Relationship of Some Cryptococcus neoformans Hypha-Forming Strains to Standard Strains and to Other Species of Yeasts as Determined by Deoxyribonucleic Acid Base Ratios and Homologies

Abstract

The taxonomic relationship between some hypha-forming Cryptococcus neoformans strains and those that morphologically fit the standard description of this species was determined on the basis of DNA base ratios and DNA-DNA duplex formation. The average guanosine plus cytosine content, as estimated from melting temperature profiles, varied between 43.0 and 45.9% for all C. neoformans strains examined. The relative homology was at least 60% for all C. neoformans strains when the labeled DNA was from either a hyphal variant or a standard strain. The nonpathogenic cryptococci, C. laurentii and C. uniguttulatus , showed less than 10% relative homology with either the hyphal or standard C. neoformans strains. Thus, hyphal and standard strains of C. neoformans were sufficiently related to be considered members of the same species.