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NATIONAL INSTITUTES OF HEALTH

National Institute of Allergy and Infectious Diseases

NIH NEWS RELEASE

EMBARGOED FOR RELEASE

Thursday, July 13, 2000

Sam Perdue

(301) 402-1663

sp189u@...

IDENTIFICATION OF YEAST MATING HABITS OPENS NEW DOORS TO

CANDIDA RESEARCH

Studies of the reproductive behavior of a major disease-

causing fungus have opened new avenues to understanding this

potentially deadly microbe. In the current issue of

Science, researchers from the University of Minnesota

report the discovery of mating behavior in the yeast Candida

albicans, an organism long thought to reproduce only by

splitting itself in half. Their studies, supported by the

National Institute of Allergy and Infectious Diseases

(NIAID), provide new opportunities for scientists to better

understand the diseases caused by this fungus.

" C. albicans has been studied for over 100 years, but it has

never revealed a sexual stage in its life cycle and has

defied attempts to mate, " explains Dennis M. Dixon, chief of

the Bacteriology and Mycology Branch of NIAID's Division of

Microbiology and Infectious Diseases. " This work is

extremely important because it begins to explain how the

organism can adapt to changes in its environment and cause

disease. "

C. albicans, a common cause of thrush, can infect the skin,

mucous membranes, and blood. In the latter case, the

organism can invade multiple organ systems where it causes

death in 30 to 50 percent of infected individuals. The

fungus is particularly prevalent as a pathogen of the oral

cavity and the female genital tract and as an opportunistic

infection that strikes people with impaired immune systems.

Existing anti-candida drugs are often highly toxic, and

drug-resistant infections are becoming more common.

Unlike baker's yeast, where the genetic systems and mating

have been extensively analyzed in the laboratory, C.

albicans has proven difficult to study until more recently.

Baker's yeast can reproduce by mating, during which two

single-celled parent yeasts fuse to produce a single

organism with the combined genetic material of both parents.

Because C. albicans has not previously been found to mate,

however, scientists have had difficulty exchanging genetic

information between different strains, thereby complicating

research efforts. Now Beatrice B. Magee, M.S., and T.

(Pete) Magee, Ph.D., are the first to produce mating strains

of C. albicans. This discovery promises to accelerate

research into the fungus and enable researchers to more

quickly understand its biology and identify new drug

targets. " There is no doubt that the identification of a

sexual cycle will facilitate ongoing drug discovery programs

and motivate pharmaceutical companies to begin new

searches, " says Dr. Magee.

Interest in C. albicans reproduction increased as scientists

began to unravel the organism's genetic blueprint, a process

that is nearing completion. Hull and

, Ph.D., researchers at the University of California

in San Francisco, analyzed this blueprint and isolated

potential genes that resembled those controlling mating in

the common baker's yeast. When the Magees removed one of

these genes from a C. albicans strain, they paired the

organism with a mate that contained the missing gene. Once

the two strains met, they fused just like their baker's

yeast cousins. Hull and accomplished the same feat

independently.

The finding has important implications beyond simplifying

Candida research. " Scientists have shown that in another

disease-causing fungus, Cryptococcus, one mating type is

much more virulent than the other. If this is true for

C. albicans it opens up a new approach to understanding how

this microbe causes disease, " explains Dr. Magee. The

researchers expect their discovery to accelerate studies on

how the fungus adapts to different environments and

how it evades the body's defense mechanisms.

The Magee's studies also illustrate an important caveat of

modern biomedical research, now rife with announcements of

newly deciphered genetic blueprints. " Determining the

sequence of the C. albicans genome was only one step in the

process, " says Dr. Dixon. " The Magees have worked for years

to painstakingly analyze the biology and genetics of

Candida. When the C. albicans DNA sequence revealed a few

hints about the organism's reproductive processes, the

Magees were poised to investigate these clues and take a

giant stride towards understanding an important human

pathogen. Without their strong history of basic research,

it is unlikely that this discovery would have been made. "

NIAID is a component of the National Institutes of Health

(NIH). NIAID conducts and supports research to prevent,

diagnose, and treat illness such as HIV disease and other

sexually transmitted diseases, tuberculosis, malaria, asthma

and allergies. NIH is an agency of the U.S. Department of

Health and Human Services.

Press releases, fact sheets and other NIAID-related

materials are available on the NIAID Web site at

http://www.niaid.nih.gov .

The National Institute of Allergy and Infectious Diseases is

a component of the National Institutes of Health, U.S.

Department of Health and Human Services.

References:

BB Magee and PT Magee. Induction of mating in Candida

albicans by construction of MTLa and MTLa strains. Science

2000;289:310-12.

CM Hull, RM Raisner, and AD . Evidence for mating of

the " asexual " yeast Candida albicans in a mammalian host.

Science 2000;289:307-309.

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