Abstract
BackgroundLignocellulose biomass has been investigated as a feedstock for second generation biofuels and other value-added products. Some of the processes for biofuel production utilize cellulases and hemicellulases to convert the lignocellulosic biomass into a range of soluble sugars before fermentation with microorganisms such as yeast Saccharomyces cerevisiae. One of these sugars is l-arabinose, which cannot be utilized naturally by yeast. The first step in l-arabinose catabolism is its transport into the cells, and yeast lacks a specific transporter, which could perform this task.ResultsWe identified Trire2_104072 of Trichoderma reesei as a potential l-arabinose transporter based on its expression profile. This transporter was described already in 2007 as d-xylose transporter XLT1. Electrophysiology experiments with Xenopus laevis oocytes and heterologous expression in yeast revealed that Trire2_104072 is a high-affinity l-arabinose symporter with a Km value in the range of sim 0.1–0.2 mM. It can also transport d-xylose but with low affinity (Kmsim 9 mM). In yeast, l-arabinose transport was inhibited slightly by d-xylose but not by d-glucose in an assay with fivefold excess of the inhibiting sugar. Comparison with known l-arabinose transporters revealed that the expression of Trire2_104072 enabled yeast to uptake l-arabinose at the highest rate in conditions with low extracellular l-arabinose concentration. Despite the high specificity of Trire2_104072 for l-arabinose, the growth of its T. reesei deletion mutant was only affected at low l-arabinose concentrations.ConclusionsDue to its high affinity for l-arabinose and low inhibition by d-glucose or d-xylose, Trire2_104072 could serve as a good candidate for improving the existing pentose-utilizing yeast strains. The discovery of a highly specific l-arabinose transporter also adds to our knowledge of the primary metabolism of T. reesei. The phenotype of the deletion strain suggests the involvement of other transporters in l-arabinose transport in this species.
Highlights
Lignocellulose biomass has been investigated as a feedstock for second generation biofuels and other value-added products
Trire2_104072 is highly expressed on l‐arabinose in ARA1‐dependent manner To identify potential l-arabinose transporters we analyzed a published transcriptome data set for the expression of sugar transporter genes [36]
In the study by Benocci et al, T. reesei strain QM9414 and its xyr1, ara1 and xyr1 ara1 deletion mutants were cultured on medium containing l-arabinose or d-galactose as the sole carbon source, and subjected to transcriptome analysis [36]
Summary
Lignocellulose biomass has been investigated as a feedstock for second generation biofuels and other value-added products. Some of the processes for biofuel production utilize cellulases and hemicellulases to convert the lignocellulosic biomass into a range of soluble sugars before fermentation with microorganisms such as yeast Saccharomyces cerevisiae. Complete substrate utilization is required for an economically competitive biofuel process, but wild-type S. cerevisiae is not able to consume these pentose sugars [6] To circumvent this issue, numerous studies have investigated metabolic engineering of yeast for the utilization of d-xylose and l-arabinose Some pectin-rich waste biomasses from the food industry (e.g. orange peels, sugar beet pulp) contain higher amounts of l-arabinose than d-xylose [10] These biomasses have gained interest as industrial feedstocks due to their low lignin content, which decreases the need for pretreatment [11, 12]. They are abundantly available at low cost, and their utilization does not interfere with food production [11,12,13]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
