A transcriptional study of acidogenic chemostat cells of Clostridium acetobutylicum--solvent stress caused by a transient n-butanol pulse

Abstract

The main product of the anaerobic fermentative bacterium Clostridium acetobutylicum is n-butanol, an organic solvent with severe toxic effects on the cells. Therefore, the identification of the molecular factors related to n-butanol stress constitutes a major strategy for furthering the understanding of the biotechnological production of n-butanol, an important industrial biofuel. Previous reports concerning n-butanol stress in C. acetobutylicum dealt exclusively with batch cultures. In this study, for the first time a comprehensive transcriptional analysis of n-butanol-stressed C. acetobutylicum was conducted using stable steady state acidogenic chemostat cultures. A total of 358 differentially expressed genes were significantly affected by n-butanol stress. Similarities, such as the upregulation of general stress genes, and differences in gene expression were compared in detail with earlier DNA microarrays performed in batch cultivation experiments. The main result of this analysis was the observation that genes involved in amino acid and nucleotide biosynthesis, as well as genes for specific transport systems were upregulated by n-butanol. Our results exclude any transcriptional response triggered by exogenous pH changes or solventogenic n-butanol formation. Finally, our data suggest that metabolic flux through the glycerolipid biosynthetic pathway increases, confirming that C. acetobutylicum modifies the cytoplasmic membrane composition in response to n-butanol stress.