Families and Functions of Novel Thermophilic Xylanases in the Facilitated Bleaching of Pulp

Abstract

Hemicellulases have shown some promise as bleaching aids in the pulp and paper industry. Novel genetic techniques have been developed to isolate xylanase and mannanase genes from both culturable organisms isolated after enrichment and non-culturable organisms that cannot be maintained in pure culture. Genomic DNA is subjected to the polymerase chain reaction (PCR) using consensus primers. The products are cloned and sequenced and genes for novel enzymes are identified. The full length sequences are obtained by genomic walking PCR, allowing the amplification of the entire gene in a form suitable for direct cloning into an expression vector. Using this technique, we have revealed the presence of a number of novel genes for xylanases of family F and family G in culturable bacteria that were believed to express only a single enzyme and from an unculturable consortium. Selected candidate enzymes have been tested for their abilities to enhance the bleaching of kraft pulps and several function as well as commercially-available enzyme preparations but at alkaline pH and at temperatures up to 50 degrees C higher than mesophilic xylanases.