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Studies on the cell walls and extracellular material of virulent and avirulent Cryptococcus species Ross, Adrianne

Abstract

Relationships between cell envelope biochemistry, pathogenicity and taxonomy of virulent and avirulent Cryptococcus species have been studied. Variation in growth medium allowed controlled production of cells with or without extensive capsule synthesis. Thiamine (10 μg/ml) and a pH of 7.0 were necessary for optimal growth. Heat treatment was used to kill cells. There was no detectable damage to cell envelope materials. Preparations of purified cell wall and extracellular material were analyzed for amino acids, amino sugars and neutral sugars after serial hydrolysis. Extracellular material was also analyzed for phosphorus and uronic acids by colorimetric methods and for 0-acetyl groups by gas-liquid chromatography. The protein portions of cell walls and extracellular material contained the same amino acids in different proportions, specific for each strain. Extracellular material from two strains of Cr. neoformans, 365-16 and 365-26, was very similar in amino acid composition. Ethanolamine and glucosamine occurred in all preparations, cysteine/cystine only in Cr. albidus and Cr. laurentii, and galactosamine only in Cr. neoformans walls. Glucose was the predominant cell wall monomer; xylose, mannose and galactose occurred in smaller quantities. Extracellular material contained large amounts of mannose, a trace of glucose and, in addition, glucuronic acid. Only the Cr. neoformans strains contained O-acetyl groups. Extracellular material and cell wall composition were sufficiently different to suggest independent synthesis. The amount of capsule synthesis and polysaccharide composition were easily affected by growth conditions . Extracellular polysaccharide produced by the most virulent strain of Cr. neoformans (365-11), contained more mannose, glucuronic acid and O-acetyl groups than the less virulent strains. Cell walls of Cr. neoformans 365-26 had more glucose and less glucosamine, mannose and xylose than did the walls of the nonpathogenic Cr. laurentii. Both cell wall and extracellular polymers were similar in composition to those produced by Tremella mesenterica and other basidiomycetes. Hyphal Cr. neoformans (Coward strain) produced septate hyphae and clamp connections. A close taxo-nomic relationship to the heterobasidiomycetes is proposed.

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