Genetic divergence at the SODA locus of six different formae speciales of Pneumocystis carinii

Genetic divergence at the SODA (manganese-dependent superoxide dismutase, M n-SOD) locus were compared in six Pneumocystis carinii formae speciales iso lated from mouse, rabbit, human, macaque and pig. A degenerate oligonucleot ide primer strategy was designed to amplify 85-90% of the full-length SODA gene from P. carinii genomic DNA isolates. DNA sequence analysis revealed a n A/T bias in the nucleotide composition (71-77.2%) and the presence of sev en small introns (41-142 bp), interrupting each P. carinii open reading fra me (ORF) at the same position. The MnSOD deduced amino acid sequences from all P, carinii isolates shared residues which were conserved within the MnS OD family and which are required for enzymatic activity and binding of the cofactor metal. Phylogenetic analysis including MnSOD sequences from repres entatives of the fungal phyla Basidiomycota and Ascomycota indicated that t he P, carinii formae speciales form a monophyletic group that is related to the budding yeasts (subphylum Saccharomycotina, previously called class He miascomycetes) in the Ascomycota. In the whole Pnemocystis group, P. carini i f. sp. hominis, P. carinii f. sp. macacae and P. carinii f. sp. oryctolag i MnSOD sequences clustered together, as did the rat-derived P. carinii and P. carinii f. sp, muris sequences.