Mode of vegetative reproduction of the bipolar budding yeast species Wickerhamomyces pijperi and related strains.

To clarify the budding pattern of Wickerhamomyces pijperi, the vegetative cells were observed by scanning electron microscopy. The cells grew by bipolar budding, but cells that budded from the shoulder of a mother cell were occasionally observed. We examined the cell morphology and phylogeny of five strains of Wickerhamomyces sp. isolated in Thailand as well as seven W. pijperi and three Wickerhamomyces sp. strains that were preserved in culture collections. Phylogenetic analysis based on three different nucleotide sequences (D1/D2 domain of 26S rDNA, the actin gene ACT1 and the elongation factor 2 gene EF2) indicated that all the strains belonged to the genus Wickerhamomyces and were neighbours of the type strain W. pijperi NBRC 1290(T). The strains fell into two groups in this analysis. The budding patterns of the strains were carefully observed by staining the bud scars, and these patterns were categorized into three groups: types I-III. Type I included cells that grew by bipolar budding and formed multiple scars, type III included cells that grew by multilateral budding and formed a single scar, and type II included cells that exhibited a mixture of type I and type III patterns. Among the 15 strains, 12 strains, including W. pijperi NBRC 1290(T), mainly exhibited type I or type II budding patterns; these strains belonged to group 1 of the phylogenetic analysis. The remaining three strains, which belonged to group 2, exhibited either type II or type III patterns. Thus the phylogenetic relationship and budding patterns are related. Moreover, some cells also exhibited budding characteristics that were intermediate between bipolar and multilateral budding.