Xylanase is produced naturally from various biological sources,
such as bacteria, fungi and insects. As a primary destroyer of wood,
termites harbor more than 200 types of microbial species that
can produce cellulase and hemicellulase, providing an important
source of enzymes for industrial applications [5]. However, the
majority of microbes are unculturable. Metagenomic technology
provides a powerful culture-independent strategy for obtaining
new enzyme genes [6,7]. In recent years, many xylanase genes
were isolated from metagenomic libraries, including xynGR40 from
goat rumen content [8], XynH from soil samples [9] and XYL6419
from termite gut [10]. However, most of these wild-type enzymes
showed poor thermostability, particularly for xylanases in the glycoside
hydrolase family
∗