Metabolic evolution of non-transgenic Escherichia coli SZ420 for enhanced homoethanol fermentation from xylose.

摘要

Efficient utilization of pentose sugars (xylose and arabinose) is an essential requirement for economically viable ethanol production from cellulosic biomass. The desirable pentose-fermenting ethanologenic biocatalysts are the native microorganisms or the engineered derivatives without recruited exogenous gene(s). In this study, we used a metabolic evolution (adaptive selection) approach to improve a non-transgenic homoethanol Escherichia coli strain SZ420 (ldhA pflB ackA frdBC pdhR:: pflBp6-aceEF-lpd ) for xylose fermentation. An improved mutant, KC01, was evolved through a three-month metabolic evolution process. This evolved mutant increased pyruvate dehydrogenase activity by 100%, cell growth rate (h-1) by 23%, volumetric ethanol productivity by 65% and ethanol tolerance by 200%. These improvements enable KC01 to complete 50 g L-1 of xylose fermentation with an ethanol titer of 23 g L-1 and a yield of 90%. The improved cell growth and ethanol production of KC01 are likely attributed to its threefold increased ethanol tolerance.