The newly discovered Polysaccharide Utilisation Loci linked to multiple cellulolytic systems in nature: how does it work?

Lignocellulosic (plant) biomass provides a giant potential source of energy and valuable products and is thought to play a major role in a future bio-based economy. Unfortunately, this enormous resource comprising of various grasses, wood, forest product residues and agricultural residues, so far remains largely untapped. This is predominantly due to the recalcitrance of lignocellulosic biomass, coinciding with a lack of understanding how this recalcitrance is overcome in nature and can be overcome industrially. Lignocellulosic biomass consists of three main components; cellulose, hemicellulose and lignin. In nature, lignocellulose can be readily deconstructed by enzyme-driven hydrolysis, and a variety of free-living organisms have subsequently evolved to take advantage of this material as a nutrient source. In particular, obligate herbivores have evolved to maintain a symbiotic relationship with a specialized consortium of gut microbes (microbiomes) that underpins lignocellulose deconstruction (and anaerobic fermentation). Microbial community analysis consistently shows the gut microbiome of herbivores (i.e. the rumen of a cow) is commonly dominated by a limited number of frequently observed bacterial phyla, namely the Firmicutes and the Bacteroidetes. The Bacteroidetes represent a numerically dominating phylum in the rumen, however their functional role is poorly understood due to their difficulty to cultivate in pure culture and thus examine in the laboratory. This project has built on the initial discoveries of putative cellulose and hemicellulose degrading gene clusters from uncultured and dominant rumen Bacteroidetes. Biochemical characterization of these gene clusters has led to two important discoveries. Firstly, we have found that the rumen Bacteroidetes use a hitherto unknown mechanism for cellulose degradation that is alternative to the classical paradigms that are well established in the field. Secondly, these gene clusters exhibit broad capabilities that enable the Bacteroidetes to metabolise the many different plant polysaccharides that are available in the environment, thus supporting their numerical dominance in the gut microbiome of ruminants.

Understanding the enzymology of plant biomass conversion is a key issue in the world's desire to establish a sustainable bio-based economy. Currently available enzyme technology is insufficiently effective, and several fundamental key questions as to how enzymes and plant cell walls interact remain. The present project will address these issues by studying a natural biomass-converting ecosystem, namely the microbial community (microbiome) resident in the digestive tract of Svalbard reindeer. The project aims to describe major as-yet uncharacterized cellulolytic gene clusters that have recently been detected in a broad range of herbivore gastrointestinal microbiomes including the reindeer, and are believed responsible for conversion of lignocellulosic bio mass. To achieve its objectives the project will generate a reconstruction of microbial community structure and metabolism using a combination of 'omics' technologies and metagenome-directed isolation strategies to target a dominant novel species (SRM-1) that harbors the cellulolytic gene cluster of interest. Relevant genes identified from the metagenome and/or SRM-1 isolate genome/transcriptome will be cloned, over-expressed, and their gene products characterized in detail. This project will link the mos t prominent Norwegian research group on biomass enzymology (Prof. Vincent Eijsink, UMB) to state of the art metagenomic technologies that will be used to access and characterize these cellulolytic gene clusters that are harbored in as-yet uncultured micro organisms that inhabit natural biomass converting ecosystems. The project complements existing activities in the host laboratory on polysaccharide converting enzymes and complements ongoing international efforts in herbivore microbiome metagenomics by foc using on a Norwegian 'niche' species.