July 11, 2005

Secret Sex Life of Killer Fungus?

Aspergillus fumigatus is a medically important fungus, causing potentially life-threatening infections in patients with weakened immune systems. It is also a major cause of respiratory allergy, and it is implicated in asthma as well. The fungus has always been thought to lack the ability to reproduce sexually, but new discoveries by a multinational group of scientists indicate that the fungus has a number of characteristics of sex. The possible presence of sex in the species is highly significant because it may affect the way researchers study--and try to control--disease associated with the fungus.

The team, headed by Paul Dyer at the University of Nottingham (UK), with lead researchers Mathieu Paoletti (University of Nottingham, UK) and Carla Rydholm (Duke University, USA), used a number of techniques to study the fungus. The genome of Aspergillus fumigatus has recently been sequenced, and investigation of the genome revealed the presence of a series of genes required for sexual reproduction.

In the new study, the researchers report that the analysis of a worldwide collection of 290 specimens of the fungus revealed nearly equal proportions of two different sexes, or "mating types," which in theory could have sex with each other. Additional work on specific populations of the fungus in America and Europe showed that genes had been, or were being, exchanged between individuals of the fungus--another strong sign of mating. The researchers also showed that some key genes involved with detecting mating partners were active in the fungus.

Taken as a whole, the study's results indicate that the fungus has a recent evolutionary history of sexual activity and might still be having sex, if thus far unseen by human eyes. These results are important because if the fungus does reproduce sexually as part of its life cycle, it might evolve more rapidly to become resistant to antifungal drugs used to control disease; sexual reproduction might lead to new strains with increased ability to cause disease and infect humans. Nevertheless, the sexual cycle could be a useful genetic tool for scientists to use in their study of the mechanisms by which the fungus causes disease. Further work is now aimed at seeing if the fungus can truly reproduce by sexual means.

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Cell Press