Molecular sequence analyses of the intergenic spacer (IGS) associated withrDNA of the two varieties of the pathogenic yeast, Cryptococcus neoformans

The pathogen Crytococcus neoformans has been traditionally grouped in two v arieties, C. neoformans var. neoformans (serotypes A, D and AD) and C. neof ormans var, gaitii (serotypes B and C). A recent taxonomic evaluation of C. neoformans var. neoformans described C. neoformans var. grubii as a new va riety represented by serotype A isolates. Despite immunological, biochemica l, ecological and molecular differences the three varieties are classified within one species. We examined the genetic variability of one hundred and five clinical and environmental isolates that included all Varieties and se rotypes. Sequence analysis of the intergenic spacer (IGS) associated with r DNA revealed significant differences in nucleotide composition between and within the varieties. Parsimony analysis showed five different genotypes re presenting distinct genetic lineages. Although there was a high degree of r elatedness between serotype and genotype this relatedness was not exclusive as serotypes were not restricted to one particular genotypic group. Seroty ping and sequence analyses indicate that C. neoformans var, grubii (serotyp e A) should not be recognized as a separate variety. Based on this study we propose to accept two separate species, C. neoformans (serotypes A, D and AD) and C. bacillisporus (serotypes B and C synonymous with C. neoformans v ar. gattii).