The Escherichia coli SLC26 homologue YchM (DauA) is a C4-dicarboxylic acid transporter

The SLC26/SulP (solute carrier/sulphate transporter) proteins are a ubiquitous superfamily of secondary anion transporters. Prior studies have focused almost exclusively on eukaryotic members and bacterial members are frequently classified as sulphate transporters based on their homology with SulP proteins from plants and fungi. In this study we have examined the function and physiological role of the Escherichia coli Slc26 homologue, YchM. We show that there is a clear YchM-dependent growth defect when succinate is used as the sole carbon source. Using an in vivo succinate transport assay, we show that YchM is the sole aerobic succinate transporter active at acidic pH. We demonstrate that YchM can also transport other C4-dicarboxylic acids and that its substrate specificity differs from the well-characterized succinate transporter, DctA. Accordingly ychM was re-designated dauA (dicarboxylic acid uptake system A). Finally, our data suggest that DauA is a protein with transport and regulation activities. This is the first report that a SLC26/SulP protein acts as a C4-dicarboxylic acid transporter and an unexpected new function for a prokaryotic member of this transporter family.