Heterobasidiomycetous Yeasts Research Articles

A survey of heterobasidiomycetous yeasts for the presence of the genes homologous to virulence factors of Filobasidiella neoformans, CNLAC1 and CAP59.

Among species of the heterobasidiomycetous yeasts, Filobasidiella neoformans is the only serious pathogen that causes fatal infections in both immunocompromised as well as immunocompetent patients. Three phenotypic characteristics, including growth at 37 degrees C, extracellular polysaccharide capsule and laccase activity, of F. neoformans are known to play major roles in the pathogenicity of the fungus. Several CAP genes involved in polysaccharide capsule formation, as well as the CNLAC1 gene encoding a laccase, have previously been cloned and characterized. To analyse the presence of these Cryptococcus neoformans virulence factors in other heterobasidiomycetous yeasts, numerous species of heterobasidiomycetous yeasts were screened for the presence of laccase activity and a polysaccharide capsule. Species exhibiting laccase activity and possessing a glucuronoxylomannan (GXM) capsule were screened for homologues of both the CAP59 gene and the CNLAC1 gene of F. neoformans. Southern blots of genomic DNA from GXM capsule-producing species exhibited no discernible hybridization to the CAP59 DNA sequence except for the two varieties of F. neoformans and Cryptococcus podzolicus. Although discernible, the hybridization band observed with the DNA of C. podzolicus was faint. Oligonucleotide primers constructed using the CAP59 gene sequence also failed to yield PCR products from DNAs of these yeasts except for the two varieties of F. neoformans. These results, coupled with the absence of a CAP59 homologue in the database, suggested the CAP59 gene to be unique to F. neoformans. C. podzolicus was the only species besides F. neoformans that possessed a capsule and expressed strong laccase activity on various media containing phenolic compounds. A CNLAC1 homologue was isolated from C. podzolicus while it was not detected in the species producing beige to faint tan colonies on media with phenolic compounds. Compared to the CNLAC1 sequence of four serotypes of F. neoformans, the CNLAC1 homologue of C. podzolicus showed the highest homology to that of serotype B/C strains and the lowest homology to that of serotype A strains.

Utilization of low molecular weight aromatic compounds by heterobasidiomycetous yeasts: taxonomic implications.

The utilization of low molecular weight aromatic compounds implies the operation of complex metabolic pathways. In order to investigate the taxonomic relevance of this property among heterobasidiomycetous yeasts, both at the species level and at higher taxonomic ranks, the capacity to assimilate twenty such compounds was tested in a total of 332 strains representing approximately 200 species. The substrates most frequently utilized were protocatechuic, caffeic, and p-hydroxybenzoic acids, whereas cinnamic, sinapic, and syringic acids and guaiacol were never assimilated. The assimilation of the majority of the aromatic compounds investigated correlated with the utilization of protocatechuic acid. Among the Urediniomycetes, the members of the Sporidiales and those of the Naohidea-Rhodotorula minuta clade showed a good ability to utilize aromatic compounds, whereas the members of the Agaricostilbum-Kondoa group were more heterogeneous, in agreement with the four subclades known. Among the Tremellomycetidae, the members of the Cystofilobasidium and Tremella clades showed a reduced or null ability to utilize aromatic compounds. In contrast, the members of the Trichosporon clade were able to utilize phenol and similar substrates, and the representatives of the Filobasidium clade assimilated various aromatic compounds, including those requiring more complex catabolic routes. Assimilation tests using, as sole carbon and energy sources, low molecular weight aromatic compounds appear to be potentially useful in taxonomic studies of basidiomycetous yeasts. In those species in which a considerable number of strains was investigated, variable assimilation patterns were frequently observed. The possibility that such discrepant results indicate an incorrect species delimitation is discussed.

Utilization of low molecular weight aromatic compounds by heterobasidiomycetous yeasts: taxonomic implications

Utilization of low molecular weight aromatic compounds by heterobasidiomycetous yeasts: taxonomic implications

Three-dimensional reconstruction of mitotic cells of Cryptococcus neoformans based on serial section electron microscopy

Ultra-thin serial sections of mitotic cells of Cryptococcus neoformans were observed by transmission electron microscope and computer-aided reconstruction of three-dimensional models were performed to understand the kinetics of the nucleus and mitochondria during mitosis. The separation of chromosomes occured in the protrusion of the nucleus extending in the bud (=daughter cell), followed by one set of chromosomes being moved back into the mother cell. These findings were similar to those reported in the heterobasidiomycetous yeasts. No giant mitochondrion, composed of a coalescence of all the mitochondria, was found. Volumetric analysis revealed the fluctuations in the mitochondrial volume: total cytoplasmic volume ratio were minimum during mitosis. In addition, methods, usefulness and limitations of observation of ultra-thin serial sections for understanding the morphology of cells and intracellular organelles were reviewed.

