A polyphasic approach to the taxonomy of Backusella reveals two new species.
The mucoralean genus Backusella comprises saprobe species commonly isolated from soil and leaf litter but also from wood, invertebrates, and toads. Molecular species recognition of Backusella has been mainly based on the ITS and LSU regions. Because mucoralean fungi tend to have high intraspecific variability of ITS sequences, we established the gene encoding the largest subunit of RNA polymerase II (RPB1) as phylogenetic marker in Backusella. The topologies of the ITS/LSU and RPB1 trees were widely similar. The maximum growth temperature is shown to represent a valuable taxonomic feature because it varied strongly within the genus. Seven Backusella spp. are capable of growing at temperatures ≥ 36 °C, four of which were positioned in a same clade. Based on the evidence of molecular phylogenetic analyses as well as on morphological and physiological (maximum growth temperature) features, Backusella gigaspora sp. nov. and B. pernambucensis sp. nov. are described.