Proposal of INTRODUCTIONZygosaccharomyces bailii is a widely distributed yeast species that is often associated with food spoilage, particularly of acidified, preserved foods containing high concentrations of fermentable sugars (Thomas & Davenport, 1985;Cole & Keenan, 1987;Makdesi & Beuchat, 1996;James & Stratford, 2011). The yeast has been proposed as a new host for several biotechnological processes (e.g. Branduardi et al., 2004) due to its ability to tolerate such environments at relatively high temperatures, which could improve the efficiency of these processes under restrictive conditions. Moreover, the high growth rate of Z. bailii and its high biomass yield make this yeast particularly attractive for heterologous protein and metabolite production (e.g. Sousa et al., 1996Sousa et al., , 1998.Despite their well-known role in food/beverage spoilage, accurate identification of Z. bailii and related yeasts to the species level using conventional taxonomic tests remains problematic. An inability to ferment and assimilate many of the carbon compounds typically used in yeast identification, as well as ambiguous tests results due to strain variability, often hampers identification (James & Stratford, 2011). Furthermore, significant intraspecific variation in internal transcribed spacer (ITS) sequences was also reported among some strains of the species (James et al., 1996), which may cause difficulties for the use of this barcode region for identifying the species (Schoch et al., 2012). We hypothesized that polyphasic analyses of the yeasts encompassed by Zygosaccharomyces bailii sensu lato may lead to a more accurate understanding of their phylogenetic relationship and taxonomic status. Here we report the molecular, physiological and morphological characterization of these yeasts, and propose two novel species near Z. bailii. METHODSYeast strains and characterization. Strains of Z. bailii sensu lato and related taxa were selected from the ATCC Mycology Collection or were provided by bioMérieux, Inc. (Table 1). Morphological observations and metabolic tests comprising the yeast standard Abbreviations: ITS, internal transcribed spacer; LSU, large subunit; SSU, small subunit.
Two new species in the anamorphic basidiomycetous genus Trichosporon (Tremellomycetes, Agaricomycotina) were uncovered in a DNA sequence-based molecular analysis of oleaginous yeasts maintained in the ATCC Mycology Collection. One yeast is named as Trichosporon cacaoliposimilis sp. nov. for its capability of synthesizing and accumulating a large amount of lipids having a composition equivalent to that of natural cacao butter. The type strain is ATCC 20505(T), originally deposited as Trichosporon sp. The other can use food industry wastes and agricultural byproducts as the substrate for growth and accumulation of a high level of oil and accordingly is named Trichosporon oleaginosus sp. nov. The type strain is ATCC 20509(T), previously identified as Cryptococcus curvatus. Molecular phylogenetic analyses indicate that T. cacaoliposimilis is a novel taxon in the Gracile clade of the genus, close to T. gracile and T. dulcitum, and that T. oleaginosus belongs to the Cutaneum clade, with T. jirovecii as the closest sister taxon. Other oleaginous yeasts were identified as new strains of known taxa, T. insectorum, Candida orthopsilosis and C. palmioleophila.
During a survey of yeasts associated with wood-ingesting insects, 69 strains in the Scheffersomyces clade and related taxa were isolated from passalid and tenebrionid beetles and the decayed wood inhabited by them. The majority of these yeasts was found to be capable of fermenting xylose, and was recognized as Scheffersomyces stipitis or its close relative Scheffersomyces illinoinensis, which are known to be associated with wood-decaying beetles and rotten wood. Yeasts in ‘Scheffersomyces’ ( = Candida) ergatensis and ‘Scheffersomyces’ ( = Candida) coipomoensis were also frequently isolated. The remaining six strains were identified as representing four novel species in the genera Scheffersomyces and Candida based on multilocus sequence analyses of nuclear rRNA genes and four protein-coding genes, as well as other taxonomic characteristics. Two xylose-fermenting species, Scheffersomyces parashehatae f.a., sp. nov. (type strain ATCC MYA-4653T = CBS 12535T = EH045T; MycoBank MB805440) and Scheffersomyces xylosifermentans f.a., sp. nov. (type strain ATCC MYA-4859T = CBS 12540T = MY10-052T; MycoBank MB805441), formed a clade with Scheffersomyces shehatae and related Scheffersomyces species. Interestingly, S. xylosifermentans can survive at 40 °C, which is a rare property among xylose-fermenting yeasts. Candida broadrunensis sp. nov. (type strain ATCC MYA-4650T = CBS 11838T = EH019T; MycoBank MB805442) is a sister taxon of C. ergatensis, while Candida manassasensis sp. nov. (type strain ATCC MYA-4652T = CBS 12534T = EH030T; MycoBank MB805443) is closely related to Candida palmioleophila in the Candida glaebosa clade. The multilocus DNA sequence comparisons in this study suggest that the genus Scheffersomyces needs to be circumscribed to the species near S. stipitis (type species) and S. shehatae that can be characterized by the ability to ferment xylose.
Four arthroconidium-producing yeasts were isolated from the gut of wood-inhabiting tenebrionid and passalid beetles. The rRNA genes of these yeast strains were sequenced, compared and analysed. The sequence results and other taxonomic characterizations placed two of the strains into Trichosporon porosum, and the remaining strains, EH024T and EH026 which were isolated from Xylopinus saperdioides (Coleoptera: Tenebrionidae), into a novel species of the genus Trichosporon in the Porosum clade. Strain EN6S23 was independently isolated from forest soil in Taiwan and was identified as the same novel species based on identical sequences in the internal transcribed spacers (ITS) and the D1/D2 region of the LSU rRNA gene and similar physiological characteristics to those of strains EH024T and EH026. The three strains can assimilate cellulose and xylan as sole carbon source, and are clearly distinguished from their closest taxon, T. porosum, by 14 nt differences in the ITS and D1/D2 region. These strains did not reproduce sexually under the laboratory conditions tested. The novel species is proposed as Trichosporon xylopini sp. nov. (type strain EH024T = ATCC MYA-4670T = CBS 11841T).
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