Microbiology Spectrum

ABSTRACT Nucleosides are essential components of all living cells. Bacteria use salvagepathways to import nucleosides from their environment and to utilize them for nucleicacid biosynthesis, but also as alternative sources of carbon, nitrogen and energy. Motilebacteria commonly show chemoattraction towards nutritionally valuable compounds,and in this work, we demonstrate that the chemotaxis pathway of Escherichia coliexhibits specific attractant response to pyrimidine nucleosides. The most sensitiveresponse, in the sub-micromolar range, was observed for pyrimidine deoxyribonucleosides, thymidine (deoxythymidine) and deoxycytidine. In contrast, pyrimidine ribonucleosides elicited weaker and less sensitive response, and no response to pyrimidinenucleobases was observed in the micromolar range of concentrations. Furthermore,no response was observed to tested purine nucleosides or nucleobases. Our subsequent analysis revealed that the pathway response to pyrimidine deoxyribonucleosidesis mediated by the minor E. coli chemoreceptor Tap, whereas the response to theribonucleoside uridine relies on a different mechanism. The observed narrow dynamicrange of this response indicates that sensing of deoxyribonucleosides is indirect, likelyvia an unknown periplasmic binding protein that interacts with Tap.IMPORTANCE Chemotactic behavior is highly important for bacterial ecology, enablingmotile bacteria to locate environments that are optimal for growth, and it became aparadigm for bacterial environmental sensing and signal transduction. However, even formodel organisms, the spectrum of stimuli sensed by the chemotaxis pathway is not fullyknown, which limits our understanding of the physiological and ecological relevanceof the chemotactic behavior. Here, we identified pyrimidine deoxyribonucleosides asa novel and highly specific class of chemoeffector metabolites for Escherichia coli, themost studied chemotaxis model. Our work expands the number of bacterial species thatexhibit chemotactic responses to nucleotide derivatives, strengthening the notion thatpyrimidines and purines constitute a highly important class of chemoeffectors for manybacteria.