Production of xylo-oligosaccharides with degree of polymerization 3–5 from wheat straw xylan by a xylanase derived from rumen metagenome and utilization by probiotics

Abstract

In this study, a new xylanase gene (RuXyn) was obtained from a rumen metagenome and heterologously expressed in Escherichia coli to produce xylo-oligosaccharides (XOS) as a prebiotic. RuXyn, which belongs to the glycosyl hydrolase 10 (GH10) family, exhibited maximum activity at pH 6.0 and 50 °C, with excellent temperature resistance at 30–50 °C. RuXyn showed preferential hydrolysis of xylan, especially rice straw xylan. RuXyn activity was significantly increased in the presence of 5 mM dithiothreitol, 0.5% Tween-20, and 0.5% Triton X-100 (31%, 37%, and 43%, respectively). Reaction time (10, 15, 30, and 45 min) and dosage (0.15, 0.31, and 0.62 U) of RuXyn affected XOS yield and composition, with a maximum yield at 0.62 U and 30 min. The primary degradation products of wheat straw xylan, resulting from RuXyn activity, were xylotetraose, xylotriose, and xylopentose, which accounted for 33.4%, 33.0%, and 26.4% of the total sugar yield, respectively. The prebiotic effects of XOS were evaluated by in vitro fermentation of XOS using known probiotic Bifidobacterium bifidum and Levilactobacillus brevis strains. Results showed that regardless of incubation time and XOS concentration, XOS stimulated the growth and xylanolytic enzyme secretion of the two probiotics compared to the controls. Supplementation with XOS significantly enhanced lactate production in B. bifidum and L. brevis. Thus, these results indicate that RuXyn is capable of hydrolyzing wheat xylan to produce XOS with a degree of polymerization 3 and 5 and to subsequently promote the growth of probiotics.