Scanning electron microscopy of the septal pore cap of the basidiomycete Schizophyllum commune

As part of a comparative study of the structure and function of pore structures in heterobasidiomycetous yeasts, dikaryotic hyphae of Schizophyllum commune were subjected to chemical fixation, freeze fracturing, maceration, and freeze substitution, and were subsequently prepared for scanning electron microscopy. The interior of the hyphal cell was visualized and revealed the perforated septal pore cap or parenthesome, mitochondria, vacuoles, and tubular endoplasmic reticulum. The septal pore cap showed connections with tubular endoplasmic reticulum. This tubular endoplasmic reticulum covered the dolipore septal surface. The results presented here complement and extend the ultrastructural image of the septal pore cap obtained from transmission electron micrographs.Key words: septal pore cap, Schizophyllum commune, freeze fracture, maceration, scanning electron microscopy.

Classification of heterobasidiomycetous yeasts: characteristics and affiliation of genera to higher taxa of heterobasidiomycetes.

Classification of heterobasidiomycetous yeasts: characteristics and affiliation of genera to higher taxa of heterobasidiomycetes.

Evolutionary Affinities of Heterobasidiomycetous Yeasts Estimated from 18S and 25S Ribosomal RNA Sequence Divergence

Summary Phylogenetic relationships among heterobasidiomycetous yeasts, including anamorphic and teleomorphic taxa, have been compared from the sequence similarity of small (18S) and large (25S) subunit ribosomal RNA. Species examined were Cystofilobasidium capitatum, Filobasidiella neoformans, Filobasidium floriforme, Leucosporidium scottii, Malassezia furfur, M. pachydermatis, Phaffia rhodozyma, Rhodosporidium toruloides, Sporidiobolus johnsonii, Sterigmatosporidium polymorphum, Trichosporon beigelii, T. cutaneum and T. pullulans. The taxa cluster into three main groups. One group contains the nonteliospore forming genera Sterigmatosporidium, Filobasidiella, Filobasidium and the anamorphic species T. beigelii and T. cutaneum. The teliospore formers Leucosporidium, Rhodosporidium and Sporidiobolus, all of which have simple septal pores, cluster into a single group, despite the heterogeneity of carotenoid formation. By contrast, C. capitatum appears separate, not only from Rhodosporidium, but also from the Filobasidiaceae with which it shares a primitive dolipore septum. The uniqueness of the genus Malassezia among yeasts is confirmed, and one might predict from nucleotide sequence similarity that teleomorphs of those lipophilic organisms would form teliospores whereas Trichosporon beigelii and T. cutaneum appear related to the family Filobasidiaceae.

Ultrastructure of the mitotic apparatus inCryptococcus neoformans

Mitosis in Cryptococcus neoformans was examined by electron microscopy. Observation of serial sections showed that the separation of chromosomes occurred in the karyokinetic nucleus in the bud, that the microtubule organizing center (MTOC) was composed of two globular elements and a bridged middle piece, and that the nuclear envelope of the karyokinetic nucleus was partially destroyed during mitosis. These findings are similar to those reported in the heterobasidiomycetous yeasts. In addition, some of the prophase cells showed extension of the karyokinetic nucleus into the bud unaccompanied by the MTOC and swelling of the middle piece of the MTOC.

Postmeiotic Mitosis, Basidiospore Development, and Septation inUstilago Maydis

Postmeiotic mitosis, basidiospore development and metabasidial septation are analyzed ultrastructurally in Ustilago maydis (Basidiomycota, Ustilaginales). The spindle pole body at mitotic prophase is composed of two globular elements connected by a middle piece. During the transition from interphase II to mitotic prophase the globular elements enlarge, the middle piece elongates, and the spindle pole body typically moves to an apical position on the migratory nucleus. Cytoplasmic microtubules are associated with organelle movement into the basidiospore. Sterigmata arise endogenously. Mitotic nuclei divide into a spindlecontaining portion which moves into the basidiospore and a nucleolar portion which degenerates in the metabasidium. One postmitotic sibling nucleus remains in the basidiospore while the other returns to the metabasidium. Primary metabasidial and sterigmal septa are traversed by a simple, eccentric to centric pore that may become walled-off. Complete, adventitious metabasidial septa result in the formation of fragmentation zones. The nuclear and spindle pole body cycles of U. maydis support the inclusion of the Ustilaginales in the Basidiomycetes, and these features are similar to those reported for the heterobasidiomycetous yeasts.

