Catabolism of amino acids by lactic acid bacteria isolated from Cheddar cheese

Fifty five percent of 152 lactic acid bacteria (LAB) isolated from 9 mature Cheddar cheeses were able to catabolise protein hydrolysates and individual amino acids in the Biolog MT1TM microplate assay. A more detailed study of 31 isolates confirmed a requirement for a-ketoglutaric acid and inter- and intra-species differences in the range and number of amino acids utilised. GCMS analysis of cell-free supernatants of 29 LAB isolates grown on a low-carbohydrate medium containing lactalbumin hydrolysate identified more than 90 compounds. Putative metabolites of valine, leucine, isoleucine, phenylalanine and sulphur-containing amino acids were detected although the metabolite profiles were isolate-specific. The occurrence and activity of amino acid converting enzymes was also monitored in the LAB isolates. Methionine, branched-chain and aromatic amino acid aminotransferase activities were detected with a-ketoglutarate as acceptor. There was no conclusive evidence for a widespread occurrence of deaminase, decarboxylase and demethiolase activities. The majority of isolates examined formed thiols from methionine via an aminotransferase-mediated reaction.