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

Abstract

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.

Keywords: Arundo donax; Biorefinery; Thermophilic enzymes; Xylan; Xylanases; Xylooligosaccharides.

Figure 1

Optimization of polysaccharide extraction from A. donax rhizomes. Experiments were performed in triplicate with lyophilized material used in appropriate amounts; data are means of the values obtained that did not differ by more than 2%. Yield was expressed in weight (%, w/w) with respect to the initial dry biomass. See Methods for details.

Figure 2

The pentasaccharide β-D-Xyl p -(1–4)-[α-L-Ara f -(1–3)]-β-D-Xyl p -(1–4)-β-D-Xyl p- (1–4)-β-D-Xyl p (1) from hydrolysis mixture using T. lanuginosus enzyme and β-D-Xyl p -(1–4)-[α-L-Ara f -(1–3)]-β-D-Xyl p -(1–4)-D-Xyl p (2) the tetrasaccharide, from the hydrolysis reaction mixture using crude extract of T. thermostercoris.

Figure 3

TLC pattern of enzymatic reactions using A. donax hemicelluloses extract as substrate. CFE-TN = cell-free extract T. neapolitana (Table 2, entry 6); ESGTM1a and ESGTM1b = extracellular suspension of Geobacillus. thermantarcticus (Table 2, entry 7 and 8); X2-X4 = β-1,4-xylooligomers.