Candida orba sp. nov., a new cactus-specific yeast species from Queensland, Australia.

A new species of yeast from decaying cladodes of Opuntia cactus, Candida orba, is described. This species is a member of a four-species clade of cactophilic yeasts. The new species has only been found in one region of Queensland, Australia, where it was presumably introduced during attempts to eradicate prickly pear cactus. DNA-DNA relatedness, phylogenetic analysis, physiological differences, killer-sensitivity profiles and mating reactions establish the distinctness of the taxon as a new species. C. orba is most closely related to Phaffomyces thermotolerans, a species found associated with columnar cacti in the North American Sonoran Desert. The type strain of C. orba, isolated from rotting cladodes of Opuntia stricta in the State of Queensland, Australia, is strain UCD-FST 84-833.1T (= CBS 8782T = NRRL Y-27336T = ATCC MYA-341). Only the h- mating type of the species has been recovered. The lack of the opposite mating type could be the result of a bottleneck during its introduction to Australia. The original geographic/host distribution of this species in the Americas is unknown.