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Applied and Environmental Microbiology, October 2005, p. 5771-5778, Vol. 71, No. 10
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.10.5771-5778.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Identification and Characterization of Di- and Tripeptide Transporter DtpT of Listeria monocytogenes EGD-e

Jeroen A. Wouters ,^1,, Torsten Hain,^2, Ajub Darji,² Eric Hüfner,^1,2 Henrike Wemekamp-Kamphuis,¹ Trinad Chakraborty,² and Tjakko Abee^1*

Wageningen Centre for Food Sciences (WCFS) and Laboratory of Food Microbiology, Wageningen University, Bomenweg 2, 6703 HD Wageningen, The Netherlands,¹ Institute of Medical Microbiology, University of Giessen, 35392 Giessen, Germany²

Received 17 September 2004/ Accepted 10 May 2005

Listeria monocytogenes is a gram-positive intracellular pathogen responsible for opportunistic infections in humans and animals. Here we identified and characterized the dtpT gene (lmo0555) of L. monocytogenes EGD-e, encoding the di- and tripeptide transporter, and assessed its role in growth under various environmental conditions as well as in the virulence of L. monocytogenes. Uptake of the dipeptide Pro-[¹⁴C]Ala was mediated by the DtpT transporter and was abrogated in a dtpT isogenic deletion mutant. The DtpT transporter was shown to be required for growth when the essential amino acids leucine and valine were supplied as peptides. The protective effect of glycine- and proline-containing peptides during growth in defined medium containing 3% NaCl was noted only in L. monocytogenes EGD-e, not in the dtpT mutant strain, indicating that the DtpT transporter is involved in salt stress protection. Infection studies showed that DtpT contributes to pathogenesis in a mouse infection model but has no role in bacterial growth following infection of J774 macrophages. These studies reveal that DptT may contribute to the virulence of L. monocytogenes.

J.A.W. and T.H. contributed equally to this work.

Present address: Department of Flavour, NIZO food research, P.O. Box 20, 6710 BA Ede, The Netherlands.