Construction of a threonine-hyperproducing strain of Serratia marcescens by amplifying the phosphoenolpyruvate carboxylase gene

Abstract

The phosphoenolpyruvate carboxylase gene (ppc) of Escherichia coli K-12 was cloned on the multi-copy plasmid pLG339. Plasmid pST101, which carried a 4.3-kb SalI fragment, was introduced into Serratia marcescens T-1165, which carried the seven regulatory mutations for three aspartokinases and two homoserine dehydrogenases. Strain T-1165[pST101] produced phosphoenolpyruvate carboxylase at a rate 26 times higher than the control strain T-1165[pLG339]. While T-1165[pST101] produced 63 mg/ml l-threonine in a medium containing sucrose and urea, whereas T-1165 only produced 52 mg/ml.