Chaotropicity: a key factor in product tolerance of biofuel-producing microorganisms
•Disruption of cellular macromolecules by alcohols limits biofuel fermentations.•Lignocellulose hydrolysis also generates chaotropic inhibitors (vanillin, phenolics, etc.).•Macromolecule disruption and stabilization by chaotropic and kosmotropic substances can be quantified.•Diverse measures can be used to mitigate or neutralize chaotrope-induced stress in microbes.•For example, stabilizing substances/conditions, physiological manipulation, strain selection, product removal.
Fermentation products can chaotropically disorder macromolecular systems and induce oxidative stress, thus inhibiting biofuel production. Recently, the chaotropic activities of ethanol, butanol and vanillin have been quantified (5.93, 37.4, 174 kJ kg−1 m−1 respectively). Use of low temperatures and/or stabilizing (kosmotropic) substances, and other approaches, can reduce, neutralize or circumvent product-chaotropicity. However, there may be limits to the alcohol concentrations that cells can tolerate; e.g. for ethanol tolerance in the most robust Saccharomyces cerevisiae strains, these are close to both the solubility limit (<25%, w/v ethanol) and the water-activity limit of the most xerotolerant strains (0.880). Nevertheless, knowledge-based strategies to mitigate or neutralize chaotropicity could lead to major improvements in rates of product formation and yields, and also therefore in the economics of biofuel production.
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Journal: Current Opinion in Biotechnology - Volume 33, June 2015, Pages 228–259