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首页> 外文期刊>Applied and Environmental Microbiology >Engineering Filamentous Fungi for Conversion of d-Galacturonic Acid to l-Galactonic Acid
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Engineering Filamentous Fungi for Conversion of d-Galacturonic Acid to l-Galactonic Acid

机译：工程丝状真菌，用于将d-半乳糖醛酸转化为l-半乳糖醛酸

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d-Galacturonic acid, the main monomer of pectin, is an attractive substrate for bioconversions, since pectin-rich biomass is abundantly available and pectin is easily hydrolyzed. l-Galactonic acid is an intermediate in the eukaryotic pathway for d-galacturonic acid catabolism, but extracellular accumulation of l-galactonic acid has not been reported. By deleting the gene encoding l-galactonic acid dehydratase (lgd1 or gaaB) in two filamentous fungi, strains were obtained that converted d-galacturonic acid to l-galactonic acid. Both Trichoderma reesei Δlgd1 and Aspergillus niger ΔgaaB strains produced l-galactonate at yields of 0.6 to 0.9 g per g of substrate consumed. Although T. reesei Δlgd1 could produce l-galactonate at pH 5.5, a lower pH was necessary for A. niger ΔgaaB. Provision of a cosubstrate improved the production rate and titer in both strains. Intracellular accumulation of l-galactonate (40 to 70 mg g biomass?1) suggested that export may be limiting. Deletion of the l-galactonate dehydratase from A. niger was found to delay induction of d-galacturonate reductase and overexpression of the reductase improved initial production rates. Deletion of the l-galactonate dehydratase from A. niger also delayed or prevented induction of the putative d-galacturonate transporter An14g04280. In addition, A. niger ΔgaaB produced l-galactonate from polygalacturonate as efficiently as from the monomer.
机译：果胶的主要单体d-半乳糖醛酸是一种具有吸引力的生物转化底物，因为富含果胶的生物质可大量获得，且果胶易于水解。 1-半乳糖酸是d-半乳糖醛酸分解代谢的真核途径的中间体，但尚未报道1-半乳糖醛酸的细胞外蓄积。通过删除两个丝状真菌中编码l-半乳糖酸脱水酶（ lgd1 或 gaaB ）的基因，获得了将d-半乳糖醛酸转化为l-半乳糖酸的菌株。里氏木霉Δ lgd1 和黑曲霉Δ gaaB 菌株均产生l-半乳糖酸酯，每克消耗的底物产量为0.6至0.9克。尽管里氏木霉Δ lgd1 在pH 5.5时可生成l-半乳糖酸酯，但较低的pH值对于黑曲霉Δ gaaB 是必需的。提供共底物提高了两种菌株的生产率和滴度。 l-半乳糖酸酯（40至70 mg g生物质？1 ）在细胞内的积累表明出口可能受到限制。发现从黑曲霉（A.niger）中删除l-半乳糖酸脱水酶延迟了d-半乳糖醛酸还原酶的诱导，并且还原酶的过表达提高了初始生产率。从黑曲霉中删除l-半乳糖酸脱水酶也延迟或阻止了推定的d-半乳糖醛酸转运蛋白An14g04280的诱导。另外，黑曲霉Δ gaaB 由聚半乳糖醛酸酯生产α-半乳糖酸酯的效率与由单体一样有效。

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