Candida ruelliae sp. nov., a novel yeast species isolated from flowers of Ruellia sp. (Acanthaceae)

Two novel yeast strains designated as 16Q1 and 16Q3 were isolated from flowers of the Ruellia species of the Acanthaceae family. The D1/D2 domain and ITS sequences of these two strains were identical. Sequence analysis of the D1/D2 domain of large-subunit rRNA gene indicated their relationship to species of the Candida haemulonii cluster. However, they differ from C. haemulonii by 14% nucleotide sequence divergence, from Candida pseudohaemulonii by 16.1% and from C. haemulonii type II by 16.5%. These strains also differ in 18 physiological tests from the type strain of C. haemulonii, and 12 and 16 tests, respectively, from C. pseudohaemulonii and C. haemulonii type II. They also differ from C. haemulonii and other related species by more than 13% sequence divergence in the internal transcribed spacer region. In the SSU rRNA gene sequences, strain 16Q1 differs by 1.7% nucleotide divergence from C. haemulonii. Sporulation was not observed in pure or mixed cultures on several media examined. All these data support the assignment of these strains to a novel species; we have named them as Candida ruelliae sp. nov., and designate strain 16Q1(T)=MTCC 7739(T)=CBS10815(T) as type strain of the novel species.