Abstract
Lignocellulosic biomass is an attractive sustainable carbon source for fermentative production of bioethanol. In this context, use of microbial consortia consisting of substrate-selective microbes is advantageous as it eliminates the negative impacts of glucose catabolite repression. In this study, a detailed in silico analysis of bioethanol production from glucose-xylose mixtures of various compositions by coculture fermentation of xylose-selective Escherichia coli strain ZSC113 and glucose-selective wild-type Saccharomyces cerevisiae is presented. Dynamic flux balance models based on available genome-scale metabolic networks of the microorganisms have been used to analyze bioethanol production and the maximization of ethanol productivity is addressed by computing optimal aerobic-anaerobic switching times. A set of genetic engineering strategies for ethanol overproduction by E. coli strain ZSC113 have been evaluated for their efficiency in the context of batch coculture process. Finally, simulations are carried out to determine the pairs of genetically modified E. coli strain ZSC113 and S. cerevisiae that significantly enhance ethanol productivity in batch coculture fermentation.
Highlights
Environmental concerns and energy security issues have renewed our interest in bioethanol as a substitute for petroleum derived liquid transportation fuel
In order to assess the validity of the developed dynamic flux balance analysis (dFBA) model, we compare the model predictions for measurable state variables against experimental observations collected from the literature and Figure 1 shows the validation results
Combinations of genetic modifications that we investigate are R01058 + Δack, R01058 + Δpfl, R00845 + Δack, and R00845 + Δpfl for various glucose/xylose mixtures
Summary
Environmental concerns and energy security issues have renewed our interest in bioethanol as a substitute for petroleum derived liquid transportation fuel. Lignocellulosic biomasses, the most abundant biological material on earth, are an attractive alternative feedstock for bioethanol production It essentially contains cellulose (∼45% of dry weight), hemicellulose (∼30% of dry weight), and lignin (∼25% of dry weight) [1]. Hydrolysis of cellulose produces fermentable hexose sugar (glucose) and hydrolysis of hemicellulose produces a mixture of hexose (glucose) and pentose sugars (xylose, arabinose) Due to this complex composition, the commercial utilization of lignocelluloses as bioethanol feedstock faces many technical and economic challenges. The productivity of the fermentation step can be enhanced by genetic manipulation of traditional strains for consumption of both glucose and xylose [2, 3] or by carrying out coculture fermentation of specialized microbes [4, 5] This second alternative is advantageous as it leads to simultaneous consumption of both glucose and xylose sugars
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