bThe entomopathogenic bacteria Xenorhabdus nematophila and Photorhabdus temperata subsp. temperata suppress insect immune responses by inhibiting the catalytic activity of phospholipase A 2 (PLA 2 ), which results in preventing biosynthesis of immune-mediating eicosanoids. This study identified PLA 2 inhibitors derived from culture broths of these two bacteria. Both X. nematophila and P. temperata subsp. temperata culture broths possessed significant PLA 2 -inhibitory activities. Fractionation of these bacterial metabolites in the culture broths using organic solvent and subsequent chromatography purified seven potent PLA 2 inhibitors, three of which (benzylideneacetone [BZA], proline-tyrosine [PY], and acetylated phenylalanine-glycine-valine [FGV]) were reported in a previous study. Four other compounds (indole, oxindole, cis-cyclo-PY, and p-hydroxyphenyl propionic acid) were identified and shown to significantly inhibit PLA 2 . X. nematophila culture broth contained these seven compounds, while P. temperata subsp. temperata culture broth contained three compounds (BZA, acetylated FGV, and cis-cyclo-PY). BZA was detected in the largest amount among these PLA 2 compounds in both bacterial culture broths. All seven bacterial metabolites also showed significant inhibitory activities against immune responses, such as phenoloxidase activity and hemocytic nodulation; BZA was the most potent. Finally, this study characterized these seven compounds for their insecticidal activities against the diamondback moth, Plutella xylostella. Even though these compounds showed relatively low toxicities to larvae, they significantly enhanced the pathogenicity of Bacillus thuringiensis. This study reports bacterial-origin PLA 2 inhibitors, which would be applicable for developing novel insecticides. Insect immune responses consist of innate cellular and humoral components (2). Upon pathogen infection, pattern recognition receptors recognize nonself and the recognition signal is transferred by immune mediators to effector tissues, such as hemocytes and fat body (7). Eicosanoids form a chemical group of oxygenated polyunsaturated C 20 fatty acids, which are derived from arachidonic acid, a catalytic product of phospholipase A 2 (PLA 2 ) on phospholipid (PL) substrate (3). Two types of eicosanoids, prostaglandins and leukotrienes, are known to mediate the nonself recognition signals against various insect pathogens, including bacteria, fungi, viruses, and parasitoid eggs in insects (38). Inhibition of PLA 2 prevents eicosanoid biosynthesis and suppresses immune responses in response to microbial pathogens (23, 37).Xenorhabdus nematophila and Photorhabdus temperata subsp. temperata are insect pathogens that are symbiotic to the entomopathogenic nematodes Steinernema carpocapsae and Heterorhabditis megidis, respectively (1, 13, 25). Infective juvenile-stage nematodes enter target insect hemocoel through natural openings (such as mouth, anus, and spiracles) and then release their symbiotic bacteria from the nematode intestine. The releas...

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In this study, according to determination of nitrogen (δ 15 N) and oxygen (δ 18 O) from nitrate (NO 3 ) in water for 2 years, 2016-2017, Gunwi, Korea, the origin of pollutants in supply water could be found. The sampling sites are including 6 points, Donggok, Yonga, Janggok1 and 2, reservoir of dam and Ingak temple around Gunwi Dam, Korea. The water samples were determined NO 3 -N using Ion Chromatography and Nitrogen (δ 15 N) and Oxygen (δ 18 O) stable isotope ratio in nitrate and isotope ratio mass spectrometry, respectively. The standard deviation of determined standard materials is less than 0.2‰ for δ 15 N AIR and 0.2‰ for δ 18 O VSMOW in water. The origin of the supply water pollution was analyzed through the correlation between the values of δ 15 N and δ 18 O in nitrate. The values indicated that these sources were originated sewage and livestock manure in the Dam. The dominant contribution of water pollutants was calculated about 50% from Donggok location in this study. In addition, the location of Yonga where has the small inflow rate also constantly contributed to the Dam. 1. 서 론 전세계적으로 수질 중 질산성질소의 오염은 환경문 제로 우려가 되고 있는 물질 중의 하나이며 자연적인 질소 순환, 축산폐수, 그리고 화학 비료 등에 의해 생 성되며 잠재적으로 지표수와 지하수 중에 높은 농도의 위험한 수준으로 나타나기도 한다. 1,2) 질산성질소로 인 한 피해를 막기 위해 미국 환경보호청(Environmental Protection Agency, EPA), 세계보건기구(World Health Organization, WHO), 유럽공동체(European Union, EU) 에서 먹는 물에 대한 질산성질소의 농도를 각각 10 mg L -1 , 10 mg L -1 그리고 50 mg L -1 이하로 규제하고 있 다. 3) 우리나라의 경우 먹는물 수질기준 및 검사 등에 관한 규칙으로 먹는물에 대하여 질산성질소의 농도가 10 mg L -1 를 넘지 않아야 한다고 규정하고 있다. 4) 질산 성질소에 의한 오염 예방 및 오염원 유입 경로 파악을 위해 질산염의 질소 동위원소 값이 연구 분야에 활용 되고 있다. 1,5-8) 질산염의 질소 안정동위원소비(δ 15 N)는 일반적으로 화학비료(−3.9‰ ~ 0.5‰), 토양 유기물(2‰ ~ 9‰) 그리 고 가축분뇨(6.8‰ ~ 20.9‰)의 영향에 따라 상이한 값 을 나타내므로 수질 시료의 질소 안정동위원소비는 오 염원을 추적할 수 있고 또한 오염원의 기여도를 평가 하는 도구로도 활용되고 있다. 5,6,9-11) 그러나 오염원별 질소 안정동위원소 값이 서로 중첩되는 범위가 존재하 고 있어 질소 안정동위원소비만을 이용하여 오염원을 추 적하는 것은 어려움이 있다.