Anaerobic fermentation of Salmonella typhimurium with and without pyruvate carboxylase

Abstract

A plasmid that expressed pyruvate carboxylase (PYC) from Rhizobium etli was introduced into Salmonella typhimurium LT2. Anaerobic fermentations of S. typhimurium with and without PYC were compared with glucose as a carbon source. The presence of PYC increased the succinate yield from glucose from 0.044 g g⁻¹ to 0.22 g g⁻¹, while the lactate yield decreased from 0.31 g g⁻¹ to 0.16 g g⁻¹. Metabolic flux calculations during the early growth phase indicate that under these growth conditions in the presence of PYC more carbon flows to oxaloacetate via pyruvate carboxylase than via phosphoenolpyruvate carboxylase. Also, under these growth and induction conditions, the presence of PYC diminished the cell growth rate from 0.34 h⁻¹ to 0.28 h⁻¹, the specific rate of ATP formation from 45 mmol l⁻¹ h⁻¹ to 27 mmol l⁻¹ h⁻¹, and the specific rate of glucose consumption from 17 mmol l⁻¹ h⁻¹ to 10 mmol l⁻¹ h⁻¹.