Qualitative 13C-isotopomer analysis characterizes short term and long term effects of butanol and butyric acid stress on the metabolism of Clostridium acetobutylicum

Due to their wide substrate range, solventogenic clostridia are seen as a promising class of organisms for biofuel and commodity chemical production. Clostridium acetobutylicum was historically used for industrial-scale fermentation and remains a potential candidate for butanol and butyric acid production today. However, a major drawback to these processes is the toxic effects of these metabolites on the cells, resulting in low product titers and inducing a metabolite stress response. While several studies have been carried out to understand the transcriptional and translational basis of this stress response, little is known about the impact of butanol and butyric acid stress on the metabolic pathways and fluxes of C. acetobutylicum. Here, we have used parallel labeling experiments and qualitative ¹³C-isotopomer analysis to characterize the short term and long term effects of butanol and butyric acid stress on the metabolism of C. acetobutylicum. We show that while butanol and butyric acid result in lower absolute values of glucose uptake and growth rates, the relative flux distributions remain relatively unchanged under stress. As there is growing evidence that the metabolite stress response is connected to tolerance, this work contributes to a systems understanding of the stress response and its regulation, which may lead to new strategies for achieving higher tolerance in C. acetobutylicum.