Study investigates the reproductive habits of the fungus that causes athlete's foot

June 28, 2018

The sexual habits of Trichophyton rubrum, the fungus that causes athlete's foot and other kinds of skin and nail infections, were the focus of a study published by Brazilian scientists and international collaborators in the journal Genetics.

The researchers' findings suggest that asexual reproduction is the rule for this species. Mating between individuals is not common and requires highly specific conditions if it does occur. As a result, the genetic variability in the population is low even when comparing isolates from different parts of the world.

"We found the population to be clonal. There's practically no mating between individuals, and few variations in the genome are created," said Gabriela Felix Persinoti, lead author of the study, which was performed during her postdoctorate with support from the São Paulo Research Foundation - FAPESP.

According to the principal investigator of the project, Nilce Martinez-Rossi, a professor at the University of São Paulo's Ribeirão Preto Medical School (FMRP-USP) in Brazil, understanding how the fungus reproduces is basic science, but progress in applied research is impossible without it.

"Genetic variability is a factor to be considered in drug development, for example, as it may point to the risk that the pathogen will adapt and develop resistance to treatment," she said.

Scientists have discovered that the greater the genetic variability among individuals of a given species is, the likelier these individuals are to adapt to adverse conditions and survive.

Persinoti's work is part of one of two research lines coordinated by Martinez-Rossi at FMRP-USP. This line's goal is to investigate how dermatophytes - fungi that cause skin, hair and nail infections - interact with their hosts. The other line aims to understand the mechanisms of drug resistance in this same group of microorganisms.

T. rubrum is a dermatophyte species that infects only humans, Martinez-Rossi explained. Infections are typically chronic and superficial since the fungus feeds on the keratin in skin and nails. These infections cause discomfort, itching, and structural damage to nails, impairing the infected individual's quality of life. In rare cases, generally associated with low immunity, the infection may spread through the patient and become life-threatening.

"We want to unpack the molecular mechanisms of pathogenicity in these dermatophytes - in other words, to understand how they cause infection. Revealing the 'weapons' these fungi use during the infectious process will contribute to the development of drugs to combat them," Martinez-Rossi said.

Persinoti conducted her study in Christina Cuomo's laboratory at the Broad Institute of MIT and Harvard in the United States during a research internship abroad funded by FAPESP.

Genomic analysis

As the authors of the article explain, the species Trichophyton rubrum is actually a complex that can be subdivided into several different morphotypes. These morphotypes are highly similar fungi with small variations in color or structure or in the compounds they produce.

In the first stage of the research, Persinoti and collaborators analyzed the genetic variability in 100 morphotypes isolated in several parts of the world. To do this, they used multilocus sequence typing (MLST), a method that sequences key fragments (or loci) of DNA rather than the whole genome.

"To complement this analysis, 12 isolates were submitted to whole-genome sequencing," said the FAPESP-funded researcher.

This more deeply analyzed sample comprised ten morphotypes of T. rubrum and two isolates of T. interdigitale, which also infects humans; none of the genomes of these isolates have been described hitherto.

After sequencing, the group focused on analyzing a genomic region known as the mating type (MAT). Individuals cannot mate unless they have complementary MATs - one must have MAT 1 and the other MAT 2, for example.

Mating has been observed in some dermatophytes in studies by other groups, but so far, mating has never been observed in T. rubrum.

"When we analyzed this genomic region, we found MAT 1 in almost all morphotypes of T. rubrum and MAT 2 in only one morphotype," Persinoti said.

The scientists conducted laboratory experiments designed to induce sexual reproduction between the MAT 2 isolate and MAT 1 individuals, but the fungi failed to mate.

"This led us to the conclusion that sexual reproduction in this species probably doesn't happen or requires a very specific condition in order to take place," Persinoti said.

The conclusion was reinforced by other experiments performed during the FAPESP-supported research, which showed that similarity in the genomes of the individuals analyzed exceeded 99%.

According to Persinoti, however, the genes required for sexual reproduction found in other dermatophytes are still present in T. rubrum. This suggests that the transition to asexual reproduction is a recent event in the species and could be associated with its specialization in infecting humans.

"We performed a series of phylogenetic comparisons between the different morphotypes, and the results enabled us to delineate the species more correctly. One of the morphotypes, known as soudanense, proved to be divergent from the rest and could come to be considered a separate species," Persinoti said.
-end-
About São Paulo Research Foundation (FAPESP)

The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the State of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration. For more information: http://www.fapesp.br/en.

Fundação de Amparo à Pesquisa do Estado de São Paulo

Related Fungus Articles from Brightsurf:

International screening of the effects of a pathogenic fungus
The pathogenic fungus Candida auris, which first surfaced in 2009, is proving challenging to control.

Research breakthrough in fight against chytrid fungus
For frogs dying of the invasive chytridiomycosis disease, the leading cause of amphibian deaths worldwide, the genes responsible for protecting them may actually be leading to their demise, according to a new study published today in the journal Molecular Ecology by University of Central Florida and the Smithsonian Conservation Biology Institute (SCBI) researchers.

Researchers look to fungus to shed light on cancer
A team of Florida State University researchers from the Department of Chemistry and Biochemistry found that a natural product from the fungus Fusicoccum amygdali stabilizes a family of proteins in the cell that mediate important signaling pathways involved in the pathology of cancer and neurological diseases.

The invisibility cloak of a fungus
The human immune system can easily recognize fungi because their cells are surrounded by a solid cell wall of chitin and other complex sugars.

Taming the wild cheese fungus
The flavors of fermented foods are heavily shaped by the fungi that grow on them, but the evolutionary origins of those fungi aren't well understood.

Candida auris is a new drug-resistant fungus emerging globally and in the US early detection is key to controlling spread of deadly drug-resistant fungus
Early identification of Candida auris, a potentially deadly fungus that causes bloodstream and intra-abdominal infections, is the key to controlling its spread.

Genetic blueprint for extraordinary wood-munching fungus
The first time someone took note of Coniochaeta pulveracea was more than two hundred years ago, when the South African-born mycologist Dr Christiaan Hendrik Persoon mentioned it in his 1797 book on the classification of fungi.

How a fungus can cripple the immune system
An international research team led by Professor Oliver Werz of Friedrich Schiller University, Jena, has now discovered how the fungus knocks out the immune defenses, enabling a potentially fatal fungal infection to develop.

North American checklist identifies the fungus among us
Some fungi are smelly and coated in mucus. Others have gills that glow in the dark.

Tropical frogs found to coexist with deadly fungus
In 2004, the frogs of El Copé, Panama, began dying by the thousands.

Read More: Fungus News and Fungus Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.