Lactic Acid Production from Lignocellulosic Biomass by a Co-culture of Enterococcus casseliflavus CW3-1 and Paucilactobacillus vaccinostercus MQ2

Abstract

Lactic acid (LA) is a growing demand platform chemical for food, pharmaceutical, and bioplastic applications. Lignocellulose offers an alternative to edible sugars as a substrate. However, its microbial conversion of mixed hexose/pentose sugars remains challenging. In this study, two new lactic acid bacteria with distinct sugar utilization profiles were isolated and evaluated for their LA production capability using a series of substrates. Enterococcus casseliflavus CW3-1 exhibited a partially homofermentative behavior and was capable of assimilating both hexose and pentose sugars. In contrast, Paucilactobacillus vaccinostercus MQ2 showed a heterofermentative manner and was a typical pentose-preferring bacterium, which did not metabolize glucose. In the simultaneous saccharification and fermentation (SSF) of alkali-pretreated corn stover and sugarcane bagasse with a commercial cellulase, co-cultivation of the two strains significantly outperformed the mono-cultures and the LA production from co-culture was slightly higher than the sum of the production from the two monocultures. Fermentation results from two types of biomasses showed that the maximum LA yield reached 0.78±0.03 g/g substrate; however, increasing the substrate concentration led to a decrease in yield. These results demonstrate the superiority of using microbial consortia for sustainable LA biorefining from lignocellulosic biomass.