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


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