LitR directly upregulates autoinducer synthesis and luminescence in Aliivibrio logei

LitR is a master-regulator of transcription in the ainS/R and luxS/PQ quorum sensing (QS) systems of bacteria from Vibrio and Aliivibrio genera. Here, we for the first time directly investigated the influence of LitR on gene expression in the luxI/R QS system of psychrophilic bacteria Aliivibrio logei . Investigated promoters were fused with Photorhabdus luminescens luxCDABE reporter genes cassette in a heterological system of Escherichia coli cells, litR A. logei was introduced into the cells under control of P lac promoter. LitR has been shown to upregulate genes of autoinducer synthase ( luxI ), luciferase and reductase ( luxCDABE ), and this effect doesn’t depend on presence of luxR gene. To a much lesser degree, LitR induces luxR1 , but not the luxR2 — the main luxI/R regulator. Enhanced litR expression leads to an increase in a LuxI-autoinducer synthesis and a subsequent LuxR-mediated activation of the luxI/R QS system. Effect of LitR on luxI transcription depends on lux -box sequence in luxI promoter even in absence of luxR ( lux -box is binding site of LuxR). The last finding indicates a direct interaction of LitR with the promoter in the lux -box region. Investigation of the effect of LitR A. logei on luxI/R QS systems of mesophilic Aliivibrio fischeri and psychrophilic Aliivibrio salmonicida showed direct luxR -independent upregulation of luxI and luxCDABE genes. To a lesser degree, it induces luxR A. fischeri and luxR1 A. salmonicida . Therefore, we assume that the main role of LitR in cross-interaction of these three QS systems is stimulating the expression of luxI .