Construction and Analysis of Food-Grade Lactobacillus kefiranofaciens β-Galactosidase Overexpression System

Lactobacillus kefiranofaciens contains two types of beta-galactosidase, LacLM and LacZ, belonging to different glycoside hydrolase families. The difference in function between them has been unclear so far for practical application. In this study, LacLM and LacZ from L. kefiranofaciens ATCC51647 were cloned into constitutive lactobacillal expression vector pMG36e, respectively. Furtherly, pMG36n-lacs was constructed from pMG36e-lacs by replacing erythromycin with nisin as selective marker for food-grade expressing systems in Lactobacillus plantarum WCFS1, designated recombinant LacLM and LacZ respectively. The results from hydrolysis of o-nitrophenyl-beta-galactopyranoside (ONPG) showed that the beta-galactosidases activity of the recombinant LacLM and LacZ was 1460% and 670% higher than that of the original L. kefiranofaciens. Moreover, the lactose hydrolytic activity of recombinant LacLM was higher than that of LacZ in milk. Nevertheless, compare to LacZ, in 25% lactose solution the galacto-oligosaccharides (GOS) production of recombinant LacLM was lower. Therefore, two beta-galactopyranosides could play different roles in carbohydrate metabolism of L. kefiranofaciens. In addition, the maximal growth rate of two recombinant strains were evaluated with different temperature level and nisin concentration in fermentation assay for practical purpose. The results displayed that 37 degrees C and 20-40 U/ml nisin were the optimal fermentation conditions for the growth of recombinant beta-galactosidase strains. Altogether the food-grade Expression system of recombinant beta-galactosidase was feasible for applications in the food and dairy industry.

Automated summary

The study investigated the differences in functionality and activity of two beta-galactosidases in Lactobacillus kefiranofaciens, showing distinct roles in lactose hydrolysis and galacto-oligosaccharides production. The findings suggest that the food-grade expression system of recombinant beta-galactosidase could be feasible for applications in the food and dairy industry.