Discovery Of A Choline-Responsive Transcriptional Regulator In Burkholderia Xenovorans

The search for effectors of novel transcriptional regulators is a challenging task. Here, we present the prediction and validation of an effector for a novel transcriptional regulator (TR). The clustering of genes around the gene coding for Bxe_A0425, a TR in Burkholderia xenovorans LB400 and its closest orthologs, suggests the conservation of a functional operon composed a several open reading frames from which a TR, a transporter, and two oxidoreductases can be easily identified. A search of operons containing these functional components revealed a remarkable resemblance of this system to the evolutionarily convergent and functionally conserved operons found in Escherichia coli, Bacillus subtilis, Staphylococcus xylosus and Pseudomonas aeruginosa. These operons are involved in the uptake and catabolism of choline to create the potent osmo-protectant molecule glycine betaine. We used frontal affinity chromatography coupled to mass spectrometry to screen for the binding of choline and other intermediates of the glycine biosynthesis pathway to the TR Bxe_0425. We then used electrophoretic mobility shift assays to confirm our results. We found that choline was the sole metabolite binding to this TR and identified choline as an effector molecule for Bxe_A0425. These findings suggest that this operon in B. xenovoransis involved in the uptake and catabolism of choline to protect the organism from osmotic stress.