Abstract
Acetone-butanol-ethanol (ABE) fermentation by clostridia has shown promise for industrial-scale production of biobutanol. However, the continuous ABE fermentation suffers from low product yield, titer, and productivity. Systems analysis of the continuous ABE fermentation will offer insights into its metabolic pathway as well as into optimal fermentation design and operation. For the ABE fermentation in continuous Clostridium acetobutylicum culture, this paper presents a kinetic model that includes the effects of key metabolic intermediates and enzymes as well as culture pH, product inhibition, and glucose inhibition. The kinetic model is used for elucidating the behavior of the ABE fermentation under the conditions that are most relevant to continuous cultures. To this end, dynamic sensitivity analysis is performed to systematically investigate the effects of culture conditions, reaction kinetics, and enzymes on the dynamics of the ABE production pathway. The analysis provides guidance for future metabolic engineering and fermentation optimization studies.
Highlights
Recent concerns about depleting crude oil reserves, environmental impact of fossil fuels, and national security threats have prompted increased interest in development of alternative fuels [1]
For the ABE fermentation in continuous Clostridium acetobutylicum culture, this paper presents a kinetic model that includes the effects of key metabolic intermediates and enzymes as well as culture pH, product inhibition, and glucose inhibition
The aim of this paper is to present a kinetic model for the ABE fermentation in continuous C. acetobutylicum that can be used for elucidating the behavior of the fermentation under culture conditions most relevant to continuous ABE production
Summary
Recent concerns about depleting crude oil reserves, environmental impact of fossil fuels, and national security threats have prompted increased interest in development of alternative fuels [1]. Biobutanol can be produced by bacteria of genus Clostridium (C.) in a process known as the acetone-butanol-ethanol (ABE) fermentation. The ABE fermentation is a biphasic process that converts sugars into acids (acetate, butyrate) and solvents (acetone, butanol, ethanol). Acidogenesis, the primary products are the acidic metabolites. As the metabolism shifts to solventogenesis, the acids are assimilated into the ABE solvents. While this metabolic shift is associated with changes in the extracellular pH and the onset of sporulation, its exact mechanism is not understood [8, 9]. Recent experiments have shown that enzyme regulation plays a key role in the phase shift [10]. The ABE fermentation is dependent on various culture conditions such as pH [8, 11, 12], nutrient shortage [9, 13], product inhibition [14, 15], PLOS ONE | DOI:10.1371/journal.pone.0158243 August 3, 2016
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