Candida is a polyphyletic genus of sexually reproducing yeasts in the Saccharomycotina with more than 400 species that occur in almost all families of the subclass and its name is strongly connected with the infectious disease candidiasis. During the last two decades, approximately half of the Candida species have been reassigned into more than 36 already existing genera and 14 newly proposed genera, but the polyphyletic feature of the genus largely remained. Candida auris is an important, globally emerging opportunistic pathogen that has caused life-threatening outbreaks in healthcare facilities worldwide. This species belongs to the Candida auris - Candida haemuli (CAH) clade in the Metschnikowiaceae , a clade that contains multidrug-resistant clinically relevant species, but also species isolated from natural environments. The clade is phylogenetically positioned remotely from the type species of the genus Candida that is Candida vulgaris (currently interpreted as a synonym of Candida tropicalis ) and belongs to the family Debaryomycetaceae . Although previous phylogenetic and phylogenomic studies confirmed the position of C. auris in the Metschnikowiaceae , these analyses failed to resolve the position of the CAH clade within the family and its delimitation from the genera Clavispora and Metschnikowia . To resolve the position of the CAH clade, phylogenomic and comparative genomics analyses were carried out to address the phylogenetic position of C. auris and related species in the Metschnikowiaceae using several metrics, such as the average amino acid identity (AAI) values, the percentage of conserved proteins (POCP), and the presence-absence patterns of orthologs (PAPO).Based on those approaches, 13 new genera are proposed for various Candida and Hyphopichia species, including members of the CAH clade in the Metschnikowiaceae . As a result, C. auris and related species are reassigned to the genus Candidozyma . Fifty-five new combinations and nine new species are introduced, and this will reduce the polyphyly of the genus Candida .

Yeasts, usually defined as unicellular fungi, occur in various fungal lineages. Hence, they are not a taxonomic unit, but rather represent a fungal lifestyle shared by several unrelated lineages. Although the discovery of new yeast species occurs at an increasing speed, at the current rate it will likely take hundreds of years, if ever, before they will all be documented. Many parts of the earth, including many threatened habitats, remain unsampled for yeasts and many others are only superficially studied. Cold habitats, such as glaciers, are home to a specific community of cold-adapted yeasts, and, hence, there is some urgency to study such environments at locations where they might disappear soon due to anthropogenic climate change. The same is true for yeast communities in various natural forests that are impacted by deforestation and forest conversion. Many countries of the so-called Global South have not been sampled for yeasts, despite their economic promise. However, extensive research activity in Asia, especially China, has yielded many taxonomic novelties. Comparative genomics studies have demonstrated the presence of yeast species with a hybrid origin, many of them isolated from clinical or industrial environments. DNA-metabarcoding studies have demonstrated the prevalence, and in some cases dominance, of yeast species in soils and marine waters worldwide, including some surprising distributions, such as the unexpected and likely common presence of Malassezia yeasts in marine habitats.

The baker’s yeast Saccharomyces cerevisiae has become a powerful model in ecology and evolutionary biology. A global effort on field survey and population genetics and genomics of S. cerevisiae in past decades has shown that the yeast distributes ubiquitously in nature with clearly structured populations. The global genetic diversity of S. cerevisiae is mainly contributed by strains from Far East Asia, and the ancient basal lineages of the species have been found only in China, supporting an ‘out-of-China’ origin hypothesis. The wild and domesticated populations are clearly separated in phylogeny and exhibit hallmark differences in sexuality, heterozygosity, gene copy number variation (CNV), horizontal gene transfer (HGT) and introgression events, and maltose utilization ability. The domesticated strains from different niches generally form distinct lineages and harbor lineage-specific CNVs, HGTs and introgressions, which contribute to their adaptations to specific fermentation environments. However, whether the domesticated lineages originated from a single, or multiple domestication events is still hotly debated and the mechanism causing the diversification of the wild lineages remains to be illuminated. Further worldwide investigations on both wild and domesticated S. cerevisiae, especially in Africa and West Asia, will be helpful for a better understanding of the natural and domestication histories and evolution of S. cerevisiae.

