Polymorphism of Sporothrix schenckii surface polysaccharides as a function of morphological differentiation

Abstract

The alkali-extractable polysaccharides from different morphological types of two Sporothrix schenckii strains (1099.12 and 1099.18) were investigated. Dissociation of morphological phase transition and temperature effects was possible in a synthetic medium which produced cultures with 100% yeast forms either at 25 or at 37 degrees C. Only rhamnomannans with single-unit alpha-L-rhamnopyranosyl side chains were formed by the yeast forms irrespective of the incubation temperature. The higher temperature inhibited formation of 4-O- and 2,4-di-O-substituted alpha-D-mannopyranose units in the rhamnomannan. An apparently unsporulated mycelium culture of one S. schenckii strain (1099.12) synthesized a galactomannan whose structure was partially determined by methylation analysis and by proton and 13C nuclear magnetic resonance spectroscopy. In another strain (1099.18), a mannan was excreted in the medium of an apparently conidia-less mycelial form at 25 degrees C with short incubation. Its structure was also partially determined. An apparent mixture of this mannan and a rhamnomannan rich in alpha-L-rhamnopyranosyl-(1 leads to 2)-alpha-L-rhamnopyranose side chains formed in these cultures on prolonged incubation. The proportion of the excreted rhamnomannan increased as the mycelium sporulated and conidia were more numerous. Mannans or galactomannans may be transient polysaccharides in the young mycelium of S. schenckii. As the culture develops, rhamnomannans are formed in amounts usually masking the presence of other mannose-containing polysaccharides. It is suggested that in S. schenckii different polysaccharides are formed with side chains containing different proportions of rhamnose, mannose, or galactose, as a function of morphological differentiation.