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Yarrowia lipolytica is the only known species in the teleomorph (i.e. sexual) genus Yarrowia and has its anamorph (i.e. asexual state) classified in the genus Candida Berkhout as Candida lipolytica. This species can be found readily in nature, has significant industrial value and is important to the food and medical fields. Candida deformans was first considered a variety of C. lipolytica and was later listed as a synonym of this species. More recent studies based on sequence variation in the nuclear rRNA gene sequences suggested C. deformans to be a separate species with no known teleomorph linked to it. In this study we show that C. deformans strains, obtained from South Africa, can mate with strains present in the CBS yeast collection and produce a Yarrowia teleomorph, described here as Yarrowia deformans. Strains of Candida yakushimensis nom. inval., a species also belonging to the Yarrowia phylogenetic clade, were also studied and described as a novel species of Yarrowia.

A new teleomorphic genus Ascohotryozyma, 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.

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.

Phylogenetic relationships of the yeast genus Lipomyces were studied using sequences from fragments of 5.8S rRNA gene and from internal transcribed spacer region ITS2 of 13 strains (7 type strains included) representing five species and subtaxa, and originating from different geographical locations (Japan, Trinidad, Nigeria, North America, Western Europe, Russia, South Africa, Mauritius). Parsimony and distance analyses were performed. Tree topology from the parsimony and distance analyses of the sequence confirmed the results of nDNA reassociation. Results segregate the 13 isolates of Lipomyces into five major clades.

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.

Lipomyces starkeyi is known to be associated with three strains-clusters showing high mutual nDNA reassociation within each cluster, but which reassociate ambiguously with the type of L. starkeyi. Representative strains of L. starkeyi and Cluster alpha were examined for possible genetic exchange by the prototrophic selection technique. Since no genetic recombination was detected, the strains are presumed to be genetically isolated. Cluster alpha is consequently assigned to the rank of species as Lipomyces mesembrius. A description of the new species is given. Lipomyces kononenkoae ssp. spencermartinsiae has been raised to the rank of species as L. spencermartinsiae.

Species delimitation in Lipomyces was attempted by nuclear genome comparison in conjunction with the re-evaluation of 48 physiological characters of 65 strains. High intraspecific (> 75%) and low interspecific (< 28%) similarity values established that L. japonicus, L. lipofer and L. tetrasporus are genetically isolated, and also distinct from L. kononenkoae and L. starkeyi. Ambiguous similarity values were obtained with L. kononenkoae and L. starkeyi. Strains previously assigned to L. 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 to L. 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 of L. 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 the L. kononenkoae and L. starkeyi complexes is around 40% and 31%, respectively. These two clusters consequently appear to be intermediate between L. kononenkoae and L. starkeyi, and will, as such, have to be considered in any delimitation of these two species. A key to the taxa of Lipomyces and related genera of the Lipomycetaceae is given.

The species described as Lipomyces anomalus Babjeva & Gorin shows significant genetic and phenotypic divergence from the type species Lipomyces starkeyi Lodder & Kreger-van Rij in terms of rRNA base sequence substitution and ascosporal and septal ultrastructure. The species is consequently reclassified in the new, unispecific genus Babjevia, as Babjevia anomala.

Three strains of an undescribed species of the genus Myxozyma were recovered. The new species differs from other accepted species of the genus in its assimilation pattern of carbon sources, mol% G + C and low DNA-DNA homology. A description of the new species, Myxozyma vanderwaltii, and a key to the species accepted in the genus are given.

The new genus Botryozyma with a single species, B. nematodophila is proposed for two isolates from nematodes (Panagrellus zymosiphilus) occurring in grapes with sour-rot. The new genus has typical ascomycetous characteristics and, being unable to produce ascospores, is placed in the family Candidaceae.

The genus Trichosporon was revised using characters of morphology, ultrastructure, physiology, ubiquinone systems, mol% G + C of DNA, DNA/DNA reassociations and 26S ribosomal RNA partial sequences. A total of 101 strains was used, including all available type and authentic cultures of previously described taxa. Nineteen taxa could be distinguished, 15 of which having Q-9 coenzyme systems and 4 having Q-10. Sixteen previously described names were reduced to synonymy. One new species was described. The genus is characterized by the presence of arthroconidia. Few species possess further diagnostic morphological characters, such as the presence of appressoria, macroconidia or meristematic conidiation. The septa of two species were found to be non-perforate, while those of the remaining species contained dolipores at variable degrees of differentiation, with or without vesicular or tubular parenthesomes. All species were able to assimilate a large number of carbon compounds; visible CO2 production was absent. The genus was found to be fairly homogeneous on the basis of a phylogenetic analysis of partial 26S rRNA sequences, with the exception of T. pullulans which proved to be unrelated. Most taxa were found to occupy well-defined ecological niches. Within the group of taxa isolated from humans, a distinction could be made between those involved in systemic mycoses and those which mainly caused pubic or non-pubic white piedras, respectively. One species was consistently associated with animals, while others came mainly from soil or water. One species was mesophilic and another psychrophilic.

