A cAMP receptor protein regulated cell-cell communication system mediates expression of a FecA homologue in Stenotrophomonas maltophilia

Department of Food Microbiology and Toxicology, University of Wisconsin-Madison, Madison, Wisconsin 53706

^* To whom correspondence should be addressed. Email: acwong{at}wisc.edu.

	Abstract

Stenotrophomomas maltophilia WR-C possesses an rpf/DSF cell-cell communication system. It produces cis-2-11-methyl-dodecenoic acid, a diffusible signal factor (DSF), and seven structural derivatives, which require rpfF and rpfB 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 to fecA, which encodes for a ferric citrate receptor that transports exogenous siderophore-ferric citrate from the environment into the bacterial periplasm. Western blot analysis with anti-FecA-6His antibody showed that the FecA homologue was induced in the iron-depleted medium supplemented with a low concentration of ferric citrate. Deletion of rpfF or rpfB resulted in reduced FecA expression compared to the wild-type. Synthetic DSF restored FecA expression by the rpfF mutant to the wild-type level. RT-PCR showed that fecA transcript was decreased in the rpfF mutant compared to the wild-type. These data suggest that DSF affected the mRNA level of fecA. Transposon inactivation of crp which encodes for cyclic-AMP receptor protein (CRP) resulted in reduced FecA expression and rpfF transcript level. Putative CRP binding sites were located upstream of rpfF promoter indicating the effect of CRP on FecA is through the rpf/DSF pathway and by directly controlling rpfF. We propose that CRP may serve as a check point for iron uptake, protease activity and hemolysis in response to environmental changes such as concentrations of glucose, cAMP, iron, or DSF.