Cellulosomal hemicellulases: Indispensable players for ensuring effective lignocellulose bioconversion

Abstract

The bioconversion of lignocellulose has attracted global attention, due to the significant potential of agricultural and forestry wastes as renewable zero-carbon resources and the urgent need for substituting fossil carbon. The cellulosome system is a multi-enzyme complex produced by anaerobic bacteria, which comprises cellulases, hemicellulases, and associated enzymatic and non-enzymatic components that promote biomass conversion. To enhance their efficiency in degrading recalcitrant lignocellulosic matrices, cellulosomes have been employed to construct biocatalysts for lignocellulose bioconversion, such as consolidated bioprocessing and consolidated bio-saccharification. Hemicelluloses, the second most abundant polysaccharides in plant cell walls, hold valuable application potential but can also induce inhibitory effects on cellulose hydrolysis, thus highlighting the indispensable roles of hemicellulases within the cellulosome complex. This review evaluated current research on cellulosomal hemicellulases, comparing their types, abundance, and regulation, primarily focusing on eight known cellulosome-producing species of different origins. We also reviewed their growth conditions, their hemicellulose-degrading capabilities, and the inhibitory effects of hemicellulose on cellulosome-based lignocellulose saccharification. Finally, we proposed strategies for targeted enhancement of hemicellulase in cellulosomes to improve lignocellulose bioconversion in future studies.