A geographically diverse set of isolates indicates two phylogenetic lineages within Stachybotrys chartarum

Stachybotrys chartarum is a black mitosporic fungus capable of dense colonization of cellulose-based building materials such as drywall. The presence of S. chartarum in indoor environments has been reported as linked to a variety of alleged environment-related illnesses including infant acute idiopathic pulmonary hemorrhage, although there continues to be insufficient (especially exposure) data to support such associations. We investigated genetic variation among 52 morphologically and geographically diverse, indoor and outdoor isolates of S. chartarum sensu lato using molecular markers based on P-tubulin, calmodulin, elongation factor-1 alpha, and trichodiene synthase genes, as well as the internal transcribed spacer region of nuclear ribosomal DNA. Gene genealogies proved concordant in dividing all isolates into two strongly supported clades. The majority of the variable sites separating these lineages were fixed within each of these clades, and there was no evidence of recombination between genotypes. The results of this study therefore provide strong support for the recognition of two phylogenetic species within S. chartarum sensu lato, and further demonstrate the limitations of morphological characters in delineating monophyletic taxa among morphologically simple fungi.