Involvement of quorum sensing in the virulence of Edwardsiella tarda towards cultured marine fish

• Main Author: Han, Yin
• Other Authors: Bossier, Peter, Zhang, Xiao-hua
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Ghent University. Faculty of Bioscience Engineering 2011
• Subjects: Biology and Life Sciences; quorum sensing; fish; Edwardsiella tarda; virulence; Turbot
• Online Access: https://biblio.ugent.be/publication/1942407; http://hdl.handle.net/1854/LU-1942407; https://biblio.ugent.be/publication/1942407/file/1942408

In this PhD study, Edw. tarda LTB-4 isolated from the brain of the infected turbot proved to be virulent to turbot. The virulent Edw. tarda LTB-4 has AHL-based and AI-2 based QS systems, and produced five kinds of acylhomoserine lactone molecules, which were identified by both TLC and GC-MS as C4-HSL, C6-oxo-HSL, C8-HSL, C8-oxo-HSL and C10-HSL. A edwR mutant strain was constructed by insertional mutagenesis with suicide plasmid pNQ705. The mutation of edwR decreased the LPS production, caused obvious reduction in swimming and swarming motility, but significantly increased the biofilm formation. However, the virulence of the edwR mutation to zebra fish via intraperitoneal (i.p.) injection and wound immersion challenge was comparable to that of the wild type strain. Edw. tarda LTB-4 produced various indole alkaloids, including indole, 2-(1H-indol-3-yl)ethanol, 4-di(1H-indol-3-yl)methylphenol, tri(1H-indol-3-yl)methane and 2-[2,2-bis(1H-indol-3-yl)]ethylphenylamine. Indole was the most abundant among these indole alkaloids, and appeared to be important in the regulation of virulence factor expression in Edw. tarda, such as motility, LPS production, antibiotics-resistances and in vivo virulence. Fyb37, is the first B. flexus strain to be reported able to significantly degrade AHL molecules of Edw. tarda in vitro, and displayed a small protective effect in the wounded zebra fish against Edw. tarda via wound immersion. The most cost-effective dosage of Fyb37 for direct addition into the rearing water was ten to the power five CFU per ml.