Method and microorganism for methionine production by fermentation with improved methionine efflux

A method for the fermentative production of methionine comprising:

• a. culturing a recombinant Escherichia coli (E. coli) strain, wherein in said microorganism, the ygaZH homologous genes of ygaZ and ygaH genes from E. coli are overexpressed;
• with the provisio that this overexpression is neither combined with overexpression of metH, and optionally of fldA and fpr from E. coli or their homologous genes from C. glutamicum nor with attenuation of expression of at least one gene selected from the group consisting of metN, metI and metQ, said ygaZH homologous genes are selected from the group of genes encoding the pair of YgaZH homologue defined respectively by:
• SEQ ID NO:
• 3 and SEQ ID NO:
• 4 from Citrobacter koseri, SEQ ID NO:
• 9 and SEQ ID NO:
• 10 from Enterobactersp. (R4-368), SEQ ID NO:
• 17 and SEQ ID NO:
• 18 from Citrobacter youngae, SEQ ID NO:
• 19 and SEQ ID NO:
• 20 from Citrobacter freundii in an appropriate culture medium comprising a fermentable source of carbon and a source of sulphur, and
• b. recovering methionine from the culture medium,
• wherein the overexpression is achieved by:
• i) increasing the number of copies of the genes in the microorganism,
• ii) using a promoter leading to a high level of expression of the genes, and/or
• iii) attenuating the activity or the expression of a transcription repressor.

A genetically modified Escherichia coli (E. coli) strain for the fermentative production of methionine, wherein in said genetically modified strain, ygaZH homologous genes of ygaZ and ygaH genes from E. coli are overexpressed said ygaZH homologous genes are selected from the group consisting of genes encoding the pair of YgaZH homologue defined respectively by:

• SEQ ID NO:
• 3 and SEQ ID NO:
• 4 from Citrobacter koseri, SEQ ID NO:
• 9 and SEQ ID NO:
• 10 from Enterobactersp. (R4-368), SEQ ID NO:
• 17 and SEQ ID NO:
• 18 from Citrobacter youngae, SEQ ID NO:
• 19 and SEQ ID NO:
• 20 from Citrobacter freundii.

A method for the fermentative production of methionine comprising:

• a. culturing a genetically modified Escherichia coli (E. coli) strain wherein in said microorganism, the ygaZH homologous genes of ygaZ and ygaH genes from E. coli are overexpressed in an appropriate culture medium comprising a fermentable source of carbon and a source of sulphur, said ygaZH homologous genes are selected from the group consisting of genes encoding the pair of YgaZH homologue defined respectively by:
• SEQ ID NO:
• 3 and SEQ ID NO:
• 4 from Citrobacter koseri, SEQ ID NO:
• 9 and SEQ ID NO:
• 10 from Enterobacter sp. (R4-368), SEQ ID NO:
• 17 and SEQ ID NO:
• 18 from Citrobacter youngae, SEQ ID NO:
• 19 and SEQ ID NO:
• 20 from Citrobacter freundii, and
• b. recovering methionine from the culture medium.