Response of Escherichia coli chemotaxis pathway to pyrimidine deoxyribonucleosides

Nucleosides are essential components of all living cells. Bacteria use salvage pathways to import nucleosides from their environment and to utilize them for nucleic acid biosynthesis, but also as alternative sources of carbon, nitrogen and energy. Motile bacteria commonly show chemoattraction towards nutritionally valuable compounds, and in this work, we demonstrate that the chemotaxis pathway of Escherichia coli exhibits specific attractant response to pyrimidine nucleosides. Particularly sensitive response, in the sub-micromolar range, was observed for deoxyribonucleosides thymidine and deoxycytidine. In contrast, ribonucleosides elicited weaker and less sensitive response, and no response to pyrimidine nucleobases was observed in the micromolar range of concentrations. Our subsequent analysis revealed that the pathway response to pyrimidine deoxyribonucleosides is mediated by the minor E. coli chemoreceptor Tap. The observed narrow dynamic range of this response indicates that sensing of deoxyribonucleosides is indirect, likely via an unknown periplasmic binding protein that interacts with Tap.