Elzbieta Johannsen

Hybridization studies within the genus Kluyveromyces van der Walt emend. van der Walt

Hybridization studies based on the prototrophic selection technique, involving the use of auxotrophic mutants of strains of all accepted species of the genus Kluyveromyces, are reported. Two main groups of mutually interfertile taxa were established within the genus. The first group comprises Kluyveromyces bulgaricus, K. cicerisporus, K. dobzhanskii, K. drosophilarum, K. fragilis, K. lactis; K. marxianus, K. phaseolosporus, K. vanudenii and K. wikenii. The second group consists of K. dobzhanskii, K. drosophilarum, K. lactis, K. vanudenii and K. wickerhamii. Hybrids were also detected in crosses involving K. drosophilarum and K. waltii as well as K. marxianus and K. thermotolerans.In terms of the concept of the biological species and in compliance with the requirements of the International Code of Botanical Nomenclature, taxa which hybridize with K. marxianus and form fertile recombinants at frequencies observed in intraspecific crosses, are accepted as varieties of K. marxianus.

A comparison of interfertility and in vitro DNA-DNA reassociation as criteria for speciation in the genus Kluyveromyces

Hybridization studies based on the use of the prototrophic selection technique were undertaken to compare interfertility and DNA-DNA reassociation as criteria for speciation purposes in the yeast genus Kluyveromyces. Degrees of DNA-DNA reassociation > 70% between strains as reported in the literature, were found to correlate with high recombination frequencies. Degrees of DNA-DNA reassociation < 20% between strains did however, not invariably coincide with the absence of interfertility between strains. If interfertility is accepted as criterion for conspecificity, the hitherto reported low degrees ( < 20%) of DNA-DNA reassociation in Kluyveromyces cannot confidently be employed for speciation purposes.

Interfertility as basis for the delimitation of Kluyveromyces marxianus

Hybridization studies between strains of Kluyveromyces marxianus and the remaining species of the genus involving the use of auxotrophic mutants, are reported. K. marxianus was found to be interfertile with K. bulgaricus, K. cicerisporus, K. dobzhanskii, K. drosophilarum, K. fragilis, K. lactis, K. phaseolosporus, K. vanudenii and K. wikenii. Accepting interfertility as criterion for conspecificity, these nine syngamous taxa are relegated to the status of biotypes or physiologic races of a single species K. marxianus.

Cell-wall structure, mitosis and urease activity in Torulopsis species of high GC content

Five Torulopsis species, in which, characteristically, the mean molar percentage of guanine plus cytosine of the DNA bases (GC content) is above 50%, were examined to determine their cell-wall structure; the mode of bud formation; course of mitosis and their urease activity. The two urease-negative species, T. gropengiesseri (% GC 57.1) and T. silvatica (% GC 56.3), were found to possess affinitive properties which characterize perfect ascomycetous yeast species.In the urease-positive species, T. fujisanensis (% GC 65.0–66.1), T. ingeniosa (% GC 55.6) and T. philyla (% GC 63.9), there appeared to be a correlation between pronounced urease activity and the affinitive properties which characterize perfect basidiomycetous yeast species. Pronounced urease activity has, however, also been found in the ascomycetous species Schizosaccharomyces pombe.Consequently neither high GC ratios nor the presence of urease activity when considered individually, can be taken as reliable criteria when attempting to establish the affinity of yeasts the perfect states of which are not known, with the Basidiomycetes.A strain of the ascomycetous species Sclerotinia trifoliorum was examined by electron microscopy for comparative purposes.

Yeast flora of non-radurised and radurised minced beef — a taxonomic study

Abstract Yeast flora present in minced beef before and after radurisation were examined. No reduction in the number of yeast cells was observed after the meat was radurised at a dose of 2.5 kGy. A definite increase in the number of psychrotrophic yeast was observed in radurised meat after 14 days of storage at 4°C. The recovered yeast flora comprised representatives of the following species: Candida famata (9 isolates); C. lipolytica (4 isolates); C. parapsilosis (20 isolates); C. sake (27 isolates); C. zeylanoides (28 isolates); Cryptococcus albidus var. albidus (6 isolates); Cr. infirmo-miniatus (1 isolate); Cr. laurentii var. laurentii (31 isolates); Trichosporon cutaneum (1 isolate); Tr. pullulans (2 isolates); Rhodotorula minuta var. texensis (1 isolate); Rh. rubra (1 isolate).

The perfect state ofTorulopsis magnoliae

The perfect state ofTorulopsis magnoliae has been identified on the basis of cytological evidence and X-ray inactivation data. This state is considered to show an affinity with the ascomycetous yeasts, but forms dangeardiens which delimit the haplophase exogenously.In accordance with established taxonomic procedure this perfect state is described as the type of the new genusEntelexis.

Kluyveromyces yarrowii sp. nov., a haploid, heterothallic, arboreal species

Summary Two yeast strains classified as Candida tannotolerans , have been found to constitute compatible mating types of an undescribed, haploid, heterothallic species of the genus Kluyveromyces . A description of the new species, Kluyveromyces yarrowii , is given.

Trichosporon terrestre sp. nov.

A single strain representative of an undescribedTrichosporon species, was recovered from soil. The cell wall of the strain corresponds in structure to cell walls of the ascomycetous yeasts. On the ground of X-ray inactivation data the strain is assumed to be diploid. A description of the new species is given.

Pichia philogaea sp. nov.

Two strains of an undescribedPichia species were recovered from soil. A description of the new species is given and its possible relationship with the other species of the genus is discussed.

Torulopsis geochares and Torulopsis azyma, two new, haploid species of ascomycetous affinity

Three strains representative of two undescribed Torulopsis species, T. geochares and T. azyma, were recovered from soil and rupicolous lichen in South Africa. Descriptions of the new species are given. Ploidy determinations by X-ray inactivation showed the type strains of the two new species to be haploid. On the basis of their affinitive characteristics the new species appear to be related to the ascomycetous yeasts.