Abstract Anaerobic gut fungi (AGF,Neocallimastigomycota) represent a phylum of zoospore-producing fungi inhabiting the gastrointestinal tracts of herbivores. Twenty mammalian-affiliated genera (M-AGF) and two tortoise-affiliated genera (T-AGF) have been described so far. Here, we report on three additional novel T-AGF isolates obtained from Texas and sulcata tortoises. Phylogenetic analysis using the D1-D2 regions of the large ribosomal RNA subunit (D1-D2 LSU), RNA polymerase II large subunit (RPB1), internal transcribed spacer-1 region (ITS1), and transcriptomics-enabled phylogenomic analysis clustered these strains into three distinct, deep-branching clades, closely related to previously described T-AGF genusTestudinimyces. All isolates displayed filamentous rhizoidal growth patterns and produced monoflagellated zoospores. Unique morphological characteristics included the production of elongated, thick, nucleated structures in GX isolates, the formation of thin hair-like projections on sporangial walls in SR isolates, and irregularly shaped sporangia in TM isolates. All strains grew optimally at 32-35 °C and showed distinct substrate utilization capacity (e.g., growth on pectin, chitin, galactose). LSU analyses revealed GX isolates as the first cultured representatives of tortoise-affiliated but previously uncultured lineage NY56, while SR and TM strains have not been encountered in prior culture-independent AGF surveys. We propose to accommodate these isolates in three new genera and species –Gopheromyces tardescens(GXA2),Gigasporangiomyces pilosus(SR0.6), andKelyphomyces adhaerens(TM0.3). Further, based on the ecological, physiological, and phylogenetic distinctions between T-AGF and M-AGF, we propose to establish a new family (Testudinimycetaceae) to accommodate the generaTestudinimyces, Gopheromyces,Gigasporangiomyces,andKelyphomyces, within a new order (Testudinimycetales), and amend the description ofNeocallimastigalesto circumscribe M-AGF genera only.
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Phylogenomic analysis of the Neocallimastigomycota: Proposal of Caecomycetaceae fam. nov., Piromycetaceae fam. nov., and emended description of the families Neocallimastigaceae and Anaeromycetaceae
The anaerobic gut fungi (AGF) represent a coherent phylogenetic clade within the Mycota. Twenty genera have been described so far. Currently, the phylogenetic and evolutionary relationships between AGF genera remain poorly understood. Here, we utilized 52 transcriptomic datasets from 14 genera to resolve AGF inter-genus relationships using phylogenomics, and to provide a quantitative estimate (amino acid identity, AAI) for intermediate rank assignments. We identify four distinct supra-genus clades, encompassing all genera producing polyflagellated zoospores, bulbous rhizoids, the broadly circumscribed genus Piromyces, and the Anaeromyces and affiliated genera. We also identify the genus Khoyollomyces as the earliest evolving AGF genus. Concordance between phylogenomic outputs and RPB1 and D1/D2 LSU, but not RPB2, MCM7, EF1α, or ITS1, phylogenies was observed. We combine phylogenomic analysis, and AAI outputs with informative phenotypic traits to propose accommodating 14/20 AGF genera into four families: Caecomycetaceae fam. nov. (encompassing the genera Caecomyces and Cyllamyces), Piromycetaceae fam. nov. (encompassing the genus Piromyces), emend the description of fam. Neocallimastigaceae to encompass the genera Neocallimastix, Orpinomyces, Pecoramyces, Feramyces, Ghazallomyces, Aestipascuomyces, and Paucimyces, as well as the family Anaeromycetaceae to include the genera Oontomyces, Liebetanzomyces, and Capellomyces in addition to Anaeromyces. We refrain from proposing families for the deeply branching genus Khoyollomyces, and for genera with uncertain position (Buwchfawromyces, Joblinomyces, Tahromyces, Agriosomyces, and Aklioshbomyces) pending availability of additional isolates and sequence data; and these genera are designated as “genera incertae sedis” in the order Neocallimastigales. Our results establish an evolutionary-grounded Linnaean taxonomic framework for the AGF, provide quantitative estimates for rank assignments, and demonstrate the utility of RPB1 as an additional informative marker in Neocallimastigomycota taxonomy.
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- Award ID(s):
- 2029478
- PAR ID:
- 10390040
- Date Published:
- Journal Name:
- International journal of systematic and evolutionary microbiology
- Volume:
- In Press
- ISSN:
- 1466-5026
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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