Pathways that produce volatile sulphur compounds from methionine in Oenococcus oeni

Determination of pathways involved in synthesis of volatile sulphur compounds (VSC) from methionine by Oenococcus oeni isolated from wine.

Production of VSC by O. oeni from methionine was investigated during bacterial cultures and in assays performed in the presence of resting cells or protein fractions. Cells of O. oeni grown in a medium supplemented with methionine produced methanethiol, dimethyl disulphide, methionol and 3-(methylthio)propionic acid. Methional was also detected, but only transiently during the exponential growth phase. It was converted to methionol and 3-(methylthio) propionic acid in assays. Although this acid could be produced alternatively from 2-oxo-4-(methylthio) butyric acid (KMBA) by oxidative decarboxylation. In addition, KMBA was a precursor for methanethiol and dimethyl disulphide synthesis. Interestingly, assays with resting cells and protein fractions suggested that a specific enzyme could be involved in this conversion in O. oeni.

This work shows that methional and KMBA are the key intermediates for VSC synthesis from methionine in O. oeni. Putative enzymatic and chemical pathways responsible for the production of these VSC are discussed.

This work confirms the capacity of O. oeni to metabolize methionine and describes the involvement of potential enzymatic pathways.