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Genetic Relatedness of Filobasidiella neoformans (Cryptococcus neoformans) and Filobasidiella bacillispora (Cryptococcus bacillisporus) as Determined by Deoxyribonucleic Acid Base Composition and Sequence Homology Studies

Laboratory of Clinical Investigation, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20205

Address reprint requests to: Dr. Stephen E. Straus, Medical Virology Section, Laboratory of Clinical Investigation, NIAID, National Institutes of Health, Building 10, Room 11N-113, Bethesda, MD 20205.

ABSTRACT

Deoxyribonucleic acid (DNA) was extracted and purified from three isolates of Filobasidiella neoformans, representing serotypes A and D, and from two isolates of Filobasidiella bacillispora, representing serotypes B and C. Portions of each DNA pool were labeled in vitro by nick translation. Thermal elution profiles were determined and were used to calculate the thermal elution midpoint temperature and moles percent guanine-plus-cytosine content for each DNA. The thermal elution midpoint temperatures of the five DNAs ranged from 91.3 to 92.9°C, and the corresponding estimated contents ranged from 53.4 to 57.2 mol%. Hybridizations were performed with all possible pairs of homologous and heterologous DNAs. The DNAs of serotypes A and D of F. neoformans demonstrated relatedness values of 87.7 to 93.5%. DNAs of serotypes B and C of F. bacillispora showed 88.5% relatedness. Hybridizations of DNAs of F. neoformans with those of F. bacillispora, however, yielded relatedness values of only 55.2 to 63%, indicating that these DNAs are significantly different. Moreover, thermal elution studies revealed substantial base mismatching in heteroduplexes formed between DNAs of F. neoformans and F. bacillispora. These data support previous conclusions suggesting that F. neoformans and F. bacillispora are closely related but different species.