STUDIES ON THE COMPOSITION OF EXTRACELLULAR POLYSACCHARIDE PRODUCED BY HYALOTHECA-DISSILIENS (DESMIDIACEAE)

The filamentous desmid Hyalotheca dissiliens (Smith) Brebisson (Desmid iaceae), strain 020CH-UFSCar, is characterized by an extracellular muc ilaginous sheath which is continuously dissolving into the surrounding medium that becomes viscous with ageing of the culture. Gas-liquid ch romatographic analysis showed that glycuronic acid is the major sugar unit followed by galactose found in this extracellular polymer. Other monosaccharides, arabinose, rhamnose, fucose and xylose are also prese nt in smaller amounts. After methylation both before and after carboxy l reduction amounts of terminal and 1 --> 4 linked glucuronic acid uni ts were found. Part of the glucuronic acid residues is also present as branchpoints, indicating that this monosaccharide is present in chain as 1 --> 4 linked units with some of them representing branchpoints t hrough the C-3 position. The linkage of the fucose units are more comp lex which shows that fucose is responsible for relatively higher amoun ts of branchpoints than other monosaccharides.