This is not your grandmother's garden: A scientist at the University of Minnesota, working with a multi-national team, has discovered a more environmentally friendly way to grow filaments for electronic devices.

The product, called a nanotube, could be used in fuel cells, batteries, biosensors and other industries. Michael Sadowsky and his colleagues manufactured the filaments (think fiber optic cable) using biological means instead of more nasty chemical processes. Many semiconductors, for example, use toxic solvents in their manufacture.

"It's part of the nanotechnology revolution," Sadowsky said. "It's in engineering devices without using harmful structures."

Sadowsky and a former student, Hor-Gil Hur, now at Gwangju Institute of Science and Technology in South Korea, found that a bacterium called shewanella has the ability to convert arsenate into arsenic sulfide nanotubes. The findings were published in a December issue of the Proceedings of the National Academy of Sciences.

Shewanella is a type of bacterium found in soil and water. "When it grows under anaerobic conditions with sulfur and arsenic, it precipitates them into these tubes," Sadowsky said. The tubes eventually become both conductive and photoactive.

The researchers found that shewanella, after converting the arsenate, leaves behind a yellow residue. They realized that the residue was a jumble of nanotubes. Sadowsky, who is in the Department of Soil, Water and Climate, and his colleagues believe that this is the first time these specialized nanotubes have been made biologically rather than with chemical means.

The discovery may allow for whole new uses for nanotubes, including "novel semiconductor devices that could not be made other ways," he said.

Before the tubes are ready for market, the team needs to figure out how to make them uniform in size. "I don't have a guess as to when they will be ready." Sadowsky said.

There will not be an environmental advantage in the disposal of devices made with the nanotubes, he said, because of the use of arsenic in their manufacture.