Cloning of a family G xylanase gene (XYNB) from the extremely thermophilic bacterium Dictyoglomus thermophilum and action of the gene product on kraft pulp.

Abstract

Xylanases can be grouped into two unrelated families, namely family F and family G. We report here the cloning of a family G xylanase gene (xynB) from the Dictyoglomus thermophilum strain Rt46B.1 and the characterisation of the expressed gene product (229B). Novel consensus-PCR and genomic-walking PCR techniques were used to isolate the xynB gene from Dictyoglomus thermophilum genomic DNA. Various 229B xylanases produced from xynB expression constructions had pH optima of 6.5, and temperature optimum ranges of between 70 and 85°C. The 229B xylanase was active on kraft pulp as shown by the release of reducing sugars.