Bioconversion of 2-amino acids to 2-hydroxy acids by Clostridium butyricum

Analysis by gas chromatography-mass spectrometry (GC-MS) of 24-h cultures of Clostridium butyricum type strain in synthetic BMG medium supplemented with various 2-amino acids (10 mM) revealed the presence of the corresponding 2-hydroxy acids. C. butyricum was able to bioconvert L-valine, DL-norvaline, L-leucine, DL-norleucine, L-methionine and L-phenylalanine as well as unusual 2-amino acids, i.e,, L-2-aminobutyric acid, L-2-amino-4-pentenoic acid, DL-2-aminooctanoic acid, and DL-2-amino-4-phenylbutanoic acid. L-Isoleucine and cycloleucine were not converted into their corresponding 2-hydroxy acids. The bioconversion rate was maximal with DL-norvaline (6.2%). Chiral GC analysis demonstrated that only D-2-hydroxy-4-methylpentanoic acid is formed from L-leucine, indicating that the bioconversion is stereospecific, with inversion of configuration. D-Leucine and D-methionine were also converted to the corresponding 2-hydroxy acids. This observation opens new aspects in the study of C. butyricum and raises questions about the amino acid metabolism by this species. (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.