Induction of Methanethiol Production by Brevibacterium linens CNRZ 918

SUMMARY: A non-inducing medium (NID) was defined for studying the induction of methanethiol production by Brevibacterium linens CNRZ 918. The lowest L-methionine concentration capable of inducing maximal methanethiol production by the cells was 7 mM. The peptides L-Ala-L-Met and L-Met-L-Ala induced greater methanethiol production than free L-methionine. D-Methionine, L-cysteine, S-methyl-L-cysteine and L-ethionine were poor inducers. Culture temperature affected the duration of induction. An Na+ concentration of 1 M in the culture medium led to maximal methanethiol production capacity of both cells and cell extracts. L-Methionine and L-ethionine were the best substrates for the crude soluble cells extract (with release of methanethiol and ethanethiol respectively). Neither the derivatives of L-methionine that acted as inducers, nor D-methionine, were substrates for demethiolation. Demethiolation activity of the crude extract was thermolabile, not stimulated by Na+ and strongly inhibited by Zn2+, Mn2+ and Cu2+. The shortest generation time obtained for B. linens CNRZ 918 in NID medium + L-methionine was 4 h at 26 °C. Only coccoid forms were present when the culture temperature was 30 °C. The presence of L-methionine in the medium favoured their appearance. The strain grew best in the presence of 1% NaCl but tolerated concentrations up to 15%. The induction of methanethiol production was due to the induction of L-methionine-γ-demethiolase. The level of induction was probably related to the intracellular concentration of L-methionine. The transport system of L-methionine by B. linens CNRZ 918 was constitutive and Na+ dependent.