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Journal of Bacteriology, December 2006, p. 8469-8478, Vol. 188, No. 24
0021-9193/06/$08.00+0     doi:10.1128/JB.01278-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Role of RelGsu in Stress Response and Fe(III) Reduction in Geobacter sulfurreducens{triangledown} ,{dagger}

Laurie N. DiDonato,1* Sara A. Sullivan,1 Barbara A. Methé,2 Kelly P. Nevin,1 Reg England,3 and Derek R. Lovley1

Department of Microbiology, University of Massachusetts, Amherst, Massachusetts 01003,1 The Institute for Genomic Research, Rockville, Maryland 20850,2 Department of Biological Science, University of Central Lancashire, Preston, Lancashire, PR1 2HE, United Kingdom3

Received 14 August 2006/ Accepted 27 September 2006

Geobacter species are key members of the microbial community in many subsurface environments in which dissimilatory metal reduction is an important process. The genome of Geobacter sulfurreducens contains a gene designated relGsu, which encodes a RelA homolog predicted to catalyze both the synthesis and the degradation of guanosine 3',5'-bispyrophosphate (ppGpp), a regulatory molecule that signals slow growth in response to nutrient limitation in bacteria. To evaluate the physiological role of RelGsu in G. sulfurreducens, a relGsu mutant was constructed and characterized, and ppGpp levels were monitored under various conditions in both the wild-type and relGsu mutant strains. In the wild-type strain, ppGpp and ppGp were produced in response to acetate and nitrogen deprivation, whereas exposure to oxygen resulted in an accumulation of ppGpp alone. Neither ppGpp nor ppGp could be detected in the relGsu mutant. The relGsu mutant consistently grew to a higher cell density than the wild type in acetate-fumarate medium and was less tolerant of oxidative stress than the wild type. The capacity for Fe(III) reduction was substantially diminished in the mutant. Microarray and quantitative reverse transcription-PCR analyses indicated that during stationary-phase growth, protein synthesis genes were up-regulated in the relGsu mutant and genes involved in stress responses and electron transport, including several implicated in Fe(III) reduction, were down-regulated in the mutant. The results are consistent with a role for RelGsu in regulating growth, stress responses, and Fe(III) reduction in G. sulfurreducens under conditions likely to be prevalent in subsurface environments.

* Corresponding author. Mailing address: Department of Microbiology, University of Massachusetts, Morrill Science Center, 639 N. Pleasant St. Amherst, MA 01003. Phone: (413) 577-2439. Fax: (413) 545-1578. E-mail: lauried{at}microbio.umass.edu.

{triangledown} Published ahead of print on 13 October 2006.

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

Journal of Bacteriology, December 2006, p. 8469-8478, Vol. 188, No. 24
0021-9193/06/$08.00+0     doi:10.1128/JB.01278-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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