Acquisition of amino acids by Lactobacillus delbrueckii subsp. bulgaricus 2038 when grown in the presence of casein

The acquisition of amino acids by Lactobacillus delbrueckii subsp. bulgaricus 2038 (Lb. bulgaricus 2038) when grown in the presence of bovine casein, the major protein in bovine milk, was investigated by examining the expression of genes related to proteolysis and amino acid biosynthesis. To support the growth on bovine casein, Lb. bulgaricus 2038 has to synthesise five kinds of amino acids de novo, as proteolysis from casein does not provide these. The incomplete hydrolysis in combination with amino acids biosynthesis may explain the slow growth of Lb. bulgaricus 2038 in a casein environment. Meanwhile, it was determined that Lb. bulgaricus 2038 uses different intracellular peptidases when grown in casein or whey medium, and initially yields the important amino acid glutamate from the C-terminal or N-terminal end of peptides imported into the cell.