The genus Exophiala is polymorphic, able to transition between yeast, hyphal and pseudohyphal forms. Species of the genus Exophiala are ubiquitous fungi that are distributed in various environments around the world. During a survey of fungal diversity in the gut of amphipods (Floresorchestia amphawaensis and undescribed Dogielinotid amphipods) from the Amphawa estuary, Samut Songkhram province, Thailand, five black yeast strains (DMKU-MG01, DMKU-MG07, DMKU-MG08, DMKU-HG10 and DMKU-FG04) were identified as representing a novel taxon on the basis of a combination of morphological and molecular phylogenetic features. The five strains did not produce filamentous hyphae or pseudohyphae. Only budding yeast cells were observed. On the basis of the phenotypic characteristics and the results of molecular analyses of the D1/D2 region of the large subunit (LSU) rRNA gene and the internal transcribed spacer (ITS) region, the five strains were identified as representing a novel species via applied nucleotide pairwise analysis. They differed from the most closely related species Exophiala alcalophiala by 3.54 % nucleotide substitutions (20 nucleotide substitutions in 572 bp) in the D1/D2 domains of the LSU rRNA gene. Moreover, the sequences of the ITS region of the five strains differed from those of the most closely related species E. alcalophiala, by 7.44-9.62 % nucleotide substitutions, and Exophiala halophiala, by 7.2-7.53 % nucleotide substitutions. The results of phylogenetic analyses based on the concatenated sequences of the ITS regions and the D1/D2 domains of the LSU rRNA gene confirmed that the five black yeast strains represented a single novel species of the genus Exophiala. In this study, Exophiala amphawaensis sp. nov. is proposed to accommodate these strains. The holotype is TBRC 15626T and the isotype is PYCC9020. The MycoBank accession number of the novel species is MB 851477.
Keywords: Exophiala amphawaensis; amphipods; black yeast; digestive tract; novel fungi.