The production of chemicals from lignocellulosic biomass has been suggested as a suitable substitute for petrochemicals. However, an inherent challenge in biomass use is the heterogeneity of the substrate, which leads to the presence of mixed sugars after hydrolysis. The fermentation of mixed sugars often leads to poor yields and the generation of several by-products, which makes subsequent further processing more difficult. Therefore, systems biocatalysis has been developed in recent years to meet this challenge. In this work, several novel enzymes with broad substrate promiscuity were identified as suitable biocatalysts in a conversion of using a sequence-based discovery approach D.-xylose and L.-Arabinose, two main components of hemicellulose in plant biomass. These promiscuous enzymes enabled the simultaneous biotransformation of D.-xylose and L.-Arabinose to 1,4-butanediol (BDO) with a maximum production rate of 3 g L.−1 H−1 and a yield of> 95%. This model system was further adapted to the production of α-ketoglutarate (2-KG) from the pentoses using O.2 as a co-substrate for cofactor recycling with a maximum production rate of 4.2 g L.−1 H−1 and a yield of 99%. To check the potential applicability of our system, we tried to scale the BDO and 2-KG production from D.-xylose and L.-arabinose. By simple optimization and reaction technology, we were able to obtain BDO and 2 KG titers of 18 g L−1 and 42 g L.−1with theoretical yields of> 75% and> 99%. One of the promiscuous enzymes identified along with auxiliary promiscuous enzymes was also suitable for stereoconvergent synthesis from a mixture of D.-Glucose and D.-galactose, the predominant sugar in food waste streams and microalgae biomass.

Graphic Summary: Convergent Conversion - Using Promiscuous Biocatalysts for Cell-Free Synthesis of Chemicals from Heterogeneous Biomass

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