%0 Journal Article
%T Thermostable and Alkalistable Xylanases Produced by the Thermophilic Bacterium Anoxybacillus flavithermus TWXYL3
%A Joshua T. Ellis
%A Timothy S. Magnuson
%J ISRN Microbiology
%D 2012
%R 10.5402/2012/517524
%X With the rising cost and finite supply of fossil energy, there is an increasing economic incentive for the development of clean, efficient, and renewable domestic energy. The activities of microorganisms offer the potential conversion of lignocellulosic materials into fermentable sugars, usable for downstream fermentation processes. Strain TWXYL3, a thermophilic facultative anaerobe, was discovered in the Alvord Basin hydrothermal system in Oregon, USA. Phylogenetic analysis of strain TWXYL3 showed it to be 99% similar to the 16S rRNA gene of Anoxybacillus flavithermus WL (FJ950739). A. flavithermus TWXYL3 was shown to secrete a large multisubunit thermostable xylanase complex into the growth medium. Xylanase induction was achieved by resuspending the isolate in a selective xylan-containing medium. Extracellular xylanase activity showed a temperature optimum of 65¡ãC and retained thermostability up to 85¡ãC. Extracellular xylanase activity showed a bimodal pH optimum, with maxima at pH 6 and pH 8. Electrophoretic analysis of the extracellular xylanase shows 5 distinct proteins with xylanase activity. Strain TWXYL3 is the first xylanolytic isolate obtained from the Alvord Basin hydrothermal system and represents a new model system for development of processes where lignocellulosics are converted to biofuel precursors. 1. Introduction Xylanases are enzymes that catalyze the hydrolysis of 1,4-¦Â-D xylosidic linkages in xylan, the second most abundant polysaccharide in nature after cellulose, and the most abundant hemicellulose in plant cell walls [1, 2]. There has been a resurgence in interest in microbial xylanases due to their numerous uses in industrial applications, such as biobleaching of pulp [3¨C5] and most notably the conversion of lignocellulosic materials into fermentable substrates for production of economical and environmentally attractive biofuels [6, 7]. The complete hydrolysis of xylan involves several main-chain cleaving enzymes: endoxylanase (endo-¦Â-1,4-xylanase), ¦Â-xylosidase (xylan 1,4-¦Â-xylosidase), and ¦Á-glucuronidase (¦Á-glucosiduronase) and side-chain cleaving enzymes: ¦Á-arabinofuranosidase (¦Á-L-arabinofuranosidase) and acetylxylan esterase [8, 9]. Endo ¦Â-1,4 xylanase is one of the most common enzymes in xylan hydrolysis. This enzyme hydrolyzes the bonds between xylose subunits in the polymer of xylan to produce oligosaccharides, which in turn can be converted to xylose by ¦Â-xylosidase [4, 10]. The microbial degradation of lignocellulose is an important process because of the reliance all earth biota have on recycling of carbon and supply
%U http://www.hindawi.com/journals/isrn.microbiology/2012/517524/