초록
<P><B>Highlights</B></P><P>► First report on cloning and expression of a thermo-alkali-stable xylanase from an extremely thermophilic bacterium. ► A 27-fold higher production was achieved by cloning and expression. ► The recombinant enzyme was purified and characterized, and compared with the native enzyme. ► The enzyme efficiently hydrolyzes xylan and agro-residues into xylooligosaccharides which have application as prebiotics.</P> <P><B>Abstract</B></P><P>A xylanase gene (<I>xyl</I>-gt) of 1.224kbp was cloned from the extremely thermophilic bacterium <I>Geobacillus thermoleovorans</I> that encodes a protein containing 408 amino acid residues. Eight conserved regions (signature sequences) of GH family 10 xylanases have been found in the xylanase. When the xylanase gene was cloned and expressed in <I>Escherichia coli</I> BL21 (DE3), the recombinant strain produced xylanase titer of 270Umg<SUP>−1</SUP> which is 27-fold higher than the wild strain. It is optimally active at 80°C and pH 8.5 with a high thermostability over broad range of pH (6–12) and temperature (40–100°C). The end products of the hydrolysis of birch wood xylan and agro-residues included xylobiose, xylotriose, xylotetraose and xylopentaose. The xylanase of <I>G. thermoleovorans</I> is one of the rare xylanases that exhibits thermo-alkali-stability, and thus, it is a suitable candidate for pre-bleaching of paper pulps and generating xylooligosaccharides from agro-residues for use as prebiotics.</P>