Abstract
Volatility of oil prices along with major concerns about climate change, oil supply security and depleting reserves have sparked renewed interest in the production of fuels from renewable resources. Recent advances in synthetic biology provide new tools for metabolic engineers to direct their strategies and construct optimal biocatalysts for the sustainable production of biofuels. Metabolic engineering and synthetic biology efforts entailing the engineering of native and de novo pathways for conversion of biomass constituents to short-chain alcohols and advanced biofuels are herewith reviewed. In the foreseeable future, formal integration of functional genomics and systems biology with synthetic biology and metabolic engineering will undoubtedly support the discovery, characterization, and engineering of new metabolic routes and more efficient microbial systems for the production of biofuels.
Highlights
The increased use of fossil fuels has caused greenhouse gas emissions and created undesirable damage to the environment
While the concept of biofuels was conceived in the 1970s when the world faced a large-scale oil crisis, recent advances in synthetic biology [3,4], metabolic engineering [4,5,6,7], and systems biology [8,9] have generated a renewed interest in the production of biofuels
E. coli genes encoding for xylose isomerase, xylulokinase, transketolase, and transaldolase were expressed in Z. mobilis CP4, allowing for growth on xylose with 86% ethanol yield [42]
Summary
The increased use of fossil fuels has caused greenhouse gas emissions and created undesirable damage to the environment. More recently Kim et al reported homoethanol fermentation from xylose and glucose using native E. coli genes with yields up to 82%, by combining the activity of pyruvate dehydrogenase, usually aerobic, with the alcohol dehydrogenase one [64] Arabinose is another pentose sugar obtained upon deconstruction of biomass. A mutant yeast strain which anaerobically converts arabinose to ethanol in batch fermentation was reported [67] This strain was obtained by introducing the bacterial pathway for arabinose utilization from Lactobacillus plantarum, overexpressing S. cerevisiae genes encoding the nonoxidative PPP enzymes, and subsequent evolutionary engineering. Efficient utilization of sugar mixtures Given the high complexity of lignocellulosic hydrolysates, metabolic engineering has been extensively used to develop recombinant strains of traditionally used ethanol producers such as S. cerevisiae and Z. mobilis, and enteric bacteria such as E. coli, that will efficiently ferment mixtures of glucose and xylose, and in some cases, arabinose [101]. The development of detailed kinetic models that include accurate regulatory network parameters will facilitate the identification of enzymatic bottlenecks in the metabolic pathways that could be harnessed in order to achieve biofuels overproduction
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