A Cyclic AMP Receptor Protein-Regulated Cell-Cell Communication System Mediates Expression of a FecA Homologue in Stenotrophomonas maltophilia

Stenotrophomonas maltophilia WR-C possesses anrpf /diffusible signal factor (DSF) cell-cell communication system. It producescis -Δ2-11-methyl-dodecenoic acid, a DSF, and seven structural derivatives, which requirerpfF andrpfB for synthesis. Acquisition of iron from the environment is important for bacterial growth as well as the expression of virulence genes. We identified a gene homologous tofecA , which encodes a ferric citrate receptor that transports exogenous siderophore ferric citrate from the environment into the bacterial periplasm. Western blot analysis with anti-FecA-His6 antibody showed that the FecA homologue was induced in the iron-depleted medium supplemented with a low concentration of ferric citrate. Deletion ofrpfF orrpfB resulted in reduced FecA expression compared to the wild type. Synthetic DSF restored FecA expression by the ΔrpfF mutant to the wild-type level. Reverse transcription-PCR showed that thefecA transcript was decreased in the ΔrpfF mutant compared to the wild type. These data suggest that DSF affected the level offecA mRNA. Transposon inactivation ofcrp , which encodes cyclic AMP (cAMP) receptor protein (CRP) resulted in reduced FecA expression andrpfF transcript level. Putative CRP binding sites were located upstream of therpfF promoter, indicating that the effect of CRP on FecA is through therpf /DSF pathway and by directly controllingrpfF . We propose that CRP may serve as a checkpoint for iron uptake, protease activity, and hemolysis in response to environmental changes such as changes in concentrations of glucose, cAMP, iron, or DSF.