Evaluation of the in vitro and in vivo dimorphism of Sporothrix schenckii, Blastomyces dermatitidis, and Paracoccidioides brasiliensis isolates after preservation in mineral oil

Molecular and phenotypic reidentification of Sporothrix schenckii clinical isolates preserved under mineral oil for 34 to 64 years in a culture collection in Brazil

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Impact of mineral oil as a method of preservation on clinical isolates of Sporothrix schenckii.

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Sporothrix spp sporulation induction using a culture medium supplemented with rose bush branches.

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Usefulness of polyphasic methodology in the re-identification of species of Sporothrix schenckii complex.

Sporotrichosis is a subcutaneous mycosis worldwide distributed reaching hyperendemic proportions in Brazil. Many isolates from patients with sporotrichosis are preserved in culture collections by different methods around the world. The preservation methods are used to maintain the viability and the morphophysiological and genetic characteristics of isolates for long periods. In this study, we evaluated 34 isolates, previously, identified as S. schenckii by a classical identification method, initially preserved by periodical subcultures and then under mineral oil at culture collection of Oswaldo Cruz Institute/Fiocruz, to re-identify them by polyphasic identification. Our results showed that seven isolates remained viable for 34 to 64 years under oil, one isolate lost the ability to sporulate which was reverted by using a medium culture supplemented with rosebush branches and all of them were identified as Sporothrix schenckii sensu stricto by morphological, physiological, partial β-tubulin gene sequencing and phylogenetic analysis.

Can passage in Galleria mellonella activate virulence factors of Paracoccidioides brasiliensis as in the murine model?

Paracoccidioidomycosis (PCM) is a fungal disease restricted to Latin countries, and its etiologic agents derive from the Paracoccidioides genus. Attenuation or loss of virulence in Paracoccidioides spp. following successive subculturing has been described. However, virulence can be recovered by passage in mammalian host. In this study, the recovery of adhesion of P. brasiliensis through passage in mice was compared to that in the insect Galleria mellonella. Analysis of in vitro fungal-host cell interaction, gene expression of adhesins, and analysis of the survival curves revealed that Galleria mellonella is useful for the reactivation of P. brasiliensis adhesion.

Transcription factors Mat2 and Znf2 operate cellular circuits orchestrating opposite- and same-sex mating in Cryptococcus neoformans

Cryptococcus neoformans is a human fungal pathogen that undergoes a dimorphic transition from a unicellular yeast to multicellular hyphae during opposite sex (mating) and unisexual reproduction (same-sex mating). Opposite- and same-sex mating are induced by similar environmental conditions and involve many shared components, including the conserved pheromone sensing Cpk1 MAPK signal transduction cascade that governs the dimorphic switch in C. neoformans. However, the homeodomain cell identity proteins Sxi1α/Sxi2a encoded by the mating type locus that are essential for completion of sexual reproduction following cell–cell fusion during opposite-sex mating are dispensable for same-sex mating. Therefore, identification of downstream targets of the Cpk1 MAPK pathway holds the key to understanding molecular mechanisms governing the two distinct developmental fates. Thus far, homology-based approaches failed to identify downstream transcription factors which may therefore be species-specific. Here, we applied insertional mutagenesis via Agrobacterium-mediated transformation and transcription analysis using whole genome microarrays to identify factors involved in C. neoformans differentiation. Two transcription factors, Mat2 and Znf2, were identified as key regulators of hyphal growth during same- and opposite-sex mating. Mat2 is an HMG domain factor, and Znf2 is a zinc finger protein; neither is encoded by the mating type locus. Genetic, phenotypic, and transcriptional analyses of Mat2 and Znf2 provide evidence that Mat2 is a downstream transcription factor of the Cpk1 MAPK pathway whereas Znf2 functions as a more terminal hyphal morphogenesis determinant. Although the components of the MAPK pathway including Mat2 are not required for virulence in animal models, Znf2, as a hyphal morphology determinant, is a negative regulator of virulence. Further characterization of these elements and their target circuits will reveal genes controlling biological processes central to fungal development and virulence.

