Comparative studies of the polysaccharides from species of the genus Ramalina -: lichenized fungi -: of three distinct habitats

Several structurally different glucans (alpha- and beta-) and galactomannans were characterized as components of four species of the genus Ramalina, namely R. dendriscoides, R. fraxinea, R. gracilis and R. peruviana. Freeze-thawing treatment of hot aqueous extracts furnished as precipitates (PW) linear alpha-(D)-glucans of the nigeran type, with regularly distributed (1-->3)- and (1-->4)-linkages in a 1:1 ratio. The supernatants (SW) contained alpha-(D)-glucans with (1-->3)- and (1-->4)-linkages in a molar ratio of 3:1. The lichen residues were then extracted with 2% aq. KOH, and the resulting extracts Submitted to the freeze-thawing treatment, giving rise to precipitates (PK2) of a mixture of alpha-glucan (nigeran) and beta-glucan, which were suspended in aqueous 0.5% NaOH at 50 degreesC, dissolving preferentially the beta-glucan. These were linear with (1-->3)-linkages (laminaran). The mother liquor of the KOH extractions (2% and 10% aq. KOH) was treated with Fehling's solution to give precipitates (galactomannans). The galactomannans are related. having (1-->6)-linked alpha-(D)-mannopyranosyl main chains, substituted at O-4 and in a small proportion at O-2,4 by beta-(D)-galactopyranosyl units. Despite the different habitats of these lichenized fungi, all species studied in this investigation have a similar pool of polysaccharides. (C) 2003 Elsevier Ltd. All rights reserved.