title: Highly thermostable GH39 β-xylosidase from a Geobacillus sp. strain WSUCF1.
abstract: BACKGROUND
  Complete enzymatic hydrolysis of xylan to xylose requires the action of endoxylanase and β-xylosidase. β-xylosidases play an important part in hydrolyzing xylo-oligosaccharides to xylose. Thermostable β-xylosidases have been a focus of attention as industrially important enzymes due to their long shelf life and role in the relief of end-product inhibition of xylanases caused by xylo-oligosaccharides. Therefore, a highly thermostable β-xylosidase with high specific activity has significant potential in lignocellulose bioconversion.
  
  
  RESULTS
  A gene encoding a highly thermostable GH39 β-xylosidase was cloned from Geobacillus sp. strain WSUCF1 and expressed in Escherichia coli. Recombinant β-xylosidase was active over a wide range of temperatures and pH with optimum temperature of 70 °C and pH 6.5. It exhibited very high thermostability, retaining 50% activity at 70 °C after 9 days. WSUCF1 β-xylosidase is more thermostable than β-xylosidases reported from other thermophiles (growth temperature ≤ 70 °C). Specific activity was 133 U/mg when incubated with p-nitrophenyl xylopyranoside, with Km and Vmax values of 2.38 mM and 147 U/mg, respectively. SDS-PAGE analysis indicated that the recombinant enzyme had a mass of 58 kDa, but omitting heating prior to electrophoresis increased the apparent mass to 230 kDa, suggesting the enzyme exists as a tetramer. Enzyme exhibited high tolerance to xylose, retained approximately 70% of relative activity at 210 mM xylose concentration. Thin layer chromatography showed that the enzyme had potential to convert xylo-oligomers (xylobiose, triose, tetraose, and pentaose) into fermentable xylose. WSUCF1 β-xylosidase along with WSUCF1 endo-xylanase synergistically converted the xylan into fermentable xylose with more than 90% conversion.
  
  
  CONCLUSIONS
  Properties of the WSUCF1 β-xylosidase i.e. high tolerance to elevated temperatures, high specific activity, conversion of xylo-oligomers to xylose, and resistance to inhibition from xylose, make this enzyme potentially suitable for various biotechnological applications.
authors.affiliation: Department of Chemical and Biological Engineering, South Dakota School of Mines and Technology, Rapid City, SD, 57701, USA. Bhalla@msu.edu.|Present address: Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI, 48824, USA. Bhalla@msu.edu.
authors.forename: Aditya
authors.initials: A
authors.lastname: Bhalla
authors.affiliation: Renewable Product Technology Research Unit, Agricultural Research Service, National Center for Agricultural Utilization Research, U.S. Department of Agriculture, Peoria, IL, 61604, USA. Kenneth.Bischoff@ars.usda.gov.
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Bischoff
authors.affiliation: Department of Chemical and Biological Engineering, South Dakota School of Mines and Technology, Rapid City, SD, 57701, USA. Rajesh.Sani@sdsmt.edu.
authors.forename: Rajesh K
authors.initials: RK
authors.lastname: Sani
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004795:Enzyme Stability; D056506:Geobacillus / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008031:Lignin / Q000378:metabolism; D008970:Molecular Weight; D014994:Xylose / Q000378:metabolism; D014995:Xylosidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C036909:lignocellulose; D008031:Lignin; D014994:Xylose; D014995:Xylosidases