Abstract
Cost-effective biofuel production from lignocellulosic biomass depends on efficient degradation of the plant cell wall. One of the major obstacles for the development of a cost-efficient process is the lack of resistance of currently used fungal enzymes to harsh conditions such as high temperature. Adapted, thermophilic microbial communities provide a huge reservoir of potentially interesting lignocellulose-degrading enzymes for improvement of the cellulose hydrolysis step. In order to identify such enzymes, a leaf and wood chip compost was enriched on a mixture of thermo-chemically pretreated wheat straw, poplar and Miscanthus under thermophile conditions, but in two different set-ups. Unexpectedly, metagenome sequencing revealed that incubation of the lignocellulosic substrate with compost as inoculum in a suspension culture resulted in an impoverishment of putative cellulase- and hemicellulase-encoding genes. However, mimicking composting conditions without liquid phase yielded a high number and diversity of glycoside hydrolase genes and an enrichment of genes encoding cellulose binding domains. These identified genes were most closely related to species from Actinobacteria, which seem to constitute important players of lignocellulose degradation under the applied conditions. The study highlights that subtle changes in an enrichment set-up can have an important impact on composition and functions of the microcosm. Composting-like conditions were found to be the most successful method for enrichment in species with high biomass degrading capacity.
Highlights
Lignocellulosic biomass is a worldwide abundant raw natural material which has gained enormous interest as substrate for environmentally friendly and sustainable biofuel production
Metagenomic studies focusing on whole microbial communities rather than isolated organisms, are more likely to identify interesting enzymes for lignocellulose degradation, especially when these communities are derived from specialized communities from lignocellulose-rich ecological niches, such as those from soil, or from specific natural or artificial environments such as compost, or the digestive tract of large herbivores or termites [4,5,6,7]
Two different set-ups were devised (Fig 1): The substrate was incubated with the compost sample either in a submerged culture under agitation, facilitating the access of microorganisms to their substrate and assuring a good repartition of the nutrients that are liberated from the insoluble substrate
Summary
Lignocellulosic biomass is a worldwide abundant raw natural material which has gained enormous interest as substrate for environmentally friendly and sustainable biofuel production. Biomass-degrading microorganisms often act in synergy in order to optimize their growth efforts by minimizing the energetic expense for production of the required degradation enzymes and by maximizing benefits of their common action For these reasons, metagenomic studies focusing on whole microbial communities rather than isolated organisms, are more likely to identify interesting enzymes for lignocellulose degradation, especially when these communities are derived from specialized communities from lignocellulose-rich ecological niches, such as those from soil, or from specific natural or artificial environments such as compost, or the digestive tract of large herbivores or termites [4,5,6,7]
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