U names 2008 McKnights

The University honors 17 faculty with McKnight professorships

Judith Berman, a new Distinguished Mcknight Professor, discovered how deadly yeast infections defeat antibiotics.

By Deane Morrison

May 6, 2008

A microbiologist who caught infectious yeast pulling a genetic trick to defeat antibiotics and an oceanographer who can claim a sliver of the 2007 Nobel Peace Prize are among the 17 University faculty honored with McKnight professorships for 2008.

The 13 McKnight Land-Grant Professors are junior faculty singled out for the promise of great things to come with two years of support. The four Distinguished McKnight University Professors are mid-career faculty honored for accomplishments of great distinction and influence; they receive $100,000 over five years. Full lists of Land-Grant and Distinguished Mcknight winners for 2008 are available.

Crafty yeast

If ever there were a Jekyll-and-Hyde group of microorganisms, it's yeast. Baker's yeast causes bread to rise and ferments grape juice into wine. But another yeast, known as Candida, causes infections ranging from relatively benign vaginal ones to deadly bloodstream infections in people with compromised immune systems, notably AIDS patients. These are the main focus of new Distinguished Mcknight University Professor Judith Berman's work.

"I'd really like to see us develop strategies for the inexpensive treatment of Candidiasis [a serious yeast infection], which is a big problem in AIDS patients, especially in Africa, where drugs are less available," says Berman, a professor of genetics and microbiology. "One drug, Fluconazole, is cheap and can be given orally, but the yeast develop resistance."

Berman found that one way Candida evades antibiotics like Fluconazole is to build a whole new chromosome tailor-made to resist the drugs. For starting material, the yeast uses a segment of its chromosome number 5 that contains two genes with drug-resisting properties.

Usually, Candida has two copies of each gene because it has two copies of chromosome 5--and, of course, its other chromosomes. But what if it had four copies of these genes? That would mean twice the number of pumps getting rid of the drugs and twice as many targets for the drugs to knock out once they did manage to get into the cells.

Berman found that one way Candida evades antibiotics like Fluconazole is to build a whole new chromosome tailor-made to resist the drugs.

The yeast accomplishes this by generating two extra copies of the segment of chromosome 5 that bears the genes. It then melds the segments together to make a peculiar structure called an isochromosome. Berman discovered the isochromosome in drug-resistant strains of Candida; it is common in these strains, but is not seen in nonresistant strains.

"We don't know if the drug induces isochromosome formation or if growth in the presence of the drug simply selects for cells in which an isochromosome has formed," says Berman, who has also discovered that yeast often have odd numbers or combinations of chromosomes. Studies of the mechanisms behind this phenomenon in Candida may lead to insights on how chromosomal abnormalities arise in cancer cells.

The life and times of carbon

The eternal cycling of carbon atoms through air, land, and water has long fascinated Katsumi Matsumoto, now a Mcknight Land-Grant Professor as well as an assistant professor of geology and geophysics. Researchers have identified carbon dioxide emissions into the atmosphere as the biggest factor driving global warming, but Matsumoto knows that it is the oceans that hold the key to how the gas affects the planet.

New McKnight Land-Grant Professor Katsumi Matsumoto studies how the ocean helps cycle carbon.

In the pre-industrial world, oceans contained 60 times as much carbon as the atmosphere and about 15 times as much as terrestrial plants, says Matsumoto, who uses numerical modeling to study the carbon cycle. It's important to understand how much of the emitted carbon dioxide is removed from the atmosphere, and oceans will eventually absorb most of it. This work, he says, "helps forecast effects of emissions on carbon dioxide levels in the atmosphere."

Today, about 10 percent of the ocean has come in contact with carbon dioxide emitted since the start of the Industrial Revolution and has taken up as much of the gas as it can, he adds.

One big factor in the ocean's response to rising carbon dioxide levels and global warming is the microscopic plants known as phytoplankton, which make up the bulk of oceanic plant life. Phytoplankton perform photosynthesis, the process by which carbon dioxide is removed from the atmosphere and locked into carbohydrate molecules. In general, rising temperatures increase organisms' metabolic rates, which means that more warmth would stimulate photosynthesis and so help phytoplankton absorb more carbon.

But in modeling phytoplankton responses to rising sea surface temperatures, Matsumoto found a surprise. In speeding up metabolism, warming also prods phytoplankton to burn more of their carbohydrate stores for energy. Called respiration, this process releases carbon dioxide.

"I found that respiration on a global scale increased more than [photosynthesis] with a rise in temperature," he says. That's because photosynthesis also requires nutrients and light, he explains. Therefore, limits on light and nutrients can keep the photosynthesis rate down even as the temperature rises. But higher temperatures always speed up respiration.

"It's a positive feedback system," he point out. "Phytoplankton release more carbon dioxide, which leads to rising atmospheric temperatures, which mean warmer surface waters, which lead to more respiration and more release of carbon dioxide."

Matsumoto is among the hundreds of scientists worldwide who have contributed to reports by the Intergovernmental Panel on Climate Change, the basis of all climate change negotiations. He was both a contributing author to and a reviewer of the physical science section of the 2007 report, which shared the Nobel Peace Prize with Al Gore. He is the only person from Minnesota with that distinction.

He helped write the section of the report that dealt with atmospheric carbon dioxide variation over the cycles of ice ages and in-between periods called interglacials. He is intrigued with a vexing question: why both carbon dioxide levels and temperatures have peaked at about the same time every 100,000 years or so--a pattern that has held for the past 400,000 years.

"We don't know why this happens," he says. "But if there is a Nobel Prize [for geologists], it will go to whoever solves this question."