Degradative actions of microbial xylanolytic activities on hemicelluloses from rhizome of Arundo donax.

Polysaccharidases from extremophiles are remarkable for specific action, resistance to different reaction conditions and other biotechnologically interesting features. In this article the action of crude extracts of thermophilic microorganisms (Thermotoga neapolitana, Geobacillus thermantarcticus and Thermoanaerobacterium thermostercoris) is studied using as substrate hemicellulose from one of the most interesting biomass crops, the giant reed (Arundo donax L.). This biomass can be cultivated without competition and a huge amount of rhizomes remains in the soil at the end of cropping cycle (10-15 years) representing a further source of useful molecules. Optimization of the procedure for preparation of the hemicellulose fraction from rhizomes of Arundo donax, is studied. Polysaccharidases from crude extracts of thermophilic microorganisms revealed to be suitable for total degradative action and/or production of small useful oligosaccharides from hemicelluloses from A. donax. Xylobiose and interesting tetra- and pentasaccharide are obtained by enzymatic action in different conditions. Convenient amount of raw material was processed per mg of crude enzymes. Raw hemicelluloses and pretreated material show antioxidant activity unlike isolated tetra- and pentasaccharide. The body of results suggest that rhizomes represent a useful raw material for the production of valuable industrial products, thus allowing to increase the economic efficiency of A. donax cultivation.

Purification and characterization of a protease produced by an aerobic haloalkaliphilic species belonging to the Salinivibrio genus.

An extracellular protease produced at the end of the exponential growth phase was purified to homogeneity and characterized from the new isolate haloalkaliphilic strain 18AG, phylogenetically related to Salinivibrio costicola subsp. costicola. The protease molecular mass was about 38 kDa. The enzyme was dependent on salt concentration for activity and stability, and it showed optimal activity at 60 degrees C in the presence of 2.0% NaCl and 2.0 mM CaCl2, while in the absence of CaCl2 the optimum temperature was 50 degrees C. The enzyme was stable for 24 h at 30 degrees C, whereas at 50 degrees C in the presence of CaCl2 the half life was about 5 h. The enzyme had an optimum pH of 8.0 with 80% of residual activity at pH 9.0. The protease was strongly inhibited by phenylmethyl sulfonylfluoride (PMSF), slightly activated by denaturing agents such as SDS and urea, and partially inhibited by thiol-containing reducing agents. The synthesis of the enzyme in culture media was influenced by the medium composition: it was specifically dependent upon the NaCl concentration and was induced by the presence of gelatin.

Purification and characterization of thermostable xylanase and beta-xylosidase by the thermophilic bacterium Bacillus thermantarcticus.

Bacillus thermantarcticus, a thermophilic bacterium isolated from Antarctic geothermal soil near the crater of Mount Melbourne, produced extracellular xylanase (1,4-beta-D-xylan xylanohydrolase; E.C. 3.2.1.8) and beta-xylosidase (1,4-beta-D-xylan xylohydrolase; E.C. 3.2.1.37). Each extracellular enzyme was separated by gel filtration with Sephacryl S-200 and further purified to homogeneity (119-fold for xylanase and 160-fold for beta-xylosidase). The optimum temperatures were 80 degrees C for xylanase at pH 5.6 and 70 degrees C for beta-xylosidase at pH 6.0. The isoelectric points and molecular masses were 4.8 and 45 kDa for xylanase and 4.2 and 150 kDa for beta-xylosidase, respectively. Xylanase was stable at 60 degrees C for 24 h, whereas it showed a half life at 70 degrees C of 24 h and at 80 degrees C for 50 min. beta-xylosidase activity did not decrease after 1 h at 60 degrees C. Km of xylanase for xylan was 1.6 mg/ml, Km of beta-xylosidase for p-nitrophenyl-beta-D-xylopyranoside was 0.5 mM and for o-nitrophenyl-beta-D-xylopyranoside was 1.28 mM. The action of two enzymes on xylan gave only xylose.