Candida glycerinogenes Strains Overexpressing Transcription Factors have Improved Furfural Tolerance in Ethanol Production from Non-detoxified Cellulose Hydrolysate.

Abstract

Cellulose is one of the main raw materials for production of green ethanol, but the presence of the growth inhibitor furfural in non-detoxified lignocellulosic hydrolysates often seriously affects their utilization. In a previous study, we obtained strains of Candida glycerinogenes that were tolerant to furfural, but at concentrations above 2.5g L-1 there was a significant increase in the growth lag phase. In this work, transcription factor genes (SEF1, STB5, CAS5, and ETP1) associated with furfural tolerance were identified and employed to obtain modified strains permitting ethanol fermentation of concentrated and non-detoxified cellulose hydrolysates containing more than 2.5g L-1 furfural. Tolerance to furfural could be increased to 4.5g L-1 by overexpression of either STB5 or ETP1, which have different regulation patterns. Moreover, in non-detoxified and concentrated cellulose hydrolysate, overexpression of ETP1 significantly shortened the growth lag phase and ethanol fermentation time was reduced by 17-20%. In batch fermentations fed with concentrated non-detoxified lignocellulose hydrolysate, ethanol productivity and maximum ethanol concentration reached 2.4g L-1 h-1 and 72.5g L-1, increases of 26.1% and 6.6%, respectively. The results provided a route for the economic use of lignocellulose for chemical production.