Signal transduction-dependent small regulatory RNA is involved in glutamate metabolism of the human pathogen Bordetella pertussis

Abstract

Bordetella pertussis is the causative agent of human whooping cough (pertussis), a highly contagious respiratory disease which despite massive vaccination programs remains the major cause of infant morbidity and mortality. The requirement of the RNA chaperone Hfq for virulence of B. pertussis suggested that Hfq-dependent small regulatory RNAs are involved in the modulation of gene expression in this re-emerging pathogen. High through-put RNA sequencing revealed hundreds of putative non-coding RNAs including the RgtA sRNA. Abundance of this sRNA is strongly decreased in the absence of the Hfq protein and its expression is modulated by the activities of the two-component regulatory system BvgAS and another response regulator RisA. Whereas RgtA levels were elevated under modulatory conditions or in the absence of bvg genes, deletion of the risA gene completely abolished RgtA expression. Profiling of the ΔrgtA mutant in the ΔbvgA genetic background identified the BP3831 gene encoding a periplasmic amino acid-binding protein of an ABC transporter as a possible target gene. The results of site-directed mutagenesis and in silico analysis indicate that the RgtA sRNA base-pairs with the region upstream of the start codon of the BP3831 mRNA and thereby weakens the BP3831 protein production. Furthermore, our data suggest that the function of the BP3831 protein is related to transport of the glutamate, an important metabolite in the B. pertussis physiology. In our working model the BvgASR/RisA interplay regulates the expression of RgtA which upon infection, when glutamate might be at scarce, could reduce the translation of the glutamate transporter and thereby assists in adaptation of the pathogen to other sources of energy.