HIGH FERMENTATIVE PRODUCTION OF L-THREONINE FROM ACETATE BY A BREVIBACTERIUM-FLAVUM STABILIZED STRAIN TRANSFORMED WITH A RECOMBINANT PLASMID CARRYING THE ESCHERICHIA-COLI THR OPERON

Decrease in L-threonine productivity caused not only by plasmid-free s egregation but also by plasmid deletion was observed in a Brevibacteri um flavum L-threonine producer when transformed with a recombinant pla smid carrying Escherichia coli thr operon. However, a recombinant stra in, HT-16, was stabilized by the addition of trimethoprim (a selective marker on the vector) at concentration of 1000 mug/ml, which was rath er higher than the minimum inhibitory one, into the stock culture medi um. Strain HT-16 produced 64.4 g/liter of L-threonine, 30% higher than that of the host strain, after 92 h of cultivation in a small jar fer mentor using acetic acid as a carbon source without trimethoprim.