Frequency and genetic diversity of the MAT1 locus of Histoplasma capsulatum isolates in Mexico and Brazil

Abstract

The MAT1-1 and MAT1-2 idiomorphs associated with the MAT1 locus of Histoplasma capsulatum were identified by PCR. A total of 28 fungal isolates, 6 isolates from human clinical samples and 22 isolates from environmental (infected bat and contaminated soil) samples, were studied. Among the 14 isolates from Mexico, 71.4% (95% confidence interval [95% CI], 48.3% to 94.5%) were of the MAT1-2 genotype, whereas 100% of the isolates from Brazil were of the MAT1-1 genotype. Each MAT1 idiomorphic region was sequenced and aligned, using the sequences of the G-217B (+ mating type) and G-186AR (- mating type) strains as references. BLASTn analyses of the MAT1-1 and MAT1-2 sequences studied correlated with their respective + and - mating type genotypes. Trees were generated by the maximum likelihood (ML) method to search for similarity among isolates of each MAT1 idiomorph. All MAT1-1 isolates originated from Brazilian bats formed a well-defined group; three isolates from Mexico, the G-217B strain, and a subgroup encompassing all soil-derived isolates and two clinical isolates from Brazil formed a second group; last, one isolate (EH-696P) from a migratory bat captured in Mexico formed a third group of the MAT1-1 genotype. The MAT1-2 idiomorph formed two groups, one of which included two H. capsulatum isolates from infected bats that were closely related to the G-186AR strain. The other group was formed by two human isolates and six isolates from infected bats. Concatenated ML trees, with internal transcribed spacer 1 (ITS1) -5.8S-ITS2 and MAT1-1 or MAT1-2 sequences, support the relatedness of MAT1-1 or MAT1-2 isolates. H. capsulatum mating types were associated with the geographical origin of the isolates, and all isolates from Brazil correlated with their environmental sources.

Fig 1

Maximum likelihood trees for the MAT1 locus of the H. capsulatum isolates studied. (A) MAT1-1 tree. (B) MAT1-2 tree. The ML analysis was based on the HKY model. The trees were generated by 1,000 replications, as outlined in Materials and Methods. The bootstrap values that were ≥70% are shown at the nodes. The G-217B (MAT1-1) and G-186AR (MAT1-2) sequences were obtained from the GenBank database and were used as reference strains. The black and gray bars indicate the different isolate groups. The isolates are named by their biological and geographical sources. The source (soil or biological) of the isolate is shown before the slash as follows: Hum, human; Ah, Artibeus hirsutus; Ln, Leptonycteris nivalis; Mm, Molossus molossus; Mmeg, Mormoops megalophylla; Tb, Tadarida brasiliensis. The geographical source of the isolate is shown after the slash. The state is shown after the slash and before the hyphen as follows: GR, Guerrero; HG, Hidalgo; LA, Louisiana; MS, Morelos (Mexico); MS, Mato Grosso do Sul (Brazil); NL, Nuevo León; PL, Puebla; PA, Panama; RJ, Rio de Janeiro; SP, São Paulo. The country is shown after the hyphen (Brazil [BR], Mexico [MX], United States [US]).

Fig 2

Concatenated maximum likelihood trees for the ITS1-5.8S-ITS2 region and each MAT1 locus of the H. capsulatum isolates studied. (A) ITS1-5.8S-ITS2 and MAT1-1 concatenated tree. (B) ITS1-5.8S-ITS2 and MAT1-2 concatenated tree. The ML analysis was based on the TrN model. The trees were generated by 1,000 replications, as outlined in Materials and Methods. The bootstrap values that were ≥70% are shown at the nodes. The black and dark gray bars indicate the different isolate groups. For abbreviations, see the legend to Fig. 1.