engineering with MD simulations provide an important route to design and develop ultra-high-performance fibers. (C) 2017 Elsevier Ltd. All rights reserved.</P>
Cadherin as a specific Cry1Ac receptor in the diamondback moth, Plutella xylostella
Youngjin Park,Yonggyun Kim 한국응용곤충학회 2013 한국응용곤충학회 학술대회논문집 Vol.2013 No.10
Putative cadherin genes, which are a receptor of the Bacillus thuringinesis toxins, were predicted from a whole genome sequencing data from the diamondback moth, Plutella xylostella. After the sequence and expression analysis, a Bt receptor cadherin gene was selected. The P. xylostella cadherin gene (PxCad1, GenBank Accession no. GU901158.1) encodes 11 cadherin repeats and a transmembrane domain. The PxCad1 gene was expressed in all developmental stage specifically in gut tissue by RT-PCR analysis. Expression of PxCad1 gene was suppressed by feeding of its specific dsRNA PxCad1 in 4th instar larval stage. The suppression of PxCad1 expression did not significantly feeding of its specific dsRNA PxCad1 in 4th instar larval stage. The suppression of PxCad1 expression did not significantly influence on pupal and adult development of P. xylostella. However, the larval treated with dsRNA PeCad1 (150 ng/larva) significantly reduced susceptibility to B. thuringiensis Cry1Ac (4.83 μg/ml). By contrast, the dsRNA PxCad1 -treated larvae did not show any change in susceptibility to B. thuringiensis Cry1Ca (0.24 μg/ml). These results suggest that PxCad1 is a specific receptor of Cry1Ac toxin from B. thuringiensis in P. xylostella.
Youngjin Park,Yonggyun Kim 한국응용곤충학회 2014 한국응용곤충학회 학술대회논문집 Vol.2014 No.04
Integrin is a cell surface protein that is composed of α and β heterodimer and mediates cell interaction with extracellular matrix or other cells including microbial pathogens. A full length cDNA sequence (2,517 bp) of a integrin subunit β1 (HaITGβ1) was cloned from the oriental tobacco budworm, Helicoverpa assulta. Phylogenetic analysis showed that HaITGβ1 was clustered with other insect β integrin subunits with the highest amino acid sequence identity (61%) to β1 of other Noctuidae such as Spodoptera exigua and S. litura. Structural analysis of the HaITGβ1 possessed all functional domains known in other insect β1 integrins. RT-PCR analysis showed that HaITGβ1 was expressed in all developmental stages and all tested tissues of H. assulta. Injection of double-stranded HaITGβ1 RNA (dsHaITGβ1) into third instar of H. assulta suppressed HaITGβ1 expression and resulted in significant delay from last larval stage to pupal stage. The dsHaITGβ1 injection significantly impaired nodule formation of H. assulta in response to bacterial challenge and hemocyte adherence. These results suggest that HaITGβ1 plays crucial roles in cellular immune responses as well as development in H. assulta.