Achievements and perspectives to overcome the poor solvent resistance in acetone and butanol-producing microorganisms

Abstract

Anaerobic bacteria such as the solventogenic clostridia can ferment a wide range of carbon sources (e.g., glucose, galactose, cellobiose, mannose, xylose, and arabinose) to produce carboxylic acids (acetic and butyric) and solvents such as acetone, butanol, and ethanol (ABE). The fermentation process typically proceeds in two phases (acidogenic and solventogenic) in a batch mode. Poor solvent resistance by the solventogenic clostridia and other fermenting microorganisms is a major limiting factor in the profitability of ABE production by fermentation. The toxic effect of solvents, especially butanol, limits the concentration of these solvents in the fermentation broth, limiting solvent yields and adding to the cost of solvent recovery from dilute solutions. The accepted dogma is that toxicity in the ABE fermentation is due to chaotropic effects of butanol on the cell membranes of the fermenting microorganisms, which poses a challenge for the biotechnological whole-cell bio-production of butanol. This mini-review is focused on (1) the effects of solvents on inhibition of cell metabolism (nutrient transport, ion transport, and energy metabolism); (2) cell membrane fluidity, death, and solvent tolerance associated with the ability of cells to tolerate high concentrations of solvents without significant loss of cell function; and (3) strategies for overcoming poor solvent resistance in acetone and butanol-producing microorganisms.

Enhanced butanol production by eukaryotic Saccharomyces cerevisiae engineered to contain an improved pathway

“…6) Using the several genes of C. acetobutylicum involved in the biosynthesis of 1-butanol, engineered Escherichia coli under aerobic conditions has been constructed. 7) E. coli has also been shown to exhibit a tolerance to up to 1.5% butanol, 8) which is comparable with the tolerance exhibited by clostridia. On the other hand, among eukaryotic cells, yeast S. cerevisiae has been described as an ideal host for butanol production.…”

Design of Sustainable Supply Chains for the Agrifood Sector: A Holistic Research Framework

“…With the cloudy consistency of milk dust powder coupled with the presence of large particles, it is likely that pockets of microbial activity and inactivity or low activity may be distributed in the culture. In addition, the pH of ABE fermentation broth is significantly influenced by the ratio of protonated acetic and butyric acids to their unprotonated forms (Farell et al 2004;Bryant and Blaschek 1988;Russell and Diez-Gonzalez 1998;Ezeji et al 2010). Given the higher acid levels detected in cultures of C. acetobutylicum and C. beijerinckii grown on milk dust powder medium, relative to cultures grown on glucose, it may be deduced that acid reassimilation was impaired in the milk dust powder medium ( Figure 3A and B).…”

Can Microbially Derived Advanced Biofuels Ever Compete with Conventional Bioethanol? A Critical Review

“…Robust microbial strains with high product yields, titers, and tolerance to products and other inhibitory compounds are prerequisites to the economic competitiveness of advanced biofuels (Connor and Liao 2008;Nicolaou et al 2010;Dunlop 2011;Lamsen and Atsumi 2012;Bujis et al 2013;Dellomonaco et al 2010;Ezeji et al 2010). However, the current titer and yield of advanced biofuel molecules is substantially lower than first-generation ethanol (Table 3).…”

“…Therefore, alternative techniques were developed that enable instantaneous product removal from the broth, which not only enriches the concentration of solvent prior to distillation, but allows continuous fermentation by maintaining a low enough titer to reduce the microbial toxicity. Some prominent strategies used for in situ product removal include gas stripping, solvent extraction, and pervaporation (Table 4) (Ezeji et al 2003;Ezeji et al 2010;Dürre 2007;Abdehagh et al 2013). (Ezeji et al 2004;Dürre 2007;Inokuma et al 2010;Baez et al 2011;Abdehagh et al 2013;Xue et al 2014 In gas stripping, nitrogen or fermentation gases are bubbled through the fermentation broth to strip away the products (de Vrije et al 2013;Xue et al 2013b;2014a;2014b;Ezeji et al 2003).…”