Multilocus phylogenetic analyses, pullulan production and xylanase activity of tropical isolates of Aureobasidium pullulans

Aureobasidium pullulans is the source of the commercially valuable polysaccharide pullulan and the enzyme xylanase. Isolates are typically off-white to pale pink or black on solid media, while some tropical isolates have been described as ‘color variants’ with bright pigments of red, yellow or purple. We sequenced 5 loci (internal transcribed spacer, intergenic spacer 1, translation elongation factor-1 alpha, beta tubulin, and RNA polymerase II) from 45 new isolates from Thailand. Based on the phylogenetic analyses, isolates were classified into 12 clades. Each clade showed different colors on different culture media including two clades with ‘color variants’ and some clades exhibited high levels of pullulan production or xylanase activity. Colony characteristics do not correlate perfectly with DNA sequence phylogeny or the physiological characters, but DNA sequence differences rapidly identify isolates with genetic novelty.     

Relation between phylogeny and physiology in some ascomycetous yeasts

The question of whether yeasts with similar physiological properties are closely related has been examined using recently published phylogenetic analyses of 26S domain D1/D2 rDNA nucleotide sequences from all currently recognized ascomycetous yeasts. When apparently unique metabolic pathways are examined, some relationships between physiology and rDNA phylogeny are evident. Most Candida and Pichia species that are able to assimilate methanol as the sole carbon source are in a clade delimited by C. nanospora and C. boidinii. Exceptions are P. capsulata and P. pastoris which are phylogenetically separated from the other methanol-assimilating yeasts. Yeasts subject to the petite mutation, resulting in respiratory deficiency, belong to three different clades, viz. a Saccharomyces clade delimited by S. cerevisiae and S. rosinii,the Dekkera/Brettanomyces clade, and some Schizosaccharomyces species (‘Archiascomycete’ clade). However, petite mutants were also found in Zygosaccharomyces fermentati and some other more distantly related species. Yeasts able to assimilate n-hexadecane, uric acid or amines as sole carbon source are broadly distributed over the ascomycetous phylogenetic tree. However, species that assimilate adenine as sole carbon source are closely related. Most of these species also assimilated glycine, uric acid, n-hexadecane, putrescine and branched-chain aliphatic compounds such as isobutanol, leucine and isoleucine. Among the Saccharomycetales, species utilizing all or the great majority of these eight compounds are in the Stephanoascus/Arxula/Blastobotrys clade. Candida blankii, which is distantly related to this clade, proved to be an exception and assimilated six of eight of these compounds. This revised version was published online in June 2006 with corrections to the Cover Date.     

Partial rRNA sequences in marine yeasts: a model for identification of marine eukaryotes.

The V3 variable region of the large subunit rRNA was examined for nucleotide sequence signatures as potential taxonomic tools. Data are presented on 117 species, representing 23 genera of basidiomycetous yeasts. The results of nucleotide sequence alignments indicate that strains within species have identical base sequences and that species may differ from one another by one to more than 100 base positions. Phylogenetic analyses of the alignments indicates relationships among species, including the prediction of synonymous species and the clustering of species belonging to the Ustilaginales and Tremellales. These results suggest that species-specific nucleotide sequences can be used for the development of techniques for population analyses of a variety of marine and other microeukaryotes.     

Growth of Hansenula holstii on Cadavers

Growth of a yeast was observed on prosected cadavers used for demonstration purposes in a medical school. An asporogenous yeast was isolated and identified as an atypical form of Hansenula holstii by analysis of the extracellular polysaccharide. The isolate showed resistance to embalming fluid but was eventually eradicated by addition of picloxidine digluconate to the fluid.     

<Emphasis Type="Italic">Ogataea saltuana</Emphasis> sp. nov., a novel methanol-assimilating yeast species

Four ascosporulating strains of an undescribed methanol-assimilating yeast species were isolated from forest habitats in Hungary. Three were recovered from rotten wood and one from leaves of a sessile oak (Quercus petraea). An additional isolate of the undescribed species sharing similar phenotypic characters with the above-noted strains was recovered from the gut of an unidentified beetle collected from under the bark of a coniferous tree in Bulgaria. A closely related, but somewhat divergent strain was recovered from insect frass in a Ponderosa pine (Pinus ponderosa) collected in New Mexico, USA. Analysis of the D1/D2 sequences of the LSU rRNA gene placed the new species in the Ogataea clade. The ITS and the D1/D2 LSU sequences of the rRNA gene repeats were compared for the above-noted strains and that of the type strain of Ogataea zsoltii, the closest neighbour among currently recognized Ogataea species. Their relatedness was investigated by parsimony network analysis as well. As a result of the sequence analysis, it was concluded that the six strains isolated from tree associated habitats represent a single new yeast species. Ogataea saltuana sp. nov. is proposed to accommodate these strains. The type strain NCAIM Y.01833^T (CBS 10795^T, NRRL Y-48448^T) was recovered from rotten wood of Scotch pine (Pinus silvestris) in Hungary. The GenBank accession number for the D1/D2 domain nuclear large subunit rRNA gene sequence of strain NCAIM Y.01833^T (CBS 10795^T, NRRL Y-48448^T) is EU327033. The MycoBank number of the new species is MB 519966.     

Multigene phylogenetic analysis of the Lipomycetaceae and the proposed transfer of Zygozyma species to Lipomyces and Babjevia anomala to Dipodascopsis

Phylogenetic relationships among species assigned to genera of the family Lipomycetaceae were determined from analysis of the nearly entire large, subunit rRNA gene, the small subunit rRNA gene, mitochondrial small subunit rRNA gene and the translation elongation factor-1alpha gene. Monophyly of the Lipomycetaceae was strongly supported, and currently described species appear genetically unique. The multigene analysis provided no support for maintaining the genera Kawasakia, Smithiozyma, Waltomyces or Zygozyma, and it is proposed that species in these genera be assigned to the genus Lipomyces. The monotypic genus Babjevia is a member of the Dipodascopsis clade and it is proposed to reassign Babjevia anomala to Dipodascopsis. The proposed changes will result in the Lipomycetaceae having two ascosporic genera, Lipomyces and Dipodascopsis, and the anamorphic genus Myxozyma.     

Glucosylation and Other Biotransformations of T-2 Toxin by Yeasts of the Trichomonascus Clade

Trichothecenes are sesquiterpenoid toxins produced by Fusarium species. Since these mycotoxins are very stable, there is interest in microbial transformations that can remove toxins from contaminated grain or cereal products. Twenty-three yeast species assigned to the Trichomonascus clade (Saccharomycotina, Ascomycota), including four Trichomonascus species and 19 anamorphic species presently classified in Blastobotrys, were tested for their ability to convert the trichothecene T-2 toxin to less-toxic products. These species gave three types of biotransformations: acetylation to 3-acetyl T-2 toxin, glycosylation to T-2 toxin 3-glucoside, and removal of the isovaleryl group to form neosolaniol. Some species gave more than one type of biotransformation. Three Blastobotrys species converted T-2 toxin into T-2 toxin 3-glucoside, a compound that has been identified as a masked mycotoxin in Fusarium-infected grain. This is the first report of a microbial whole-cell method for producing trichothecene glycosides, and the potential large-scale availability of T-2 toxin 3-glucoside will facilitate toxicity testing and development of methods for detection of this compound in agricultural and other products.