A novel xylose isomerase suitable for D-fructose production and synergistic catalysis with D-allulose 3-epimerase for the biosynthesis of D-allulose

The enzyme xylose isomerase is well known for its pivotal role in converting D-glucose into D-fructose. This study reports the characterization of a novel xylose isomerase gene (xylM) from a hot-spring metagenome. This manganese-dependent enzyme (Xyl_M) works efficiently in slightly acidic to alkaline pH ranges of 6.0–9.0. It is a thermoactive enzyme, showing high-level activity in the temperature range of 75–90 °C, with optimum activity at 80 °C. It is a thermostable enzyme, maintaining more than 50 % of its activity even after 13 days of heat exposure at 70 °C. Xyl_M could achieve ∼53 % conversion of D-glucose into D-fructose under optimum conditions. Further, its synergistic activity with D-allulose-3-epimerase resulted in D-allulose synthesis from D-glucose, with a product yield of 94.35 g/L from 500 g/L D-glucose. Henceforth, this is a potential biocatalyst for developing an industrial process for D-fructose production and synergistic catalysis with D-allulose 3-epimerase for D-allulose biosynthesis.