Budding in the Dimorphic Fungus Phialophora dermatitidis

Ultrastructural comparisons of yeast and hyphal bud formation in Phialophora dermatitidis reveal that bud initiation is characterized by a blastic rupture of the outer portion of the yeast or hyphal wall and the emergence of a bud protuberance through the resulting opening. The wall of the emerging bud is continuous, with only an inner wall layer of the parental yeast or hypha. The outer, ruptured portion of the parental wall typically forms a collar around the constricted emergence region of the developing bud. The cytoplasm within the very young emerging bud invariably contains a small number of membrane-bound vesicles. The septum formed between the daughter bud and the parental yeast or hypha is a complete septum devoid of a septal pore, septal pore plug, or any associated Woronin bodies characteristic of simple septa of the moniliform or true hyphae. These observations suggest that yeast bud formation and lateral hyphal bud formation in the dimorphic fungus P. dermatitidis involve a growth process which occurs identically in both the yeast and mold phase of this human pathogenic organism.     

Morphological and Structural Changes During the Yeast-to-Mold Conversion of Phialophora dermatitidis

The details of the morphological and structural events occurring during yeast-to-mold conversion of the human pathogenic fungus Phialophora dermatitidis as seen by phase-contrast microscopy and electron microscopy are described and illustrated. Budding yeasts growing exponentially were observed to have thin walls and a cytoplasm exhibiting the characteristics of rapidly growing cells including numerous mitochondria, abundant ribosomes, few vacuoles, and little accumulation of storage material. In contrast, thick-walled yeasts were characterized by less apparent or significantly fewer mitochondria and ribosomes and the presence of considerable amounts of storage materials. Microscope observations of yeast-to-mold conversion revealed that only thick-walled yeasts having prominent lipid bodies in their cytoplasm converted to hyphal forms. Typically, the thick-walled yeast formed two to a number of moniliform hyphal cells which in turn often produced true hyphae. The results indicated that yeasts of P. dermatitidis must acquire spore-like characteristics by becoming thick-walled and by accumulating considerable endogenous substrate reserves before they convert and produce hyphae.     

Protein Profiling of the Dimorphic Pathogenic Fungus, Sporothrix schenckii

Sporotrichosis is a common cutaneous mycosis caused by the dimorphic fungus Sporothrix schenckii, which exhibits a temperature-dependent dimorphic switch. At 25°C, it grows in a mycelial phase, while at 37°C, it forms unicellular yeast cells. The formation of yeast cells was thought to be a requisite for the pathogenicity of S. schenckii. To identify fragments that might be related to morphogenesis, whole-cell proteins from the mold and early yeast stages of S. schenckii were analyzed using 2DE. Among thousands of protein molecules displayed, more than 300 showed a differential expression between the two phases. In particular, 24 yeast-specific proteins were identified using MALDI-TOF/MS. One of the most interesting proteins was a hybrid histidine kinase, DRK1, a global regulator of dimorphism and virulence in Blastomyces dermatitidis and Histoplasma capsulatum that was abundant in the yeast phase. Our study introduced a new approach to study dimorphism in S. schenckii, and the data may help us better understand the molecular mechanisms of phase transition.     

Functional Analysis of the MATB Mating-Type Idiomorph of the Dimorphic Fungus Yarrowia lipolytica

The whole MATA cassette from Yarrowia lipolytica, a dimorphic fungus, was replaced by the URA3 gene through a double homologous recombination. This MAT-less strain lost its mate capacity with A or B Y. lipolytica strains. Introduction of polymerase chain reaction-synthesized idiomorph MATB in a null strain of A locus by double homologous recombination gave rise to a "transsexual" B strain. Mating capacity of this engineered mutant was assayed using Y. lipolytica strains of either A or B mating type. Mating took place only with an A strain, demonstrating the MATB idiomorph functionality in a MATA phenotype. Our data suggest that specific downstream genes are responsible for the final A or B phenotypes present in all Y. lipolytica cells, independent of their MAT idiomorph phenotype.     

