Enhanced bioconversion of grass straw into bioethanol by a novel consortium of lignocellulolytic bacteria aided by combined alkaline-acid pretreatment

Grass straw represents an attractive and renewable resource for the production of value-added products like bioethanol. However, due to its recalcitrant structure and heterogeneity, efficient biodegradation of the grass straw remains a challenge for biorefinery. In view of this objective, the efficiency of the bacterial consortium was evaluated on grass straw pretreated with mild alkaline acid solutions. The results revealed that the pretreatment of the grass straw significantly enhanced the saccharification efficiency of the bacterial consortium. The Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses revealed that chemical pretreatment altered the structure of the grass straw, removing the majority of the lignin and hydrogen bonding between cellulose and hemicellulose. The field emission scanning electron microscopy (FESEM) showed an altered surface of the pretreated grass straw with pores and tunnels. During saccharification, the highest reducing sugars (224.33 ± 1.15 µg/mL) were released for 3% grass straw loadings using 2.5% of the bacterial consortium after 14 days of incubation, signifying the synergism of bacterial strains for lignocellulose bioconversion. Subsequently, the highest ethanol yield of 3.59 ± 0.85% (v/v) was attained at pH 5.5 on the 4th day of fermentation by Saccharomyces cerevisiae using 8% of yeast culture/inoculum. The overall obtained results highlight the significance of the cellulolytic bacterial consortium towards lignocellulosic biorefinery by secreting grass straw hydrolyzing cellulases and hemicellulases, signifying its valorization as feedstock as well as ethanol fermentation. Graphical Abstract