High level expression of a novel β-mannanase from Chaetomium sp. exhibiting efficient mannan hydrolysis

A novel β-mannanase gene (CsMan5A) was cloned from Chaetomium sp. CQ31 and expressed in Pichia pastoris. It had an open reading frame of 1251bp encoding 416 amino acids and contained two introns. The deduced amino acid sequence shared the highest similarity (73%) with the β-mannanase from Emericella nidulans and belongs to glycosyl hydrolase family 5. The recombinant β-mannanase (CsMan5A) was secreted at extremely high levels of 50,030UmL^-1 and 6.1mgmL^-1 in high cell density fermentor. The purified enzyme was optimally active at pH 5.0 and 65°C and displayed broad pH stability (pH 5.0-11.0) and exhibited specificity towards locust bean gum (K_m=3.1mgmL^-1), guar gum (K_m=9.3mgmL^-1) and konjac powder (K_m=10.5mgmL^-1). It efficiently degraded mannan polysaccharides into mannose and mannooligosacccharides, and also hydrolyzed mannotriose and mannotetraose. These properties make CsMan5A highly useful in food, feed and paper/pulp industries.