Cyclic Guanosine 3′,5′-Monophosphate in the Dimorphic Fungus Mucor racemosus

The dimorphic fungus Mucor racemosus was found to contain the cyclic nucleotide guanosine 3′,5′-monophosphate (cGMP). Approximately equivalent amounts of the compound were found in ungerminated spores, yeastlike cells, and mycelia. Germinating spores contained severalfold higher amounts of cGMP than the other cell forms. cGMP levels did not change significantly during the morphogenetic conversion of yeast to mycelia. Added exogenous cGMP or the dibutyryl derivative did not influence cell morphology in any way and did not alter the effect that cyclic adenosine 3′,5′-monophosphate has upon cell morphology.     

Evaluation of skin test for chromoblastomycosis using antigens prepared from culture filtrates ofFonsecaea pedrosoi,Phialophora verrucosa,Wangiella dermatitidis andExophiala jeanselmei

Antigenic substances were prepared from culture filtrates ofFonsecaea pedrosoi, Phialophora verrucosa, Wangiella dermatitidis andExophiala jeanselmei. These antigenic substances were evaluated for detecting cutaneous delayed hypersensitivity in rats experimentally-infected withF. pedrosoi, P. verrucosa, W. dermatitidis, E. jeanselmei, Cladosporium carrionii andFonsecaea compactum and in patients with chromoblastomycosis caused byF. pedrosoi. TheF. pedrosoi antigen elicited positive reactions in all of the animals infected withF. pedrosoi and in 5 of 6 patients. TheP. verrucosa, W. dermatitidis andE. jeanselmei antigens elicited positive reactions in all of the animals infected with the homologous species. These antigens displayed cross-reactivity in some of the animals and patients, whereas more than half of them exhibited positive reactions only to the antigens prepared from the homologous species. These results suggest that a delayed-type skin test using the antigens prepared by the authors may be useful not only for the diagnosis of chromoblastomycosis but also for the identification of species of the causative agent.     

Dimorphic spore production in the genus Acaulospora

Species of the genus Acaulospora are partly characterized by the production of ‘acaulosporoid’ spores. The simultaneous formation of glomoid and acaulosporoid spores by some species in the Glomeromycota has been used as a basis for taxonomic classification. We report the presence of both glomoid and acaulosporoid spores in four Acaulospora species. Analysis of the 18S rRNA gene confirmed that only A. spinosa was present in a pot culture that produced two morphs. The functional significance of dimorphic spore production is unknown but the production of blastic spores is not a characteristic that can have any significance as a taxonomic character.     

Conjugation in streptococci

The problem of conjugation in Streptococci is reviewed as a form of genetical information exchange in bacteria. The theoretical and experimental data of the recent years on the nature, mechanisms and role of conjugation in the spreading of drug resistance in the populations of pathogenic microorganisms are presented.     

Dimorphic mating-type chromosomes in the fungus Microbotryum violaceum

Fungi often mate as haploids, and sex chromosomes (i.e., mating-type chromosomes) that are dimorphic for their size or overall DNA content have never been reported in this kingdom. Using electrophoretic techniques for karyotype analysis, a highly dimorphic chromosome pair that determines mating compatibility is shown to occur in populations of the fungus Microbotryum violaceum. This substantiates the evolution of such dimorphism as a general feature associated with haploid determination of mating compatibility, which previously had been known only in haplodioecious plants (mosses and liverworts). Size-dimorphic sex chromosomes are present in a lineage of M. violaceum native to Europe, as well as a lineage native to North America. However, they are very different in size between these lineages, indicating either independent evolution of the dimorphism or a large degree of divergence since their isolation. Several DNA sequences that show sequence similarity to transposons were isolated from these sex chromosomes.     

Conjugation in bacilli

The review considers experimental data on the conjugal transfer of plasmids in the Bacillus cereus and Bacillus subtilis groups (the transfer of large self-transmissible plasmids and the mobilization of small plasmids). Conjugation in bacilli is compared with conjugation in E. coli dependent on the F factor. Conjugation of bacilli in their natural habitats is also discussed.     

Conjugation in Bacilli

The review considers experimental data on the conjugal transfer of plasmids in the Bacillus cereus andBacillus subtilis groups (the transfer of large self-transmissible plasmids and the mobilization of small plasmids). Conjugation in bacilli is compared with conjugation in E. coli dependent on the F factor. Conjugation of bacilli in their natural habitats is also discussed.