Molecular characterization of the phenolic acid metabolism in the lactic acid bacteria Lactobacillus plantarum

The lactic acid bacteria Lactobacillus plantarum displays substrate-inducible decarboxylase activities on p-coumaric, caffeic and ferulic acids. Purification of the p-coumaric acid decarboxylase (PDC) was performed. Sequence of the N-terminal part of the PDC led to the cloning of the corresponding pdc gene. Expression of this gene in Escherichia coli revealed that PDC displayed a weak activity on ferulic acid, detectable in vitro in the presence of ammonium sulfate. Transcriptional studies of this gene in L. plantarum demonstrated that the pdc transcription is phenolic acid-dependent. A mutant deficient in the PDC activity, designated LPD1, was constructed to study phenolic acid alternate pathways in L. plantarum. LPD1 mutant strain remained able to metabolize weakly p-coumaric and ferulic acids into vinyl derivatives or into substituted phenyl propionic acids. These results indicate that L. plantarum has a second acid phenol decarboxylase enzyme and also displays inducible acid phenol reductase activity. Finally, PDC activity was shown to confer a selective advantage for LPNC8 grown in acidic media supplemented with p-coumaric acid, compared to the LPD1 mutant devoid of PDC activity.