Sporothrix davidellisii : A new pathogenic species belonging to the Sporothrix pallida complex

Abstract

Sporothrix species (Ascomycota, Ophiostomatales) are dimorphic fungi with diverse ecological niches, ranging from mammalian, plant, and insect pathogens to fungicolous organisms. Here, we describe Sporothrix davidellisii (CBS 147636T), a novel pathogenic species within the S. pallida complex isolated from a case of feline sporotrichosis in Melbourne, Australia. Phylogenetic analyses based on ITS, β-tubulin (BT2), calmodulin (CAL), and translation elongation factor 1-α (EF1-α) sequences confirmed its distinctiveness, with ITS sequence identity to its closest relative (S. chilensis) not exceeding 97.6%. The assembled genome is 39.02 Mb (eight contigs) with a 27.2 kb mitochondrial genome and a total of 12,631 predicted genes. Genetic diversity analyses revealed moderate nucleotide variation in the ITS region (π = 0.055), greater diversity in BT2 (π = 0.098), and CAL (π = 0.118), supporting its status as a unique species. Morphological studies revealed distinctive characteristics differentiating S. davidellisii from its nearest relatives, including elongated clavate sympodial conidia and sessile conidia. Notably, S. davidellisii exhibits yeast-like growth at 37°C, forming ellipsoid to ovoid budding cells in liquid media, although cigar-shaped yeasts, characteristic of highly virulent Sporothrix species, are rarely observed. This ability to transition to a yeast-like form, combined with its high-temperature tolerance (growth up to 40°C), underscores its opportunistic pathogenic potential. The pathogenic role of S. davidellisii highlights the importance of monitoring atypical Sporothrix infections in feline hosts, which may serve as environmental sentinels for emerging fungal pathogens. These findings expand the taxonomy of Sporothrix, contributing to our understanding of the evolutionary complexity and zoonotic potential of species within the S. pallida complex.

Keywords: Sporothrix davidellisii; Sporothrix pallida complex; dimorphic fungi Ophiostomatales; feline sporotrichosis; sporotrichosis.

Figure 1.

Evolutionary relationships among Sporothrix species inferred from ITS1 + 5.8S + ITS2 rDNA sequences, visualized through phylogenetic analysis and ordination methods. (A) ML phylogenetic tree. Branch support values (NJ/ML/MP) from 1000 bootstrap replicates via NJ, ML, and MP analyses are displayed at the nodes. Branch lengths reflect the estimated number of nucleotide substitutions. The inset shows the MP statistics: consistency index (CI), retention index (RI), and composite index (RCI). The type strains are indicated by ‘T’. (B) PCA plot (3D) based on the same sequence data, illustrating the relationships between isolates, colored by species or species complex. (C) MDS plot (3D) representing genetic distances between isolates on the basis of the rDNA sequence data.

Figure 2.

Evolutionary relationships among Sporothrix species inferred from beta-tubulin sequences, visualized through phylogenetic analysis and ordination methods. (A) ML phylogenetic tree. Branch support values (NJ/ML/MP) from 1000 bootstrap replicates via NJ, ML, and MP analyses are displayed at the nodes. Branch lengths reflect the estimated number of nucleotide substitutions. The inset shows the MP statistics: consistency index (CI), retention index (RI), and composite index (RCI). The type strains are indicated by ‘T’. (B) PCA plot (3D) based on the same sequence data, illustrating the relationships between isolates, colored by species or species complex. (C) MDS plot (3D) representing genetic distances between isolates on the basis of the rDNA sequence data.

Figure 3.

Evolutionary relationships among Sporothrix species inferred from calmodulin sequences (exons 3–5), visualized through phylogenetic analysis and ordination methods. (A) ML phylogenetic tree. Branch support values (NJ/ML/MP) from 1000 bootstrap replicates via NJ, ML, and MP analyses are displayed at the nodes. Branch lengths reflect the estimated number of nucleotide substitutions. The inset shows the MP statistics: consistency index (CI), retention index (RI), and composite index (RCI). The type strains are indicated by ‘T’. (B) PCA plot (3D) based on the same sequence data, illustrating the relationships between isolates, colored by species or species complex. (C) MDS plot (3D) representing genetic distances between isolates on the basis of the rDNA sequence data.

Figure 4.

Evolutionary relationships among Sporothrix species inferred from elongation factor 1-α sequences, visualized through phylogenetic analysis and ordination methods. (A) ML phylogenetic tree. Branch support values (NJ/ML/MP) from 1000 bootstrap replicates via NJ, ML, and MP analyses are displayed at the nodes. Branch lengths reflect the estimated number of nucleotide substitutions. The inset shows the MP statistics: consistency index (CI), retention index (RI), and composite index (RCI). The type strains are indicated by ‘T’. (B) PCA plot (3D) based on the same sequence data, illustrating the relationships between isolates, colored by species or species complex. (C) MDS plot (3D) representing genetic distances between isolates on the basis of the rDNA sequence data.

Figure 5.

SOMs showing the genetic relationships among the Sporothrix species colored according to genetic group. (A) Internal transcribed spacer (ITS1 + 5.8S + ITS2; n = 69), (B) beta-tubulin (BT2; n = 60), (C) calmodulin (CAL; n = 47), and (D) translation elongation factor (EF1-α; n = 33). Thicker lines on the map indicate significant boundaries, often separating different clusters, groups, or categories of data points. The color of these lines, which can range from lighter to darker shades, visually reinforces the separation between these clusters. For example, thicker and lighter boundaries help distinguish different species or intraspecific groups, quickly identifying and interpreting patterns within the molecular data. The input data for each SOM analysis were the same multiple-sequence alignment used in the phylogenetic analysis (Supplementary Table 1).

Figure 6.

Overview of the phenotypic characteristics of Sporothrix davidellisii. Sporothrix davidellisii (ex-type CBS 147636^T). (A–C): colonies on OA (A), MEA (B), and PDA (C); (D–F), (H), (J–L): conidiophores and conidiogenous cells; (G), (T), (V), (W): lateral blastoconidia; (I): fasciculate hyphae (arrows indicate clusters of conidium-bearing denticles); (M), (O–Q): details of conidium-bearing denticles at the tips of conidiophores; (N): sympodially proliferating conidiogenous cells; (R), (S): secondary conidia formation; (U): conidia showing small apical conidiogenous rachis; (X-Y): conidia. Scale bars: (D)–(H), (I)–(K), (M), (T), (Y) = 10 μm; (L), (N)–(S), (U)–(X) = 5 μm.

Figure 7.

Yeast cell formation of Sporothrix davidellisii . Sporothrix davidellisii (ex-type CBS 147636). (A) Yeast-like cells showing single, double, and multilateral buds formed after 48 h of incubation in BHI at 37°C. Scale bar = 10 μm.