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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVING BIOCHEMICAL PROCESSES FOR THE PRODUCTION OF SUSTAINABLE FUELS AND CHEMICALS

Location: Renewable Product Technology Research Unit

Title: Thermostable hemicellulases of a bacterium, Geobacillus sp. DC3, isolated from the former Homestake Gold Mine in Lead, South Dakota

Authors
item Bergdale, Terran -
item Hughes, Stephen
item Bang, Sookie -

Submitted to: Applied Biochemistry and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 5, 2014
Publication Date: April 1, 2014
Citation: Bergdale, T.E., Hughes, S.R., Bang, S.S. 2014. Thermostable hemicellulases of a bacterium, Geobacillus sp. DC3, isolated from the former Homestake Gold Mine in Lead, South Dakota. Applied Biochemistry and Biotechnology. 172(7):3488-3501.

Interpretive Summary: Demand for renewable energy has led scientists to search extreme environments, such as the Homestake gold mine in South Dakota, for microorganisms with novel enzymes to improve industrial processes for producing biofuels from lignocellulosic biomass. These enzymes include thermostable cellulases and hemicellulases capable of converting cellulosic biomass to sugars that can be used for biofuel. In this study, a thermophilic bacterial strain, Geobacillus sp. DC3, which produces hemicellulolytic enzymes, was isolated from the mine at a depth of 1.5 km. This strain expressed a high level of extracellular endoxylanase and lower levels of two other hemicellulases after 24-h growth in xylan. The endoxylanase exhibited a molecular mass of approximately 43 kDa with optimal pH of 7 and optimal temperature of 70ºC. It was highly stable and maintained 70% of its original activity after 16 h at 70ºC. The thermostable properties and presence of three different hemicellulases support the potential application of the Geobacillus sp. DC3 strain for industrial hydrolysis of renewable biomass such as lignocellulose.

Technical Abstract: A thermophilic strain, Geobacillus sp. DC3, capable of producing hemicellulolytic enzymes was isolated from the 1.5-km depth of the former Homestake gold mine in Lead, South Dakota. The DC3 strain expressed a high level of extracellular endoxylanase at 39.5 U/mg protein with additional hemicellulases including ß-xylosidase (0.209 U/mg) and arabinofuranosidase (0.230 U/mg), after the bacterium was grown in xylan for 24 h. Partially purified DC3 endoxylanase exhibited a molecular mass of approximately 43 kDa according to zymography with an optimal pH of 7 and optimal temperature of 70 °C. The kinetic constants, Km and Vmax, were 13.8 mg/mL and 77.5 µmol xylose/min•mg xylan, respectively. The endoxylanase was highly stable and maintained 70 % of its original activity after 16 h incubation at 70 °C. The thermostable properties and presence of three different hemicellulases of Geobacillus sp. DC3 strain support its potential application for industrial hydrolysis of renewable biomass such as lignocelluloses.

Last Modified: 9/1/2014
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