Category Archives: Advances in Biochemical Engineering/Biotechnology

Engineering Arabinose Utilization in S. cerevisiae

The first attempt to introduce an L-arabinose utilization pathway in S. cere­visiae by heterologous expression of the complete E. coli L-arabinose pathwaydid not result in appreciable arabinose utilization [70], most likely due to the absence of functional expression of the L-arabinose isomerase. It was only when the E. coli araA gene encoding the L-arabinose isomerase was substi­tuted by the corresponding […]

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Outlook

Functional expression in S. cerevisiae of a highly active fungal XI has paved the way for metabolic engineering of this yeast towards high-yield, rapid production of ethanol from D-xylose under fully anaerobic conditions. On theoretical grounds, this XI-based approach is superior to the extensively studied xylose reductase/xylitol dehydrogenase strategy. While considerable experimental proof to substantiate this statement has been obtained […]

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Strain Construction for Utilization of C5 Sugars

An early attempt was made to construct a xylose-utilizing strain of Z. mo — bilis by Liu et al. [45,46] involving expression of genes for xylose isomerase (XI), xylulokinase (XK) and the xylose transport protein from X. albilineans XA1-1. Although the recombinant strain was shown to possess both XI and XK activity, it was unable to grow on xylose as […]

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European Union

For the member states of the European Union, the primary policy tool behind the development of a bioethanol industry is the Directive on the promotion of the use of biofuels for transport (Directive 2003/30/EC) [31]. The motiva­tions behind this Directive include improving the security of energy supply, and reducing the environmental impact of the transportation sector [32]. The Directive mandates […]

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Glycolytic Flux

In addition to the transport flux and the flux through the initial pentose­converting enzymes, the “pulling” effect [55] of the flux through enzymatic reactions downstream of xylitol, as well as through glycolysis, appears to be equally important for ethanolic pentose fermentation. It was early recognized that the presence of glucose during xylose fermentation enhanced the gly­colytic activity [122-124]. Furthermore, it […]

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Utilized Substrates

The utility of KO11 for production of ethanol from biomass has been demon­strated with multiple substrates including, but not limited to, rice hulls [19], sugar cane bagasse [20], agricultural residues [20], Pinus sp. hydrolysate [21], corn cobs, hulls and AFEX-pretreated fibers [22,23], orange peel [12], wil­low [24], pectin-rich beet pulp [25], sweet whey [26], brewery waste [27], and cotton gin […]

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Discussion and Conclusions

As outlined in the earlier reviews and summarized in Table 3, wild-type strains of Z. mobilis (and their mutants) can convert simple sugars to ethanol at faster rates and higher yields compared to yeasts. However, the ethanol industry has traditionally used yeasts, and despite the apparent advantages of Z. mobilis, there appears to be little incentive for change with sugar […]

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Performance of Commercial Fungal Preparations at Elevated Temperatures

The activities of commercial reference preparations were first measured at higher temperatures in order to evaluate their general performance and to es­timate the role of the background activities originating from the production strain. The hydrolysis of the pretreated spruce substrate by the commercial preparations (with and without added в-glucosidase, BG) at various tempera­tures from 50 to 70 °C was estimated […]

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One-Step Conversion of D-Xylose into D-Xylulose via Xylose Isomerase

In view of the intrinsic redox restrictions associated with the combined in­troduction of xylose reductase and xylitol dehydrogenase into S. cerevisiae, it is relevant to explore alternative metabolic engineering strategies. As will be discussed below, expression of heterologous genes for xylose isomerase (an enzyme that does not naturally occur in S. cerevisiae) offers such an alterna­tive [14]. In the following […]

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Reducing the Requirement for Fungal Cellulases

Cellulose is organized into insoluble crystalline ribbons with extensive hydro­gen bonds between strands [98,99]. This structure is not easily hydrated and the fungal cellulase enzymes used for hydrolysis have low catalytic rates in comparison to other glycosidases. Thus, the cost of these enzymes is a ma­jor consideration in cellulose utilization [100]. An additional challenge is the feedback inhibition of cellulose […]

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