Pathway dissection, regulation, engineering and application: lessons learned from biobutanol production by solventogenic clostridia

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-butanolethanol (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.

Transcriptomic and Phenotypic Analysis of a spoIIE Mutant in Clostridium beijerinckii

“…Once the spores are mature, the solvent producing cells lyse, and the metabolically inactive spores are left behind (Al-Hinai et al, 2015). That is why in industry, spores are seen as undesirable (Tracy et al, 2012;Li et al, 2020), and many efforts were made to engineer asporogenous solvent producing strains (Scotcher and Bennett, 2005;Bi et al, 2011;Al-Hinai et al, 2014). However, the sporulation process and the associated regulatory network in these microorganisms are still poorly characterized (Patakova et al, 2013).…”

Thermophysical Properties of 1-Butanol at High Pressures

“…provided that ∆p = p 2 -p 1 is small. The initial values of u(T, p 0 = 0.101325 MPa), ρ(T, p 0 = 0.101325 MPa), and c p (T, p 0 = 0.101325 MPa) were used in the Equation (8). The specific isobaric heat capacity at p 2 is acquired by:…”

“…The International Energy Agency forecasts that the demand for biofuels will be 690 million tons per year in 2050 [1]. The strong renewed interest in 1-butanol as a sustainable vehicle fuel has led to the development of improved biobutanol production processes including both biotechnological production processes as well as separation techniques [1,[7][8][9][10][11]. Various species of the Clostridium bacteria such as C. acetobutylicum, C. beijerinckii, C. saccharoperbutylacetonicum and C. saccharobutylicum are mainly used for 1-butanol production [7].…”

“…However, Clostridium can be genetically modified in order to increase its ability to produce 1-butanol, and others have extracted enzymes from bacteria and incorporated them into other microbes such as yeast in order to turn them into 1-butanol production. Yeast (for example, Sacharomyces cerevisiae [8]) and Escherichia coli, one of the major bacteria in the human gut, are believed to be easily grown on an industrial scale [7]. The produced biobutanol can be separated by several methods including adsorption, gas stripping pervaporation, and liquid-liquid extraction using, for example, ionic liquids [6,8,11].…”

“…Yeast (for example, Sacharomyces cerevisiae [8]) and Escherichia coli, one of the major bacteria in the human gut, are believed to be easily grown on an industrial scale [7]. The produced biobutanol can be separated by several methods including adsorption, gas stripping pervaporation, and liquid-liquid extraction using, for example, ionic liquids [6,8,11]. The next stage is the test of the properties of biobutanol in terms of its use in engines.…”