Methods for producing methionine by culturing a microorganism modified to enhance production of cysteine

1. A method for producing methionine, derivatives or precursors thereof comprising:

culturing a microorganism modified to enhance production of cysteine, as compared to cysteine production in an unmodified microorganism, in a culture medium comprising a source of carbon and a source of sulfur; and

recovering methionine from the culture medium,

wherein said microorganism has a methionine repressor encoded by metJ gene that is deleted or mutated, and has an increased expression of the cysE gene encoding serine acetyltransferase and an increased expression of metH gene encoding methionine synthase, as compared to the expression of the cysE and metH genes in an unmodified microorganism.

2. The method of claim 1 , wherein at least one other gene involved in cysteine production is overexpressed, as compared to the expression in an unmodified microorganism, said gene being selected from the group consisting of:

cysA

sulfate permease,

cysU, cysT

component of sulfate ABC transporter,

cysW

membrane bound sulfate transport protein,

cysH

adenylylsulfate reductase,

cysI

sulfite reductase, alpha subunit,

cysJ

sulfite reductase, beta subunit,

cysM

O-acetyl-sulfhydrylase,

cysZ

sulfate transport, and

sbp

Periplasmic sulfate-binding protein.

3. The method of claim 1 , wherein the expression of at least one other gene, which is involved in the production of C1 units and transfer potential onto homocysteine, is increased, as compared to the expression in an unmodified microorganism, and/or driven by a heterologous promoter.

4. The method of claim 3 , wherein the at least one other gene, which is involved in production of C1 units and transfer potential onto homocysteine, is selected from the group consisting of:

metE encoding methionine synthase,

metF encoding 5,10-methylenetetrahydrofolate reductase,

glyA encoding serine hydroxymethyltransferase, and

gcvTHP, lpd encoding the glycine cleavage complex.

5. The method of claim 4 , wherein expression of metE, metH and/or metF is increased, as compared to the expression in an unmodified microorganism, and/or at least one of the genes is expressed from a heterologous promoter.

6. The method of claim 1 , further comprising increasing expression of additional genes involved in production of methionine, as compared to the expression of said additional genes in an unmodified microorganism.

7. The method of claim 1 , wherein the sulfur source in the culture medium is sulfate, thiosulfate, hydrogen sulfide, dithionate, dithionite, sulfite or a combination of different sources.

8. The method of claim 7 , wherein the sulfur source in the culture medium is sulfate or thiosulfate, or a mixture thereof.

9. The method of claim 1 , comprising isolating desired amino acids/ constituents of the fermentation medium and/or biomass optionally remaining in portions or in a total amount (0-100%) in an end product.

10. A method for producing methionine, derivatives or precursors thereof comprising:

culturing a microorganism modified to enhance production of cysteine, as compared to cysteine production in an unmodified microorganism, in a culture medium comprising a source of carbon and a source of sulfur, and

recovering methionine from the culture medium,

wherein said microorganism has a methionine repressor encoded by metJ gene that is deleted or mutated, has an increased expression of the cysE gene encoding serine acetyltransferase, and an increased expression of the metH gene encoding methionine synthase, as compared to the expression of cysE and metH genes in an unmodified microorganism, and that expresses a metA allele encoding homoserine succinyltransferase enzyme with reduced feed-back sensitivity to S-adenosylmethionine and/or methionine, as compared feed-back sensitivity of a wild-type enzyme, and a thrA allele encoding homoserine aspartokinase enzyme with reduced feed-back sensitivity to threonine, as compared to feed-back sensitivity of a wild-type enzyme.

11. A method for producing methionine, derivatives or precursors thereof comprising:

culturing a microorganism modified to enhance production of cysteine, as compared to cysteine production in an unmodified microorganism, in a culture medium comprising a source of carbon and a source of sulfur; and

recovering methionine from the culture medium,

wherein said microorganism has a methionine repressor encoded by metJ gene that is deleted or mutated, and has an increased expression of the cysE gene encoding serine acetyltransferase, and an increased expression of the metH gene encoding methionine synthase, and an increased expression of the metF gene encoding 5,10-methylenetetrahydrofolate reductase, as compared to the expression of the cysE, metH and metF genes in an unmodified microorganism, and that expresses a metA allele encoding homoserine succinyltransferase enzyme with reduced feed-back sensitivity to S-adenosylmethionine and/or methionine, as compared to feed-back sensitivity of a wild-type enzyme, and a thrA allele encoding homoserine aspartokinase enzyme with reduced feed-back sensitivity to threonine, as compared to feed-back sensitivity of a wild-type enzyme.

12. A method for producing methionine, derivatives or precursors thereof comprising:

culturing a microorganism modified to enhance production of cysteine, as compared to cysteine production in an unmodified microorganism in a culture medium comprising a source of carbon and a source of sulfur; and

recovering methionine from the culture medium,

wherein said microorganism has an increased expression of the cysE gene encoding serine acetyltransferase, and an increased expression of the metH gene encoding methionine synthase, and an increased expression of the metF gene encoding 5,10-methylenetetrahydrofolate reductase, as compared to the expression of the cysE, metH, and metF genes in an unmodified microorganism, and expresses a metA allele encoding homoserine succinyltransferase enzyme with reduced feed-back sensitivity to S-adenosylmethionine and/or methionine, as compared to feed-back sensitivity of a wild-type enzyme, and a thrA allele encoding homoserine aspartokinase enzyme with reduced feed-back sensitivity to threonine, as compared to feed-back sensitivity of a wild-type enzyme, and has a methionine repressor encoded by metJ gene that is deleted or mutated, and an increased expression of the cysM gene encoding O-acetyl-sulfhydrylase, as compared to the expression of the cysM gene in an unmodified microorganism.