beta-D-galactosidase of Lactobacillus species

The activity of beta-D-galactosidase was studied in 13 strains of lactobacilli (groups Streptobacterium, Thermobacterium and Betabacterium). Using 2-nitrophenyl galactopyranoside as substrate, the enzyme activity varied with the strain. The values found in the Thermobacterium group were superior to those in the Streptobacterium group. The optimum pH for the species belonging to the Thermobacterium group was uniform, in contrast to the pH for those from the Streptobacterium which varied according to the species. The optimum temperature was quite uniform within each group and higher in the Streptobacterium. Lactose acted as a competitive inhibitor. MgCl2 protected the enzyme from thermal denaturation. The calcium ions inhibited the activity in all cases. The behaviour of the protectors of the SH groups varied according to the strain. 6-Phospho-beta-D-galactosidase activity was also determined, levels lower than beta-D-galactosidase were found, except in Lactobacillus plantarum ATCC 8014 and 14917.