Isolation of a Cryptococcus neoformans serotype A MATa strain from the Italian environment.

Cryptococcus neoformans is a heterothallic basidiomycete which possesses a bipolar mating system based on two mating type alleles, MATa and MATalpha. In the type variety, C. neoformans var. neoformans, both mating types have been found among strains of one serotype, serotype D, whereas only MATalpha was identified after extensive survey of serotype A strains. Serotype A MA Ta appeared to be extinct or to exist only in a vestigial, non-functional form. We report the isolation of a C. n. var. neoformans serotype A MATa strain from the Italian environment. The strain was serotyped by slide agglutination test, genotyped by polymerase chain reaction (PCR) fingerprinting using the (GACA)4 primer, and its haploid state was determined by flow cytometry. The mating type was identified by PCR amplification of the pheromone a gene. In addition, the amplification of the four STE20 alleles, specific for the mating type of serotypes A and D, showed that the strain contains only the MATa locus. By crossing experiments the strain was found to be fertile. The interest in the finding of this fertile isolate is related to the possibility to construct a congenic pair of serotype A MATa/MATalpha strains to be used in genetic and pathogenesis studies.