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Journal of Bacteriology, February 2008, p. 946-953, Vol. 190, No. 3
0021-9193/08/$08.00+0     doi:10.1128/JB.01571-06
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

RpoS Expression and the General Stress Response in Azotobacter vinelandii during Carbon and Nitrogen Diauxic Shifts{triangledown} ,{dagger}

James R. Sandercock and William J. Page*

Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G2E9

Received 10 October 2006/ Accepted 8 November 2007

The general stress response mediated by the sigma factor RpoS is important for survival of bacteria in adverse environments. A mutant unable to produce RpoS was constructed using the diazotrophic bacterium Azotobacter vinelandii strain UW. Under nondesiccating, solid-medium growth conditions the wild type was culturable for 16.5 years, while the rpoS mutant remained viable for only 10 months. The rpoS mutant exhibited reduced survival compared to the wild type following hydrogen peroxide stress, and stationary phase cells were killed rapidly by 15 mM H2O2. Three catalases (Kat1, Kat2, and Kat3) were expressed in the wild type under the conditions used. Kat2 was expressed in exponential phase during shake flask growth and could be induced under highly aerated conditions in all growth phases, suggesting that there was induction by reactive oxygen intermediates. Kat3 was possibly an isoform of Kat2. In contrast, Kat1 was expressed in an RpoS-dependent manner during the mid-exponential to late stationary phases. RpoS expression did not occur exclusively in stationary phase but was influenced by changes in carbon and nitrogen source availability. There was 26- to 28-fold induction of the RpoS protein during acetate-to-glucose and ammonium-to-N2 diauxic shifts. Following recovery of growth on the alternative carbon or nitrogen source, RpoS protein concentrations declined rapidly to a basal level. However, rpoS mRNA levels did not correlate directly to RpoS levels, suggesting that there was posttranscriptional regulation. Evidence obtained using the RpoS-dependent reporter Kat1 suggested that there is regulation of the RNAP:RpoS holoenzyme at the level of complex formation or activity.

* Corresponding author. Mailing address: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G2E9. Phone: (780) 492-4758. Fax: (780) 492-7033. E-mail: bill.page{at}ualberta.ca

{triangledown} Published ahead of print on 30 November 2007.

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

Journal of Bacteriology, February 2008, p. 946-953, Vol. 190, No. 3
0021-9193/08/$08.00+0     doi:10.1128/JB.01571-06
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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