Studies on neutral exopolysaccharides produced by the ectomycorrhiza Thelephora terrestris.

The ectomycorrhizal hymenomycete Thelephora terrestris was grown in synthetic pure culture and the production of extracellular polysaccharide was monitored. The exopolysaccharides were prepared by ethanol precipitation and then fractionated into two components using a DEAE-Sepharose column. A neutral fraction (NeP) was fractionated on Sepharose CL-6B, which resulted in three peaks: NeP1, NeP2 and NeP3. NeP1 was filtered through an exclusion membrane and two polysaccharides were obtained (fractions: NeA, NeB). Fraction NeB was submitted to methylated derivatives and 1H-, 13C- and 2D NMR spectroscopic analyses. These analyses showed a main chain of a (1-->6)-linked alpha-D-Manp units substituted at O-2 by a variety of side chains containing alpha-Fucp, beta-Xylp and beta-Galp residues. The main fraction corresponds to mannan as shown by methylation analysis. Size exclusion chromatography (HPSEC-MALLS) of fraction NeB showed a main component of 15.0 kDa. It contained mannose, galactose, fucose and xylose in a molar ratio of 50:29:11:10. The fractions NeP2 and NeP3 were characterised as a (1-->6)-linked beta-glucan (pustulan) and (1-->3)-linked beta-glucan, respectively.