Threonine Production Strain Having Attenuated Expression of the yafV Gene

Abstract

Improved production of threonine from E. coli by fermentation is accomplished by attenuation but not elimination of the expression of either or both of the yafV gene encoding omega-amidase (a.k.a. 2-oxoglutaramate amidase). In certain embodiments the strain also has attenuated expression of the ilvA gene encoding threonine dehydratase (a.k.a threonine deaminase) in cases where there is attenuated express of the ilvA gene there is no need to express an exogenous cimA gene. In examples of both cases, attenuation is accomplished by engineering these genes to contain a weaker ribosome site. Further improvements in threonine production are made by expression of a heterologous pyruvate carboxylase gene exemplified by expression of the Corynebacterium glutamicum pyc gene under control of an E. coli promoter, to provide expression of pyruvate carboxylase that is not naturally expressed in E. coli. Still further improvement is accomplished by overexpression of the rhtC gene encoding the E. coli threonine transporter protein, exemplified by inserting a stronger ribosome binding site upstream of the open reading frame for the rhtC gene.

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