Genetic advances in dermatophytes

Millions of superficial fungal infections are annually observed in humans and animals. The majority of these mycoses are caused by dermatophytes, a specialized group of filamentous fungi that exclusively infect keratinized host structures. Despite the high prevalence of the disease, dermatophytosis, little is known about the pathogenicity mechanisms of these microorganisms. This drawback may be related to the fact that dermatophytes have been investigated poorly at the molecular level. In contrast to many other pathogenic fungi, they grow comparatively slowly under in vitro conditions, and in the last decades, only a limited number of molecular tools have been established for their manipulation. In recent years, however, major promising approaches were undertaken to improve genetic analyses in dermatophytes. These strategies include efficient systems for targeted gene inactivation and gene silencing, and broad transcriptional profiling techniques, which have even been applied in sophisticated infection models. As a fundamental prerequisite for future genetic analyses, full genome sequences of seven different dermatophyte species have become available recently. Therefore, it appeared timely to review the available molecular tools and methodologies in dermatophyte research, which may provide future insights into the virulence of these clinically important pathogens

Investigations of electron beam hardening on TiAlN coated heat-treatable steel

In this investigation, an electron beam hardening (EBH) procedure was applied to heat-treatable steel 51CrV4 coated with Ti₍₁₋x₎AlxN hard coatings, where x ranged from 0.3 to 0.6. The coatings with variable composition and mechanical properties were deposited by reactive magnetron sputtering. For electron beam surface hardening following hard coating deposition, the energy distribution within the energy transfer field caused a nearly constant hardening temperature on the treated material surface. Morphology, composition, and mechanical properties of the coatings remained mostly unchanged, whereas the coating-substrate interface and the steel surface region were highly modified. Diffusion of the near-interface coating elements into the substrate occurred, and the corresponding region of the substrate showed clear changes in morphology and composition. These changes can be correlated with substantial improvements of the coating adhesion properties. Based on temperature measurements and calculations of electron penetration depths, a plausible description of the observed effects was derived. The EBH caused a significant improvement of delamination resistance, especially for coatings with insufficient adhesion properties

Surface hardening after hard coating deposition - combining TiAlN tribological coatings with subsequent electron beam treatment

In this investigation an electron beam hardening (EBH) procedure was applied to heat-treatable steel 51CrV4 coated with Ti(1-x)AlxN hard coatings, where x ranged from 0.3 to 0.6. The coatings with variable composition and mechanical properties were deposited by reactive magnetron sputter deposition. For electron beam surface hardening followed by hard coating deposition, the energy distribution within the energy transfer field caused a nearly constant hardening temperature on the treated material surface. Morphology, composition and mechanical properties of the coatings remained nearly unchanged, whereas the coating-substrate interface and the steel surface region were highly modified. Diffusion of interface-near coating elements into the substrate occurred and the corresponding region of the substrate showed clear changes in morphology and composition. These changes can be correlated with substantial improvements of the coating adhesion properties. Based on temperature measurements and calculations of electron penetration depths a plausible description of the observed effects was derived. The electron beam hardening caused a significant improvement of delamination resistance, especially for coatings with insufficient adhesion properties

The zinc-binding protein Hot13 promotes oxidation of the mitochondrial import receptor Mia40

A disulphide relay system mediates the import of cysteine-containing proteins into the intermembrane space of mitochondria. This system consists of two essential proteins, Mia40 and Erv1, which bind to newly imported proteins by disulphide transfer. A third component, Hot13, was proposed to be important in the biogenesis of cysteine-rich proteins of the intermembrane space, but the molecular function of Hot13 remained unclear. Here, we show that Hot13, a conserved zinc-binding protein, interacts functionally and physically with the import receptor Mia40. It improves the Erv1-dependent oxidation of Mia40 both in vivo and in vitro. As a consequence, in mutants lacking Hot13, the import of substrates of Mia40 is impaired, particularly in the presence of zinc ions. In mitochondria as well as in vitro, Hot13 can be functionally replaced by zinc-binding chelators. We propose that Hot13 maintains Mia40 in a zinc-free state, thereby facilitating its efficient oxidation by Erv1

Factors Supporting Cysteine Tolerance and Sulfite Production in Candida albicans.

The amino acid cysteine has long been known to be toxic at elevated levels for bacteria, fungi, and humans. However, mechanisms of cysteine tolerance in microbes remain largely obscure. Here we show that the human pathogenic yeast Candida albicans excretes sulfite when confronted with increasing cysteine concentrations. Mutant construction and phenotypic analysis revealed that sulfite formation from cysteine in C. albicans relies on cysteine dioxygenase Cdg1, an enzyme with similar functions in humans. Environmental cysteine induced not only the expression of the CDG1 gene in C. albicans, but also the expression of SSU1, encoding a putative sulfite efflux pump. Accordingly, the deletion of SSU1 resulted in enhanced sensitivity of the fungal cells to both cysteine and sulfite. To study the regulation of sulfite/cysteine tolerance in more detail, we screened a C. albicans library of transcription factor mutants in the presence of sulfite. This approach and subsequent independent mutant analysis identified the zinc cluster transcription factor Zcf2 to govern sulfite/cysteine tolerance, as well as cysteine-inducible SSU1 and CDG1 gene expression. cdg1Δ and ssu1Δ mutants displayed reduced hypha formation in the presence of cysteine, indicating a possible role of the newly proposed mechanisms of cysteine tolerance and sulfite secretion in the pathogenicity of C. albicans. Moreover, cdg1Δ mutants induced delayed mortality in a mouse model of disseminated infection. Since sulfite is toxic and a potent reducing agent, its production by C. albicans suggests diverse roles during host adaptation and pathogenicity