Tolerance in Solventogenic Clostridia for Enhanced Butanol Production: Genetic Mechanisms and Recent Strain Engineering Advances

Biobutanol is a promising candidate for replacing fossil fuels due to its superior properties compared to ethanol. Solventogenic clostridia can naturally produce biobutanol among other valuable chemicals. Lignocellulosic material stands out as a promising source for biobutanol production, avoiding competition with food production and making use of residues from both agroindustry and forestry activities. However, Clostridium strains are subject to different chemical stressors, including oxygen, self-product inhibition, inhibitors generated during biomass pretreatment and hydrolysis, and others. Recent advances in genetic engineering tools have enabled the metabolic engineering of Clostridium strains to increase their robustness and tolerance to these stressors. This review provides a summary of the various types of inhibitors, the genetic mechanisms related to tolerance, and recent strain engineering efforts for tolerance enhancement. In addition, we offer a valuable perspective on the future research directions in this area.