A new xylanase from thermoacidophilic Alicyclobacillus sp. A4 with broad-range pH activity and pH stability

We have identified a highly pH-adaptable and stable xylanase (XynA4) from the thermoacidophilic Alicyclobacillus sp. A4, a strain that was isolated from a hot spring in Yunnan Province, China. The gene (xynA4) that encodes this xylanase was cloned, sequenced, and expressed in Escherichia coli. It encodes a 338-residue polypeptide with a calculated molecular mass of 42.5 kDa. The deduced amino acid sequence is most similar to (53% identity) an endo-1,4-beta-xylanase from Geobacillus stearothermophilus that belongs to family 10 of the glycoside hydrolases. Purified recombinant XynA4 exhibited maximum activity at 55 degrees C and pH 7.0, had broad pH adaptability (>40% activity at pH 3.8-9.4) and stability (retaining >80% activity after incubation at pH 2.6-12.0 for 1 h at 37 degrees C), and was highly thermostable (retaining >90% activity after incubation at 60 degrees C for 1 h at pH 7.0). These properties make XynA4 promising for application in the paper industry. This is the first report that describes cloning and expression of a xylanase gene from the genus Alicyclobacillus.