Production of L-threonine by auxotrophic mutants of Escherichia coli.

Two auxotrophic mutants of Escherichia coli have been shown to accumulate significant amounts of l-threonine in the culture medium. One mutant, 13071, is deficient in alpha,epsilon-diaminopimelic acid (DAP), and the other, 13070, is deficient in both DAP and methionine. Accumulation of l-threonine by 13071 in a synthetic medium with mannitol as the carbon source at 37 C incubation temperature was greatly influenced by initial DAP concentration. At an optimal level of DAP a yield of 1.5 g/liter l-threonine was obtained in 28 hr. l-Threonine accumulation by 13070 with sorbitol as the carbon source at 28 C incubation temperature was dependent upon the initial concentration of both DAP and methionine. At optimal levels of the two deficient amino acids, a yield of 2.0 g/liter l-threonine was obtained in 44 to 48 hr. By adding to the medium suitable quantities of beet molasses or sucrose supplemented with corn steep liquor the yield could be raised to almost 4 g/liter.l-Threonine of extremely high purity was isolated from fermentation broth from both mutants. The product was not contaminated with any detectable amounts of d-threonine or allothreonine.