More than 2 000 yeast strains isolated from 1 200 samples mostly collected from Tibet and Yunnan provinces in China were identified as 462 species according to the internal transcribed spacer including the 5.8S rDNA (ITS) and the D1/D2 domains of the large subunit rDNA (LSU) sequence analyses. Among them, 70 new basidiomycetous yeast species were proposed based on the multi-locus phylogenetic analyses including the D1/D2 domains, the ITS, the small subunit rDNA (SSU), the largest subunit of RNA polymerase II ( RPB1 ), the second largest subunit of RNA polymerase II ( RPB2 ) and translation elongation factor 1-α ( TEF1 ), as well as the phenotypic comparisons. The average nucleotide identity (ANI) analysis with the genomic metric was also used in the evaluation of the species delimitation for the genera Holtermannia , Mrakia and Takashimella that contain closely related species with low sequence heterogeneity in both ITS and D1/D2 regions. Forty-six new species belonged to 16 genera in the Agaricomycotina , 13 new species occurred in 12 genera in the Pucciniomycotina , three new species were distributed in three genera in the Ustilaginomycotina, and eight new species were classified in seven newly established genera. One new family was also proposed based on one of these new genera. The analyses revealed several inaccurate species names attributed to genomes deposited in GenBank, indicating the necessity of a more rigorous quality checks of the genomes deposited in the public databases.

Species is the fundamental unit to quantify biodiversity. In recent years, the model yeast Saccharomyces cerevisiae has seen an increased number of studies related to its geographical distribution, population structure, and phenotypic diversity. However, seven additional species from the same genus have been less thoroughly studied, which has limited our understanding of the macroevolutionary events leading to the diversification of this genus over the last 20 million years. Here, we show the geographies, hosts, substrates, and phylogenetic relationships for approximately 1,800 Saccharomyces strains, covering the complete genus with unprecedented breadth and depth. We generated and analyzed complete genome sequences of 163 strains and phenotyped 128 phylogenetically diverse strains. This dataset provides insights about genetic and phenotypic diversity within and between species and populations, quantifies reticulation and incomplete lineage sorting, and demonstrates how gene flow and selection have affected traits, such as galactose metabolism. These findings elevate the genus Saccharomyces as a model to understand biodiversity and evolution in microbial eukaryotes.

A correct classification of fungi, including yeasts, is of prime importance to understand fungal biodiversity and to communicate about this diversity. Fungal genera are mainly defined based on phenotypic characteristics and the results of single or multigene-based phylogenetic analyses. However, because yeasts often have less phenotypic characters, their classification experienced a strong move towards DNA-based data, from short ribosomal sequences to multigene phylogenies and more recently to phylogenomics. Here, we explore the usefulness of various genomics-based parameters to circumscribe fungal genera more correctly taking the yeast domain as an example. Therefore, we compared the results of a phylogenomic analysis, average amino acid identity (AAI) values, the presence of conserved signature indels (CSIs), the percentage of conserved proteins (POCP) and the presence- absence patterns of orthologs (PAPO). These genome-based metrics were used to investigate their usefulness in demarcating 13 hitherto relatively well accepted genera in Saccharomycetaceae , namely Eremothecium , Grigorovia , Kazachstania , Kluyveromyces , Lachancea , Nakaseomyces , Naumovozyma , Saccharomyces , Tetrapisispora , Torulaspora , Vanderwaltozyma , Zygosaccharomyces and Zygotorulaspora. As a result, most of these genera are supported by the genomics-based metrics, but the genera Kazachstania , Nakaseomyces and Tetrapisispora were shown to be genetically highly diverse based on the above listed analyses. Considering the results obtained for the presently recognized genera, a range of 80–92% POCP values and a range of 60–70 % AAI values might be valuable thresholds to discriminate genera in Saccharomycetaceae. Furthermore, the genus-specific genes identified in the PAPO analysis and the CSIs were found to be useful as synapomorphies to characterize and define genera in Saccharomycetaceae . Our results indicate that the combined monophyly-based phylogenomic analysis together with genomic relatedness indices and synapomorphies provide promising approaches to delineating yeast genera and likely those of filamentous fungi as well. The genera Kazachstania , Nakaseomyces and Tetrapisispora are revised and we propose eight new genera and 41 new combinations.