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Journal of Bacteriology, August 2002, p. 4466-4474, Vol. 184, No. 16
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.16.4466-4474.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

The nptA Gene of Vibrio cholerae Encodes a Functional Sodium-Dependent Phosphate Cotransporter Homologous to the Type II Cotransporters of Eukaryotes

Michael Lebens,1* Patrik Lundquist,2 Lars Söderlund,3 Mirjana Todorovic,1 and Nils I. A. Carlin3

Department of Medical Microbiology and Immunology, University of Göteborg, SE-431 46 Göteborg,1 Department of Oral Biochemistry, University of Göteborg, SE-405 30 Göteborg,2 Department of Molecular Biology, SBL Vaccin AB, SE-105 21 Stockholm, Sweden3

Received 29 January 2002/ Accepted 16 May 2002

The nptA gene of Vibrio cholerae has significant protein sequence homology with type II sodium-dependent phosphate (Pi) cotransporters found in animals but not previously identified in prokaryotes. The phylogeny of known type II cotransporter sequences indicates that nptA may be either an ancestral gene or a gene acquired from a higher eukaryotic source. The gene was cloned into an expression vector under the control of an inducible promoter and expressed in Escherichia coli. The results demonstrate that nptA encodes a functional protein with activity similar to that of the animal enzyme, catalyzing high-affinity, sodium-dependent Pi uptake with comparable affinities for both sodium and phosphate ions. Furthermore, the activity of NptA is influenced by pH, again in a manner similar to that of the NaPi-2a subtype of the animal enzyme, although it lacks the corresponding REK motif thought to be responsible for this phenomenon. Pi uptake activity, a component of which appeared to be sodium dependent, was increased in V. cholerae by phosphate starvation. However, it appears from the use of a reporter gene expressed from the nptA promoter that none of this activity is attributable to the induction of expression from nptA. It is thus proposed that the physiological function of NptA protein may be the rapid uptake of Pi in preparation for rapid growth in nutrient-rich environments and that it may therefore play a role in establishing infection.

* Corresponding author. Mailing address: University of Göteborg, Department of Medical Microbiology and Immunology, Guldhedsgatan 10A, S-431 46 Göteborg, Sweden. Phone: 46 31 3424857. Fax: 46 31 820160. E-mail: michael.lebens{at}microbio.gu.se.

Journal of Bacteriology, August 2002, p. 4466-4474, Vol. 184, No. 16
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.16.4466-4474.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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