Clarifying Key Cellulase Component Cooperated With Lactic Acid Bacteria for Alfalfa Lignocellulose Degradation to Improve Lactic Acid Production

Abstract

Clarifying key cellulase component that played synergistic roles with lactic acid bacteria (LAB) in fermenting alfalfa lignocellulose into lactic acid (LA) is valuable in low-temperature seasons. Last cut and low dry matter (DM) alfalfa was ensiled by 9 treatments, combinations of cellulase component genes engineered Lactoc. lactis subsp. lactis MG1363 strains (HT2, HT3, HT4, HT5, E1C1, E1B1, and C1B1, separately containing bgl1, cbh2, and egl3 gene were mixed at 1:1:1, 2:1:1, 1:2:1, 1:1:2, 1:1:0, 1:0:1, and 0:1:1), cellulase (EN), and a combination of Lactobacillus plantarum and cellulase (LPEN), and without treatments, as the control, with 4 replicates each. After anaerobic preservation in a silo from late fall through winter (3-20℃) for 140 d, the ensiled alfalfa was sampled and analysed. EN degraded lignocellulose best but the pH was the key limiting factor for lignocellulose saccharification of commercial EN in the simultaneous saccharification and fermentation of LPEN. The optimal combination HT4 caused the fewest disaccharide (1.02 g/kg DM) and the highest conversion of water-soluble carbohydrates (WSC) to LA (170%) and increased LA content to 80.0 g/kg DM maximally since cellobiohydrolase better cooperated with Lactoc. lactis host to ferment lignocellulose into LA than endoglucanase and β-glucosidase. Therefore, strong LA production was approached in HT4 by clarifying key cellulase component played synergistic roles with Lactoc. lactis host. This study could benefit the development of LA production in fermenting lignocellulosic biomass.