Trichophyton rubrum

This student page has not been curated.

A Microbial Biorealm page on the genus Trichophyton rubrum

Classification

Higher order taxa

Domain: Eukaryota; Kingdom: Fungi; Phylum: Ascomycota; Class: Eurotiomycetes; Order: Onygenales; Family: Arthrodermactaceae

Species

Electron micrograph of T. petrophila from Takahata et al., 2001.¹ Toga (t) and cell wall (cw) are labled. The scale bar measures 1 μm.

Genus: Trichophyton; Species: T. rubrum

Description and significance

Trichophyton rubrum, is the most common causitive of dermatophytosis worldwide, mainly occupying the humans’ feet, skin, and between fingernails. T. rubrum is known to be one of the most prominent anthrophilic species of dermatophtyes, appearing in various shades of white, yellow, brown, and red. It may also be found in various textures, being waxy, cottony, or smooth. Even though it is commonly observed, T. rubrum infections are incredibly hard to diagnose, and difficult to differentiate from other dermatophytes. Because this fungal pathogen is poorly understood, the discovery of its structure may significantly reduce the health costs of those who suffer various forms of dermatophytosis caused by T. rubrum.

Genome structure

In the absence of complete m-RNA-based evidence, the complexity of filamentous fungi gene structures make gene interpretations challenging. Due to the lack of biochemical identification techniques available, pleomorphism, and cultural variability of Dermatophytes, the current knowledge of the T. rubrum genomic sequencing is limited and is in progress. Thus far, the cloning of cDNAs have enabled the generation of expressed sequence tags (ESTs) and have be found to effectively attribute to the identification processes undertaken. The T. rubrum genome has now been organized into five chromosomes. Altogether, estimated to be 22Mb in which 5 to 10% of the genome are repetitive DNA subunits of 8 and 50% AT content. To date, 43 unique nuclear-encoded genes have been analyzed, approximately more than half are proteases.

Cell and colony structure

Due to pleomorphism, many strains and varieties of Trichophyton rubrum have been described. T. rubrum colonies typically produce a white to cream color pigmentation on its surface and have a reverse side that can be yellow-brown to wine-red. The texture ranges from being suede-like, waxy, to being downy, in which the colony structure can appear as flat to being slightyly raised. The growth of downy type strain T. rubrum ranges from being scanty to moderated numbers of slender clavate microconidia and macroconidia is absent. On the contrary, in the granular strain, the growth of clavate to pyriform microconidia ranges from being moderate to abundant, singly forming along the hyphae. In this strain, macroconidia can be found in moderate to abundant numbers, thin walled, and bacillus form. Macroconidia can form singly on thick hyphae or in fives.

Metabolism

Based on recent studies and annotations, more than half of the T. rubrum genome sequence is composed of proteases. Thus, the growth of T. rubrum is dependent of the secretion of proteases, making them keratinophilic filamentous fungus. Sequentially, the maintenance of homeostatic pH is highly influential in the metabolism’s protein activity. Fortunately the metabolic rate of T. rubrum, is flexible, and modeled to adapt to the environmental pH that had been sensed. Their ability to invade keratinized tissues enables their ingestion of several proteases. This allows the pH level of carbon, nitrogen, and oxygen sources to shift from being acidic to alkaline and is a major virulence factor for this fungal pathogen.

Ecology

Trichophyton rubrum is an anthrophilic dermatophyte, known to inhabit moist areas of the human skin, where skins fold, or even nails, where keratin and other proteins may be secreted for its growth and survival. T. rubrum may also contaminate items such as clothing or bedding. Though much of T. rubrum is still unknown and what is known lacks beneficiary purposes, through the identification processes of its genome sequence that have been undertaken, its appears some of its’ gene expressions had been linked in the presence of selected drugs. For the time being, T. rubrum may not be making any direct contributions to the environment, but the studies of it may lead to many technological advances and methodologies to diagnose other forms of dermatophytosis.

Pathology

T. rubrum is the most common infectious, anthrophilic specie of dermatophytes. Though it is usually not life-threatening, infections are long-lasting, recurring, and incredibly difficult to cure, due the mystery of its genome sequence. Through validated information of what is known on its genome sequence, it is however known that T. rubrum is a keratinophilic filamentous fungus. The fungal pathogen’s ability to secrete proteins and produce proteolitic enzymes is a major virulence factor. T. rubrum attacks the human skin and nails via keratin degradation as an environmental adaption. This allows T. rubrum to regulate the expression of several genes. Keratin, a fibrous protein, is a major structural component of the human skin and nails, thus invades through the stratum corneum. This invasion becomes the cause of dermatophytosis infections such as athletes’s foot, fungal infections in between nails, jock itch, ring worms, etc., and may be painful. The infections may be transmitted from person to person.

References

1. White, T., Henn, M., et al., Genomic Determinants of Infection in Dermatophyte Fungi. The Fungal Genome Initiative, Mar. 2012

2. De Biervre, C. and Dujon, B., Organisation of the mitochondrial genome of Trichophyton rubrum. Current Genetics, Volume 26, Issue 6: 553-559.

Edited by Melinda Dao of Dr. Lisa R. Moore, University of Southern Maine, Department of Biological Sciences, http://www.usm.maine.edu/bio