To study the structures of the epitopes of the extracellular polysaccharides from Penicilium and Aspergillus species, an exo-13-D-galactofuranosidase was purified from a commercial crude enzyme preparation from Trichoderma harzianum. Analysis of ring size and linkage position of the galactose residues of the extracellular polysaccharide of Penicillium digitatum, before and after enzymatic treatment, was determined by the reductive-cleavage technique. In addition to terminal and 13(1-5)-linked galactofuranosides, P(1-6)-linked and P(1,5,6)-linked branched galactofuranose residues could be identified. After degradation with the purified exo-13-D-galactofuranosidase, all initial linkages of the galactofuranose residues were still present, but the amount of D(1-5)-linked galactofuranose residues had decreased considerably. Treatment of the extracellular polysaccharides ofPenicillium and Aspergils species with the purified exo-o-D-galactofuranosidase resulted in complete disappearance of the enzyme-linked immunosorbent assay reactivity of these polysaccharides, using immunoglobulin G antibodies raised against P. digitatum. Therefore, with the use of this enzyme, it was proved that the 13(1-5)-linked galactofuranosyl residues only are responsible for the antigenicity of the extracellular polysaccharides ofPenicillium and Aspergills molds. A new structural model for the antigenic galactofuranose side chains of the galactomannan from P. digitatum is proposed. Molds are able to excrete a large variety of polysaccharides, some of them with antigenic properties (22, 29). Several authors studied the chemical structure of polysaccharides isolated from mycelium of mold species belonging to the genera Penicillium and Aspergillus (3-5). Penicillium and Aspergillus species are important fungi which are distributed worldwide and are the cause of many cases of food spoilage. Medically, some members are significant because of their ability to cause aspergillosis in humans and the release of mycotoxins. The polysaccharides are constituted mainly of mannose, galactose, and glucose, with minor amounts of protein (3-5). Galactosamine has been found in the polysaccharides of several Aspergillus species (2, 13, 27). Extracellular polysaccharides (EPSs) produced by these molds appeared to have similar structures (12, 24).

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In this study, polyclonal IgG antibodies raised against extracellular polysaccharides (EPS) of Mucor racemosus were characterised as almost specific for moulds belonging to the order of Mucorales. Cross-reactivity in the ELISA could be observed only towards the yeast Pichia membranaefaciens. EPS were isolated from various cultures of M. hiemalis growing on six different carbon sources and two nitrogen sources, with ratios varying from 0.13 to 0.44 relative to the amount of biomass. Other strains including Mucor spp., Rhizopus spp., Rhizomucor spp., Absidia corymbifera and Syncephalastrum racemosum also excreted EPS, with ratios varying from 0.05 to 0.23. In all cases, the excreted EPS had similar antigenic properties as determined by ELISA. No enzymatic degradation of the antigenic parts of the polysaccharides could be observed upon prolonged incubation. Considering that all tested strains formed similar amounts of antigenic EPS there might be scope for the specific detection of biomass of Mucoralean moulds using ELISA techniques for example in food.

A monoclonal antibody (mAb) was raised against extracellular polysaccharides from Mucor racemosus after intrasplenic immunization of mice. An indirect ELISA and a dot-blot assay were developed with this mAb. The IgG antibody was found to be very specific for all mould species tested belonging to the order of Mucorales, except species belonging to the genus Mortierella sensu stvicto. No cross-reactions were observed with other moulds or yeasts. The immunoreactivity of the polysaccharides of these moulds with this mAb is based on carbohydrate epitopes, in which fucose residues probably play an important role. The mAb may be suited for specific detection of species of the genera Mucor, Rhizopus, Rhizomucor, Thamnidium, Absidia, Syncepkalastrum and species belonging to the Mortierella isabellina group in food, and possibly for diagnosis of mucormycosis in humans.

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