EFFECT OF INDUCIBLE THRB EXPRESSION ON AMINO-ACID PRODUCTION IN CORYNEBACTERIUM-LACTOFERMENTUM ATCC-21799

Amplification of the operon hom(dr)-thrB encoding a feedback-insensiti ve homoserine dehydrogenase and a wild-type homoserine kinase in a Cor ynebacterium lactofermentum lysine-producing strain resulted in both h omoserine and threonine accumulation, with some residual lysine produc tion. A plasmid enabling separate transcriptional control of each gene was constructed to determine the effect of various enzyme activity ra tios on metabolite accumulation. By increasing the activity of homoser ine kinase relative to homoserine dehydrogenase activity, homoserine a ccumulation in the medium was essentially eliminated and the final thr eonine titer was increased by about 120%. Furthermore, a fortuitous re sult of the cloning strategy was an unexplained increase in homoserine dehydrogenase activity. This resulted in a further decrease in lysine production along with a concomitant increase in threonine accumulatio n.