Although sexual reproduction typically involves partners of opposite mating type (sexuality), sex can occur with just one mating type and even with single individuals (parthenogenesis, homothallism). For example, Cryptococcus neoformans, a fungal pathogen that causes cryptococcal meningitis, can undergo opposite-sex mating and same-sex mating. The ability to undergo bisexual and unisexual mating provides this fungus a unique opportunity to maintain its ability to undergo sexual reproduction in largely unisexual natural populations (α). However, the molecular mechanisms underlying these two sexual reproduction processes are unclear. By random mutagenesis and gene expression profiling, we have identified two key transcription factors, Mat2 and Znf2, that operate cellular circuits orchestrating opposite- and same-sex mating in C. neoformans. The findings presented here provide a foundation to further elucidate the circuits evoking two different modes of sexual reproduction and to investigate the relationship between morphological differentiation and virulence in this ubiquitous pathogen. Recent studies suggest that unisexual mating might occur in several major human pathogenic fungi, and thus knowledge about the molecular mechanisms controlling the two sexual reproduction modes in C. neoformans may also provide insights on the evolution of bifurcate mating systems in other organisms.

Isolation of a novel yeast strain Candida digboiensis TERI ASN6 capable of degrading petroleum hydrocarbons in acidic conditions

A novel yeast species Candida digboiensis TERI ASN6 was isolated from soil samples contaminated with acidic oily sludge (pH 1-3) from the Digboi refinery (Northeast India). The strain TERI ASN6 could degrade 73% of the total petroleum hydrocarbons present in the medium at pH 3 in a week. This strain presents a dimorphic behaviour and showed mycelia morphology when grown under stressed conditions such as low pH and in a medium containing petroleum hydrocarbons. The C. digboiensis strain could efficiently degrade the aliphatic and aromatic fractions of the acidic oily sludge at pH 3 as confirmed by gas chromatography. During the growth of TERI ASN6 in dibenzothiophene (DBT), DBT-sulfone and biphenyl-2-ol were detected. An active cytochrome P450 system, implicated in hydrocarbon oxidation, was also detected in this yeast using degenerated primers based on its conserved regions. This yeast is a potential candidate for petroleum bioremediation treatment of hydrocarbon contaminated acidic soils. Its physiological behaviour allows the strain to work efficiently where other hydrocarbon-degrading bacteria may not survive.

Virulence attributes and hyphal growth of C. neoformans are quantitative traits and the MATalpha allele enhances filamentation

Cryptococcus neoformans is a fungal human pathogen with a bipolar mating system. It undergoes a dimorphic transition from a unicellular yeast to hyphal filamentous growth during mating and monokaryotic fruiting. The traditional sexual cycle that leads to the production of infectious basidiospores involves cells of both alpha and a mating type. Monokaryotic fruiting is a modified form of sexual reproduction that involves cells of the same mating type, most commonly alpha, which is the predominant mating type in both the environment and clinical isolates. However, some a isolates can also undergo monokaryotic fruiting. To determine whether mating type and other genetic loci contribute to the differences in fruiting observed between alpha and a cells, we applied quantitative trait loci (QTL) mapping to an inbred population of F2 progeny. We discovered that variation in hyphal length produced during fruiting is a quantitative trait resulting from the combined effects of multiple genetic loci, including the mating type (MAT) locus. Importantly, the alpha allele of the MAT locus enhanced hyphal growth compared with the a allele. Other virulence traits, including melanization and growth at 39 degrees C, also are quantitative traits that share a common QTL with hyphal growth. The Mac1 transcription factor, encoded in this common QTL, regulates copper homeostasis. MAC1 allelic differences contribute to phenotypic variation, and mac1Delta mutants exhibit defects in filamentation, melanin production, and high temperature growth. Further characterization of these QTL regions will reveal additional quantitative trait genes controlling biological processes central to fungal development and pathogenicity.

Current awareness on yeast

In order to keep subscribers up‐to‐date with the latest developments in their field, this current awareness service is provided by John Wiley & Sons and contains newly‐published material on yeasts. Each bibliography is divided into 10 sections. 1 Books, Reviews & Symposia; 2 General; 3 Biochemistry; 4 Biotechnology; 5 Cell Biology; 6 Gene Expression; 7 Genetics; 8 Physiology; 9 Medical Mycology; 10 Recombinant DNA Technology. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted. (4 weeks journals ‐ search completed 10th. Nov. 2004)