Structure elucidation of a galactofuranose-rich heteropolysaccharide from aciduric fungus penicillium purpurogenum JS03-21.

The exopolysaccharide-producing fungus Penicillium purpurogenum JS03-21 from the acidic purple clay was screened to develop greater insights into microbial exopolysaccharide resources from extremophilic microorganisms. An exopolysaccharide JS1-1 was purified from the fermented broth of the aciduric fungus using a combination of ethanol precipitation, anion-exchange and size-exclusion chromatography. JS1-1 was found to be a neutral heteropolysaccharide composed of galactose, mannose and glucose in the ratio of 7.9:2.1:1.0, with a molecular weight of about 26 kDa. JS1-1 was subjected to a series of methylation and partial acid hydrolysis reactions, as well as being analyzed by one- and two-dimensional nuclear magnetic resonance, and the results of these analyses revealed JS1-1 to be a galactofuranose-rich polysaccharide. The main chain of JS1-1 contained two regions, including a galactose part composed of a repeating trisaccharide unit [i.e., →5)-β-D-Galf(1 → 5)-β-D-Galf(1 → 6)-β-D-Galf(1→], and a mannose section consisting of (1 → 6)-linked α-D-Manp residues. Two further segments [i.e., α-D-Glcp(1 → 2)-α-D-Galf (1 → and α-D-Galf(1 → 2)-α-D-Manp(1→] existed as branches that were linked to the O-2 atoms of the (1 → 6)-β-D-Galf and (1 → 6)-α-D-Manp regions of the main chain, respectively. The results of the current study demonstrate that JS1-1 is a unique polysaccharide that is rich in both α and β galactofuranose units and therefore different from most of the other known extracellular polysaccharides. The function of this polysaccharide is currently being researched in our laboratory.