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Applied and Environmental Microbiology, October 2002, p. 4710-4716, Vol. 68, No. 10
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.10.4710-4716.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Multiple Deletions of the Osmolyte Transporters BetL, Gbu, and OpuC of Listeria monocytogenes Affect Virulence and Growth at High Osmolarity

Henrike H. Wemekamp-Kamphuis,1,2 Jeroen A. Wouters,1,2,{dagger} Roy D. Sleator,3 Cormac G. M. Gahan,3 Colin Hill,3 and Tjakko Abee1,2*

Laboratory of Food Microbiology, Wageningen University,1 Wageningen Centre for Food Sciences (WCFS), Wageningen, The Netherlands,2 National Food Biotechnology Centre, University College, Cork, Ireland3

Received 14 February 2002/ Accepted 4 July 2002

The success of Listeria monocytogenes as a food-borne pathogen owes much to its ability to survive a variety of stresses, both in the food environment and, after ingestion, within the animal host. Growth at high salt concentrations is attributed mainly to the accumulation of organic solutes such as glycine betaine and carnitine. We characterized L. monocytogenes LO28 strains with single, double, and triple deletions in the osmolyte transport systems BetL, Gbu, and OpuC. When single deletion mutants were tested, Gbu was found to have the most drastic effect on the rate of growth in brain heart infusion (BHI) broth with 6% added NaCl. The highest reduction in growth rate was found for the triple mutant LO28BCG ({Delta}betL {Delta}opuC {Delta}gbu), although the mutant was still capable of growth under these adverse conditions. In addition, we analyzed the growth and survival of this triple mutant in an animal (murine) model. LO28BCG showed a significant reduction in its ability to cause systemic infection following peroral coinoculation with the wild-type parent. Altering OpuC alone resulted in similar effects (R. D. Sleator, J. Wouters, C. G. M. Gahan, T. Abee, and C. Hill, Appl. Environ. Microbiol. 67:2692-2698, 2001), leading to the assumption that OpuC may play an important role in listerial pathogenesis. Analysis of the accumulation of osmolytes revealed that betaine is accumulated up to 300 µmol/g (dry weight) when grown in BHI broth plus 6% NaCl whereas no carnitine accumulation could be detected. Radiolabeled-betaine uptake studies revealed an inability of BGSOE ({Delta}betL {Delta}gbu) and LO28BCG to transport betaine. Indeed, for LO28BCG, no accumulated betaine was found, but carnitine was accumulated in this strain up to 600 µmol/g (dry weight) of cells, indicating the presence of a possible fourth osmolyte transporter.

* Corresponding author. Mailing address: Laboratory of Food Microbiology, Wageningen University, Bomenweg 2, 6703 HD Wageningen, The Netherlands. Phone: 31-317-484981. Fax: 31-317-484978. E-mail: Tjakko.Abee{at}micro.fdsci.wau.nl.

{dagger} Present address: Department of Flavour, Nutrition & Ingredients, NIZO food research, 6710 BA, Ede, The Netherlands.

Applied and Environmental Microbiology, October 2002, p. 4710-4716, Vol. 68, No. 10
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.10.4710-4716.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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