CsrA modulates luxR transcript levels in Vibrio fischeri

The quorum-sensing and CsrA regulons of Vibrios control overlapping cellular functions during growth. Hence, the potential exists for regulatory network interactions between the pathways that enable them to be coordinately controlled. In Vibrio cholerae, CsrA indirectly modulates the activity of LuxO in the quorum-sensing signaling pathway. In this study, it was demonstrated that in Vibrio fischeri, CsrA causes an increase in the transcript levels of a downstream quorum-sensing regulatory gene, luxR, which does not exist in the V. cholerae system. In V. fischeri, the increase in luxR transcripts caused by CsrA does not depend on the LitR transcriptional activator nor does the CsrA effect seem to occur through the global regulator cAMP-CRP. Thus, there appears to be more than one mechanism whereby the CsrA and quorum-sensing pathways integrate regulatory outputs in Vibrios.