Effect of dissolved oxygen on l-methionine production from glycerol by Escherichia coli W3110BL using metabolic flux analysis method

Abstract

l-Methionine is an essential amino acid in humans, which plays an important role in the synthesis of some important amino acids and proteins. In this work, metabolic flux of batch fermentation of l-methionine with recombinant Escherichia coli W3110BL was analyzed using the flux balance analysis method, which estimated the intracellular flux distributions under different dissolved oxygen conditions. The results revealed the producing l-methionine flux of 4.8 mmol/(g cell·h) [based on the glycerol uptake flux of 100 mmol/(g cell·h)] was obtained at 30% dissolved oxygen level which was higher than that of other dissolved oxygen levels. The carbon fluxes for synthesizing l-methionine were mainly obtained from the pathway of phosphoenolpyruvate to oxaloacetic acid [15.6 mmol/(g cell·h)] but not from the TCA cycle. Hence, increasing the flow from phosphoenolpyruvate to oxaloacetic acid by enhancing the enzyme activity of phosphoenolpyruvate carboxylase might be conducive to the production of l-methionine. Additionally, pentose phosphate pathway could provide a large amount of reducing power NADPH for the synthesis of amino acids and the flux could increase from 41 mmol/(g cell·h) to 51 mmol/(g cell·h) when changing the dissolved oxygen levels, thus meeting the requirement of NADPH for l-methionine production and biomass synthesis. Therefore, the following modification of the strains should based on the improvement of the key pathway and the NAD(P)/NAD(P)H metabolism.