Molecular cloning and characterization of a multidomain endoglucanase fromPaenibacillus sp BP-23: evaluation of its performance in pulp refining

The gene celB encoding an endoglucanase from Paenibacillus sp. BP-23 was cl oned and expressed in Escherichia coli. The nucleotide sequence of a 4161 b p DNA fragment containing the celB gene was determined, revealing an open r eading frame of 2991 nucleotides that encodes a protein of 106,927 Da. Comp arison of the deduced amino acid sequence of endoglucanase B with known bet a -glycanase sequences showed that the encoded enzyme is a modular protein and exhibits high homology to enzymes belonging to family 9 cellulases. The celB gene product synthesized in E. coli showed high activity on carboxyme thyl cellulose and lichenan while low activity was found on Avicel. Activit y was enhanced in the presence of 10 mM Ca2+ and showed its maximum at 53 d egreesC and pH 5.5. The effect of the cloned enzyme in modifying the physic al properties of pulp and paper from Eucalyptus was tested (CelB treatment) . An increase in mechanical strength of paper and a decrease in pulp dewate ring properties were found, indicating that CelB treatment can be considere d as a biorefining. Treatment with CelB gave rise to an improvement in pape r strength similar to that obtained with 1,000 revolutions increase in mech anical refining. Comparison with the performances of recently developed end oglucanase A from the same strain and with a commercial cellulase showed th at CelB produced the highest refining effect.