Peptidases and amino acid catabolism in lactic acid bacteria

The conversion of peptides to free amino acids and their subsequent utiliza tion is a central metabolic activity in prokaryotes. At least 16 peptidases from lactic acid bacteria (LAB) have been characterized biochemically and/ or genetically. Among LAB, the peptidase systems of Lactobacillus helveticu s and Lactococcus lactis have been examined in greatest detail. While there are homologous enzymes common to both systems, significant differences exi st in the peptidase complement of these organisms. The characterization of single and multiple peptidase mutants indicate that these strains generally exhibit reduced specific growth rates in milk compared to the parental str ains. LAB can also catabolize amino acids produced by peptide hydrolysis. W hile the catabolism of amino acids such as Arg, Thr, and His is well unders tood, few other amino acid catabolic pathways from lactic acid bacteria hav e been characterized in significant detail. Increasing research attention i s being directed toward elucidating these pathways as well as characterizin g their physiological and industrial significance.