Science News - March 31, 2007

SCIENCE
NEWS
This Week

a set of different enzymes in its fuel cells to extract more of the sugar’s energy.

Another potential advantage of biological fuel cells—compared to ordinary fuel cells or batteries—is that they might become a mass-produced power source that’s completely biodegradable, Minteer says.

It could take as little as 3 years to bring the technology into consumer products, Minteer predicts. The U.S. Department of Defense, which is funding the research, is also interested in using sugar as a densely packed energy source on the battlefield.

Klotzbach presented the current work this week at the American Chemical Society meeting in Chicago. —D. CASTELVECCHI

In fuel cells, chemical reactions generate electrical currents. The process usually relies on precious metals, such as platinum, acting as catalysts. In living cells, enzymes perform a similar job, breaking down sugars to extract electrons and produce energy.

When researchers previously used enzymes in fuel cells, they had trouble keeping them humming, says Shelley D. Minteer of St. Louis University. Whereas biological cells continually produce fresh enzymes, there’s no mechanism in fuel cells to replace enzymes as they quickly degrade.

Minteer and Tamara Klotzbach, also of St. Louis University, have now developed polymers that wrap around an enzyme and preserve it in a microscopic pocket. “We tailor these pockets to provide the ideal microenvironment” for the enzyme, Minteer says. The polymers keep the enzyme active for months instead of days.

In the new fuel cell, tiny polymer bags of enzyme are embedded in a membrane that coats one of the electrodes. When glucose from a sugary liquid penetrates a pocket,

the enzyme oxidizes it, releasing electrons and protons. The electrons cross the membrane and enter a wire through which they travel to the other electrode, where they react with oxygen in the atmosphere to produce water. This flow of electrons through the wire constitutes an electrical current that can generate power.

“The elimination of noble metals is saving cost, but [using enzymes] also widens the range of fuels that can be used,” says Paul Kenis, a chemical engineer at the Univer - sity of Illinois at Urbana-Champaign.

Enzymatic fuel cells developed by other research groups typically run on more conventional fuels, such as ethanol.

Direct use of sugars as fuel would be more energy efficient than fermenting corn, sugarcane, or other crops to turn their sugars into ethanol, Minteer says.

The current version of Minteer’s fuel cell oxidizes glucose only partially, so it yields only small amounts of power. “Still,” Kenis says, “just getting it to work is a major accomplishment.”

Minteer’s team is now working to embed

Pollution
Fallout
Are unattractive males
Great-gram’s fault?

A new study of mate preferences in rodents raises the prospect that pollutant exposures can have behavioral repercussions that persist generation after generation. In the experiment, female rats shunned males whose grandfathers had been exposed in the womb to a fungicide used on fruit crops.

Though brief, the vinclozolin exposures occurred when the fetal males’ reproductive organs were developing. The laboratory doses were “four- to fivefold higher than you might expect to see in the environment,” notes Michael K. Skinner of Washington State University in Pullman. Some farm workers might incur similar doses, he says.

The fungicide, known as a hormone mimic, prevents male-sex hormones from binding to cells (SN: 7/2/94, p. 15).

The hormones then cannot correctly program gene activity in the male fetus’ reproductive organs. Reproductive tissues in fetal females appear unaffected.

Skinner’s team reported 2 years ago that although neither the animals nor their descendants encountered the fungicide again, all the males exposed in utero developed cancers

and other diseases in middle age, as did all their male descendants.

The vinclozolin exposure didn’t cause mutations, notes evolutionary biologist David Crews, who led the new study with neuroscientist Andrea C. Gore, both at

SUGAR ME UP With fuel cells that use enzymes, people might someday feed sweet drinks to their portable gadgets.

the University of Texas at Austin. The fungicide instead altered regulatory switches—methyl groups that can bind to DNA—thereby misprogramming some unidentified genes that later become inappropriately active or inactive. Scientists refer to methylation of DNA as an epigenetic influence.

The new study examined 24 young-adult rats, 12 male and 12 female, provided by Skinner. Half of the animals had a grandfather that had been exposed prenatally to the fungicide.

Crews and Gore designed tests to see whether fungicide exposure in a previous generation influences an animal’s attractiveness as a mate. They presented each individual with two opposite-sex rats at a time—one from an unexposed line, the other from a vinclozolin-affected line. The researchers measured how long the test animal spent in the area closest to each of the opposite-sex rats. Wire screens separated the animals.

Regardless of their exposure history, males distinguished between females from the fungicide-exposed or the clean line. However, after briefly checking out pairs of males, females from both groups spent most of their time hovering near the males from the unexposed line. To the researchers, all the males appeared healthy.

A report of the study was posted online this week for publication in an upcoming Proceedings of the National Academy of Sciences.

The team suspects that epigenetic changes, triggered by the fungicide two generations back, altered the males’ scent signals. However, Crews’ team also recently identified epigenetic changes in the brains of the vinclozolin descendants.

Reproductive biologist Frederick vom Saal of the University of Missouri– Columbia calls the behavioral findings “scary stuff.” Scientists hadn’t expected parents’ lifelong collection of epigenetic changes to reach the next generation. “What’s interesting,” vom Saal says, is that “a fetus may escape normal deprogramming” that wipes clean the epigenetic record.

“That it even impacts behavior,” he adds—“that’s wild.”

The new finding also suggests that cleaning up a polluted area may not erase its impacts on exposed populations, vom Saal says.

“It is all pretty remarkable—and novel,” agrees L. Earl Gray Jr., a reproductive toxicologist with the U.S. Environmental Protection Agency in Research Triangle Park, N.C. However, he adds that he and his colleagues have reservations because the sample size is so small and the animals in each group came from just two litters.