Nutritional requirements of the human pathogenic fungus, Trichophyton rubrum, and nutritional immunity of the human skin as barrier against colonization

Trichophyton rubrum is a pathogenic fungus infecting human skin, hairs and nails. These substrates are colonized only by very few fungal species. In this review, we summarise the nutritional requirements of fungal species, with a focus on T. rubrum, and compare them with nutrients available in the keratinized tissues. The outer layers of the human skin are low in most nutrients required for fungal growth, the basis of nutritional immunity. Carbohydrate availability is low and protein, in the form of keratin, is used for energy and carbon by the fungus. In addition to the nitrogen derived from keratin, the skin is rich in phosphorus, sulfur, potassium and chloride. The concentration of trace elements is very low, especially in the outermost layer of the skin, and magnesium, iron and zinc are likely the most relevant limiting elements for T. rubrum. We point to the evolutionary adaption of the fungus to the human skin. T. rubrum has a sophisticated system for the digestion and utilization of extracellular protein and a relative low demand for micronutrients.