Method for the production of L-threonine by fermentation, using mutated DNA encoding aspartokinase III

Abstract

A DNA containing a gene which codes for aspartokinase III originating in Escherichia bacteria and which has in the coding region a mutation which releases the feedback inhibition by lysine on the aspartokinase III, a recombinant DNA wherein the DNA is linked to a vector DNA capable of autonomous replication in Escherichia bacteria, a microorganism belonging to the genus Escherichia which has been transformed by the introduction of the above mentioned recombinant DNA into the cells thereof, and a method for the production of L-threonine which comprises culturing the microorganism in a fermentation medium, producing and accumulating L-threonine in the culture medium, and collecting the L-threonine from said-culture medium. Escherichia bacteria-derived AK III genes are obtained which sufficiently release the feedback inhibition due to lysine. Introduction of these genes into threonine-producing bacteria results in new threonine-producing bacteria which are much improved in their threonine production over those of the prior art. Use of these threonine-producing bacteria provides a much more excellent method for the production of L-threonine by fermentation than the conventional methods.

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