Production of xylonic acid by recombinant Escherichia coli immobilized on magnetic nanoparticles

Abstract

Conversion of xylose to xylonic acid has obtained growing interest over the years. As the native metabolic pathway of Escherichia coli (E. coli) was unable to convert xylose to xylonic acid, native E. coli has been genetically modified to charter for the production of xylonic acid. However, production of xylonic acid by free cells has encountered some drawbacks that include low yield, lack of stability and reusability of using free cell. Thus, cell immobilization was used for the production of xylonic acid because it can counter the drawbacks of using free cells and elevate the production of xylonic acid. In this study, the parameters affecting the production of xylonic acid by recombinant E. coli immobilized on magnetic nanoparticles were studied. The effect of post induction temperature, Isopropyl ß-D-1-thiogalactopyranoside (IPTG) concentration, xylose concentration, medium pH and expression media towards xylonic acid production, cell density and plasmid stability of the immobilized recombinant E. coli were investigated. The parameters were further optimized by using response surface methodology with the optimum condition of 0.6 mg/mL magnetic nanoparticles at post induction temperature of 30 °C, 0.1 mM IPTG concentration and 50 gL-1 of xylose concentration in expression medium. The immobilized recombinant E. coli produced up to 24.58 gL-1 xylonic acids during one factor at a time screening with the productivity of 1.024 gL-1h-1 and yield of 0.492 g g-1, which has 3-fold increment as compared to free cell. The cells immobilized on the magnetic nanoparticles exhibited a 47 % increment in stability of the plasmid as compared to free cells and can be used for up to 4 times while retaining xylonic acid productivity more than 50 %. Hence, the immobilization of recombinant E. coli using magnetic nanoparticles was demonstrated to increase xylonic acid production, cell stability and reusability.