Simultaneous saccharification and fermentation of kraft pulp by recombinant Escherichia coli for phenyllactic acid production

Abstract

Simultaneous saccharification and fermentation (SSF) of renewable cellulose for the production of 3-phenyllactic acid (PhLA) by recombinant Escherichia coli was investigated. Kraft pulp recovered from biomass fractionation processes was used as a model cellulosic feedstock and was hydrolyzed using 10–50 filter paper unit (FPU) g−1 kraft pulp of a commercial cellulase mixture, which increased the glucose yield from 21% to 72% in an enzyme dose-dependent manner. PhLA fermentation of the hydrolyzed kraft pulp by a recombinant E. coli strain expressing phenylpyruvate reductase from Wickerhamia fluorescens TK1 produced 1.9mM PhLA. The PhLA yield obtained using separate hydrolysis and fermentation was enhanced from 5.8% to 42% by process integration into SSF of kraft pulp (20gL−1) in a complex medium (pH 7.0) at 37°C. The PhLA yield was negatively correlated with the initial glucose concentration, with a five-fold higher PhLA yield observed in culture medium containing 10gL−1 glucose compared to 100gL−1. Taken together, these results suggest that the PhLA yield from cellulose in kraft pulp can be improved by SSF under glucose-limited conditions.