Systematic assessment of Pichia pastoris system for optimized β -galactosidase production

bGalactosidase (commonly known as b-lactase; EC 3.2.1.23) is a multifunctional enzyme that can catalyze the hydrolysis of terminal non-reducing b-D-galactose residues in b-D-galactosides or transfer the galactosyl residue to saccharide acceptors to yield galactooligosaccharides (GOS). b-Galactosidase has a variety of applications in food and medical industries such as hydrolysis of lactose in milk, manufacture of galactooligosaccharides (GOS) and treatment of lactose malabsorption [1]. Although b-galactosidase is an ubiquitous enzyme existing in plants, animals and microorganisms, only a few b-galactosidases from Kluveromyces lactis, Aspergillus niger and Aspergillus oryzae are regarded as safe for food related industry applications. To achieve commercial scale production of b-galactosidase, heterologous expression systems were applied including Saccharomyces cerevisiae and Pichia pastoris [1]. P. pastoris is a methylotrophic yeast with great protein expression potential, and has been used as host for expression of many proteins both experimentally and industrially. P. pastoris has also been used for the extracellular expression of b-galactosidase from Paecilomyces aerugineus [2], Lactobacillus crispatus [3] and strains belonging to Aspergillus spp