Production of β-xylanase and β-xylosidase by the extremely halophilic archaeon Halorhabdus utahensis
The extremely halophilic archaeon, Halorhabdus utahensis, isolated from the Great Salt Lake, Utah, produced β-xylanase and β-xylosidase activities. Both enzymes were active over a broad NaCl range from near zero to 30% NaCl when tested with culture broth. A broad NaCl optimum was observed for β-xylanase activity between 5% and 15% NaCl, while β-xylosidase activity was highest at 5% NaCl. Almost half of the maximum activities remained at 27%–30% NaCl for both enzyme activities. When dialyzed culture supernatant and culture broth were employed for determination of β-xylanase and β-xylosidase stabilities, approximately 55% and 83% of the initial β-xylanase and β-xylosidase activities, respectively, remained after 24 h incubation at 20% NaCl. The enzymes were also shown to be slightly thermophilic; β-xylanase activity exhibiting two optima at 55° and 70°C, while β-xylosidase activity was optimal at 65°C. SDS-PAGE and zymogram techniques revealed the presence of two xylan-degrading proteins of approximately 45 and 67 kDa in culture supernatants. To our knowledge, this paper is the first report on hemicellulose-degrading enzymes produced by an extremely halophilic archaeon.
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