Morphological observations on Absidia corymbifera and Absidia blakesleeana strains preserved under mineral oil. Morphologische Beobachtungen an Stammen von Absidia corymbifera und Absidia blakesleeana unter Mineralol-Aufbewahrung

Revision of the genus Absidia (Mucorales, Zygomycetes) based on physiological, phylogenetic, and morphological characters; thermotolerant Absidia spp. form a coherent group, Mycocladiaceae fam. nov

The genus Absidia comprises ubiquitously distributed soil fungi inhabiting different growth temperature optima ranging from 20-42 degrees C. Some of the mesophilic species are important biotechnologically in the biotransformation of steroids or as producers of rennin-like components, whereas species with higher growth temperature optima are of clinical relevance as opportunistic human pathogens. The aim of this study was to investigate the phylogenetic relationships between these species and to establish a revision of their systematics. For this purpose single and combined genealogies based on distance, MP, ML, and Bayesian analyses of aligned nucleotide sequences of the nuclear-encoded genes for actin (act) and for the 5.8S ribosomal RNA flanked by the ITS regions 1 and 2 (comprising 807 and 828 characters, respectively) of 16 Absidia species were reconstructed. The phylogenetic reconstructions suggest a trichotomy of the Absidia genus consisting of a mesophilic, a fast-growing thermotolerant, and a slowly-growing mycoparasitic Absidia group. The trichotomous phylogenetic grouping is concordant with the morphology of the zygospores, which are zygotes resulting from sexual conjugation between two compatible mating partners. Whereas the mesophilic group comprises the majority of absidiaceaeous species forming sterile hair-like, mycelial appendages on the suspensors of their zygospores, the thermotolerant group is characterised by the formation of smooth-walled zygospores, and the mycoparasitic group, namely Absidia parricida and A. zychae, by Mucor-like rough-walled zygospores. Based on the phylogenetic coherence of mesophilic and thermotolerant Absidia species, we propose that the two groups are separated into two distinct genera, Absidia for the mesophilic Absidia species resembling the Absidiaceae and Mycocladus for the thermotolerant species A. corymbifera, A. blakesleeana and A. hyalospora. Because Mycocladus is physiologically, phylogenetically, and morphologically distinct from the Absidiaceae s. str. we suggest that they are classified as a separate family, Mycocladiaceae fam. nov., which comprises the three species M. corymbifer, M. blakesleeanus and M. hyalospora.

Sexual reproduction in subcultures of Absidia blakesleeana after years of preservation under mineral oil

Two subcultures of Absidia blakesleeana IOC No. 2425 (-) mating type strain preserved in 1959 and 1981 on a thick layer of potato dextrose agar (PDA) medium under sterile mineral oil and maintained at room temperature in the Fungal Cultural Collection of Institute Oswaldo Cruz--IOC--were paired with the defined Absidia blakesleeana URM-UFP No. 2076 (+) mating type strain. Portions of the line where mycelia of the two strains met were observed under light microscopy. Zygospores belonging to Subgenus Mycocladus were observed. The results demonstrated conservation and re-establishment of the physiological and genetic metabolic processes of two subcultures preserved under mineral oil.