by Janet Howard and Cindy Clark
March 3, 1997

from ScrippsInstitutionOfOceanographyNews Website

recovered through WayBackMachine Website

Diatoms, tiny single-celled plants that cover much of the world's oceans, come in a variety of beautiful and sometimes odd-looking shapes. Made of silicon, their rigid cell walls can resemble everything from pillboxes to pinwheels.

Now scientists at UCSD's (University of California, San Diego) Scripps Institution of Oceanography have isolated a family of genes that allow diatoms to build their shell-like exteriors by encoding a protein responsible for transporting silicon across the cell membrane.

The researchers reported their finding in the February 20 issue of the journal Nature.

"One of the things that fascinates people about diatoms is that they can make incredible structures out of silicon, but no one knows how they do it," said Mark Hildebrand, a marine biologist at Scripps who headed up the research. "This provides the first step toward understanding the process."

Silicon is essential in biological systems, affecting development and cellular metabolism. It is second only to oxygen in abundance and is widely distributed on the Earth's surface. Diatoms take up silicon in the form of silicic acid from the surrounding ocean, transport it across their cell membrane and use it to build structures that have chemical and physical characteristics similar to glass.

"It has been known for over 40 years that silicon plays essential roles in biological systems, but up until now no one has identified a protein that interacts with silicon," Hildebrand said.

While the diatom provides a perfect model for studying silicon transport, Hildebrand said the information learned also may be applied to mammals, including humans.

"No one yet understands the role that silicon plays in bone formation, but it is clearly an important part of the whole process," Hildebrand said. "So if we can learn more about silicon transport mechanisms, it should give us new insight into how bones are formed."

Scientists estimate there are more than 10,000 species of diatoms, each characterized on the basis of their shape, which is handed down from generation to generation. Because diatoms are so tiny - ranging between 10 and 20 microns in size - Hildebrand said new information on how they reproduce their structures could be applied to the manufacture of nano-structured materials.

These novel materials, which measure only a few nanometers in size, are being explored for uses such as nanofabrication, making devices on an extremely small scale.

"In some diatom species you can see that they have very defined pores, so it could perhaps be used as a type of microscopic filtering device," he said.

Hildebrand said continued work using advanced molecular genetic techniques should allow he and his colleagues to discover the underlying mechanism that allows silicon to be transported into different compartments within the cell.

They also hope to learn how silicon transport across the cell membrane is regulated.

The work was done in the laboratory of Benjamin E. Volcani, professor emeritus in the Scripps Marine Biology Research Division, and collaborators were Walter Gassman and Julian Schroeder, UCSD's Department of Biology and Center for Molecular Genetics.