K-109. Base Resistance and Acid Resistance of Bacillus subtilis Are Associated with Transcriptomic Responses Including High-pH Upregulation of Respiratory Complexes and Arginine Catabolism

G. E. Lee1, S. H. Cleeton1, C. S. Ugwu1, J. C. Wilks1, S. S. BonDurant2, B. D. Jones1, J. L. Slonczewski1;
1Kenyon Coll., Gambier, OH, 2Univ. of Wisconsin, Madison, WI.

The transcriptomic response of Bacillus subtilis AG174 during vegetative growth in acid or base was tested using Affymetrix B. subtilis genome arrays. The role of adaptive stress in extreme-pH survival was tested. B. subtilis was cultured to log phase at 37o in LBK (100 mM KCl) medium buffered with HOMOPIPES at pH 6, at pH 7, and at pH 9. Log-phase cells grown at pH 6.0 showed 60-100% survival after 2 h exposure at pH 4.5, whereas cells grown at pH 7.0 showed 5-15% survival. Cells grown at pH 9.0 showed 40-100% survival after 2 h at pH 10, whereas cells grown at pH 7.0 showed 1-5% survival. Thus, growth in moderate acid or base induced adaptation to survival in more extreme acid or base, respectively. Acid or base adaptation in B. subtilis may involve transcriptomic responses, as seen in E. coli. Expression indices were obtained for 4,350 genes of B. subtilis expressed at pH 6, pH 7, and pH 9 (five replicate cultures at each pH). High pH (pH 9) strongly up-regulated arginine deaminase catabolism (rocABC and rocDEF) and the respiratory cytochrome oxidase complexes caa3 (ctaA, cBCDEFG) and bd (cydABCD). Arginine catabolism can counteract base stress by consuming amines. The response in B. subtilis differed from Escherichia coli, however, where base up-regulates tryptophan-cysteine deaminase (tnaA) and serine deaminase (sdaA). Up-regulation of respiratory complexes can help the cell maintain proton motive force at high pH, which requires inversion of the pH difference across the membrane in order to maintain internal pH homeostasis. At low pH (pH 6) the operons of unknown function, ydiBCD, ydiGH, and ydiKL were up-regulated. As in E. coli, in B. subtilis acid up-regulated decarboxylases such as arginine decarboxylase speA (formerly cad); but other decarboxylases differed from those up-regulated by acid in E. coli: alpha-acetolactate decarboxylase (alsD), diaminopimelate decarboxylase (lysA), and phosphatidylserine decarboxylase (psd). Overall, B. subtilis pH stress responses showed differences as well as similarities to pH stress in E. coli.