Phylogenetic characterization of Histoplasma capsulatum strains based on ITS region sequences, including two new strains from Thai and Chinese patients in Japan.

Abstract

Two strains of Histoplasma capsulatum var. capsulatum were isolated in Japan: one from a Thai AIDS patient and the other from a Chinese non-immunocompromised patient. The phylogenetical relationship among the two isolates and reference strains of H. capsulatum from other geographical populations was investigated. Random amplified polymorphic DNA (RAPD) analysis of the two H. capsulatum strains showed that they had RAPD band patterns similar to those of the reference Thai isolates and North American strains, although the patterns differed slightly from those of the reference strains. Phylogeny of thirty geographically diverse H. capsulatum isolates representing the three varieties, var. capsulatum, var. duboisii and var. farciminosum were evaluated using nucleotide sequences of the internal transcribed spacer (ITS) region (ITS1-5.8S rDNA -ITS2). We found that the ITS region contained sufficient information to resolve the phylogenetic relationship among the fungal isolates. An unrooted dendrogram constructed from the ITS sequences showed that thirty strains of H. capsulatum could be classified into eight geographic clades; Asia type (i), South America types A (ii) and B (iii), North American types 1 (iv) and 2 (v), H. duboisii types A (vi) and B (vii), and East Asia type (viii). Based on the ITS region sequence analysis, the two strains isolated from the Thai and Chinese patients in Japan were found to be distinct from Asia type (i) in which eight Thai, one Chinese, one English and one Indonesian isolate were included. Some extent of DNA polymorphism was observed between the North America type 1 isolates and the Thai and Chinese strains isolated in Japan. We believe that the Thai and Chinese isolates were unique and propose a new clade, East Asia type (viii) for the two strains. DNA sequence analysis of the ITS region provided useful information to understand the epidemiology and evolution of H. capsulatum.