From lignocellulosic metagenomes to lignocellulolytic genes: trends, challenges and future prospects

Lignocellulose is the most abundant biomass on Earth with immense potential to act as a primary resource for the production of a range of compounds currently obtained from fossil fuel sources. However, lignocellulosic feedstocks remain largely underexploited due to the complex mixture of recalcitrant polymers present, whose structural features hinder access to the utilizable monosaccharide reservoir within cellulose. Various fungi and bacteria have been identified that can enzymatically decompose lignocellulose to its monomeric compounds for use as carbon sources. The investigation of such lignocellulolytic organisms has proven very useful in gaining primary insights into degradation processes and key microbial enzymes, but the established limitations of culture-based approaches suggest that we have yet to understand the full range of lignocellulolytic mechanisms, likely expressed within natural systems. In this review, we focus on metagenomic approaches to study lignocellulose degradation from structural and functional perspectives, which may provide novel insights into this process in order to rationally design methods for the extraction of compounds from biomass that could enhance biorefinery efficiencies.