title: Enhanced β-galactosidase production from whey powder by a mutant of the psychrotolerant yeast Guehomyces pullulans 17-1 for hydrolysis of lactose.
abstract: In order to isolate β-galactosidase overproducers of the psychrotolerant yeast Guehomyces pullulans 17-1, its cells were mutated by using nitrosoguanidine (NTG). One mutant (NTG-133) with enhanced β-galactosidase production was obtained. The mutant grown in the production medium with 30.0 g/l lactose and 2.0 g/l glucose could produce more β-galactosidase than the same mutant grown in the production medium with only 30.0 g/l lactose while β-galactosidase production by its wild type was sensitive to the presence of glucose in the medium. It was found that 40.0 g/l of the whey powder was the most suitable for β-galactosidase production by the mutant. After optimization of the medium and cultivation conditions, the mutant could produce 29.2 U/ml of total β-galactosidase activity within 132 h at the flask level while the mutant could produce 48.1 U/ml of total β-galactosidase activity within 144 h in 2-l fermentor. Over 77.1% of lactose in the whey powder (5.0% w/v) was hydrolyzed in the presence of the β-galactosidase activity of 280 U/g of lactose within 9 h while over 77.0% of lactose in the whey was hydrolyzed in the presence of β-galactosidase activity of 280 U/g of lactose within 6 h. This was the first time to show that the β-galactosidase produced by the psychrotolerant yeast could be used for hydrolysis of lactose in the whey powder and whey.
authors.affiliation: UNESCO Chinese Center of Marine Biotechnology and Institute of Marine Biodiversity and Evolution, Ocean University of China, Yushan Road, No. 5, Qingdao 266003, China.
authors.forename: Jin-Li
authors.initials: JL
authors.lastname: Xu
authors.forename: Jun
authors.initials: J
authors.lastname: Zhao
authors.forename: Ling-Fei
authors.initials: LF
authors.lastname: Wang
authors.forename: Huai-Yong
authors.initials: HY
authors.lastname: Sun
authors.forename: Chun-Li
authors.initials: CL
authors.lastname: Song
authors.forename: Zhen-Ming
authors.initials: ZM
authors.lastname: Chi
mesh_terms: D000864:Antarctic Regions; D001203:Ascomycota / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D019149:Bioreactors; D003611:Dairy Products; D005285:Fermentation; D019015:Geologic Sediments / Q000382:microbiology; D005947:Glucose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007218:Industrial Microbiology; D007785:Lactose / Q000378:metabolism*; D016296:Mutagenesis; D009154:Mutation; D009604:Nitrosoguanidines / Q000494:pharmacology; D011208:Powders; D001616:beta-Galactosidase / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D009604:Nitrosoguanidines; D011208:Powders; D001616:beta-Galactosidase; D005947:Glucose; D007785:Lactose