Postmeiotic Mitosis, Basidiospore Development, and Septation in Ustilago maydis

Postmeiotic mitosis, basidiospore development and metabasidial septation are analyzed ultrastructurally in Ustilago maydis (Basidiomycota, Ustilaginales). The spindle pole body at mitotic prophase is composed of two globular elements connected by a middle piece. During the transition from interphase II to mitotic prophase the globular elements enlarge, the middle piece elongates, and the spindle pole body typically moves to an apical position on the migratory nucleus. Cytoplasmic microtubules are associated with organeUe movement into the basidiospore. Sterigmata arise endogenously. Mitotic nuclei divide into a spindle- containing portion which moves into the basidiospore and a nucleolar portion which degenerates in the metabasidium. One postmitotic sibhng nucleus remains in the basidiospore while the other returns to the metabasidium. Primary metabasidial and sterigmal septa are traversed by a simple, eccentric to centric pore that may become walled-off. Complete, adventitious metabasidial septa result in the formation of fragmentation zones. The nuclear and spindle pole body cycles of U. maydis support the inclusion of the Ustilaginales in the Basidiomycetes, and these features are similar to those reported for the heterobasidiomycetous yeasts.

Fimbrial Variation in Smuts and Heterobasidiomycete Fungi

The distribution and relatedness of long, surface, proteinaceous fibrils (fimbriae) in a number of species in the Ustilaginales and related heterobasidiomycetous yeast were studied using electron microscopy and an antifimbrial antibody prepared against a pure fimbrial preparation from a1 cells of Ustilago violacea. Only one examined species (Tilletia caries) from the family Tilletiaceae lacked fimbriae. All species in the Ustilaginaceae and the heterobasidiomycetous yeasts produced long fimbriae similar in size and shape to those of U. violacea. The cells from all of the tested species in the Ustilaginaceae were agglutinated by this antibody and, therefore, appear to have a similar or identical protein subunit in their fimbriae. The temperature range in which fimbriae were produced varied among species and among physiologic races of U. violacea. None of the tested heterobasidiomycetous yeasts was agglutinated by the U. violacea antibody, and the protein subunit in their fimbriae is a distinct type Cells of either mating type a1 or a2 and diploid a1a2 cells of U. violacea were agglutinated by the antibody prepared against fimbriae from a1 cells. Although fimbriae appear to have a role in cell communication during conjugation, the evidence suggests that the fimbriae of each mating type are identical rather than sex specific and, therefore, either perform a purely mechanical function or are modified in a sex-specific manner.

Requirements of chemical structure for hormonal activity of lipopeptidyl factors inducing sexual differentiation in vegetative cells of heterobasidiomycetous yeasts

Biological activities of both peptidyl and isoprenyl constituents of yeast sex hormones (lipopeptides), rhodotorucine A and farnesyl tremerogen A -10, were examined. The chemically synthesized simple peptides (peptidyl constituents) and farnesyl cystein (isoprenyl one) did not exhibit any biological activities, such as hormonal and hormone-inhibitory (or -accelerative) activities. The mixture of both constituents also had no activity. Then, it is assumed that the heterobasidiomycetous yeasts ( Rhodosporidium toruloides and Tremella mesenterica ) recognize the total structure of lipopeptidyl molecule for the biological response, sexual differentiation, and the term “Pattern Recognition” is proposed for the mode of this recognition.

Mitosis in heterobasidiomycetous yeasts. II. Rhodosporidium sp. (Rhodotorula glutinis) and Aessosporon salmonicolor (Sporobolomyces salmonicolor).

ABSTRACT Mitotic events similar to those in Leucosporidium scottii also take place in 2 other hetero-basidiomycetous yeasts – Rhodosporidium sp. and Aessosporon salmonicolor, which were formerly known as Rhodotorula glutinis and Sporobolomyces salmonicolor. Therefore it is proposed that a mitosis which takes place within the bud may be a distinctive characteristic of heterobasidio-mycetous yeasts which can be used as a taxonomic indicator of basidiomycete relationships in asporogenous yeasts. Mitosis in A. salmonicolor seems to be identical to that which we have previously described in L. scottii but a few differences have been found in Rhodosporidium sp. These are now described in detail.

Apical vesicles in growing bud cells of heterobasidiomycetous yeasts.

Clusters of cytoplasmic vesicles resembling those in growing hyphal apices of mycelial fungi are found near the tips of buds in three heterobasidiomycetous yeasts, Rhodotorula glutinis, Candida scottii, and Sporobolomyces salmonicolor.