THE SECRET SEX LIFE of a killer fungus Irish Times 12.04.08

[Guest guest]

Asexual revolution breaks out in the lab

Céline OGorman and Hubert Fuller with a culture of the fungus Aspergillus

fumigatus on which two mating types have been crossed; sexual structures form

at the junctions of the colonies.

Photograph: Fitzsimons

CLAIRE O'CONNELL

UCD researchers have discovered a deadly fungus that may help transplant and

other patients who are at high risk from a common fungus

THE SECRET SEX LIFE of a killer fungus has been discovered for the first time

- and it happened in an Irish lab. The discovery has taken nearly a century

and a half to find and could now pave the way for more effective measures

against Aspergillus fumigatus , which poses a major medical threat to people on

chemotherapy or following a transplant.

The mould grows on decaying organic matter - such as compost heaps, damp hay

and debris in ventilation systems - and releases its spores into the air to

disperse in nature. Each day we inhale around 100 of those spores, and for

healthy people it's not a problem.

But for people with weakened immune systems the spores can cause a

potentially lethal infection called aspergillosis, which is the leading

infectious

cause of death in leukaemia and bone-marrow transplant patients. In addition,

the spores can trigger asthma and allergies in susceptible people.

First described 145 years ago, the fungus was thought to reproduce only

asexually, but recent advances in genetics signalled something else was afoot,

according to mycologist Hubert Fuller from University College Dublin's school of

biology and environmental science.

" Because it's such an important human pathogenic fungus it was selected a few

years ago to have its genome sequenced, and genes were identified that were

known to have some involvement in mating, " he says.

" It contains all of the genetic machinery needed to engage in sex, and

populations of the fungus were also shown to consist of two different 'mating

types' or sexes - the fungal equivalent of males and females. This was strong

evidence that the fungus might have a covert sexual cycle. "

Fuller and Ircset-funded PhD student Céline O'Gorman collected airborne

spores of A fumigatus from five sites around Dublin over the course of a year

and

set up mating crosses in the lab, growing them on plates of oatmeal-based

food.

" We put them away in an incubator, but we weren't too hopeful about them,

because no one had ever seen a sexual stage in this fungus, " says Fuller.

Around six months later, O'Gorman took out the cultures and saw some tiny

whitish-yellow structures, which she examined under the microscope and found to

be fruiting bodies, indicating the cultures had reproduced sexually.

" I still remember the moment, " she says. " One day I said it's about time to

go back to them, so I started to look at a couple of the cultures. When I saw

the fruiting bodies I knew what they were straight away, and of around 80

cultures, practically every strain had them. "

O'Gorman travelled to the University of Nottingham where she and collaborator

Dr Dyer used DNA analysis to confirm that the parent moulds were A

fumigatus and not lookalikes, and that the offspring had inherited traits of

both parents. The results showed that a full sexual exchange had taken place.

The world-first observation, published online in the important journal Nature

this week, means that scientists can now carry out experiments on the fungus

to better understand its genetics and hopefully develop new strategies to

control it, says Fuller.

" The discovery is significant for both good and bad reasons. On the downside,

the fact that Aspergillus fumigatu s can reproduce sexually, generating

genetic variation, means that it is more likely to become resistant to

anti-fungal drugs over shorter time periods, and the sexual spores are better at

surviving harsh environmental conditions, " he says.

" But on the positive side, the newly discovered sexual cycle can be used as a

valuable tool in lab experiments to try to work out how the fungus causes

disease, and once the genetic basis of disease is understood, then researchers

can look to devising methods to control and overcome the fungus. It may also

help identify better markers for infection in the early stage. "

Fuller notes that some other medically important fungi, like the organism

that produces penicillin, have no known sexual stage, but it could be a case of

needing to look a little further. " Some of these species have apparently

functional sex-related genes, and [our] discovery could lead to a sexual

revolution for many other of these supposed 'asexuals'. "

This article appears in the print edition of the Irish Times

Sharon Noonan Kramer

**************Stay in touch with ALL of your friends: update your AIM, Bebo,

Facebook, and MySpace pages with just one click. The NEW AOL.com.

(http://www.aol.com/?optin=new-dp & icid=aolcom40vanity & ncid=emlcntaolcom00000012)

[Guest guest]

You always post such interesting information. Thanks. llaci