DNA pulldown assays were performed as previously described 43. Briefly, the biotin-labeled DNA fragment containing the promoter region of chsR was amplified from Vibrio cholerae O1 El Tor strain E12382 genomic DNA. The biotinylated bait DNA was bound to streptavidin-coated Dynabeads (catalog no. 11205D; Invitrogen), followed by incubation with crude extracts obtained from Vibrio cholerae O1 El Tor WT cells. After washing extensively with the nonspecific competitor poly (dI-dC) at a low salt concentration, bound proteins were released by elution buffer containing 500 mM NaCl. The eluted proteins were separated by SDS‒PAGE and stained with Coomassie brilliant blue. Proteins were excised from the gel and analyzed by matrix-assisted laser desorption ionization–time-of-flight tandem mass spectrometry (MALDI-TOF MS/MS) analysis after tryptic digestion. Sequence and peptide fingerprint data were analyzed using the NCBI database.