Capsule-associated genes of serotypes of Cryptococcus neoformans, especially serotype AD.

Cryptococcus neoformans has been divided into five serotypes (A, B, C, D and AD) by the slide agglutination test against antigens of the polysaccharide capsule component. The isolates of serotype AD show positive reactions with both serotype A and D antigens. In this study, the nucleotide sequences of the capsule-associated genes CAP10, CAP59, CAP60 and CAP64 from five serotypes of C. neoformans were analyzed for their phylogenetic relationships, with special regard to serotype AD. The nucleotide sequence analyses showed that serotype AD had two different sequences in these four genes. Phylogenetic analysis revealed that these genes from serotype AD are included in the two clusters of serotypes A and D, but not in serotypes B or C. Southern blot analysis of genomic DNAs of serotypes A, D and AD digested with BamH I by hybridizing with a CAP64 probe indicated that both bands of fragments detected in serotypes A and D were also detected in serotype AD. These results confirm that serotype AD could be a mixture of serotypes A and D in the four CAP genes, consistent with its putative origin detected by the hybridization of these two serotypes. The present results indicated that serotypes of C. neoformans could be identified by the phylogenetic analyses of CAP genes.