Genetic and proteomic analysis of the role of luxS in the enteric phytopathogen, Erwinia carotovora

Erwinia carotovora is a Gram-negative phytopathogen that is an important cause of soft rot disease, including stem and tuber rot in potatoes. Quorum sensing is the process by which bacteria detect their population density and regulate gene expression accordingly. Quorum sensing, an important example of intercellular communication, involves the production and detection of chemical signal molecules. The enzyme LuxS is responsible for the production of Autoinducer-2 (AI-2), a molecule that has been implicated in quorum sensing in many bacterial species. In this study, the role of luxS in Erwinia carotovora ssp. carotovora strain ATTn10 and Erwinia carotovora ssp. atroseptica SCRI1043 has been examined. Both strains have been shown to produce luxS-dependent extracellular AI-2 activity and the phenotypes of defined luxS mutants in these strains have been characterized. Inactivation of luxS in Er. carotovora was found to have a strain-dependent impact on the intracellular proteome (using two-dimensional difference in gel electrophoresis), secreted proteins, motility and virulence in planta. No link was detected with the N-acyl-L-homoserine lactone quorum sensing system in these organisms. Although the molecular mechanism(s) of luxS regulation in Erwinia remain to be determined, this is the first report of any luxS-dependent phenotypes in a plant pathogen.