A Two-Component Regulatory System Integrates Redox State and Population Density Sensing in Pseudomonas putida

A two-component system formed by a sensor histidine kinase and a response regulator has been identified as an element participating in cell density signal transduction inPseudomonas putida KT2440. It is a homolog of thePseudomonas aeruginosa RoxS/RoxR system, which in turn belongs to the RegA/RegB family, described in photosynthetic bacteria as a key regulatory element. In KT2440, the two components are encoded by PP_0887 (roxS ) and PP_0888 (roxR ), which are transcribed in a single unit. Characterization of this two-component system has revealed its implication in redox signaling and cytochrome oxidase activity, as well as in expression of the cell density-dependent geneddcA , involved in bacterial colonization of plant surfaces. Whole-genome transcriptional analysis has been performed to define theP. putida RoxS/RoxR regulon. It includes genes involved in sugar and amino acid metabolism and the sulfur starvation response and elements of the respiratory chain (acbb3 cytochrome oxidase, Fe-S clusters, and cytochromec -related proteins) or genes participating in the maintenance of the redox balance. A putative RoxR recognition element containing a conserved hexamer (TGCCAG) has also been identified in promoters of genes regulated by this two-component system.