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Applied and Environmental Microbiology, February 2009, p. 981-990, Vol. 75, No. 4
0099-2240/09/$08.00+0     doi:10.1128/AEM.01652-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Acid and Base Stress and Transcriptomic Responses in Bacillus subtilis^,

Jessica C. Wilks,^1, Ryan D. Kitko,^1, Sarah H. Cleeton,¹ Grace E. Lee,¹ Chinagozi S. Ugwu,¹ Brian D. Jones,² Sandra S. BonDurant,³ and Joan L. Slonczewski^1*

Department of Biology, Kenyon College, Gambier, Ohio 43022,¹ Department of Mathematics, Kenyon College, Gambier, Ohio 43022,² Gene Expression Center, University of Wisconsin, Madison, Wisconsin 53706³

Received 17 July 2008/ Accepted 16 December 2008

Acid and base environmental stress responses were investigated in Bacillus subtilis. B. subtilis AG174 cultures in buffered potassium-modified Luria broth were switched from pH 8.5 to pH 6.0 and recovered growth rapidly, whereas cultures switched from pH 6.0 to pH 8.5 showed a long lag time. Log-phase cultures at pH 6.0 survived 60 to 100% at pH 4.5, whereas cells grown at pH 7.0 survived <15%. Cells grown at pH 9.0 survived 40 to 100% at pH 10, whereas cells grown at pH 7.0 survived <5%. Thus, growth in a moderate acid or base induced adaptation to a more extreme acid or base, respectively. Expression indices from Affymetrix chip hybridization were obtained for 4,095 protein-encoding open reading frames of B. subtilis grown at external pH 6, pH 7, and pH 9. Growth at pH 6 upregulated acetoin production (alsDS), dehydrogenases (adhA, ald, fdhD, and gabD), and decarboxylases (psd and speA). Acid upregulated malate metabolism (maeN), metal export (czcDO and cadA), oxidative stress (catalase katA; OYE family namA), and the SigX extracytoplasmic stress regulon. Growth at pH 9 upregulated arginine catabolism (roc), which generates organic acids, glutamate synthase (gltAB), polyamine acetylation and transport (blt), the K⁺/H⁺ antiporter (yhaTU), and cytochrome oxidoreductases (cyd, ctaACE, and qcrC). The SigH, SigL, and SigW regulons were upregulated at high pH. Overall, greater genetic adaptation was seen at pH 9 than at pH 6, which may explain the lag time required for growth shift to high pH. Low external pH favored dehydrogenases and decarboxylases that may consume acids and generate basic amines, whereas high external pH favored catabolism-generating acids.

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* Corresponding author. Mailing address: Department of Biology, Kenyon College, 202 N. College Road, Gambier, OH 43022. Phone: (740) 427-5397. Fax: (740) 427-5741. E-mail: slonczewski{at}kenyon.edu

Published ahead of print on 29 December 2008.

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

These two authors contributed equally to this work.

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Applied and Environmental Microbiology, February 2009, p. 981-990, Vol. 75, No. 4
0099-2240/09/$08.00+0     doi:10.1128/AEM.01652-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.