Protein that allows transport of D-serine across the inner membrane, does not transport D-alanine nor probably glycine. Is probably a H(+) symporter, as CCCP inhibits transport. Transports D-serine more efficiently than CycA. Uptake of D-serine is inhibited by carbonyl cyanide m-chlorophenylhydrazone (CCCP), and at high concentrations of D-threonine, stimulated by D-cycloserine and not affected by D-alanine or glycine. Single deletion, grows on D-serine, D-serine plus glycerol and D-alanine. A double dsdX-cycA deletion grows in D-serine plus glycerol, but not D-serine or D-alanine alone, growth on D-serine (but not D-alanine) is restored by dsdX, while growth on both D-alanine and D-serine is restored by cycA. Double dsdX-cycA deletion cannot take up D-serine. E.coli CFT073, a uropathogenic strain (UPEC), was originally isolated from urine, which has a high concentration of D-serine. D-serine is toxic to bacteria. The abililty to take up D-serine coupled with the activity of D-serine dehydratase (dsdA) may allow use of this amino acid as a carbon source in a sugar-poor environment. Belongs to the GntP permease family.