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.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a 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 were modified in a way that the methionine / carbon source yield is increased. The isolation of methionine or its derivates from the fermentation medium is also claimed.PRIOR ART[0002]Sulphur-containing compounds such as cysteine, homocysteine, methionine or S-adenosylmethionine are critical to cellular metabolism and are produced industrially to be used as food or feed additives and pharmaceuticals. In particular methionine, an essential amino acid, which cannot be synthesized by animals, plays an important role in many body functions. Aside from its role in protein biosynthesis, methionine is involved in transmethylation and in the bioavailability of selenium and zinc. Methionine is also directly used as ...

AI Technical Summary

Benefits of technology

[0020]In a specific embodiment of the invention methionine / carbon source yield is increased by decreasing the deformylation of formyl-THF, which is accomplished by attenuating the expression of the purU gene (YP—001137322 in C. glutamicum). The PurU enzyme catalyzes the formyl-THF deformylase reaction. The attenuation of the deformylase activity increases the production of methyl-THF that is required for methylation of homocysteine. Loss of C1 metabolites by deformylation leads to an increased production of homocysteine that cannot be transformed into methionine. Homocysteine can then be a substrate for the enzyme cystathionine gamma synthase (MetB) that can catalyze the reaction between O-succinylhomoserine and homocysteine resulting in the production of homolanthionine.

[0078]In another specific embodiment of the invention, the production of the byproduct homolanthionine is reduced. Homolanthionine is an amino acid that is produced form activated homoserine and homocysteine (Kromer et al (2006) J Bacteriol 188, 609-18; and patent application WO 2007 / 051725 by BASF). Homolanthionine is an amino acid that can be separated from methionine only with great difficulty increasing drastically the cost for the production of pure methionine. In addition, homolanthionine comprises two aspartate derived homoserine molecules and a reduced sulfur molecule, all of which could increase methionine / carbon source yield, if transformed into methionine. Therefore it is desirable that the production of homolanthionine is kept as low as possible and the used precursors are transformed into methionine. The PCT application WO 2007 / 051725 proposes some means to reduce the production of homolanthionine. The inventors have found other means to reduce the production of homolanthionine that at the same time permit the transformation of the substrate homocysteine to methionine. Means that favor the transformation of homocysteine to methionine specifically are the attenuation of the formyl-THF deformylase activity encoded by the purU gene, the overexpression of methylene-THF reductase activity encoded by the metF gene, the attenuation of the expression of the pykA and / or pykF gene, the overexpression of serA, serB or serC or the overexpression of the lpd gene.

Problems solved by technology

Nevertheless the racemic mixture does not perform as well as pure L-methionine, as for example in chicken feed additives (Saunderson, C. L. (1985) British Journal of Nutrition 54, 621-633).

Pure L-methionine can be produced from racemic methionine e.g. through the acylase treatment of N-acetyl-D,L-methionine which increases production costs dramatically.

Consequently only the required amounts of metabolites, such as amino acids, are synthesized and can usually not be detected in the culture supernatant of wild-type strains.

This side reaction is not desirable for the industrial production of methionine, since the two amino acids are difficult to separate.

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