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.

Optimisation of culture conditions and development of a novel fed‐batch strategy for high production of β‐galactosidase by Kluyveromyces lactis

“…Compared with other fed‐batch cultures, β‐galactosidase activity (111.61 U mL −1 ) in this study was about 3‐fold of that (36.7 U mL −1 ) by Bifidobacterium longum (Hsu et al ., ) and about 2.32‐fold of that (48.1 U mL −1 ) by the mutant of G. pullulans NTG‐113 (Xu et al ., ), but lower than the reports of 173.5 U mL −1 by Pichia pastoris Mut + Strains (Maghsoudi et al ., ) and 121.0 U mL −1 by the disruptant (mig1 mutant) KM‐15 under the optimal conditions (Zhou et al ., ). However, K. lactis CICC1773 as a nonrecombinant microorganism, has an important advantage that it has more stable biological characters during fermentation compared with the recombinant strains (Oliveira et al ., ).…”

Microbial Reduction of Chromate in the Presence of Nitrate by Three Nitrate Respiring Organisms

“…An alternative mechanism is that Cr(VI) is reduced by Fe(II) produced through dissimilatory iron reduction. Cr(VI) reduction by Fe(II) is well established (Kamaludeen et al, 2003; Cheng et al, 2010; Xu et al, 2012). Amending the FWA-NO 3 medium with ferric citrate did indeed result in the reduction of Cr(VI) however, whether the process is abiotic or biologically induced remains to be determined.…”