S93: Thermostable xylanase of a bacterium, Geobacillus sp. DC3, isolated from the former Homestake gold mine in Lead, South Dakota

The Sanford Underground Research Facility (SURF) at the former Homestake gold mine in Lead, SD, provides a unique environment favorable to extremophiles that may express novel thermostable enzymes, including biomass-degrading proteins.  Due to the fact that pretreatment processes for biomass degradation often accompany extreme pH or temperature in order to increase surface area and mass transfer efficiency, it may be desirable to apply thermostable enzymes for biomass conversion.  Thermophilic bacterial strains were isolated from a SURF wood slime sample located 1.48 km beneath the surface through enrichment in lignocellulosic biomass at 60°C.  The thermophilic endospore forming strain isolated from SURF, Geobacillus sp. DC3, was most closely related to Geobacillus thermoleovorans.  The DC3 strain was capable of producing a high level of extracellular endoxylanase at 39.5 U/mg protein and additional hemicellulases including β-xylosidase (0.209 U/mg) and arabinofuranosidase (0.230 U/mg) after the organism was grown in beechwood xylan for 24 h.  A partially purified DC3 endoxylanase exhibited a molecular mass of approximately 43 kDa according to zymography with an optimal pH and temperature of pH 7 and 70°C, respectively, and maintained 70% of its original activity after 16 h incubation at 70°C.