12 research outputs found
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 pathogen
Keratin degradation by dermatophytes relies on cysteine dioxygenase and a sulfite efflux pump.
Millions of people suffer from superficial infections caused by dermatophytes. Intriguingly, these filamentous fungi exclusively infect keratin-rich host structures such as hair, nails, and skin. Keratin is a hard, compact protein, and its utilization by dermatophytes for growth has long been discussed as a major virulence attribute. Here, we provide strong support for the hypothesis that keratin degradation is facilitated by the secretion of the reducing agent sulfite, which can cleave keratin-stabilizing cystine bonds. We discovered that sulfite is produced by dermatophytes from environmental cysteine, which at elevated concentrations is toxic for microbes and humans. We found that sulfite formation from cysteine relies on the key enzyme cysteine dioxygenase Cdo1. Sulfite secretion is supported by the sulfite efflux pump Ssu1. Targeted mutagenesis proved that dermatophyte mutants in either Cdo1 or Ssu1 were highly growth-sensitive to cysteine, and mutants in Ssu1 were specifically sensitive to sulfite. Most notably, dermatophyte mutants in Cdo1 and Ssu1 were specifically growth-defective on hair and nails. As keratin is rich in cysteine, our identified mechanism of cysteine conversion and sulfite efflux supports both cysteine and sulfite tolerance per se and progression of keratin degradation. These in vitro findings have implications for dermatophyte infection pathogenesis
Differential gene expression in the pathogenic dermatophyte Arthroderma benhamiae in vitro versus during infection.
Although dermatophytes are the most common agents of superficial mycoses in humans and animals, the molecular basis of the pathogenicity of these fungi is largely unknown. In vitro digestion of keratin by dermatophytes is associated with the secretion of multiple proteases, which are assumed to be responsible for their particular specialization to colonize and degrade keratinized host structures during infection. To investigate the role of individual secreted proteases in dermatophytosis, a guinea pig infection model was established for the zoophilic dermatophyte Arthroderma benhamiae, which causes highly inflammatory cutaneous infections in humans and rodents. By use of a cDNA microarray covering approximately 20-25 % of the A. benhamiae genome and containing sequences of at least 23 protease genes, we revealed a distinct in vivo protease gene expression profile in the fungal cells, which was surprisingly different from the pattern elicited during in vitro growth on keratin. Instead of the major in vitro -expressed proteases, others were activated specifically during infection. These enzymes are therefore suggested to fulfil important functions that are not exclusively associated with the degradation of keratin. Most notably, the gene encoding the serine protease subtilisin 6, which is a known major allergen in the related dermatophyte Trichophyton rubrum and putatively linked to host inflammation, was found to be the most strongly upregulated gene during infection. In addition, our approach identified other candidate pathogenicity-related factors in A. benhamiae, such as genes encoding key enzymes of the glyoxylate cycle and an opsin-related protein. Our work provides what we believe to be the first broad-scale gene expression profile in human pathogenic dermatophytes during infection, and points to putative virulence-associated mechanisms that make these micro-organisms the most successful aetiological agents of superficial mycoses