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Effects of Salt Concentration on Motility and Expression of Flagellin Genes in the Fish Pathogen Edwardsiella tarda

염 농도가 어류 병원체 Edwardsiella tarda의 운동성과 편모발현에 미치는 영향

  • Yu, Jong-Earn (Department of Microbiology, Pusan National University) ;
  • Park, Jun-Mo (Department of Microbiology, Pusan National University) ;
  • Kang, Ho-Young (Department of Microbiology, Pusan National University)
  • Received : 2011.10.19
  • Accepted : 2011.10.25
  • Published : 2011.10.31

Abstract

E. tarda, a fish pathogen, can survive in seawater under relatively high salt conditions as well as in fish under physiological salt conditions. Bacterial growth under different salt concentrations may influence the expression of genes involved in bacterial structure and physiology. The growth rate of E. tarda culture in high salt (3.5% NaCl) was similar to that in low salt (1.0% NaCl, physiological salt concentration). Interestingly, the strain moved much faster in low salt conditions than in high salt conditions. Electron microscopic observation demonstrated that the bacterial cells grown in high salt had less or no flagellation. Obvious flagellation was observed in the parental strain E. tarda CK41 grown in low-salt condition. Two putative genes coding flagellin were identified in the E. tarda genome sequences. The amino acid sequence comparison of each gene revealed 93% identities. A flagellin gene was PCR amplified and cloned into a cloning vector. Using an E. coli protein expression system, a part of flagellin protein was overexpressed. Using the purified protein, an anti-flagellin antibody was raised in the rabbit. Immunoblot analyses with flagellin specific antibody demonstrated that E. tarda CK41 expressed falgellin in low salt conditions, which is consistent with the results seen in motility assay and microscopic observation. This is the first report of salt regulated flagella expression in E. tarda.

염농도에 따른 E. tarda CK41의 운동성을 알아보기 위하여 1.0%와 3.5%의 염농도를 가지는 운동성 측정 배지에서 집락의 변화를 관찰한 결과, 3.5% 염농도 조건에서 운동성이 감소하는 것을 확인할 수 있었다. 1.0%과 3.5% 염농도 조건에서의 생육도를 측정해본 결과 각 염농도 조건에 따른 생균수의 차이는 매우 적은 것으로 보아, 높은 염농도에서의 운동성의 감소는 생육정체가 아닌 실질적인 운동성의 차이에 의함을 알 수 있었다. 이러한 염농도에 의한 운동성의 차이가 편모에 의한 것인지를 알아보기 위하여 투과 전자 현미경으로 형태학적 관찰을 해본 결과, 3.5% 염농도에서는 편모의 형성이 되지 않음을 확인하였다. E. tarda는 PFAD와 FDP 두개의 편모 유전자를 가지며 이들간의 아미노산 상동률은 93%로 높은 편이다. 편모의 발현양의 확인을 위하여 PFAD 특이적인 다클론성 항체를 제작하기 위하여, PFAD를 과발현시키는 재조합 플라스미드 pBP793을 구축하여 대장균 발현시스템으로 발현시켜 정제한 후, 토끼에서 면역반응을 유도하여 특이 항체를 제작하였다. PFAD 특이적인 다클론성 항체를 이용한 immunoblot assay 결과, 3.5% 염농도 조건에서 배양한 E. tarda CK41의 경우 1.0% 염농도에서 보다 반응하는 면역 활성 단백질 밴드가 낮은 것으로 측정되었다. 이러한 결과를 종합하여 볼 때, 염농도가 높은 해수환경에서의 운동성의 감소는 E. tarda CK41의 편모 단백질이 제대로 발현되지 않아 기능적인 편모의 형성이 이루어지지 않는다는 것을 예증하고 있다. 향후 연구에서 어떠한 메카니즘에 의해 염농도가 flagellin의 발현을 조절하는지를 밝힐 필요가 있다.

Keywords

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