Roles of Three Transporters, CbcXWV, BetT1, and BetT3, in Pseudomonas aeruginosa Choline Uptake for Catabolism

Abstract

ABSTRACTPseudomonas aeruginosauses the quaternary amine choline as a carbon source, osmoprotectant, and macromolecular precursor. The importance of choline inP. aeruginosaphysiology is highlighted by the presence of multiple known and putative choline transporters encoded within its genome. This report describes the relative roles of three choline transporters, the ABC transporter CbcXWV and two symporters, BetT1 and BetT3, inP. aeruginosagrowth on choline under osmotic conditions that are physiologically relevant to eukaryotic hosts. The increased lag phases exhibited by the ΔbetT1and ΔbetT1ΔbetT3mutants relative to the wild type upon transfer to medium with choline as a sole carbon source suggested roles for BetT1 and BetT3 in cells newly exposed to choline. BetT3 and CbcXWV, but not BetT1, were sufficient to support growth on choline.betT1andbetT3expression was regulated by the repressor BetI and choline, whereascbcXWVexpression was induced by the activator GbdR and glycine betaine. The data support a model in which, upon transfer to a choline-based medium, the glycine betaine derived from choline taken up by BetT1 and BetT3 promotes subsequent GbdR-mediatedcbcXWVinduction. Furthermore, growth data indicated that the relative contributions of each transporter varied under different conditions, as BetT1 and CbcXWV were the primary choline transporters under hypo-osmolar conditions whereas BetT3 was the major choline transporter under hyperosmolar conditions. This work represents the first systematic approach to unravel the mechanisms of choline uptake inP. aeruginosa, which has the most complex bacterial choline uptake systems characterized to date.