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Journal of Bacteriology, September 2006, p. 6661-6668, Vol. 188, No. 18
0021-9193/06/$08.00+0     doi:10.1128/JB.00641-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Thiamine Is Synthesized by a Salvage Pathway in Rhizobium leguminosarum bv. viciae Strain 3841

R. Karunakaran, K. Ebert, S. Harvey, M. E. Leonard, V. Ramachandran, and P. S. Poole*

School of Biological Sciences, University of Reading, Reading RG6 6AJ, United Kingdom

Received 5 May 2006/ Accepted 10 July 2006

In the absence of added thiamine, Rhizobium leguminosarum bv. viciae strain 3841 does not grow in liquid medium and forms only "pin" colonies on agar plates, which contrasts with the good growth of Sinorhizobium meliloti 1021, Mesorhizobium loti 303099, and Rhizobium etli CFN42. These last three organisms have thiCOGE genes, which are essential for de novo thiamine synthesis. While R. leguminosarum bv. viciae 3841 lacks thiCOGE, it does have thiMED. Mutation of thiM prevented formation of pin colonies on agar plates lacking added thiamine, suggesting thiamine intermediates are normally present. The putative functions of ThiM, ThiE, and ThiD are 4-methyl-5-(ß-hydroxyethyl) thiazole (THZ) kinase, thiamine phosphate pyrophosphorylase, and 4-amino-5-hydroxymethyl-2-methyl pyrimidine (HMP) kinase, respectively. This suggests that a salvage pathway operates in R. leguminosarum, and addition of HMP and THZ enabled growth at the same rate as that enabled by thiamine in strain 3841 but elicited no growth in the thiM mutant (RU2459). There is a putative thi box sequence immediately upstream of the thiM, and a gfp-mut3.1 fusion to it revealed the presence of a promoter that is strongly repressed by thiamine. Using fluorescent microscopy and quantitative reverse transcription-PCR, it was shown that thiM is expressed in the rhizosphere of vetch and pea plants, indicating limitation for thiamine. Pea plants infected by RU2459 were not impaired in nodulation or nitrogen fixation. However, colonization of the pea rhizosphere by the thiM mutant was impaired relative to that of the wild type. Overall, the results show that a thiamine salvage pathway operates to enable growth of Rhizobium leguminosarum in the rhizosphere, allowing its survival when thiamine is limiting.

* Corresponding author. Mailing address: School of Biological Sciences, University of Reading, Whiteknights, P.O. Box 228, Reading RG6 6AJ, United Kingdom. Phone: (44) 118 378 8895. Fax: (44) 118 378 6671. E mail: p.s.poole{at}reading.ac.uk.

Journal of Bacteriology, September 2006, p. 6661-6668, Vol. 188, No. 18
0021-9193/06/$08.00+0     doi:10.1128/JB.00641-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Karunakaran, R., Ramachandran, V. K., Seaman, J. C., East, A. K., Mouhsine, B., Mauchline, T. H., Prell, J., Skeffington, A., Poole, P. S. (2009). Transcriptomic Analysis of Rhizobium leguminosarum Biovar viciae in Symbiosis with Host Plants Pisum sativum and Vicia cracca. J. Bacteriol. 191: 4002-4014 [Abstract] [Full Text]  
  • White, J. P., Prell, J., Ramachandran, V. K., Poole, P. S. (2009). Characterization of a {gamma}-Aminobutyric Acid Transport System of Rhizobium leguminosarum bv. viciae 3841. J. Bacteriol. 191: 1547-1555 [Abstract] [Full Text]  


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