DNA relatedness among aquatic yeasts of the genus Metschnikowia and proposal of the species Metschnikowia australis comb. nov.

DNA hybridization studies were conducted to determine the taxonomic status of the aquatic group of Metschnikowia species and their varieties. Among the DNAs of the four varieties of Metschnikowia bicuspidata, that of Metschnikowia bicuspidata var. australis showed 37 to 51% relative binding with the DNAs of Metschnikowia bicuspidata var. bicuspidata and of the varieties chathamia and californica. On this basis, low intervarietal fertility, and unique habitat in antarctic seawater, we have proposed to raise M. bicuspidata var. australis to the rank of species, Metschnikowia australis, comb. nov. DNA complementarity of Metschnikowia bicuspidata var. californica and Metschnikowia bicuspidata var. chathamia DNA was greater than 80% with that of M. bicuspidata var. bicuspidata. Metschnikowia australis can be differentiated from other Metschnikowia species and varieties by its inability to form chlamydospores, the formation of two needle-shaped ascospores per ascus, lack of glucose fermentation, and lack of assimilation of both methyl-alpha-D-glucoside and glucono-delta-lactone. Other DNA-DNA reassociation experiments showed that Metschnikowia zobellii is a distinct species when compared with both aquatic and terrestrial species of the genus.

DNA base composition and DNA relatedness among species of Trichosporon Behrend.

The nuclear DNA of 28 species (30 strains investigated) of yeasts classified currently or previously in the genus Trichosporon. was analysed for its molar percentage of guanine + cytosine (mol% G + C). This criterion, together with biochemical characteristics, suggested the separation of the organisms studied into two groups. The first group, which appears related to the Ascomycetes, includes thirteen species with a G + C content lower than 50 mol% (34.7-48.8), and lacks urease (except T. margaritiferum). The second group appears related to the Basidiomycetes and includes fifteen species with a G + C content higher than 50 mol% (57-64) and has the ability to hydrolyse urea. A DNA homology experiment with T. beigelii and twelve other species of the second group showed very low values of complementarity with T. beigelii-labeled DNA. All these species must be considered as taxa other than T. beigelii.