Abstract
BackgroundXylanases are one of the most extensively used enzymes for biomass digestion. However, in many instances, their use is limited by poor performance under the conditions of pH and temperature required by the industry. Therefore, the search for xylanases able to function efficiently at alkaline pH and high temperature is an important objective for different processes that use lignocellulosic substrates, such as the production of paper pulp and biofuels.ResultsA comprehensive in silico analysis of family GH11 sequences from the CAZY database allowed their phylogenetic classification in a radial cladogram in which sequences of known or presumptive thermophilic and alkalophilic xylanases appeared in three clusters. Eight sequences from these clusters were selected for experimental analysis. The coding DNA was synthesized, cloned and the enzymes were produced in E. coli. Some of these showed high xylanolytic activity at pH values > 8.0 and temperature > 80 °C. The best enzymes corresponding to sequences from Dictyoglomus thermophilum (Xyn5) and Thermobifida fusca (Xyn8). The addition of a carbohydrate-binding module (CBM9) to Xyn5 increased 4 times its activity at 90 °C and pH > 9.0. The combination of Xyn5 and Xyn8 was proved to be efficient for the saccharification of alkali pretreated rice straw, yielding xylose and xylooligosaccharides.ConclusionsThis study provides a fruitful approach for the selection of enzymes with suitable properties from the information contained in extensive databases. We have characterized two xylanases able to hydrolyze xylan with high efficiency at pH > 8.0 and temperature > 80 °C.
Highlights
Xylanases are one of the most extensively used enzymes for biomass digestion
We present the results of the prospective application of the more active enzymes under the defined conditions, for the hydrolysis of rice straw xylan
From the total number of GH11 sequences listed in the CAZy database, 1306 sequences were analyzed, after discarding those showing coverage lower than 80% of the consensus sequence of the GH11 domain
Summary
Xylanases are one of the most extensively used enzymes for biomass digestion. in many instances, their use is limited by poor performance under the conditions of pH and temperature required by the industry. The search for xylanases able to function efficiently at alkaline pH and high temperature is an important objective for different processes that use lignocellulosic substrates, such as the production of paper pulp and biofuels. Xylanases produced by many microbial species are an important type of industrial enzymes with multiple applications. They are used as additives to enhance the quality of baked goods [3] and animal feeds [4], as well as to bleach kraft pulp [5, 6]. Enzymatic biotransformation of xylan is limited by different factors such as the nature of the substrate, physicochemical conditions (pH, temperature), presence of Talens‐Perales et al Biotechnol Biofuels (2020) 13:198 inhibitors and cost of enzyme product. Xylanases and xylosidases play the most important role in depolymerization of the xylan backbone, while other enzymes act on the cleavage of the side chains [9]
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