Multigene Assessment of the Species Boundaries and Sexual Status of the Basidiomycetous Yeasts Cryptococcus flavescens and C. terrestris (Tremellales)

Abstract

Cryptococcus flavescens and C. terrestris are phenotypically indistinguishable sister species that belong to the order Tremellales (Tremellomycetes, Basidiomycota) and which may be mistaken for C. laurentii based on phenotype. Phylogenetic separation between C. flavescens and C. terrestris was based on rDNA sequence analyses, but very little is known on their intraspecific genetic variability or propensity for sexual reproduction. We studied 59 strains from different substrates and geographic locations, and used a multilocus sequencing (MLS) approach complemented with the sequencing of mating type (MAT) genes to assess genetic variation and reexamine the boundaries of the two species, as well as their sexual status. The following five loci were chosen for MLS: the rDNA ITS-LSU region, the rDNA IGS1 spacer, and fragments of the genes encoding the largest subunit of RNA polymerase II (RPB1), the translation elongation factor 1 alpha (TEF1) and the p21-activated protein kinase (STE20). Phylogenetic network analyses confirmed the genetic separation of the two species and revealed two additional cryptic species, for which the names Cryptococcus baii and C. ruineniae are proposed. Further analyses of the data revealed a high degree of genetic heterogeneity within C. flavescens as well as evidence for recombination between lineages detected for this species. Strains of C. terrestris displayed higher levels of similarity in all analysed genes and appear to make up a single recombining group. The two MAT genes (STE3 and SXI1/SXI2) sequenced for C. flavescens strains confirmed the potential for sexual reproduction and suggest the presence of a tetrapolar mating system with a biallelic pheromone/receptor locus and a multiallelic HD locus. In C. terrestris we could only sequence STE3, which revealed a biallelic P/R locus. In spite of the strong evidence for sexual recombination in the two species, attempts at mating compatible strains of both species on culture media were unsuccessful.

Yeasts from peat in a tropical peat swamp forest in Thailand and their ability to produce ethanol, indole-3-acetic acid and extracellular enzymes

“…3). These four strains remain unidentified, because a high degree of genetic heterogeneity within P. flavescens has been reported (Yurkov et al 2015), and thus further analysis is needed for identification.…”

Evolution of Mating Systems in Basidiomycetes and the Genetic Architecture Underlying Mating-Type Determination in the YeastLeucosporidium scottii

“…Studies with a similar scope on other tetrapolar species (viz. K. mangrovensis, K. heveanensis, Cryptococcus flavescens, and C. terrestris (Tremellales, Agaricomycotina) (Metin et al 2010;Guerreiro et al 2013;Yurkov et al 2015) readily detected arbitrary assortment of MAT alleles, even within a more restricted number of isolates. Although we cannot rule out that other mechanisms may cause the apparent nonrandom association between P/R (A) and HD (B) loci in L. scottii, we highlight two possibilities in particular.…”

Papiliotrema leoncinii sp. nov. and Papiliotrema miconiae sp. nov., two tremellaceous yeast species from Brazil

“…Liu et al (2015a) recognized the aureus clade as monophyletic, although they included only Cryptococcus aureus, Cryptococcus flavescens and Cryptococcus terrestris in their analysis, and suggested that new genera need to be proposed to accommodate the monophyletic clades within tremellomycetous yeasts. Two additional cryptic species in the aureus clade, C. baii and C. ruineniae, were described based on multigene analysis (Yurkov et al, 2015). In order to avoid new genera for aureus, Auriculibuller, laurentii, Papiliotrema and pseudoalba clades, Liu et al (2015b) accommodated these small clades in the genus Papiliotrema.…”

“…Kurtzman (1973), however, reported sexual activity with strains of Cryptococcus laurentii. In addition, Yurkov et al (2015) detected genetic recombination and the presence of sexual reproduction related genes (MAT genes) in P. flavescens and P. terrestris, although they failed to induce mating. The authors suggest that their failure could be due to the need of specific media components or conditions for sexual reproduction, and not to an intrinsic inability of the strains to mate.…”

“…After 3 weeks in Dalmau plate culture on cornmeal agar, pseudohyphae and true hyphae are not formed. Sexual reproduction is (Takashima et al, 2003); 5, P. terrestris (Crestani et al, 2009); 6, P. baii (Yurkov et al, 2015); 7, P. ruineniae (Yurkov et al, 2015); 8, P. wisconsinensis (Sylvester et al, 2015 In YPD broth after 5 days at 25 uC, the yeast cells are oval to ellipsoid and occur singly or in pairs (3.2-8.1| 2.4-7.8 mm) (Fig. 2c).…”