The hemicellulose-degrading enzyme system of the thermophilic bacterium Clostridium stercorarium: comparative characterisation and addition of new hemicellulolytic glycoside hydrolases

Abstract

BackgroundThe bioconversion of lignocellulosic biomass in various industrial processes, such as the production of biofuels, requires the degradation of hemicellulose. Clostridium stercorarium is a thermophilic bacterium, well known for its outstanding hemicellulose-degrading capability. Its genome comprises about 50 genes for partially still uncharacterised thermostable hemicellulolytic enzymes. These are promising candidates for industrial applications.ResultsTo reveal the hemicellulose-degrading potential of 50 glycoside hydrolases, they were recombinantly produced and characterised. 46 of them were identified in the secretome of C. stercorarium cultivated on cellobiose. Xylanases Xyn11A, Xyn10B, Xyn10C, and cellulase Cel9Z were among the most abundant proteins. The secretome of C. stercorarium was active on xylan, β-glucan, xyloglucan, galactan, and glucomannan. In addition, the recombinant enzymes hydrolysed arabinan, mannan, and galactomannan. 20 enzymes are newly described, degrading xylan, galactan, arabinan, mannan, and aryl-glycosides of β-d-xylose, β-d-glucose, β-d-galactose, α-l-arabinofuranose, α-l-rhamnose, β-d-glucuronic acid, and N-acetyl-β-d-glucosamine. The activities of three enzymes with non-classified glycoside hydrolase (GH) family modules were determined. Xylanase Xyn105F and β-d-xylosidase Bxl31D showed activities not described so far for their GH families. 11 of the 13 polysaccharide-degrading enzymes were most active at pH 5.0 to pH 6.5 and at temperatures of 57–76 °C. Investigation of the substrate and product specificity of arabinoxylan-degrading enzymes revealed that only the GH10 xylanases were able to degrade arabinoxylooligosaccharides. While Xyn10C was inhibited by α-(1,2)-arabinosylations, Xyn10D showed a degradation pattern different to Xyn10B and Xyn10C. Xyn11A released longer degradation products than Xyn10B. Both tested arabinose-releasing enzymes, Arf51B and Axh43A, were able to hydrolyse single- as well as double-arabinosylated xylooligosaccharides.ConclusionsThe obtained results lead to a better understanding of the hemicellulose-degrading capacity of C. stercorarium and its involved enzyme systems. Despite similar average activities measured by depolymerisation tests, a closer look revealed distinctive differences in the activities and specificities within an enzyme class. This may lead to synergistic effects and influence the enzyme choice for biotechnological applications. The newly characterised glycoside hydrolases can now serve as components of an enzyme platform for industrial applications in order to reconstitute synthetic enzyme systems for complete and optimised degradation of defined polysaccharides and hemicellulose.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1228-3) contains supplementary material, which is available to authorized users.

Recent Development of Extremophilic Bacteria and Their Application in Biorefinery

“…Another challenge is that a biorefinery needs a whole enzyme platform, and it is difficult for a single thermostable enzyme to integrate into the conventional enzyme system. A single enzyme will lead to a synergistic effect and affect the application of the enzyme system in biorefineries (Broeker et al, 2018). Therefore, building a whole enzyme platform of the thermostable enzyme system may be one of the important research directions in the future.…”

Global Transcriptomic Responses of Roseithermus sacchariphilus Strain RA in Media Supplemented with Beechwood Xylan

“…Other CAZymes-for example, α-l-rhamnosidase, α-glucuronidase, α-n-arabinofuranosidase, and endo-1,4-β-galactanase were also upregulated. These enzymes can putatively degrade polymers or side chains made up of arabinose, galactose, and rhamnose sugar monomers [6,65,66].…”

Structural and biochemical characterization of bifunctional XynA

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