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Journal of Bacteriology, May 2009, p. 3132-3141, Vol. 191, No. 9
0021-9193/09/$08.00+0     doi:10.1128/JB.01570-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Mqo, a Tricarboxylic Acid Cycle Enzyme, Is Required for Virulence of Pseudomonas syringae pv. tomato Strain DC3000 on Arabidopsis thaliana{triangledown} ,{dagger}

Eve M. Mellgren,* Andrew P. Kloek,{ddagger} and Barbara N. Kunkel

Washington University in Saint Louis, Department of Biology, 1 Brookings Drive, Campus Box 1137, St. Louis, Missouri 63130

Received 4 November 2008/ Accepted 12 February 2009

Plant pathogenic bacteria, such as Pseudomonas syringae pv. tomato strain DC3000, the causative agent of tomato bacterial speck disease, grow to high levels in the apoplastic space between plant cells. Colonization of plant tissue requires expression of virulence factors that modify the apoplast to make it more suitable for pathogen growth or facilitate adaptation of the bacteria to the apoplastic environment. To identify new virulence factors involved in these processes, DC3000 Tn5 transposon insertion mutants with reduced virulence on Arabidopsis thaliana were identified. In one of these mutants, the Tn5 insertion disrupted the malate:quinone oxidoreductase gene (mqo), which encodes an enzyme of the tricarboxylic acid cycle. mqo mutants do not grow to wild-type levels in plant tissue at early time points during infection. Further, plants infected with mqo mutants develop significantly reduced disease symptoms, even when the growth of the mqo mutant reaches wild-type levels at late stages of infection. Mutants lacking mqo function grow more slowly in culture than wild-type bacteria when dicarboxylates are the only available carbon source. To explore whether dicarboxylates are important for growth of DC3000 in the apoplast, we disrupted the dctA1 dicarboxylate transporter gene. DC3000 mutants lacking dctA1 do not grow to wild-type levels in planta, indicating that transport and utilization of dicarboxylates are important for virulence of DC3000. Thus, mqo may be required by DC3000 to meet nutritional requirements in the apoplast and may provide insight into the mechanisms underlying the important, but poorly understood process of adaptation to the host environment.

* Corresponding author. Mailing address: Washington University in Saint Louis, Department of Biology, 1 Brookings Dr., Campus Box 1137, St. Louis, MO 63130. Phone: (314) 935-4728. Fax: (314) 935-4432. E-mail: mellgren{at}biology2.wustl.edu

{triangledown} Published ahead of print on 27 February 2009.

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

{ddagger} Present address: BioMedical Insights, Inc., 601 Montgomery St., Ste. 518, San Francisco, CA 94111.

Journal of Bacteriology, May 2009, p. 3132-3141, Vol. 191, No. 9
0021-9193/09/$08.00+0     doi:10.1128/JB.01570-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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