Effect of bile on the $\beta$-galactosidase activity of dairy propionibacteria

Abstract

In the present study, the effect of bile on the growth, cell permeabilization and β-galactosidase activity of dairy propionibacteria was determined. Two groups of strains with different behavior in media with oxgall (dehydrated fresh bile) could be observed, and were named bile-tolerant and non bile-tolerant groups. The β-galactosidase activity of bile-tolerant strains increased during the growth in media containing 0.15 and 0.30% oxgall. The incubation of cell suspensions in phosphate buffer with oxgall increased the β-galactosidase activity of all the studied strains. They were permeabilized by bile, permitting more substrate to enter the cells to be hydrolyzed by β-galactosidase. A higher specific activity was observed in cell-free extracts obtained from cultures in media with oxgall, indicating increased enzyme synthesis in the presence of bile. The enzyme activity was also increased by sodium taurocholate and sodium chloride. These results suggest that bile-tolerant strains of propionibacteria can provide meaningful β-galactosidase activity by permeabilization of the cells and increased enzyme synthesis during growth in the gut. The non bile-tolerant strains did not grow in media with bile. They were permeabilized, but their β-galactosidase was inactivated when they were exposed for a long time to bile in the growth media. Thus, their contribution to the β-galactosidase activity in the gut does not appear to be significant.