The gene encoding a xylanase from Geobacillus sp. 71 was isolated, cloned, and sequenced. Purification of the Geobacillus sp 7.1 xylanase, XyzGeo71, following overexpression in E. coli produced an enzyme of 47 kDa with an optimum temperature of 75°C. The optimum pH of the enzyme is 8.0, but it is active over a broad pH range. This protein showed the highest sequence identity (93%) with the xylanase from Geobacillus thermodenitrificans NG80-2. XyzGeo71 contains a catalytic domain that belongs to the glycoside hydrolase family 10 (GH10). XyzGeo71 exhibited good pH stability, remaining stable after treatment with buffers ranging from pH 7.0 to 11.0 for 6 h. Its activity was partially inhibited by Al(3+) and Cu(2+) but strongly inhibited by Hg(2+). The enzyme follows Michaelis-Menten kinetics, with K(m) and V(max) values of 0.425 mg xylan/ml and 500 μmol/min.mg, respectively. The enzyme was free from cellulase activity and degraded xylan in an endo fashion. The action of the enzyme on oat spelt xylan produced xylobiose and xylotetrose.

The aim of this study was screening of xylanase and glucose isomerase producing thermophilic bacteria isolated from some hot springs located in Aegean Region of Turkey. Total sixty eight thermophilic isolates (Anoxybacillus, Brevibacillus, Geobacillus, Aneurinibacillus, Thermus, Paenibacillus and Proteobacter) were collected previously from these fields and identified based on 16S rDNA gene sequences. Isolates were screened by plate assay for determining the xylanase and glucose isomerase production abilities seperately in order to find new strains for industrial processes. After an incubation period of two days for xylanase and 5-6 days for glucose isomerase at 50-60 °C, positive isolates were determined. Enzyme producing isolates were confirmed by spectrophotometric measurements with crude enzyme extracts, birchwood xylan and glucose were used as substrates. Most of the isolates (fifty nine) were positive for xylan degradation while only sixteen of them were positive for glucose isomerase activity. Fourteen of the isolates showed both xylanase and glucose isomerase activity. None of the isolates belong to the genera Paenibacillus, Aneurinibacillus, and Proteobacter were glucose isomerase positive, although the glucose isomerase activity of Geobacillus isolates were notably high. Both xylanase and glucose isomerase activities were observed at 50-60 °C which is suitable for biotechnological applications.

IntroductionAnoxybacillus is a relatively new genus compared to the well-studied genera Geobacillus or Bacillus. The genus Anoxybacillus represents aerobic or facultatively anaerobic, neutrophilic, obligately thermophilic, endospore-forming bacteria (İnan et al., 2011). Most of the reported data have revealed that the members of this genus produce interesting enzymes that are thermostable and tolerant to alkaline pH. Some of the well-studied enzymes were discovered through partnerships with industry; for example, the raw starch-degrading amylase was discovered by a Novozyme team (Viksø-Nielsen et al., 2006), and the BfιI RE was discovered by New England Biolabs (D'Souza et al., 2004;Goh et al., 2013).L-ribulokinase (RK; EC 2.7.1.16) is 1 of 3 major enzymes of the arabinose catabolic pathway. L-arabinose is 1 of the major polysaccharide components in plant cell walls and among the most abundant monosaccharides in nature. Furthermore, its utilization pathway in bacteria has been investigated extensively (Zhang et al., 2012). The arabinose regulon is 1 of many gene systems in Escherichia coli and the regulon consists of 4 operons, araBAD, araC, araE, and araFGH, which are responsible for L-arabinose catabolism, gene regulation, low-affinity transport, and high-affinity transport, respectively (Englesberg and Wilcox, 1974;Lichenstein et al., 1987). In the lowaffinity transport system, the transporter, the araE gene product, is bound to the inner membrane and utilizes the electrochemical potential to transport arabinose. The araFGH genes encode arabinose-specific components of a high-affinity transport system, ABC transporters. These are 3 proteins of the ATP-binding cassette transporter family. AraF is the periplasmic arabinose-binding protein, AraG is the ATP-binding component, and AraH is the membrane-bound component (Schleif, 2010). AraC acts directly as an inducer or an activator of gene expression.The araBAD operon encodes 3 different enzymes required for catabolism of L-arabinose, which are responsible for the conversion of L-arabinose into D-xylulose-5-phosphate. AraA, as an isomerase (L-arabinose isomerase), converts arabinose to L-ribulose; AraB, as a kinase (L-ribulokinase), phosphorylates L-ribulose; and AraD, as an epimerase (L-ribulose-5phosphate 4-epimerase), converts L-ribulose-phosphate

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