Sex Life Of Killer Fungus
Aspergillus fumigatus Finally Revealed
Mold growing on dirt on a brick wall
in the United Kingdom
The discovery of
a sexual cycle in the fungal pathogen Aspergillus fumigatus is highly
significant in understanding the biology and evolution of the species and
will shed new light on its ability to adapt to new environments and its
resistance to antifungal drugs. (Credit: Image courtesy of University of
ScienceDaily (Dec. 1, 2008) —
Biologists at The University of Nottingham and University College Dublin
have announced a major breakthrough in our understanding of the sex life of
a microscopic fungus which is a major cause of death in immune deficient
patients and also a cause of severe asthma.
The discovery of a sexual cycle
in the fungal pathogen Aspergillus fumigatus is highly significant in
understanding the biology and evolution of the species and will shed new
light on its ability to adapt to new environments and its resistance to
antifungal drugs. It is hoped the results of this research will lead to new
ways of controlling this deadly disease and improved treatments for patients
infected with it.
First described 145 years ago
this killer fungus, until now, had no known sexual cycle and was only
thought to reproduce by production of asexual spores. But researchers from
the School of Biology at The University of Nottingham and from University
College Dublin, have finally been able to induce sexual reproduction in this
potentially lethal pathogen showing, for the first time, that A. fumigatus
possesses a fully functional sexual reproductive cycle.
Dr Paul Dyer is an expert in
the sexual development and population variation of fungi and co-author of a
new article in Nature on the topic.
Dr Dyer said: “This discovery
is significant for providing both good and bad news. The bad news is that we
now know that Aspergillus fumigatus can reproduce sexually, meaning that it
is more likely to become resistant to antifungal drugs in a shorter period,
and the sexual spores are better at surviving harsh environmental
conditions. The good news is that we can use the newly discovered sexual
cycle as a valuable tool in laboratory experiments to try to work out how
the fungus causes disease and triggers asthmatic reactions. Once we
understand the genetic basis of disease we can then look forward to devising
methods to control and overcome the fungus”.
The spores of A. fumigatus,
which feeds on dead or decaying organic matter, are widespread in the
atmosphere. It has been estimated that everybody inhales around 200 spores
each day. These spores are normally eliminated by the innate immune
response. However, this fungus has become the most prevalent airborne fungal
pathogen due to its ability to cause infections in hosts with a weakened
immune system, with at least a 50 per cent mortality rate in humans. Four
per cent of patients in modern European teaching hospitals have invasive
aspergillosis; it is the leading infectious cause of death in leukaemia and
bone marrow transplant patients. The fungus is also associated with severe
asthma and sinusitis.
Almost one-fifth of all fungi
have no known sexual stage — these include many Aspergillus, Penicillium,
Coccidioides and Malassezia species which are of major economic and medical
importance. However, some of these species have apparently functional sex
related genes and this research could lead to a sexual revolution for many
other of these supposed ‘asexuals’.
The research was carried out in
collaboration with Dr Hubert Fuller and his final year PhD student Céline
O’Gorman from the UCD School of Biology and Environmental Science at
University College Dublin. The study was funded by an IRCSET Postgraduate
Research Scholarship, an EC Marie Curie Training Fellowship and a grant from
the British Mycological Society, which facilitated research visits by Céline
O’Gorman to The University of Nottingham.
Many fungi reproduce by sexual
means. The molecular-genetic and physiological mechanisms controlling sex in
fungi are being investigated at The University of Nottingham with the aim of
devising new methods for the control of fungal diseases and promoting sex in
beneficial species. The consequences of sex for genetic variation and
evolution are being studied in model species of fungi including plant
pathogens and Antarctic lichen-forming fungi.
O'Gorman et al. Discovery of a sexual cycle in the opportunistic
fungal pathogen Aspergillus fumigatus. Nature, November 30, 2008;
University of Nottingham
(2008, December 1). Sex Life Of Killer Fungus Finally Revealed.
ScienceDaily. Retrieved December 3, 2008, from http://www.sciencedaily.com