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

In the present study, the effect of bile on the growth, cell permeabilizati on and beta-galactosidase activity of dairy propionibacteria was determined . Two groups of strains with different behavior in media with oxgall (dehyd rated fresh bile) could be observed, and were named bile-tolerant and non b ile-tolerant groups. The beta-galactosidase activity of bile-tolerant strai ns increased during the growth in media containing 0.15 and 0.30% oxgall. T he incubation of cell suspensions in phosphate buffer with oxgall increased the beta-galactosidase activity of all the studied strains. They were perm eabilized by bile, permitting more substrate to enter the cells to be hydro lyzed by beta-galactosidase. A higher specific activity was observed in cel l-free extracts obtained from cultures in media with oxgall, indicating inc reased enzyme synthesis in the presence of bile. The enzyme activity was al so increased by sodium taurocholate and sodium chloride. These results sugg est that bile-tolerant strains of propionibacteria can provide meaningful b eta-galactosidase activity by permeabilization of the cells and increased e nzyme synthesis during growth in the gut. The non bile-tolerant strains did not grow in media with bile. They were permeabilized, but their beta-galac tosidase was inactivated when they were exposed for a long time to bile in the growth media. Thus, their contribution to the beta-galactosidase activi ty in the got does not appear to be significant.