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Journal of Bacteriology, March 2003, p. 1503-1508, Vol. 185, No. 5
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.5.1503-1508.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Two Nucleoside Uptake Systems in Lactococcus lactis: Competition between Purine Nucleosides and Cytidine Allows for Modulation of Intracellular Nucleotide Pools

Jan Martinussen,* Steen L. L. Wadskov-Hansen, and Karin Hammer

Microbial Physiology and Genetics, Biocentrum-DTU, Technical University of Denmark, DK-2800 Lyngby, Denmark

Received 12 August 2002/ Accepted 2 December 2002

A method for measuring internal nucleoside triphosphate pools of lactococci was optimized and validated. This method is based on extraction of 33P-labeled nucleotides with formic acid and evaluation by two-dimensional chromatography with a phosphate buffer system for the first dimension and with an H3BO3-LiOH buffer for separation in the second dimension. We report here the sizes of the ribo- and deoxyribonucleotide pools in laboratory strain MG1363 during growth in a defined medium. We found that purine- and pyrimidine-requiring strains may be used to establish physiological conditions in batch fermentations with altered nucleotide pools and growth rates by addition of nucleosides in different combinations. Addition of cytidine together with inosine to a purine-requiring strain leads to a reduction in the internal purine nucleotide pools and a decreased growth rate. This effect was not seen if cytidine was replaced by uridine. A similar effect was observed if cytidine and inosine were added to a pyrimidine-requiring strain; the UTP pool size was significantly decreased, and the growth rate was reduced. To explain the observed inhibition, the nucleoside transport systems in Lactococcus lactis were investigated by measuring the uptake of radioactively labeled nucleosides. The Km for for inosine, cytidine, and uridine was determined to be in the micromolar range. Furthermore, it was found that cytidine and inosine are competitive inhibitors of each other, whereas no competition was found between uridine and either cytidine or inosine. These findings suggest that there are two different high-affinity nucleoside transporters, one system responsible for uridine uptake and another system responsible for the uptake of all purine nucleosides and cytidine.

* Corresponding author. Mailing address: Microbial Physiology and Genetics, Biocentrum-DTU Building 301, Technical University of Denmark, DK-2800 Lyngby, Denmark. Phone: 45 45 25 24 98. Fax: 45 45 88 26 60. E-mail: jma{at}biocentrum.dtu.dk.

Journal of Bacteriology, March 2003, p. 1503-1508, Vol. 185, No. 5
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.5.1503-1508.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Defoor, E., Kryger, M.-B., Martinussen, J. (2007). The orotate transporter encoded by oroP from Lactococcus lactis is required for orotate utilization and has utility as a food-grade selectable marker. Microbiology 153: 3645-3659 [Abstract] [Full Text]  
  • Nicoloff, H., Elagoz, A., Arsene-Ploetze, F., Kammerer, B., Martinussen, J., Bringel, F. (2005). Repression of the pyr Operon in Lactobacillus plantarum Prevents Its Ability To Grow at Low Carbon Dioxide Levels. J. Bacteriol. 187: 2093-2104 [Abstract] [Full Text]  
  • Jorgensen, C. M., Hammer, K., Martinussen, J. (2003). CTP Limitation Increases Expression of CTP Synthase in Lactococcus lactis. J. Bacteriol. 185: 6562-6574 [Abstract] [Full Text]  


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