Plesiozyma aurantiaca gen. et sp. nov. (Ustilaginaceae, Ustilaginales), a novel Ustilaginomycetes yeast from an urban lake in Portugal

A novel yeast-like basidiomycete was recovered from an urban lake in a public park in the city of Aveiro, Portugal. Sequence comparisons based on LSU rRNA, SSU rRNA, internal transcribed spacer (ITS) region and tef1-α gene sequences, together with phylogenetic analysis using the widely available ITS and LSU markers, placed the isolate within the family Ustilaginaceae , where it forms a well-supported and distinct lineage within clade 7, clearly separated from the closely related genera Moesziomyces and Macalpinomyces . Clade 7 comprises species traditionally assigned to the genera Ustilago , Sporisorium and Macalpinomyces , a grouping that reflects the taxonomic complexity and instability of this lineage. Morphological, physiological, biochemical characteristics and antifungal susceptibility determination were performed to characterize the isolate. Colonies were orange and mucoid, with ovoid to elongated budding vegetative cells and occasional pseudohyphae. Optimal growth occurred at 30 °C, with tolerance up to 40 °C, indicating an unusual degree of thermotolerance among ustilaginaceous yeasts. Biochemical profiling revealed broad assimilation of simple sugars, organic acids and polyols, together with urease activity and nitrate assimilation, consistent with adaptation to dissolved organic matter in urban freshwater environments. Antifungal susceptibility testing showed low MICs for amphotericin B, whereas echinocandins exhibited reduced in vitro activity, consistent with patterns reported for other ustilaginaceous and basidiomycetous yeasts. Based on our findings, we propose a new genus, Plesiozyma gen. nov., and a new species, Plesiozyma aurantiaca sp. nov. (MUM 25.31 as type species, MycoBank number: MB862570), to accommodate this novel yeast-like fungus isolated from urban water.