Cloning, expression and characterization of a novel cold-active and halophilic xylanase from Zunongwangia profunda
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A new xylanase gene (xynA) from the marine microorganism Zunongwangia profunda was identified to encode 374 amino acid residues. Its product (XynA) showed the highest identity (42.78 %) with a xylanase from Bacillus sp. SN5 among the characterized xylanases. XynA exhibited the highest activity at pH 6.5 and 30 °C, retaining 23 and 38 % of the optimal activity at 0 and 5 °C, respectively. XynA was not only cold active, but also halophilic, and both its activity and thermostability could be significantly increased by NaCl, showing the highest activity (180 % of the activity) at 3 M NaCl and retaining nearly 100 % activity at 5 M NaCl, compared to the absence of NaCl. In the presence of 3 M NaCl, the kcat/Km value of XynA exhibited a 3.41-fold increase for beechwood xylan compared to no added NaCl, and the residual activity of XynA increased from 23 % (no added NaCl) to 58 % after 1 h incubation at 45 °C. This may be the first report concerning a cold-adapted xylanase from a non-halophilic species that displays the highest activity at a NaCl concentration range from 3 to 5 M. The features of cold activity and salt tolerance suggest the potential application of XynA in the food industry and bioethanol production from marine seaweeds.
KeywordsXylanase Cold activity Salt tolerance Zunongwangia profunda
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