An α-galactosidase from an acidophilic Bispora sp. MEY-1 strain acts synergistically with β-mannanase

An α-galactosidase gene (AgalB) was cloned from the acidophilic fungus Bispora sp. MEY-1 and expressed in Pichia pastoris. The deduced amino acid sequence showed highest identity (35%) to the α-galactosidase from Penicillium simplicissimum, belonging to the glycosyl hydrolase family 27. The purified recombinant α-galactosidase (r-AgalB) exhibited optimal activity at pH 3.5 and 55 °C, was stable at pH 2.2-8.0, and showed higher hydrolytic activity towards galactomannan polysaccharides (guar gum and locust bean gum) than toward small galacto-oligosaccharides (melibiose, raffinose and stachyose). A synergistic (3-fold) increase in guar gum hydrolysis was observed when β-mannanase Man5A from Bispora sp. MEY-1 and r-AgalB were combined. Further, an increase in the reaction time from 5 h to 12 h or increase of the temperature from 37 °C to 55 °C enhanced guar gum degradation by the enzyme combination. These properties make r-AgalB a good candidate for extensive application in the pulp/paper, food, and feed industries.