EVIDENCE FOR A PHYLOGENETIC CONNECTION BETWEEN COCCIDIOIDES-IMMITIS AND UNCINOCARPUS-REESII (ONYGENACEAE)

Coccidioides immitis is an anomaly amongst the human systemic fungal p athogens. Its unique parasitic cycle has contributed to confusion over its taxonomy. Early investigators mistakenly suggested that the patho gen is a protist, while others agreed it to be a fungus but placed it in four different divisions of the Eumycota. The taxonomy of C. immiti s is still unresolved, Ultrastructural examinations of its parasitic a nd saprobic phases have revealed features that are diagnostic of the a scomycetous fungi. Moreover, striking similarities between the kind of asexual reproduction (i.e. arthroconidium formation) of this pathogen and certain anamorphic and teleomorphic members of the genus Malbranc hea have suggested a close relationship. Teleomorphs of these Malbranc hea species are members of the Onygenaceae (Order, Onygenales). This f amily also includes teleomorphs of two human respiratory pathogens, Hi stoplasma capsulatum and Blastomyces dermatitidis. Although the 18S rR NA gene sequences (1713 bp) of these two pathogenic forms differ from that of C. immitis by only 35 and 33 substitutions, respectively, thei r mode of conidiogenesis is characterized by production of solitary al eurioconidia rather than alternate arthroconidia. In this study we hav e used characters derived from biochemical, immunological and molecula r analyses to compare relatedness between C. immitis, H. capsulatum, B . dermatitidis, and six non-pathogenic species of Malbranchea (the Mal branchea states of Uncinocarpus reesii and Auxarthron zuffianum, as we ll as M. albolutea, M. dendritica, M. filamentosa and M. gypsea). Evid ence is presented which supports inclusion of C. immitis in the Onygen aceae, and indicates that a close phylogenetic relationship exists bet ween the Malbranchea state of U. reesii and this respiratory pathogen.