Integrated and Enhanced Coassimilation of Formate and Acetate for Efficient Utilization of Lignocellulosic Hydrolysate

Abstract

Hydrolysis of lignocellulosic biomass is widely recognized as the most commonly used pretreatment method. The presence of formate and acetate, which constitute a notable proportion of inhibitory compounds in lignocellulosic hydrolysate, hinders their efficient utilization as a carbon source. Herein, we performed metabolic engineering on E. coli strains by introducing a heterologous RuMP pathway and increasing the intracellular pools of the essential cofactors NADPH and ATP to achieve formate assimilation and enhance acetate assimilation, respectively. 13C-isotope analysis indicated that formate assimilation occurred through the exogenous heterologous RuMP pathway rather than through the endogenous formate-fixing mechanisms. Enhancement of acetate assimilation can be obtained by genetic modification to increase the intracellular support of NADPH and ATP. Furthermore, we incorporated the ability for formate assimilation and improved acetate assimilation into the E. coli strains that have been engineered for L-tryptophan biosynthesis, resulting in the recombinant strain FATrp16. When lignocellulosic hydrolysate was utilized as the sole carbon source, FATrp16 showed a marked improvement in the consumption of formate and acetate, along with the high production of l-Trp (0.38 g/gDCW) in flask culture. This study presents an integrated approach to facilitate the efficient utilization of lignocellulosic hydrolysate.