A gene cluster involved in the metabolism of prebiotic short-chain fructooligosaccharides (scFOS) has recently been identified in the extra-intestinal avian pathogenic Escherichia coli strain BEN2908. This gene cluster, called the fos locus, plays a major role in the initiation stage of chicken intestinal colonization. This locus is composed of six genes organized as an operon encoding a sugar transporter and enzymes involved in scFOS metabolism, and of a divergently transcribed gene encoding a transcriptional regulator, FosR, belonging to the LacI/GalR family. To decipher the regulation of scFOS metabolism, we monitored the fos operon promoter activity using a luciferase reporter gene assay. We demonstrated that the expression of fos genes is repressed by FosR, controlled by catabolite repression and induced in the presence of scFOS. Using electrophoretic mobility shift assays and surface plasmon resonance experiments, we showed that FosR binds to two operator sequences of the fos operon promoter region. This binding to DNA was inhibited in the presence of scFOS, especially by GF2. We then propose a model of scFOS metabolism regulation in a pathogenic bacterium, which will help to identify the environmental conditions required for fos gene expression and to understand the role of this locus in intestinal colonization.
© 2011 Blackwell Publishing Ltd.