Genetically Engineered Escherichia Coli for Ethanol Production from Xylose : Substrate and Product Inhibition and Kinetic Parameters

Abstract

Arecombinant strain of Escherichia coli FBR5 was characterized for ethanol production from xylose in batch reactors. Up to a salt (NaCl) concentration of 10 gL−1, the culture exhibited no inhibition. Above 10 gL−1 of salt concentration the culture experienced inhibition and the maximum concentration of salt that E. coli FBR5 could tolerate was 40 gL−1. At 40 gL−1 NaCl concentration, the value of μmax (maximum specific growth rate, h21) was reduced significantly as compared to control where salt concentration was 0 gL−1. The culture could tolerate a maximum xylose concentration of 250 gL−1, however, at that concentration a reduced cell growth was obtained. A maximum cell concentration of 0.30 gL−1 was obtained at this sugar concentration as compared to 0.75 gL−1 at 100 gL−1 initial xylose. As the concentration of xylose increased, ethanol specific productivity (v) decreased from 0.98 to 0.70 h−1. In these experiments a maximum yield of 0.50 (g ethanol g−1 xylose) was achieved with a productivity of 0.73 gL−1 h−1. Ethanol inhibition studies suggested that the maximum tolerance of the culture was 50 gL−1 ethanol. However, the maximum ethanol that could be produced was 43.5 gL−1. In pH controlled experiments, the maximum ethanol productivity of 0.90 gL−1h−1 was obtained. The value of Km (Michaelis–Menten constant) was evaluated to be 4.38 gL−1.