G. A. Poot

Polyphasic re-examination of Debaryomyces hansenii strains and reinstatement of D. hansenii, D. fabryi and D. subglobosus

The type species of the genus Debaryomyces, Debaryomyces hansenii, is a highly heterogeneous species. It has been isolated from a large diversity of natural sources including fruit, air, water, soil, but most frequently from processed food products. The species delineation of this yeast species urgently needs clarification. The heterogeneity in taxonomic characteristics has resulted in the description of varieties linked to D. hansenii. The aim of this study was to re-examine and classify D. hansenii using a polyphasic approach. A total of 65 D. hansenii isolates were examined, 57 representing the variety hansenii and nine the variety fabryi. The selection of strains for DNA reassociation and phylogenetic analysis was based on polymerase chain reaction mediated fingerprints using four mini- and microsatellite-specific primers. The discriminating power of growth at 35 °C and 37 °C was re-examined and ascospore production was observed. DNA reassociations and phylogenetic analyses were performed on selected isolates from each of the clusters obtained from the DNA fingerprint analyses. The data indicated the presence of three distinct species within the D. hansenii group, which were represented by type strains of former species and that are proposed to be reinstated: D. hansenii (CBS 767T = MUCL 49680T), D. fabryi (CBS 789T = MUCL 49731T) and D. subglobosus (CBS 792T = MUCL 49732T).

Genome comparisons in the yeastlike fungal genus Galactomyces Redhead et Malloch.

The G+C contents of the DNAs of 41 strains belonging to the genus Galactomyces Redhead et Malloch were determined by the thermal denaturation method. Melting profiles revealed that the DNAs of these strains are heterogeneous. Four groups were recognized on the basis of this heterogeneity. However, DNA similarity values, which were calculated by using DNA-DNA reassociation kinetics, revealed that the strains could be divided into six subgroups. Strains belonging to the same subgroup exhibited high levels of DNA similarity (84 to 100%). The members of two subgroups, corresponding to Galactomyces citri-aurantii and Galactomyces reessii, exhibited low levels of DNA similarity with the members of the other subgroups (20 to 27%). The members of the four remaining subgroups, which contained only strains previously identified as Galactomyces geotrichum, exhibited intermediate levels of reassociation (41 to 59%). Some combinations of phenotypic characteristics correlated with the subgroups; a key based on phenotypic characteristics that can be used to distinguish the subgroups is presented.

Species delineation in the genus Nadsonia Sydow

The genus Nadsonia Sydow is revised on the basis of morphology, physiology, amino acid and fatty acid composition, electrophoretic patterns of some enzymes and DNA relatedness. Two species, N. commutata (type CBS 6640) and N. fulvescens, with two varieties, N. fulvescens var. fulvescens (type CBS 2596) and N. fulvescens var. elongata (type CBS 2594) nov. comb. are recognized. A modified diagnosis of the genus and a key are given.

Re-examination of some species of the genus Geotrichum Link: Fr

The nutritional physiology and the growth rate of thirty-four strains representing species of Geotrichum without known teleomorph states were examined. From twenty-seven strains the mol% G+C were calculated from the DNA melting curves. The first derivatives of the melting curves of seven strains, including the type strain of Geotrichum clavatum, demonstrated the presence of two peaks, 12% away from each other; the remaining strains showed only a single broad peak. DNA homology values among strains of the former group were high, indicating their conspecificity. The strains of the latter group could be subdivided into six DNA homology groups, four of which could be identified with recognized species and two may represent novel taxa. A combined key of Geotrichum and its teleomorph states Galactomyces and Dipodascus is presented.

Species delimitation in the genus Lipomyces by nuclear genome comparison

Species delimitation inLipomyces was attempted by nuclear genome comparison in conjuction with the re-evaluation of 48 physiological characters of 65 strains.High intraspecific (>75%) and low interspecific (<28%) similarity values established thatL. japonicus, L. lipofer andL. tetrasporus are genetically isolated, and also distinct fromL. kononenkoae andL. starkeyi.Ambiguous similarity values were obtained withL. kononenkoae andL. starkeyi. Strains previously assigned toL. kononenkoae constitute two related clusters. While similarity values within each cluster range from 76–99%, representatives of the two clusters reassociate for only 47%. Since these clusters are differentiated by their ecologically relevant maximum growth temperature,L. kononenkoae is subdivided. Strains previously assigned toL. starkeyi resolve into four closely related clusters. While similarity values within each cluster range from 78–100%, representatives of the four clusters reassociate for only 59–69%. Since these four clusters are poorly differentiated, the subdivision ofL. starkeyi does not appear possible without recourse to other criteria.Four unassigned strains constitute a further two clusters. Reassociation within these clusters is of the order of 91–100%, while reassociation between them occurs only at 59%. Reassociation of representatives of these clusters with those of theL. kononenkoae andL. starkeyi complexes is around 40% and 31%, respectively. These two clusters consequently appear to be intermediate betweenL. kononenkoae andL. starkeyi, and will, as such, have to be considered in any delimitation of these two species. A key to the taxa ofLipomyces and related genera of the Lipomycetaceae is given.

