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Journal of Bacteriology, September 2006, p. 6622-6628, Vol. 188, No. 18
0021-9193/06/$08.00+0     doi:10.1128/JB.00634-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

DsdX Is the Second D-Serine Transporter in Uropathogenic Escherichia coli Clinical Isolate CFT073

Andrew T. Anfora and Rodney A. Welch*

Department of Medical Microbiology & Immunology, University of Wisconsin—Madison, 1300 University Ave., Room 481 MSC, Madison, Wisconsin 53706

Received 4 May 2006/ Accepted 28 June 2006

D-Serine is an amino acid present in mammalian urine that is inhibitory to Escherichia coli strains lacking a functional dsdA gene. Counterintuitively, a dsdA strain of E. coli clinical isolate CFT073 hypercolonizes the bladder and kidneys of mice relative to wild type during a coinfection in the murine model of urinary tract infection. We are interested in the mechanisms for uptake of D-serine in CFT073. D-Serine enters E. coli K-12 via CycA, the D-alanine transporter and D-cycloserine sensitivity locus. CFT073 cycA can grow on minimal medium with D-serine as a sole carbon source. The dsdX gene of the dsdCXA locus is a likely candidate for an additional D-serine transporter based on its predicted amino acid sequence similarity to gluconate transporters. In minimal medium, CFT073 dsdX can grow on D-serine as a sole carbon source; however, CFT073 dsdX cycA cannot. Additionally, CFT073 dsdXA cycA is not sensitive to inhibitory concentrations of D-serine during growth on glycerol and D-serine minimal medium. D-[14C]serine uptake experiments with CFT073 dsdX cycA harboring dsdX or cycA recombinant plasmids confirm that D-serine is able to enter E. coli cells via CycA or DsdX. In whole-cell D-[14C]serine uptake experiments, DsdX has an apparent Km of 58.75 µM and a Vmax of 75.96 nmol/min/mg, and CycA has an apparent Km of 82.40 µM and a Vmax of 58.90 nmol/min/mg. Only D-threonine marginally inhibits DsdX-mediated D-serine transport, whereas D-alanine, glycine, and D-cycloserine inhibit CycA-mediated D-serine transport. DsdX or CycA is sufficient to transport physiological quantities of D-serine, but DsdX is a D-serine-specific permease.

* Corresponding author. Mailing address: Department of Medical Microbiology & Immunology, University of Wisconsin—Madison, 1300 University Ave., Room 481 MSC, Madison, WI 53706. Phone: (608) 262-7814. Fax: (608) 262-8418. E-mail: rawelch{at}wisc.edu.

Journal of Bacteriology, September 2006, p. 6622-6628, Vol. 188, No. 18
0021-9193/06/$08.00+0     doi:10.1128/JB.00634-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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