Trichosporon porosum comb. nov., an anamorphic basidiomycetous yeast inhabiting soil, related to the loubieri/laibachii group of species that assimilate hemicelluloses and phenolic compounds.

Several isolates representing the genus Trichosporon were collected over a 6-year period from soils in The Netherlands. Based on classical growth tests with carbon and nitrogen compounds these were identical. Three of these (CBS 8396, CBS 8397 and CBS 8522) were subjected to molecular analysis of the D1/D2 region of the large subunit of rDNA. This confirmed that the three strains were identical, yet distinct from other members of the genus. Conspecificity was demonstrated with the type strain (CBS 2040) of Apiotrichum porosum Stautz (1931), with the exception that A. porosum, which had been isolated from exudate of a yew tree, differed morphologically from the soil strains. Based on the identity of DNA base sequences, morphology was not considered to be an adequate parameter to separate otherwise identical strains into two genera. Therefore, the new combination Trichosporon porosum is presented. Based on molecular sequence analysis, T. porosum may be related to T. sporotrichoides, within a weakly related clade that includes species such as Trichosporon laibachii and Trichosporon loubieri. The strains of T. porosum degrade phenolic compounds and hemicelluloses, which are characteristics with potential ecological importance in soil habitats. Characters distinguishing the nine species of the laibachii/loubieri group of species were listed. These include traditionally used tests as well as assimilation patterns of some aliphatic and phenolic compounds. Based on these tests, species such as Trichosporon multisporum and T. laibachii could be separated.