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Regulation of autoinducer 2 production and luxS expression in a pathogenic Edwardsiella tarda strain

¹ Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, PR China
² Graduate University of the Chinese Academy of Sciences, Beijing 100049, PR China

Correspondence
Li Sun
lsun{at}ms.qdio.ac.cn

Edwardsiella tarda is a bacterial pathogen that can infect both humans and animals. TX1, an Ed. tarda strain isolated from diseased fish, was found to produce autoinducer 2 (AI-2)-like activity that was growth phase dependent and modulated by growth conditions. The gene coding for the AI-2 synthase was cloned from TX1 and designated luxS_Et. LuxS_Et was able to complement the AI-2 mutant phenotype of Escherichia coli strain DH5. Expression of luxS_Et correlated with AI-2 activity and was increased by glucose and decreased by elevated temperature. The effect of glucose was shown to be mediated through the cAMP-CRP complex, which repressed luxS_Et expression. Overexpression of luxS_Et enhanced AI-2 activity in TX1, whereas disruption of luxS_Et expression by antisense RNA interference (i) reduced the level of AI-2 activity, (ii) impaired bacterial growth under various conditions, (iii) weakened the expression of genes associated with the type III secretion system and biofilm formation, and (iv) attenuated bacterial virulence. Addition of exogenous AI-2 was able to complement the deficiencies in the expression of TTSS genes and biofilm production but failed to rescue the growth defects. Our results (i) demonstrated that the AI-2 activity in TX1 is controlled at least in part at the level of luxS_Et expression, which in turn is regulated by growth conditions, and that the temporal expression of luxS_Et is essential for optimal bacterial infection and survival; and (ii) suggested the existence in Ed. tarda of a LuxS/AI-2-mediated signal transduction pathway that regulates the production of virulence-associated elements.

The GenBank/EMBL/DDBJ accession number for the sequence of the luxS_Et region is EU070919.