Submitted to: Proceedings of the National Academy of Sciences(PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2000
Publication Date: N/A
Interpretive Summary: Filamentous fungi that produce nonmotile spores within an enclosed spore case are classified as Zygomycetes. The most important group within the Zygomycetes, the Mucorales, includes many economically-important species used in the production of a wide range of organic compounds and in fermentation processes in the food industry. Furthermore, fatal infections of humans caused by mucoralean fungi are increasing in number due the rise in immunocompromised and immunosuppresed patients. For this reason, there is an urgent need to develop molecular methods to distinguish between harmful and beneficial strains rapidly and accurately. We have taken advantage of automated DNA sequencing technologies in this study to develop an electronically portable DNA sequence data base for all genera of the Mucorales. Relationships among the various genera were measured from the DNA data. These analyses indicate that most of the genera are misplaced taxonomically due to their simple anatomy. Results of this study provide a powerful illustration of how DNA sequence data can be used to diagnose anatomically simple microbes important to agriculture, industry and medicine.
Technical Abstract: Mucorales (Zygomycota) are ubiquitous, morphologically simple terrestrial fungi that are united taxonomically by possession of a coenocytic mycelium upon which nonmotile mitotic spores are produced asexually in uni- to multispored sporangia, and zygospores, where known, are produced following fusion of sexually compatible hyphae. Here we report the first comprehensive phylogenetic analysis of essentially all genera of Mucorales (63 species, 54 genera and 13 families) based on partial nucleotide sequence data of nuclear small subunit (18S) ribosomal RNA, nuclear large subunit (28S) ribosomal RNA, translation elongation factor-1alpha exons, and a morphological data set consisting of 1826, 389, 1092 and 11 characters, respectively. Individual and combined data sets were analyzed by unequally weighted maximum parsimony (MP) to investigate evolutionary relationships among and within mucoralean families. A Micromucor- Umbelopsis clade, traditionally included in the Mortierellaceae, was identified as the basal sister-group to all other Mucorales. A major discovery of this study is that traditional family-level classification schemes for this order appear to be highly artificial as evidenced by polyphyly of four of the seven families containing two or more genera. As presently circumscribed, these four families include 83 percent of the Mucorales. In addition, the largest and best known genera, Mucor and Absidia, were resolved as polyphyletic. The results provide a robust phylogenetic framework for additional evolutionary studies of the Mucorales.