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Journal of Bacteriology, November 2007, p. 7643-7652, Vol. 189, No. 21
0021-9193/07/$08.00+0     doi:10.1128/JB.00920-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

RelA-Dependent (p)ppGpp Production Controls Exoenzyme Synthesis in Erwinia carotovora subsp. atroseptica{triangledown}

Jinhong Wang,§ Noemie Gardiol, Tom Burr,{dagger} George P. C. Salmond, and Martin Welch*

Department of Biochemistry, Tennis Court Road, University of Cambridge, Cambridge CB2 1QW, United Kingdom

Received 12 June 2007/ Accepted 22 August 2007

In this report, we investigate the link between nutrient limitation, RelA-mediated (p)ppGpp production, and virulence in the phytopathogen Erwinia carotovora subsp. atroseptica. A relA null mutant (JWC7) was constructed by allelic exchange, and we confirmed that, unlike the wild-type progenitor, this mutant did not produce elevated levels of (p)ppGpp upon nutrient downshift. However, (p)ppGpp production could be restored in strain JWC7 during nutrient limitation by supplying relA in trans. During growth on exoenzyme-inducing minimal medium, the relA mutant showed a diminution in secreted pectate lyase and protease activities and a severe defect in motility. The relA mutant was also impaired in its ability to cause rot in potato tubers. In the presence of serine hydroxamate (a competitive inhibitor of seryl tRNA synthase and a potent inducer of the stringent response in wild-type E. carotovora subsp. atroseptica), exoenzyme production was essentially abolished in JWC7 but could be restored in the presence of plasmid-borne relA. The inhibition of exoenzyme production in JWC7 caused by serine hydroxamate could not be overcome by addition of the quorum-sensing signal molecule, N-3-oxohexanoyl-L-homoserine lactone. Quantitative reverse transcription-PCR analysis of selected RNA species confirmed that the effects of relA on secreted pectate lyase activity and motility could be attributed to a reduction in transcription of the corresponding genes. We conclude that nutrient limitation is a potent environmental cue that triggers (p)ppGpp-dependent exoenzyme production in E. carotovora subsp. atroseptica. Furthermore, our data suggest that nutrient limitation [or rather, (p)ppGpp accumulation] is a prerequisite for effective quorum-sensing-dependent activation of exoenzyme production.

* Corresponding author. Mailing address: Department of Biochemistry, Tennis Court Road, University of Cambridge, Cambridge CB2 1QW, United Kingdom. Phone: 44 (0)1223 333 653. Fax: 44 (0)1223 333 345. E-mail: mw240{at}mole.bio.cam.ac.uk

{triangledown} Published ahead of print on 31 August 2007.

§ Present address: Department of Veterinary Medicine, Madingley Road, University of Cambridge, Cambridge CB3 0ES, United Kingdom.

Present address: Ludwig Institute for Cancer Research, Lausanne Branch, Ch. des Boveresses 155, 1066 Epalinges, Switzerland.

{dagger} Present address: Geneservice Ltd., 2 Cambridge Science Park, Milton Road, Cambridge, CB4 0FE, United Kingdom.

Journal of Bacteriology, November 2007, p. 7643-7652, Vol. 189, No. 21
0021-9193/07/$08.00+0     doi:10.1128/JB.00920-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

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