Dipodascus capitatus, Dipodascus spicifer and Geotrichum clavatum: genomic characterization.

The G+C contents of 25 strains of Dipodascus capitatus, Dipodascus spicifer and Geotrichum clavatum were found to be heterogeneous on basis of derivative graphs of the melting profiles. Strains showing similar derivative graphs of the melting curve exhibited high levels of DNA homology (80-100%); strains showing dissimilar derivative graphs exhibited low levels of DNA homology (5 to 45%). Being considered separate taxa on basis of these parameters, D. capitatus, D. spicifer and G. clavatum could be identified by a combination of the key characteristics growth on xylose, cellobiose, salicin and arbutin.

Recurrent isolation of an uncommon yeast, Candida pararugosa, from a sarcoma patient

A yeast was repeatedly isolated from the saliva of a sarcoma patient. A relatively uncommon species, Candida maris, was identified based on the API 20C profile. The yeast species most frequently obtained from the patients mother and from clinic staff was Candida albicans. A comparison of the yeast obtained from the patient with the type strain of C. maris strongly suggested that the former was not representative of C. maris. Analysis of partial ribosomal DNA sequences of the patient strain and from the type strain of C. maris showed that the two are phylogenetically not closely related. The patient strain was very close to Candida pararugosa, a relatively uncommon asporogenous yeast. DNA reassociation studies among C. pararugosa and patient isolates showed that they were conspecific. We could not determine the source of the yeast infection. This case will alert hospital staff to be aware of the possibility of unexpected environmental microorganisms as causes of infections, colonizations and persistent environmental contamination events in immunocompromised patients.

Ascobotryozyma cognata sp. nov., a new ascomycetous yeast associated with nematodes from wood-boring beetle galleries

A new species of Ascobotryozyma, A. cognata sp. nov. (anamorph Botryozyma cognata), was isolated from beetle galleries in Idaho, USA. A. cognata was found on the surface of free-living nematodes, Panagrellus dubius, collected from galleries created by the long-horned beetle Saperda calcarata in Populus (aspen), and the weevil Cryptorhynchus lapathi in Salix (willow). A. cognata isolates were collected from similar habits and in relatively close proximity to those of A. americana, the only species described from North America. The recognition of A. cognata as a distinct species was supported by morphological and molecular data. Thallus cells of A. cognata were significantly shorter than those of A. americana. Low DNA reassociation values, notably different randomly amplified polymorphic DNA (RAPD), inter-sequence simple repeat (ISSR), and amplified fragment-length polymorphic (AFLP) fingerprints, and sequence divergence in both the D1/D2 domain of the nuc-LSU rDNA and an additional unidentified region were all consistent with the recognition of a new species.

Conspecificity of Hanseniaspora nodinigri and Hanseniaspora vineae: comparison by DNA reassociation

Hanseniaspora nodinigri Lachance 1981, found in black knots (caused byDibotryon morbosum) ofPrunus virginiana, was described as a new species, some time after publication of the extensive study by Meyer et al. (1978) on the systematics ofHanseniaspora Zikes and its imperfect counterpartKloeckera Janke. Lachance delimited the species from other members of the genus because of absence of growth on glucono-δ-lactone. He also stated that this species, although evidently similar in many ways toH. vineae van der Walt et Tscheuschner andH. osmophila (Niehaus) Phaff et al., has ‘diverged from them, possibly in its adaptation to growth in association with black knots’.

Ascobotryozyma americana gen. nov. et sp. nov. and its anamorph Botryozyma americana, an unusual yeast from the surface of nematodes.

A new teleomorphic genus Ascobotryozyma, with a single species, A. americana, is proposed. Its anamorph is a Botryozyma that differs from the type species, B. nematodophila, on distributional, physiological, and molecular criteria; it is described as Botryozyma americana, anam. sp. nov. Ascobotryozyma is characterized by globose asci bearing four lunate ascospores. Fusion of thallus cells precedes ascus formation. Ascobotryozyma americana was isolated from the surface of nematodes (Panagrellus dubius) associated with galleries of the poplar borer (Saperda calcarata) in trembling aspen (Populus tremuloides) in eastern Washington, USA. The teleomorph has not been produced in pure culture.