Ajellomyces crescens sp. nov., taxonomy of Emmonsia spp., and relatedness with Blastomyces dermatitidis (teleomorph Ajellomyces dermatitidis).

Adiaspiromycosis is known primarily as a pulmonary infection of small burrowing mammals and rarely of humans, in which the tissue spore form consists of a large, globose, thick-walled, non-proliferating structure called an adiaspore. The causative agents have been placed in Emmonsia or Chrysosporium and treated as either two species or varieties. Emmonsia parva (= Chrysosporium parvum var. parvum) has been distinguished from E. crescens (= C parvum var. crescens) by differences in maximum growth temperature, size of adiaspores, host range and geographical distribution. Phenotypic similarities between Emmonsia spp. and Blastomyces dermatitidis and chance observation of Ajellomyces-type ascomatal hyphae led to the hypothesis that the teleomorph of Emmonsia spp. could occur in Ajellomyces. Isolates preliminarily identified as E. parva or E. crescens were examined by morphology and physiology and tested for compatibility in mating experiments. Ajellomyces crescens Sigler sp. nov. is described for the teleomorph of Emmonsia crescens based on compatibility among 12 of 22 strains, stellate gymnothecial ascomata composed of obtuse diamond-shaped cells, helically coiled appendages and small, globose, muriculate ascospores. The agents of adiaspiromycosis are here treated as species with adiaspore size and morphology and temperature of induction as their major defining features. The species differ also in cycloheximide tolerance and in their abilities to form a teleomorph. With evidence of a connection between Emmonsia crescens and a teleomorph in Ajellomyces, Emmonsia is favoured over Chrysosporium as the correct name for the agents of adiaspiromycosis. This finding also corroborates earlier suggestions of a close phylogenetic relationship between Emmonsia spp. and the dimorphic pathogens Blastomyces dermatitidis and Histoplasma capsulatum.