Anaerobic fermentation of glycerol: a path to economic viability for the biofuels industry.

Department of Chemical and Biomolecular Engineering, Rice University, 6100 Main Street, MS-362, Houston, TX 77005, USA.
Current Opinion in Biotechnology (Impact Factor: 8.04). 07/2007; 18(3):213-9. DOI: 10.1016/j.copbio.2007.05.002
Source: PubMed

ABSTRACT Although biofuels such as biodiesel and bioethanol represent a secure, renewable and environmentally safe alternative to fossil fuels, their economic viability is a major concern. The implementation of biorefineries that co-produce higher value products along with biofuels has been proposed as a solution to this problem. The biorefinery model would be especially advantageous if the conversion of byproducts or waste streams generated during biofuel production were considered. Glycerol-rich streams generated in large amounts by the biofuels industry, especially during the production of biodiesel, present an excellent opportunity to establish biorefineries. Once considered a valuable 'co-product', crude glycerol is rapidly becoming a 'waste product' with a disposal cost attributed to it. Given the highly reduced nature of carbon in glycerol and the cost advantage of anaerobic processes, fermentative metabolism of glycerol is of special interest. This review covers the anaerobic fermentation of glycerol in microbes and the harnessing of this metabolic process to convert abundant and low-priced glycerol streams into higher value products, thus creating a path to viability for the biofuels industry. Special attention is given to products whose synthesis from glycerol would be advantageous when compared with their production from common sugars.

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    ABSTRACT: Metabolic engineered targeting for increased succinate production in Escherichia coli using glycerol as a low cost carbon source has attracted global attention in recent years. Succinate production in engineered E. coli has progressed significantly using an experimental trial and error approach. The use of a model-guided, targeted metabolic gene knockout prediction for increased succinate production from glycerol under anaerobic conditions in E. coli still remains largely underexplored. In this study, we applied a model-driven, targeted glpC/b2243 in silico metabolic gene knockout using E. coli genome scale model iJO1366 under the OptFlux software platform with the aim of predicting high succinate flux. The results indicated that the mutant model lacking the glpC/b2243 gene will demonstrate increased succinate flux that is 30% higher than its wild-type control model. We can hypothesize that an additional NADH molecule was generated following the deletion of the gene and/or the alternatively preferred GldA-DhaKLM fermentative route for glycerol metabolism in E. coli may have been activated. Although the exact metabolic mechanism involved in increasing the succinate flux still remains obscure; the current study informs other studies that a model-driven, metabolic glpC/b2243 gene knockout could be applicable in filling our knowledge gap using a comprehensive experimental inquiry in the future; leading to a better understanding of the underlying metabolic function of this gene in relation to succinate production in E. coli from glycerol.
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    ABSTRACT: The use of genome-scale models of Escherichia coli to guide future metabolic engineering strategies for increased succinic acid production has received renewed attention in recent years. Substrate selectivity such as glycerol is of particular interest, because it is currently generated as a by-product of biodiesel industry and therefore can serve as a solitary carbon source. However, study on the prediction of gene knockout candidates for enhanced succinate production from glycerol using Minimization of Metabolic Adjustment Algorithm with the OptFlux software platform remained underexplored. Here, we show that metabolic engineering interventions by gene knockout simulation of some pyruvate dissimilating pathway enzymes (lactate dehydrogenase A and pyruvate formate lyase A) using E. coli genome-scale model can reduce acetate flux and enhance succinic acid production under anaerobic conditions. The introduced genetic perturbations led to substantial improvement in succinate flux of about 597% on glycerol and 120% on glucose than that of the wild-type control strain BSKO. We hypothesize that the deletion of pyruvate formate lyase A (pflA) in E. coli can led to no acetate production from glucose, lower acetate production from glycerol and increased succinic acid productivities on both substrates under anaerobic conditions. Our results demonstrate a predicted increase in succinate production (597% higher than the wild-type model) among others, from glycerol after deletion of pflA/b0902 gene in E. coli genome-scale model. This would open up a novel platform for model-guided experimental inquiry and/or allow a comprehensive biological discovery on the metabolic processes of pflA in E. coli for succinate production when glycerol is the substrate.
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    ABSTRACT: Multiple entry selections of big bluestems and three native C4 grass species, including switchgrass, miscanthus, and Conservation Reserve Program (CRP) mixture grass, were evaluated for their chemical composition and ethanol yields via diluted sulfuric acid pretreatment following simultaneous saccharification and fermentation (SSF). Big bluestem and switchgrass had a similar glucan content that was significantly higher than miscanthus and CRP grass. Big bluestem had the highest average mass recovery (55.56%) after acid pretreatment, and miscanthus had the lowest mass recovery (46.3%). A positive correlation was observed between glucan recovery and mass recovery. No significant difference in average efficiency of SSF was observed among four native grasses, but ethanol yields from big bluestem entries, which averaged 26.2%, were consistently greater than the other three grasses. The highest ethanol yield among the 10 entries was from big bluestem cultivar KAW (27.7%). Approximately 0.26 kg ethanol with 9.4 g/L concentration can be produced from 1 kg of big bluestem biomass under current processing conditions. A negative relationship exists between lignin content and the efficiency of SSF with R = −0.80, and a positive relationship exists between ethanol yield and glucan content with R = 0.71.
    Energy 03/2015; DOI:10.1016/ · 4.16 Impact Factor

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