Abstract
Enzyme stability and activity at elevated temperatures are important aspects in biotechnological industries, such as the conversion of plant biomass into biofuels. In order to reduce the costs and increase the efficiency of biomass conversion, better enzymatic processing must be developed. Hot springs represent a treasure trove of underexplored microbiological and protein chemistry diversity. Herein, we conduct an exploratory study into the diversity of hot spring biomass-degrading potential. We describe the taxonomic diversity and carbohydrate active enzyme (CAZyme) coding potential in 71 publicly available metagenomic datasets from 58 globally distributed terrestrial geothermal features. Through taxonomic profiling, we detected a wide diversity of microbes unique to varying temperature and pH ranges. Biomass-degrading enzyme potential included all five classes of CAZymes and we described the presence or absence of genes encoding 19 glycosyl hydrolases hypothesized to be involved with cellulose, hemicellulose, and oligosaccharide degradation. Our results highlight hot springs as a promising system for the further discovery and development of thermo-stable biomass-degrading enzymes that can be applied toward generation of renewable biofuels. This study lays a foundation for future research to further investigate the functional diversity of hot spring biomass-degrading enzymes and their potential utility in biotechnological processing.
Highlights
Lignocellulose is one of the most abundant polymers on Earth and is used in many industrial settings including textile processing, paper milling, and biofuel conversion (Cabrera and Blamey, 2018)
Lignocellulose is composed of lignin, hemicellulose, and cellulose in varying compositions depending on the plant source (Gupta and Verma, 2015; He et al, 2018)
Geothermal features were distributed across six countries, with the majority located in the United States (Figure 1); this is because of the long tradition of hot spring research in Yellowstone National Park (YNP), which hosts approximately 55% of the world’s geothermal features
Summary
Lignocellulose is one of the most abundant polymers on Earth and is used in many industrial settings including textile processing, paper milling, and biofuel conversion (Cabrera and Blamey, 2018). Lignin degradation occurs from laccases and peroxidases most commonly in the Auxiliary Activity (AA) families 1 and 2, respectively (Levasseur et al, 2014) These enzymes catalyze oxidation reactions of phenolic compounds and have been widely studied in fungi and some aerobic bacteria (Bugg et al, 2011). Industrial chemical pretreatment can range from pH 1 to 13 (Pedersen et al, 2011) with variable activity of the pretreatment processes toward the different components of lignocellulose depending on the pH of the system Such extreme conditions are typically absent from most natural systems but are normal in geothermal systems where thermostable enzymes have been selected to be active across a broad range of temperature and pH. The diversity of biomass-degrading potential described here will provide new targets for future in vitro functional assays of thermophilic CAZymes that can be tested using methods, such as synthetic biology in conjunction with functional assays
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