Florida State University : Research in Review

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Size counts for little in the amazing lives of diatoms.

Each is smaller than a period on this page, but en masse, diatoms pack an environmental wallop as strong as any organism on the planet.

Perhaps better known for the striking, intricate patterns of their silica walls, the otherwise low-key organisms play critical roles in ecology. A major component of phytoplankton, diatoms are at the base of the aquatic food chain and have been credited by scientists for absorbing as much carbon dioxide, a major greenhouse gas, as all of the world's tropical rain forests.

Beyond nourishing animals of all kinds and helping to keep the planet's carbon in balance, the single-cell organisms also are valued in human industries ranging from the lucrative oil sector to environmental monitoring.

Despite their ubiquity and diverse roles, the ancient microbes (their fossils date back 180 million years) remain a curiosity.

Just recently, scientists have learned that at least one diatom species uses a molecular pathway—the urea cycle—previously found only in animals. In 2004, a team of 46 researchers, led by the U.S. Department of Energy Joint Genome Institute, became the first to sequence the genome of a diatom species. The researchers were surprised to find that some of the diatom's genes have some counterparts in plants and others in animals, proof of how much there is still to learn about the multifaceted organisms.

Even on a far simpler level than genetic identity, scientists have barely made a dent in cataloging the world's diatoms by physical appearance. About 10,000 diatom species, living and extinct, have been identified so far, but many more remain to be discovered.

"Nobody knows how many there are," says Akshinthala Prasad, FSU scholar/scientist in biological science. "Scientists believe there are at least 100,000 species of diatoms still to be described."

In his 25 years at FSU studying diatoms, Prasad has described a dozen new species with 16 more candidates in queue to be scrutinized and confirmed as species in their own right.

The tough part is making sure a diatom species hasn't already been described somewhere in the world. With no comprehensive database or manual, particularly for marine diatoms, determining whether a species is different from the thousands of others already described is a long, tedious process, Prasad says, and there are not many diatomists to go around.

In 2004 when the first (and, so far, the only) diatom genome was sequenced, the journal Science, which published the findings, reported that only about 100 or so researchers called themselves diatom ?pecialists.

Among these relatively small ranks, Prasad's detailed work has earned him a spot among the top tier. He has been elected secretary of the International Phycological Society and to the International Committee of Nomenclature of Algae. And his research draws high praise from those familiar with it.

"I've always been impressed by his scholarship," says Paul Silva, chairman of the International Committee of Nomenclature of Algae and research botanist emeritus at the University of California-Berkeley.

James Nienow, professor and diatomist at Valdosta State University in Georgia who has worked with Prasad over the past 20 years, says, "He is one of the top diatomists in the state—if not the world—for coastal marine diatoms."

Further understanding of the under-studied organisms could clearly help scientists in a variety of fields, with those in environmental monitoring near the top of the beneficiary list.

"These diatoms are sensitive to certain environmental conditions," Prasad says. "That's why diatoms are routinely being used in water-quality studies…But we have to have an inventory of the species in our waters so we can think about conservation. We don't have that."

Prasad is working to fill in at least part of this knowledge gap. He has examined diatoms from all corners of the globe—from the South China Sea to the Antarctic to the Galapagos. But his specialty has been in cataloging diatoms in the estuaries and bays of Alabama and Florida. The 12 species Prasad has described and named so far come from Florida coastal waters. His goal is to compile the first identification manual of Florida's coastal diatoms.

But countless thousands of other diatoms remain to be studied before scientists can draw a truly comprehensive map, complete with seasonal population fluctuations, of the diatomic compositions of the world's water bodies. A major hurdle, say diatomists, is getting new students interested in the field. Valdosta State's Nienow says students are moving away from microscopy and morphology studies in favor of the sexier fields of molecular biology and genetics.

So progress is slow—but increasingly essential for a number of scientists, industries, and for those like Prasad whose passion is the tiny—put powerful—diatom. —C.S.     


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