Abstract
Taphrinomycotina is the smallest subphylum of the phylum Ascomycota. It is an assemblage of distantly related early diverging lineages of the phylum, comprising organisms with divergent morphology and ecology; however, phylogenomic analyses support its monophyly. In this study, we report the isolation of a yeast strain, which could not be assigned to any of the currently recognised five classes of Taphrinomycotina. The strain of the novel budding species was recovered from extra virgin olive oil and characterised phenotypically by standard methods. The ultrastructure of the cell wall was investigated by transmission electron microscopy. Comparisons of barcoding DNA sequences indicated that the investigated strain is not closely related to any known organism. Tentative phylogenetic placement was achieved by maximum-likelihood analysis of the D1/D2 domain of the nuclear LSU rRNA gene. The genome of the investigated strain was sequenced, assembled, and annotated. Phylogenomic analyses placed it next to the fission Schizosaccharomyces species. To accommodate the novel species, Novakomyces olei, a novel genus Novakomyces, a novel family Novakomycetaceae, a novel order Novakomycetales, and a novel class Novakomycetes is proposed as well. Functional analysis of genes missing in N. olei in comparison to Schizosaccharomyces pombe revealed that they are biased towards biosynthesis of complex organic molecules, regulation of mRNA, and the electron transport chain. Correlating the genome content and physiology among species of Taphrinomycotina revealed some discordance between pheno- and genotype. N. olei produced ascospores in axenic culture preceded by conjugation between two cells. We confirmed that N. olei is a primary homothallic species lacking genes for different mating types.
Highlights
Taphrinomycotina, introduced by Eriksson & Winka [1], is one of the three subphyla of Ascomycota [2] and it is an assemblage of early diverging lineages of the phylum [3].Taphrinomycotina is a sister group of the remaining Ascomycota (Saccharomycotina and Pezizomycotina) [4]
According to single locus or multigene phylogenetic analyses, the fungi assigned to Taphrinomycotina form either mono- or paraphyletic groups depending on the taxon sampling, the analysed phylogenetic markers, and the applied algorithm [3]
It must be uncommon in this substrate because we have not isolated additional strains of this species, more than 100 olive oil samples, including Spanish ones, were processed in our laboratories and more than 200 yeast strains were isolated from them, which were identified based on the DNA sequences of their LSU rRNA gene D1/D2 domain
Summary
Taphrinomycotina, introduced by Eriksson & Winka [1], is one of the three subphyla of Ascomycota [2] and it is an assemblage of early diverging lineages of the phylum [3]. The genus Saitoella (family Protomycetaceae, order Taphrinales) contains merely two described species, which are believed to be saprophytic. The type species of the genus, was recovered from soil [17], and S. coloradoensis from insect frass [18] They reproduce by multilateral budding, but a sexual state is not known. A. finlayi was the first cultivated species of the Soil Clone Group I (SCGI) [28,29], which has been known earlier only from environmental DNA sequences As according to phylogenomic analyses, the novel species cannot be assigned to any of the currently recognized five classes of Taphrinomycotina, we propose a novel genus, a novel family, a novel order, and a novel class to accommodate the novel species
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