Thermostable Xylanases from Rhodothermus marinus

Abstract: Abstract Hot springs in Iceland can serve as sources of thermophilic, xylanolytic bacteria secreting very thermostable xylanolytic enzymes. The aerobic, thermophilic bacteria Rhodothermus marinus secretes multiple xylanases and xylosidases. One of the xylanases was purified to electrophoretic homogeneity and was characterized. The N-terminal sequence showed no homology with other xylanases. The purified enzyme had a half-life of nearly three hours at 80 °C and the end products of hydrolysis were xylobiose and xylotriose. This strongly suggests that the thermostable enzyme is a true endo-1,4-ß-xylanase. The catalytic domain of one of the xylanase genes in R. marinus was sequenced and was overexpressed in E. coli. The xylanase belongs to family 10 of the glycosyl hydrolases. The closest homology was found to be with the Pseudomonas flourescens xylanase B catalytic domain. No homology was found with the N-terminal sequence of the purified xylanase. The gene product, the xylanase, was purified to electrophoretic homogeneity and was characterized. The half-life was 100 min at 80 °C, the thermostability of the xylanase being enhanced by the presence of calcium. The end products of hydrolysis were xylobiose and xylotriose, suggesting that this enzyme is also a true endo-1,4-ß-xylanase. The cloned xylanase showed positive preliminary results when tested for its ability to bleach and de-colour birch pulp.