Xylitol production of recombinant escherichia coli immobilized on multi walled carbon nanotubes

Abstract

Xylitol is currently produced in a large scale by a chemical reduction process that needs high energy and cost. Biological conversion of xylitol utilizing microorganisms could be an alternative methodology that is environmentally friendly and economical. This method has been proven to offer a high-yield and competitive. However, one of the major drawback in xylitol production using bacteria is the low yield. Cell immobilization is a promising solution for the enhancement of xylitol production. This study was carried out to improve the xylitol production, cell stability and performance by immobilizing recombinant Escherichia coli (E. coli) on untreated multiwalled carbon nanotubes (MWCNT) using optimum cultural condition. The influence of different treatment on MWCNT and cultural environments on xylitol production, xylose reductase activity, cell viability and lysis of immobilized E. coli were investigated. The immobilized cells on untreated MWCNT exhibited about 2-8-fold increase in xylitol production compared to free cells. The immobilized cells also demonstrated a 22-315% reduction of β-galactosidase activity, as indication of reduced cell lysis and a 17-401% increase in plasmid stability compared to free cells. The xylitol production was successfully improved using central composite design for the response surface methodology. The optimized cultivation conditions obtained for pH, temperature and isopropyl β-D-1-thiogalactopyranoside concentration were 7.42, 29 oC and 0.005 mM, respectively. Under the optimized conditions, the xylitol concentration was 6.325 g/L, representing 91.5% of the predicted value (6.905 g/L) and 1.16-fold higher than the value before optimization process (5.467 g/L). This study demonstrated that the immobilized cells system could be a promising approach to improve the productivity of xylitol using recombinant E. coli.