Topics of current studies include 1. Urease activity of Cryptococcus neoformans; 2. Restriction fragment patterns of mitochondrial DNA from the two varieties of C. neoformans; 3. melanogenesis in C. neoformans; 4. parasexual genetic studies of Candida and Torulopsis species; 5. DNA synthetic cycle of Candida species; and 6. Isolation of a new fungal pathogen. The influence of EDTA on the urease activity of C. neoformans var neoformans and C. neoformans var. gattii, was studied. Urease activity, one of the consistent diagnostic feature of the species, was inhibited by EDTA in the var. neoformans but not in the var. gattii. Nickel was found to be the only cation which eliminated the inhibitory effect of EDTA. This suggested that the urease of C. neoformans is a nickel associated enzyme and that the mechanism of the enzyme synthesis is different in the two varieties although they cause the same disease. The mitochondrial DNA from the four serotypes within the two varieties were digested with several endonucleases. The restriction pattern showed extensive polymorphism among the isolates of different serotypes indicating their different origin. Research was shown that phenoloxidase produced by Cr. neoformans oxidizes dihydroxyphenyl-alanine to dopaquinone after which melanin synthesis proceeds from dopaquinone via dopachrome and 5,6-dihydroxyindole, by auto-oxidation. Based on these observations, the pathway of melanogenesis in Cr neoformans was proposed to be the same as the classic Mason- Raper scheme found in melanoma cells with one exception, melanogenesis in Cr. neoformans is initiated from dopa and not from tyrosine. Parasexual genetic studies of Torulopsis glabrata, Candida parapsilosis, and Candida kruse revealed that Torulopsis glabrata is a hapoid organism while the two Candida species are not. Flow cytometric studies on three important species of Candida, C. albicans, C., tropicalis, and C. parapsilosis, showed that total DNA/cell of stationary phase cultures was markedly different between the species. The DNA content of C. parapsilosis and C. tropicalis were as high or higher than that of C. albicans. Histograms of Candida isolates in the exponential growth phase demonstrated that the majority of the population was in the G2-M phase of the DNA synthetic cycle. The doubling time was fastest in the most virulent species. A new fungal pathogen, Cokeromyces recurvatus, was found to cause chronic cystitis in man.
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