Simultaneous co-fermentation of mixed sugars: a promising strategy for producing cellulosic ethanol.

Department of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign, Urbana, IL 61821, USA.
Trends in Biotechnology (Impact Factor: 10.04). 02/2012; 30(5):274-82. DOI: 10.1016/j.tibtech.2012.01.005
Source: PubMed

ABSTRACT The lack of microbial strains capable of fermenting all sugars prevalent in plant cell wall hydrolyzates to ethanol is a major challenge. Although naturally existing or engineered microorganisms can ferment mixed sugars (glucose, xylose and galactose) in these hydrolyzates sequentially, the preferential utilization of glucose to non-glucose sugars often results in lower overall yield and productivity of ethanol. Therefore, numerous metabolic engineering approaches have been attempted to construct optimal microorganisms capable of co-fermenting mixed sugars simultaneously. Here, we present recent findings and breakthroughs in engineering yeast for improved ethanol production from mixed sugars. In particular, this review discusses new sugar transporters, various strategies for simultaneous co-fermentation of mixed sugars, and potential applications of co-fermentation for producing fuels and chemicals.

  • [Show abstract] [Hide abstract]
    ABSTRACT: We here describe a unique β-D-glucosidase (BGL; Blon_0625) derived from Bifidobacterium longum subsp. infantis ATCC 15697. The Blon_0625 gene was expressed by recombinant Escherichia coli. Purified recombinant Blon_0625 retains hydrolyzing activity against both p-nitrophenyl-β-D-glucopyranoside (pNPG; 17.3 ± 0.24 U mg−1) and p-nitrophenyl-β-D-xylopyranoside (pNPX; 16.7 ± 0.32 U mg−1) at pH 6.0, 30˚C. To best of our knowledge, no previously described BGL retains the same level of both pNPGase and pNPXase activity. Furthermore, Blon_0625 also retains the activity against 4-nitrophenyl-α-l-arabinofranoside (pNPAf; 5.6 ± 0.09 U mg−1). In addition, the results of the degradation of phosphoric acid swollen cellulose (PASC) or xylan using endoglucanase from Thermobifida fusca YX (Tfu_0901) or xylanase from Kitasatospora setae KM-6054 (KSE_59480) show that Blon_0625 acts as a BGL and as a β-D-xylosidase (XYL) for hydrolyzing oligosaccharides. These results clearly indicate that Blon_0625 is a multi-functional glycoside hydrolase which retains the activity of BGL, XYL, and also α-l-arabinofuranosidase. Therefore, the utilization of multi-functional Blon_0625 may contribute to facilitating the efficient degradation of lignocellulosic materials and help enhance bioconversion processes.
    Enzyme and Microbial Technology 01/2014; · 2.97 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Sustainable production of energy, fuels, organic chemicals and polymers from biomass in an integrated biorefinery is extremely important to reduce enslavement on limited fossil fuels. In the present article, the biomass was classified into four general types based on their origin: energy crops, agricultural residues and waste, forestry waste and residues and industrial and municipal wastes. The article further elucidates the chemistry of various types of biomass used in the biorefinery. The biorefinery was classified into three broad categories based on the chemistry of biomass: triglyceride, sugar and starchy and lignocellulosic. The article further presents a comprehensive outlines of opportunities and recent trends of each type of biorefinery. A brief overview of original and revised list of platform chemicals, their sources from biomass and derivative potentials were also articulated. The article also provides comparisons of different types of biorefinery, broad challenges and availability of biomass. Furthermore, the article provides an overview of hydrocarbon biorefinery for production of hydrocarbon fuels and building block chemicals from biomass.
    Renewable and Sustainable Energy Reviews 01/2015; 43:1427-1445. · 5.51 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Simultaneous utilization of mixed sugars is one of the major challenges for biofuel production utilizing lignocellulosic biomass as feedstock. Our previous work proved that the oleaginous yeast Cryptococcus curvatus could efficiently produce lipids, the precursors of hydrocarbons with high energy density, from lignocellulosic hydrolysates. However, the strain's capability of simultaneously utilizing primary sugars was still unknown. Thus, this work comprehensively explored the co-utilization of glucose, xylose and cellobiose by C. curvatus. The results indicated that the consumption of both xylose and cellobiose was repressed by glucose, while xylose and cellobiose could be simultaneously consumed at similar rates. The total sugar consumption rates remained constant at about 0.6 g L−1 h−1 regardless of the sugar composition in the mixtures, and the cell biomass and lipid production by C. curvatus cultured on the different sugar mixtures were similar. Moreover, compared with glucose and xylose, cellobiose could lead to higher dry cell weights and lipid yields, suggesting an excellent carbon source for lipid production. Based on these findings, this study demonstrated an effective approach for alleviating glucose repression for microbial lipid production by C. curvatus through xylose/cellobiose co-utilization which would greatly contribute to a more efficient and economical cellulosic biofuel production.
    Biomass and Bioenergy 11/2014; · 3.41 Impact Factor