Abstract
Xylanases are in important class of industrial enzymes that are essential for the complete hydrolysis of lignocellulosic biomass into fermentable sugars. In the present study, we report the cloning of novel xylanases with interesting properties from compost metagenomics libraries. Controlled composting of lignocellulosic materials was used to enrich the microbial population in lignocellulolytic organisms. DNA extracted from the compost samples was used to construct metagenomics libraries, which were screened for xylanase activity. In total, 40 clones exhibiting xylanase activity were identified and the thermostability of the discovered xylanases was assayed directly from the library clones. Five genes, including one belonging to the more rare family GH8, were selected for subcloning and the enzymes were expressed in recombinant form in E. coli. Preliminary characterization of the metagenome-derived xylanases revealed interesting properties of the novel enzymes, such as high thermostability and specific activity, and differences in hydrolysis profiles. One enzyme was found to perform better than a standard Trichoderma reesei xylanase in the hydrolysis of lignocellulose at elevated temperatures.
Highlights
Lignocellulosic biomass represents an attractive raw material base for the production of alternative fuels in the future due to its great abundance and renewability (Geddes et al 2011)
Families GH10 and GH11 both contain over 200 characterized members and have over 30 structure entries listed in PDB according to the carbohydrate active enzymes (CAZy) database (Cantarel et al 2009)
We report the cloning of novel bacterial xylanases from metagenomic libraries derived from the composting of lignocellulosic materials
Summary
Lignocellulosic biomass represents an attractive raw material base for the production of alternative fuels in the future due to its great abundance and renewability (Geddes et al 2011). Producing renewable fuels and chemicals from lignocellulosic biomass along the biochemical conversion route requires the hydrolysis of the polysaccharide components of biomass, cellulose and hemicellulose, into their constituent sugars. Enzymatic hydrolysis has been identified as the most efficient means to this end (Girio et al 2010), but current enzyme systems remain inefficient and high doses of expensive enzymes are required. Xylanases (endo-β-1,4-xylanases, EC 3.2.1.8) are an important class of lignocellulose degrading enzymes that cleave the β-1,4-glycosidic backbone linkages in xylan, the most prominent non-cellulosic polysaccharide in the cell walls of land plants (Girio et al 2010). Family GH30 has been found to include several xylanases (St John et al 2010), many
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