A new hybrid fungus is found in hospitals and linked to lung disease
(Left) Candida yeasts live on parts of the human body. Imbalance of microbes on the body can allow these yeasts, some of which are hybrids, to grow and cause infection. (Right) Cryptococcus yeasts, including ones that are hybrids, can cause life-threatening infections in primarily immunocompromised people. Credit: Centers for Disease Control and Prevention

From the mythical minotaur to the mule, creatures created from merging two or more distinct organisms – hybrids – have played defining roles in human history and culture. However, not all hybrids are as fantastic as the minotaur or as dependable as the mule; in fact, some of them cause human diseases.

We are evolutionary biologists who are trying to understand why certain fungi infect hundreds of thousands of patients each year while others are harmless. We are particularly interested in infections caused by Aspergillus fungi, a group of molds—multicellular fungi that typically grow by forming networks of hairlike filaments—that can cause very serious infections in patients with weak immune systems.

While examining Aspergillus strains isolated from patients with lung-related diseases, we unexpectedly discovered an Aspergillus hybrid that infects humans. This finding is significant not only because this is the first known example of a hybrid mold infecting humans but also because accurate identification of the species causing disease is key for managing fungal infections.

When looking through a microscope isn’t close enough

For the last few years, our team at Vanderbilt University, Gustavo Goldman’s team at São Paulo University in Brazil and many other collaborators around the world have been collecting samples of fungi from patients infected with different species of Aspergillus molds. One of the species we are particularly interested in is Aspergillus nidulans, a relatively common and generally harmless fungus.

Clinical laboratories typically identify the species of Aspergillus causing the infection by examining cultures of the fungi under the microscope. The problem with this approach is that very closely related species of Aspergillus tend to look very similar in their broad morphology or physical appearance when viewing them through a microscope.

Interested in examining the varying abilities of different A. nidulans strains to cause disease, we decided to analyze their total genetic content, or genomes.

What we saw came as a total surprise. We had not collected A. nidulans but Aspergillus latus, a close relative of A. nidulans and, as we were to soon find out, a hybrid species that evolved through the fusion of the genomes of two other Aspergillus species: Aspergillus spinulosporus and an unknown close relative of Aspergillus quadrilineatus.

Thus, we realized not only that these patients harbored infections from an entirely different species than we thought they were, but also that this species was the first ever Aspergillus hybrid known to cause human infections.

Source/Further Reading: TheConversation