Increasing methionine yield

Abstract

Process for the production of methionine or its derivatives by culturing a microorganism in an appropriate culture medium comprising a source of carbon and a source of sulfur. The microorganism and/or the culture medium are modified in such way that the methionine/carbon source yield is increased. The isolation of methionine or its derivates from the fermentation medium is also described.

1 . A method for the production of methionine, a derivative thereof, or a precursor in a fermentative process comprising the following steps:
 culturing a modified microorganism in an appropriate culture medium comprising a source of carbon and a source of sulfur, and   recovering methionine from the culture medium,   
       wherein compared to a non-modified microorganism and/or method, the microorganism and/or the method has been modified to present an enhanced methionine/carbon source yield by at least one of the following modifications and combinations thereof:
 decreasing the deformylation of formyl-THF in the microorganism 
 decreasing the consumption of PEP in the microorganism 
 limiting growth and biomass production of the modified microorganism by limiting or starving the microorganism for one or several inorganic substrate(s) in the culture medium. 
 
     
     
         2 . The method of  claim 1  wherein the deformylation of formyl-THF is reduced by the attenuation of the expression of the gene purU. 
     
     
         3 . The method of  claim 1  wherein the consumption of PEP is reduced by the attenuation of the expression of at least one of the following genes:
 pykA   pykF   
     
     
         4 . The method of  claim 1  wherein the microorganism is limited or starved for phosphate and/or potassium. 
     
     
         5 . The method of  claim 1 , wherein the deformylation of formyl-THF is reduced by the attenuation of the expression of the gene purU, wherein the consumption of PEP is reduced by the attenuation of the expression of the pykA or pykF gene or both and wherein the microorganism is limited or starved for phosphate and/or potassium. 
     
     
         6 . The method of  claim 1 , wherein the deformylation of formyl-THF is reduced by the attenuation of the expression of the gene purU, and wherein the consumption of PEP is reduced by the attenuation of the expression of the pykA or pykF gene or both 
     
     
         7 . The method of  claim 1 , wherein the deformylation of formyl-THF is reduced by the attenuation of the expression of the gene purU and wherein the microorganism is limited or starved for phosphate and/or potassium. 
     
     
         8 . The method of  claim 1 , wherein the consumption of PEP is reduced by the attenuation of the expression of the pykA or pykF gene or both and wherein the microorganism is limited or starved for phosphate and/or potassium. 
     
     
         9 . The method of  claim 1  wherein the expression of at least one of the following genes is increased in the microorganism: cysP, cysU, cysW, cysA, cysM, cysJ, cysI, cysH, cysE, gcvT, gcvH, gcvP, lpd, sera, serB, serC, glyA 
     
     
         10 . The method of  claim 9  wherein the expression of the operons cysPUWAM and/or cysJIH is increased in the microorganism. 
     
     
         11 . The method of  claim 9  wherein the expression of the glycine cleavage complex encoded by the genes gcvTHP and or lpd is increased in the microorganism. 
     
     
         12 . The method of  claim 9  wherein at least one gene involved in the glycine biosynthesis pathway such as serA, serB, serC or glyA is overexpressed. 
     
     
         13 . The method of  claim 1  wherein at least one of the following genes is overexpressed in the microorganism: metF, metA alleles encoding enzymes with reduced feed-back sensitivity to S-adenosylmethionine and/or methionine, thrA or thrA alleles with reduced feed-back inhibition to threonine, cysE, meth 
     
     
         14 . The method of  claim 1  wherein the expression of the methionine repressor encoded by the metJ gene is attenuated in the microorganism. 
     
     
         15 . 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 the different sources. 
     
     
         16 . The method of  claim 15  wherein the sulfur source in the culture medium is sulfate or thiosulfate, or a mixture of the two. 
     
     
         17 . The method of  claim 1  wherein the carbon source is glucose or sucrose. 
     
     
         18 . The method of  claim 1  comprising the step of isolation of the desired amino acids/constituents of the fermentation broth and/or the biomass optionally remaining in portions or in the total amount (0-100%) in the end product. 
     
     
         19 . The method of  claim 18  in which the methionine derivative, N-acetyl-methionine is transformed into methionine by deacylation, before methionine is recovered. 
     
     
         20 . A modified microorganism wherein when compared to a non-modified microorganism, said microorganism presents an enhanced methionine/carbon source yield obtained by at least one of the following modifications and combinations thereof:
 decreasing the deformylation of formyl-THF in the microorganism   decreasing the consumption of PEP in the microorganism.   
     
     
         21 ) The modified microorganism of  claim 20  wherein the deformylation of formyl-THF is reduced by the attenuation of the expression of the gene purU. 
     
     
         22 ) The modified microorganism of  claim 20  wherein the consumption of PEP is reduced by the attenuation of the expression of at least one of the following genes:
 pykA   pykF.   
     
     
         23 ) The modified microorganism of  claim 20 , wherein the deformylation of formyl-THF is reduced by the attenuation of the expression of the gene purU, and wherein the consumption of PEP is reduced by the attenuation of the expression of the pykA or pykF gene or both. 
     
     
         24 ) The modified microorganism of  claim 20  wherein the expression of at least one of the following genes is increased in the microorganism: cysP, cysU, cysW, cysA, cysM, cysJ, cysI, cysH, cysE, gcvT, gcvH, gcvP, Ipd, sera serB, serC, glyA. 
     
     
         25 ) The modified microorganism of  claim 24  wherein the expression of the operons cysPUWAM and or cysJIH is increased in the microorganism. 
     
     
         26 ) The modified microorganism of  claim 24  wherein the expression of the glycine cleavage complex encoded by the genes gcvTHP and/or Ipd is increased in the microorganism. 
     
     
         27 ) The modified microorganism of  claim 24  wherein at least one gene involved in the glycine biosynthesis pathway is overexpressed. 
     
     
         28 ) The modified microorganism of  claim 20  wherein at least one of the following genes is overexpressed in the microorganisms: metF, metA alleles encoding enzymes with reduced feed-back sensitivity to S-adenosylmethionine and/or methionine, thrA or thrA alleles with reduced feed-back inhibition to threonine, cysE, metH. 
     
     
         29 ) The modified microorganism of  claim 20  wherein the expression of the methionine repressor encoded by the metJ gene is attenuated in the microorganism.