The currently accepted type species of the genus Trichosporon Behrend is T. beigelii. This species has formerly been regarded as identical to T. cutaneum. However, these fungi are now known to represent separate species with different ecology. The first species described in Trichosporon was T. ovoides, an agent of human white piedra. A neotype strain is designated for this species, while a lectotype strain is indicated for T. cutaneum. The name T. beigelii is considered as doubtful and consequently cannot be maintained.

Septal micropores or plasmadesmal canals have been observed in two species of the lipomycetaceous genus Zygozyma. The presence of these canals is considered as further evidence for the connexion between the Lipomycetaceae and the Dipodascaceae. The genus Zygozyma has been emended.

Four strains of an undescribed species of the genus Williopsis were isolated from brackish water. A description of the new species, Williopsis salicorniae (type strain, CBS 8071, NRRL Y-12834), is given.

Genome comparison in strains of the genus Arthroascus indicates that two species, A. javanensis (CBS 2555, Type) and A. schoenii (CBS 7223, Type), can be recognized.

The new genus Arxula is proposed for the classification of xerotolerant, ascomycetous, anamorphic, arthroconidial yeasts. The genus is considered to be of endomycetaceous affinity.

Transmission electron micrographs of septa in Blastobotrys species invariably showed central micropores. Septa of species of Sporothrix, however, exhibited three types of pores: micropores which were central if single, or scattered; central simple pores with Woronin bodies; dolipores. The results confirm the heterogeneity of the genus Sporothrix.

A new ascogenous yeast species, Dekkera anomala, is described. The strains studied were isolated from spoiled soft drinks. This species differs morphologically and physiologically from the species presently accepted in the genus Dekkera by the formation of blastese and the ability to ferment lactose.

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.

A new, soil-associated species of the genus Debaryomyces, D. udenii, is described. The species is characterized by pusticulate rather than verrucate ascospores, and slowly lytic asci.

The morphological and physiological characters of the species of Blastobotrys, and of a number of similar species of Sporothrix, Trichosporiella and Candida were studied. Blastobotrys is defined as having mother cells (primary conidia) which form distinct, secondary conidia. Sporothrix has non-catenulate conidia, or the conidia are catenulate without marked differentiation of conidia of first and second order. Trichosporiella is delimited from Candida by a stronger coherence between hyphal cells, arthroconidia being absent. Four new Blastobotrys species are described, and two unnamed species; two new combinations are proposed in Trichosporiella. Related species in other genera are briefly discussed. A new Stephanoascus teleomorph is described in two strains originally identified as Sp. fungorum. Two diagnostic keys to the described taxa, using either morphological or physiological characters, are given.

The type strain of Candida polymorpha Ohara et Nonomura, nom. nud. was found to produce hat-shaped ascospores. On the basis of its morphology and physiology, it is considered a new species of the genus Pichia and is described as Pichia triangularis sp. nov.

The physiological and morphological characteristics of eighty-two strains of Hanseniaspora and Kloeckera, represented twenty-nine described species, were examined. These results along with DNA base composition and DNA/DNA reassociation experiments revealed that the genus Hanseniaspora comprises six distinct species, viz. H. valbyensis, H. uvarum, H. guilliermondii, H. occidentalis, H. osmophila and H. vineae, with K. japonica, K. apiculata, K. apis, K. javanica, K. corticis and K. africana, respectively, as their imperfect states.

K. apiculata var. apis (nom. nud.) was found to be the imperfect state of H. guilliermondii Pijper by a high degree of DNA reassociation. The name is validated and raised to species rank, K. apis Lavie ex Smith, Simione and Meyer. K. apis and H. guilliermondii could be distinguished from H. uvarum and H. valbyensis by a low DNA reassociation and by growth at 37 C.

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

Morphological taxonomy of simple Hyphomycetes is complicated by the frequent occurrence of pleoanamorphism. In some groups of yeast-like fungi, uncommon synanamorphs are diagnostic. Differences in conidiogenesis do not always delimit natural groups. Some nomenclatural problems are mentioned, with an emphasis on the need of neotypification. Prospects are sketched for future taxonomic research.

A new species of the genus Zygozyma, Z. suomiensis, is described, based on the study of a single strain, derived from a bovine skin lesion.

The new species, Hyphozyma roseonigra, characterized by pink colonies, budding cells with minute annellated zones and brown, septate hyphae, is described. It is non-fermentative, shows no colouration with Diazonium Blue B, and has an ascomycete-type cell wall ultrastructure. A key to the accepted species and varieties of Hyphozyma is given.

The anamorphic yeast species Candida hellenica, C. inositophila and C. steatolytica were found to constitute haploid mating types of an undescribed, filamentous heterothallic Endomycete. The new genus Zygoascus is proposed for the teleomorph. Descriptions are given of the genus and type species, Z. hellenicus.