Effect of Temperature on Threonine Production by a Auxotroph of E. coli

Abstract

The effect of cultural temperature on l-threonine production by E. coli strain No. 234, a methionine-valine auxotroph, was investigated and it was found that the yield of l-threonine was greatly dependent on temperature. Appreciable amounts of acetoin (or α-acetolactate) and pyruvate were detected in the broth when the strain No. 234 was cultured in the presence of a limited amount of l-valine. It was suggested that temperature and the presence of l-valine gave a great influence on l-threonine production by their effect on valine-isoleucine metabolism. Effect of temperature on the formation of aspartokinase, threonine deaminase and α-acetolactate synthetase were studied using cell-free extracts of the strain No. 234. The specific activity of α-acetolactate synthetase was greatly repressed and that of aspartokinase appreciably derepressed when the strain No. 234 was cultured at higher temperature in the presence of l-valine. Effect of a temperature-shift on l-threonine fermentation was investigated and it was found that the yield of l-threonine from glucose was greatly increased by a shift-down before stationary phase of growth.