CULTURE CONDITIONS FOR IMPROVEMENT OF L-THREONINE PRODUCTION USING A GENETICALLY SELF-CLONED L-THREONINE HYPERPRODUCING STRAIN OF ESCHERICHIA-COLI K-12

We had constructed an L-threonine-hyperproducing strain of E. coli K-12 by recombinant DNA techniques, In this paper, culture conditions for the practical production of L-threonine were investigated using this strain. Cultivation temperature, concentration of required amino acids, and dissolved oxygen greatly influenced the yield of L-threonine, High production of L-threonine was obtained at a high level of dissolved oxygen for the recombinant strain, but not for the parent. This improved production was accompanied by a high copy number of recombinant plasmids and high activity of aspartokinase. Initial addition of L-threonine together with required amino acids greatly reduced the net production of L-threonine. To remove the reductive effect, methods for the addition of the required amino acids were tested, Lowering the required amino acids at a later stage of cultivation seemed to be effective to avoid the reductive effect of the accumulated L-threonine. By using the optimal conditions, the highest level of L-threonine production, 65 g/l, 48% yield, was achieved.