Hemicellulose is the second most prevalent polysaccharide in nature, following cellulose, and accounts for nearly one-third of all renewable organic carbon on Earth [1]. Xylan, the principal component of hemicellulose, is extensively found in plant cell walls [2]. Xylan is a heteropolysaccharide consisting of β-1, 4-glycosidic linked xylose monomers, characterized by its complex structure and slow natural degradation. hemicellulases are enzymes that degrade hemicellulose by fully hydrolyzing the linear polysaccharide β-1, 4-xylan into simpler compounds, primarily xylose [3]. This enzyme family includes β-1, 4-endoxylanase, β-xylosidase, α-L-arabinosidase, α-D-glucuronidase, acetylxylanase, and phenolic esterase, all of which catalyze the hydrolysis of xylosidic bonds. These enzymes can degrade xylan hemicellulose, which is abundant in nature. The most crucial enzyme among them is β-1, 4-endoxylanase, which breaks down xylan into smaller oligosaccharides such as xylobiose, along with minor amounts of xylose and arabinose.

Extensive research has documented the production of xylanase by fungi, bacteria, yeast, seaweed [4], seeds, crustaceans, and snails [5], with fungi and bacteria being the primary sources. However, xylanases from different origins exhibit distinct characteristics, leading to varied potential utilization values. Microbial xylanases have attracted significant attention for their potential applications in industries such as food, feed, pulp, and paper, showing considerable promise in enhancing the production of single-cell protein, enzymes, liquid or gaseous fuels, solvents, and syrups in a cost-effective manner. The lowered production cost of these bioproducts primarily stems from the application of biomass-degrading enzymes (e.g., cellulases, amylases, and xylanases) in feedstock hydrolysis processes [6]. Consequently, the global market for xylanase has grown substantially in recent years [3] and is considered a critical enzyme in industry [7].

Due to the specific application requirements of xylanases, such as high temperature and pressure, research into xylanases from extreme environments has intensified. Many extremophilic xylanases have been isolated, particularly from thermophilic, alkalophilic, and acidophilic bacteria. However, pure cultivation of microorganisms from extreme environments is challenging, and metagenomic technology offers a solution. This technology can directly retrieve the nucleotide sequences of most genes from environmental DNA without the constraints of culture techniques, allowing for the analysis of microbial genetic information and the screening of functional genes [8]. Therefore, metagenomic technology holds significant advantages in extracting thermophilic xylanase from uncultured microorganisms in extreme environments [9].

In this study, a novel xylanase gene, XynAES of the GH10 family, was identified from Aiding Lake, Xinjiang using metagenomic technology. The gene sequence was cloned and heterologously expressed in Escherichia coli DH5α. The enzymatic properties of xylanase were examined using xylan as the substrate. The findings revealed that XynAES is a thermophilic, alkali-tolerant, and salt-tolerant xylanase.