Characterization of a new quorum sensing regulator luxT and its roles in the extracellular protease production, motility, and virulence in fish pathogen Vibrio alginolyticus.

Vibrio alginolyticus, an opportunistic pathogen that causes vibriosis in miscellaneous fish species, has brought about serious economic damage to the mariculture industry in South China. The mechanism of virulence regulation in V. alginolyticus is yet not known except a Vibrio harveyi-like quorum sensing (QS) system that is established to manipulate the expression of diverse genes including those encoding virulence determinants. In this study, a new TetR family QS regulator, luxT, was identified and characterized in V. alginolyticus. The transcription of luxT gene was cell density dependent and was positively regulated by LuxU, an established QS component relaying the signal from three paralleled QS regulatory systems in V. harveyi. In addition, luxT positively regulated both luxO at transcriptional level and luxR at post-transcriptional level, which is thoroughly different from the established QS regulation mode in V. harveyi and Vibrio vulnificus. The mutant of luxT deletion produced markedly decreased total extracellular proteases and reduced motility ability compared to the wild type and the complemented strain luxT (+). The fish infection results indicated that mutation of luxT led to marginal attenuation in the virulence of V. alginolyticus, suggesting that LuxT might play a role in the fine-tuning of the virulence via QS in V. alginolyticus.