Characterization of the novel xylanase from the thermophilic Geobacillus thermodenitrificans JK1.

Thermophilic strain JK1 was isolated from compost using xylan as a single carbon source. On the basis of 16S rRNA gene phylogenetic analysis and spo0A gene sequence similarity analysis, strain JK1 was identified as Geobacillus thermodenitrificans strain. During the exponential culture growth, the strain JK1 was found to produce the single xylan degrading enzyme -45 kDa in size. Xylose was not an inducer of this xylanase. Cloning, expression and characterization of the recombinant xylanase were performed. Xylanase of G. thermodenitrificans JK1 was cellulase-free; pH and temperature optimums were found to be 6.0 and 70 degrees C, respectively. The metal ions Na+, K+, Ca2+, and Co2+ showed partial inhibition of the activity, while Mn2+ had slight stimulating effect on the enzymatic activity. Recombinant xylanase was thermostable over the temperature range of 55-70 degrees C. It presented the highest stability after incubation at 55 degrees C for 60 min showing 84% residual activity. 50% residual activity was revealed after incubation at 60 degrees C for 60 min as well as at 65 and 70 degrees C for 30 min. Results of the thermostability experiments showed xylanase of JK1 having quite low thermostability when compared with the respective enzymes of the other geobacilli.