A novel psychrophilic yeast species, Mrakia wardhuntensis sp. nov., isolated from Ward Hunt Lake in the extreme High Arctic.

Two yeast strains, JCM 37756 and JCM 37757, were isolated from the sediments of Ward Hunt Lake, the northernmost lake in Canada, located at 83° N on Ward Hunt Island, Nunavut. Molecular phylogenetic analysis based on the internal transcribed spacer (ITS) region and the D1/D2 domain of the large subunit ribosomal DNA (rDNA) showed that these strains represent a novel species in the genus Mrakia. The two strains showed 100% sequence identity in the ITS region and only a single nucleotide difference in the D1/D2 domain, confirming their conspecificity. Phylogenetic trees constructed using maximum likelihood, maximum parsimony and Bayesian inference consistently placed this new lineage as sister to the clade comprising Mrakia fibulata and the Mrakia soli clade. Although bootstrap support values were 59% (maximum-likelihood, ML) and 55% (maximum-parsimony, MP), the Bayesian posterior probability was 1.0, providing robust evidence for its taxonomic independence. Both strains are psychrophilic, growing at -3 °C in vitamin-free and amino acid-free media. We propose the name Mrakia wardhuntensis sp. nov., with JCM 37756 (=UAMH 12645) as the holotype. The MycoBank accession number is MB 858003.