Expression analysis of the yersiniabactin receptor gene fyuA and the heme receptor hemR of Yersinia enterocolitica in vitro and in vivo using the reporter genes for green fluorescent protein and luciferase

The enteropathogenic Yersinia enterocolitica strains have several systems f or scavenging iron from their environment. We have studied the expression o f the fyuA gene, which encodes the outer membrane receptor for the sideroph ore yersiniabactin (Ybt), and the hemR gene, which encodes the receptor for heme, using the reporter genes gfp (encoding green fluorescent protein) an d luc (encoding firefly luciferase). To study gene expression in vitro as w ell as in vivo, we have constructed several translational reporter gene fus ions to monitor simultaneously expression of fyuA and hemR or expression of one gene by a gfp-luc tandem reporter. Results of the in vitro expression analysis (liquid media) indicated that fyuA and hemR are strongly derepress ed under iron starvation conditions, resulting in strong fluorescence and/o r luminescence at 27 degreesC. In the in vivo BALB/C mouse infection model, tissue-specific expression of fyuA and hemR reporter fusions was observed. Surprisingly,fyuA and hemR reporter constructs were weakly expressed by ye rsiniae located in the liver and intestinal lumen, whereas strong expressio n was found for yersiniae in the peritoneal cavity and moderate expression was found in the spleen. Strikingly, yersiniae carrying fyuA or hemR report er fusions exhibited threefold-stronger signals when grown in the peritonea l cavity of mice than those growing under iron derepression in vitro. This hyperexpression suggests that besides Fur derepression, additional activato rs may be involved in the enhanced expression of fyuA and hemR under perito neal growth conditions. Differential expression of the fyuA and hemR report er fusions could not be observed, suggesting similar regulation of fyuA and hemR in the mouse infection model.