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Summary: Quorum-sensing control of luminescence in Vibrio harveyi, which involves an indirect autoinducer-mediated phosphorelay signal transduction system, contrasts with the prototypical quorum-sensing system of Vibrio fischeri, in which the autoinducer and the transcriptional activator LuxR directly activate lux operon expression. In V. harveyi, a regulator not homologous to V. fischeri LuxR and also designated LuxR (LuxR[sub vh]), binds specifically to the lux operon promoter region and activates the expression of luminescence. A direct connection has not been identified previously between V. harveyi LuxR[sub vh] and the autoinducer-mediated phosphorelay system. Here, we demonstrate by mobility shift assays and measurement of luxR[sub vh] mRNA levels with luxO[sup +] and luxO[sup –] cells that the central response regulator of the V. harveyi phosphorelay system (LuxO) represses the level of LuxR[sub vh]. Expression of a luxR[sub vh]-bearing plasmid strongly stimulated luminescence of a luxO[sup –] mutant but had no effect on luminescence of wild-type luxO[sup +] cells, indicating tight regulation of luxR[sub vh] by LuxO. Furthermore, luxO null mutants of V. fischeri MJ-1 and two autoinducer mutants, MJ-211 (luxI[sup –]) and MJ-215 (luxI[sup –]ainS[sup –]), emitted more light and exhibited more elevated levels of litR, a newly identified V. harveyi luxR[sub vh] homologue, than their luxO[sup +] counterparts. These results suggest that activity of the autoinducer-mediated phosphorelay system is coupled to LuxR[sub vh]/LitR control of luminescence through LuxO in V. harveyi and V. fischeri. The presence of homologues of V. harveyi LuxR[sub vh], LuxO and other phosphorelay system proteins in various Vibrio species and the control of LuxR[sub vh] and its homologues by LuxO identified here in V. harveyi and V. fischeri and recently in Vibrio cholerae suggest that the luxO–luxR[sub vh] couple is a central feature of this... [ABSTRACT FROM AUTHOR] |
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