The Campylobacter jejuni PhosS/PhosR operon represents a non-classical phosphate-sensitive two-component system.

The bacterial pathogen Campylobacter jejuni carries several putative two-component signal transduction systems of unknown function. Here we report that the PhosS (Cj0889) and PhosR (Cj0890) proteins constitute a two-component system that is activated by phosphate limitation. Microarray analysis, real-time RT-PCR, and primer extension experiments indicated that this system regulates 12 genes (including the pstSCAB genes) present in three transcriptional units. Gel shift assays confirmed that recombinant PhosR protein bound DNA fragments containing the promoter regions upstream of these three transcriptional units. Although functionally similar, the PhosS/PhosR does not exhibit sequence homology with the classical PhoBR systems, has a different pho box (5'-GTTTCNAAAANGTTTC-3') recognized by the C. jejuni response regulator, and is not autoregulated. Because of these atypical properties, we designated the Cj0889-Cj0890 operon as the C. jejuni PhosS/PhosR system (phosphate sensor/phosphate response regulator) and the phosphate-regulated genes as the pho regulon of C. jejuni.