Supplementary Material for: Genome-Wide Gene Expression Analysis of the Switch between Acidogenesis and Solventogenesis in Continuous Cultures of <i>Clostridium acetobutylicum</i>

<i>Clostridium acetobutylicum</i> is able to switch from acidogenic growth to solventogenic growth. We used phosphate-limited continuous cultures that established acidogenic growth at pH 5.8 and solventogenic growth at pH 4.5. These cultures allowed a detailed transcriptomic study of the switch from acidogenesis to solventogenesis that is not superimposed by sporulation and other growth phase-dependent parameters. These experiments led to new insights into the physiological role of several genes involved in solvent formation. The <i>adc </i>gene for acetone decarboxylase is upregulated well before the rest of the <i>sol</i> locus during the switch, and pyruvate decarboxylase is induced exclusively for the period of this switch. The aldehyde-alcohol dehydrogenase gene <i>adhE1 </i>located in the <i>sol </i>operon is regulated antagonistically to the paralog <i>adhE2 </i>that is expressed during acidogenic conditions. A similar antagonistic pattern can be seen with the two paralogs of thiolase genes, <i>thlA </i>and <i>thlB</i>. Interestingly, the genes coding for the putative cellulosome in <i>C. acetobutylicum </i>are exclusively transcribed throughout solventogenic growth. The genes for stress response are only induced during the shift but not in the course of solventogenesis when butanol is present in the culture. Finally, the data clearly indicate that solventogenesis is independent from sporulation.