Abstract
Efficient enzymatic hydrolysis of lignocellulose to fermentable sugars requires a complete repertoire of biomass deconstruction enzymes. Hemicellulases play an important role in hydrolyzing hemicellulose component of lignocellulose to xylooligosaccharides and xylose. Thermostable xylanases have been a focus of attention as industrially important enzymes due to their long shelf life at high temperatures. Geobacillus sp. strain WSUCF1 produced thermostable xylanase activity (crude xylanase cocktail) when grown on xylan or various inexpensive untreated and pretreated lignocellulosic biomasses such as prairie cord grass and corn stover. The optimum pH and temperature for the crude xylanase cocktail were 6.5 and 70°C, respectively. The WSUCF1 crude xylanase was found to be highly thermostable with half-lives of 18 and 12 days at 60 and 70°C, respectively. At 70°C, rates of xylan hydrolysis were also found to be better with the WSUCF1 secretome than those with commercial enzymes, i.e., for WSUCF1 crude xylanase, Cellic-HTec2, and AccelleraseXY, the percent xylan conversions were 68.9, 49.4, and 28.92, respectively. To the best of our knowledge, WSUCF1 crude xylanase cocktail is among the most thermostable xylanases produced by thermophilic Geobacillus spp. and other thermophilic microbes (optimum growth temperature ≤70°C). High thermostability, activity over wide range of temperatures, and better xylan hydrolysis than commercial enzymes make WSUCF1 crude xylanase suitable for thermophilic lignocellulose bioconversion processes.
Highlights
Lignocellulosic agricultural and forestry waste materials are the key substrates for second generation biofuels
Thermophilic bacteria are excellent source of thermostable xylanases, which have the potential to be utilized in lignocellulose hydrolysis (Bhalla et al, 2013, 2014a,b)
Thermostable xylanases, optimally active at high temperatures and wide range of pHs are useful under harsh industrial processing conditions (Turner et al, 2007)
Summary
Lignocellulosic agricultural and forestry waste materials are the key substrates for second generation biofuels. Hemicelluloses are classified according to the main sugar in the backbone of the polymer, e.g., xylan (β-1,4-linked xylose) or mannan (β-1,4-linked mannose) (Jørgensen et al, 2007). To obtain these linked sugars, there is a need to effectively break the locked polysaccharides from recalcitrant lignocellulose. There have been various reports published on deconstruction of hemicellulose utilizing hemicellulases Endoxylanases and β-xylosidases are reported to be the main components responsible for effective conversion of xylan fraction of biomass to monomeric xylose (Qing and Wyman, 2011; Bhalla et al, 2014a,b)
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