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Applied and Environmental Microbiology, September 2008, p. 5276-5284, Vol. 74, No. 17
0099-2240/08/$08.00+0     doi:10.1128/AEM.00883-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Global Transcriptional Response of the Alkali-Tolerant Cyanobacterium Synechocystis sp. Strain PCC 6803 to a pH 10 Environment{triangledown} ,{dagger}

Tina C. Summerfield and Louis A. Sherman*

Department of Biological Sciences, Purdue University, 201 S. University St., Hansen Hall, West Lafayette, Indiana 47907

Received 17 April 2008/ Accepted 26 June 2008

Many cyanobacterial strains are able to grow at a pH range from neutral to pH 10 or 11. Such alkaline conditions favor cyanobacterial growth (e.g., bloom formation), and cyanobacteria must have developed strategies to adjust to changes in CO2 concentration and ion availability. Synechocystis sp. strain PCC 6803 exhibits similar photoautotrophic growth characteristics at pH 10 and pH 7.5, and we examined global gene expression following transfer from pH 7.5 to pH 10 to determine cellular adaptations at an elevated pH. The strategies used to develop homeostasis at alkaline pH had elements similar to those of many bacteria, as well as components unique to phototrophic microbes. Some of the response mechanisms previously identified in other bacteria included upregulation of Na+/H+ antiporters, deaminases, and ATP synthase. In addition, upregulated genes encoded transporters with the potential to contribute to osmotic, pH, and ion homeostasis (e.g., a water channel protein, a large-conductance mechanosensitive channel, a putative anion efflux transporter, a hexose/proton symporter, and ABC transporters of unidentified substrates). Transcriptional changes specific to photosynthetic microbes involved NADH dehydrogenases and CO2 fixation. The pH transition altered the CO2/HCO3– ratio within the cell, and the upregulation of three inducible bicarbonate transporters (BCT1, SbtA, and NDH-1S) likely reflected a response to this perturbed ratio. Consistent with this was increased transcript abundance of genes encoding carboxysome structural proteins and carbonic anhydrase. Interestingly, the transition to pH 10 resulted in increased abundance of transcripts of photosystem II genes encoding extrinsic and low-molecular-weight polypeptides, although there was little change in photosystem I gene transcripts.

* Corresponding author. Mailing address: Department of Biological Sciences, Purdue University, 201 S. University St., Hansen Hall, West Lafayette, IN 47907. Phone: (765) 494-8106. Fax: (765) 496-1496. E-mail: lsherman{at}purdue.edu

{triangledown} Published ahead of print on 7 July 2008.

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

Applied and Environmental Microbiology, September 2008, p. 5276-5284, Vol. 74, No. 17
0099-2240/08/$08.00+0     doi:10.1128/AEM.00883-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Hedger, J., Holmquist, P. C., Leigh, K. A., Saraff, K., Pomykal, C., Summers, M. L. (2009). Illumination stimulates cAMP receptor protein-dependent transcriptional activation from regulatory regions containing class I and class II promoter elements in Synechocystis sp. PCC 6803. Microbiology 155: 2994-3004 [Abstract] [Full Text]  
  • Shcolnick, S., Summerfield, T. C., Reytman, L., Sherman, L. A., Keren, N. (2009). The Mechanism of Iron Homeostasis in the Unicellular Cyanobacterium Synechocystis sp. PCC 6803 and Its Relationship to Oxidative Stress. Plant Physiol. 150: 2045-2056 [Abstract] [Full Text]  


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