Yeast sexes: mating types do not determine the sexes in Metschnikowia species.

Although filamentous Ascomycetes may produce structures that are interpreted as male and female gametangia, ascomycetous yeasts are generally not considered to possess male and female sexes. In haplontic yeasts of the genus Metschnikowia, the sexual cycle begins with the fusion of two morphologically identical cells of complementary mating types. Soon after conjugation, a protuberance emerges from one of the conjugants, eventually maturing into an ascus. The originating cell can be regarded as an ascus mother cell, hence as female. We tested the hypothesis that the sexes, female or male, are determined by the mating types. There were good reasons to hypothesize further that mating type α cells are male. In a conceptually simple experiment, we observed the early stages of the mating reaction of mating types differentially labeled with fluorescent concanavalin A conjugates. Three large-spored Metschnikowia species, M. amazonensis, M. continentalis, and M. matae, were examined. In all three, the sexes were found to be independent of mating type, cautioning that the two terms should not be used interchangeably.

New species of the genus Metschnikowia isolated from flowers in Indonesia, Metschnikowia cibodasensis sp. nov.

A novel species, Metschnikowia cibodasensis, is proposed to accommodate eight strains (ID03- 0093(T), ID03-0094, ID03-0095, ID03-0096, ID03-0097, ID03-0098, ID03-0099, and ID03-0109) isolated from flowers of Saurauia pendula, Berberis nepalensis, and Brunfelsia americana in Cibodas Botanical Garden, West Java, Indonesia. The type strain of M. cibodasensis is ID03- 0093(T) (= NBRC 101693(T) =UICC Y-335(T) = BTCC-Y25(T)). The common features of M. cibodasensis are a spherical to ellipsoidopedunculate shaped ascus, which contains one or two needleshaped ascospores, and lyse at maturity. Asci generally develop directly from vegetative cells but sometimes from chlamydospores. The neighbor-joining tree based on the D1/D2 domain of nuclear large subunit (nLSU) ribosomal DNA sequences strongly supports that M. cibodasensis (eight strains) and its closest teleomorphic species, M. reukaufii, are different species by a 100% bootstrap value. The type strain of M. cibodasensis, ID03-0093(T), differed from M. reukaufii NBRC 1679(T) by six nt (five substitutions and one deletion) in their D1/D2 region of nLSU rDNA, and by 18 nt (five deletions, four insertions, and nine substitutions) in their internal transcribed spacer regions of rDNA, respectively. Four strains representative of M. cibodasensis (ID03-0093(T), ID03-0095, ID03-0096, and ID03-0099) showed a mol% G+C content of 44.05 ± 0.25%, whereas that of M. reukaufii NBRC 1679(T) was 41.3%. The low value of DNADNA homology (5-16%) in four strains of M. cibodasensis and M. reukaufii NBRC 1679(T) strongly supported that these strains represent a distinct species.

An atypical, pigment-producing Metschnikowia strain from a leukaemia patient.

A yeast strain was isolated from the sputum sample of a leukaemia patient in the Spirito Santo Hospital of Pescara, Italy. The fungus produced a pigment that formed a reddish halo around colonies, and was identified and deposited as a Metschnikowia spp. (accession number IHEM 25107-GenBank accession number JQ921016) in the BCCM/IHEM collection of biomedical fungi and yeasts (Bruxelles, Belgium). Although the physiology of the strain was close to that of Metschnikowia sinensis, the D1/D2 sequence did not correspond to any previously described Metschnikowia species. Phylogeny of the genus Metschnikowia is complex and requires far more analysis. We present the first non-M. pulcherrima Metschnikowia spp. isolate recovered from a human, and emphasize the role of man as a transient carrier of environmental yeasts, the pathogenicity of which still needs to be defined.