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Journal of Bacteriology, June 2009, p. 4002-4014, Vol. 191, No. 12
0021-9193/09/$08.00+0     doi:10.1128/JB.00165-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Transcriptomic Analysis of Rhizobium leguminosarum Biovar viciae in Symbiosis with Host Plants Pisum sativum and Vicia cracca{triangledown} ,{dagger}

R. Karunakaran,1 V. K. Ramachandran,2 J. C. Seaman,2 A. K. East,1 B. Mouhsine,2 T. H. Mauchline,2 J. Prell,1 A. Skeffington,1 and P. S. Poole1*

Department of Molecular Microbiology, John Innes Centre, Colney Lane, Norwich, NR4 7UH United Kingdom,1 School of Biological Sciences, University of Reading, Reading, RG6 6AJ United Kingdom2

Received 6 February 2009/ Accepted 3 April 2009

Rhizobium leguminosarum bv. viciae forms nitrogen-fixing nodules on several legumes, including pea (Pisum sativum) and vetch (Vicia cracca), and has been widely used as a model to study nodule biochemistry. To understand the complex biochemical and developmental changes undergone by R. leguminosarum bv. viciae during bacteroid development, microarray experiments were first performed with cultured bacteria grown on a variety of carbon substrates (glucose, pyruvate, succinate, inositol, acetate, and acetoacetate) and then compared to bacteroids. Bacteroid metabolism is essentially that of dicarboxylate-grown cells (i.e., induction of dicarboxylate transport, gluconeogenesis and alanine synthesis, and repression of sugar utilization). The decarboxylating arm of the tricarboxylic acid cycle is highly induced, as is {gamma}-aminobutyrate metabolism, particularly in bacteroids from early (7-day) nodules. To investigate bacteroid development, gene expression in bacteroids was analyzed at 7, 15, and 21 days postinoculation of peas. This revealed that bacterial rRNA isolated from pea, but not vetch, is extensively processed in mature bacteroids. In early development (7 days), there were large changes in the expression of regulators, exported and cell surface molecules, multidrug exporters, and heat and cold shock proteins. fix genes were induced early but continued to increase in mature bacteroids, while nif genes were induced strongly in older bacteroids. Mutation of 37 genes that were strongly upregulated in mature bacteroids revealed that none were essential for nitrogen fixation. However, screening of 3,072 mini-Tn5 mutants on peas revealed previously uncharacterized genes essential for nitrogen fixation. These encoded a potential magnesium transporter, an AAA domain protein, and proteins involved in cytochrome synthesis.

* Corresponding author. Mailing address: Department of Molecular Microbiology, John Innes Centre, Colney Lane, Norwich, NR4 7UH, United Kingdom. Phone: (44) 1603 450750. Fax: (44) 1603 450778. E-mail: philip.poole{at}bbsrc.ac.uk

{triangledown} Published ahead of print on 17 April 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, June 2009, p. 4002-4014, Vol. 191, No. 12
0021-9193/09/$08.00+0     doi:10.1128/JB.00165-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Prell, J., White, J. P., Bourdes, A., Bunnewell, S., Bongaerts, R. J., Poole, P. S. (2009). Legumes regulate Rhizobium bacteroid development and persistence by the supply of branched-chain amino acids. Proc. Natl. Acad. Sci. USA 106: 12477-12482 [Abstract] [Full Text]  


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