Abstract
The global energy crisis and limited supply of petroleum fuels have rekindled the interest in utilizing a sustainable biomass to produce biofuel. Butanol, an advanced biofuel, is a superior renewable resource as it has a high energy content and is less hygroscopic than other candidates. At present, the biobutanol route, employing acetone–butanol–ethanol (ABE) fermentation in Clostridium species, is not economically competitive due to the high cost of feedstocks, low butanol titer, and product inhibition. Based on an analysis of the physiological characteristics of solventogenic clostridia, current advances that enhance ABE fermentation from strain improvement to product separation were systematically reviewed, focusing on: (1) elucidating the metabolic pathway and regulation mechanism of butanol synthesis; (2) enhancing cellular performance and robustness through metabolic engineering, and (3) optimizing the process of ABE fermentation. Finally, perspectives on engineering and exploiting clostridia as cell factories to efficiently produce various chemicals and materials are also discussed.
Highlights
Due to the limited supply of petroleum oil, mounting environmental concerns, and an awareness of the energy crisis, it has become necessary to investigate a renewable biofuel as a substitute for oil [1, 2]
The thiolase of C. acetobutylicum was engineered to reduce sensitivity towards coenzyme A (CoA‐SH), significantly alleviating feedback inhibition through three amino acid substitutions (R133G, H156N, G222V) and, correspondingly, increasing the production of ethanol and butanol by 46% and 18%, respectively, acetone production was similar to the vector control strain [136]
Optimization of culture conditions Effects of exogenous additives on acetone–butanol– ethanol (ABE) fermentation According to the metabolic pathway and physiological characteristics, various organic acids could serve as alternative substrates for butanol production, and maintain the robust expression of enzymes associated during the solventogenic and solventogenesis phase [169, 170]
Summary
Due to the limited supply of petroleum oil, mounting environmental concerns, and an awareness of the energy crisis, it has become necessary to investigate a renewable biofuel as a substitute for oil [1, 2]. SolR can positively control sporulation and solvent production, so that the combination of inactivating SolR and overexpressing aad was used to improve cellular performance, increasing the production of butanol, acetone, and ethanol to 17.6 g/L, 8.2 g/L, and 2.2 g/L, respectively [103].
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