Scientists sequence genome of kind of organism central to biosphere's ca...( urea cycle something no one ever suspe...)

urea cycle, something no one ever suspected," Armbrust says. A urea cycle is a nitrogen waste pathway found in animals and has never before been seen in a photosynthetic eukaryote like a diatom, she says. Nitrogen is crucial for diatom growth and is often in short supply in sea water, depending on ocean conditions. The genome work revealed that diatom Thalassiosira pseudonana has the genes to produce urea-cycle enzymes that may help to reduce its dependence on nitrogen from the surrounding waters.

The genome work also shed additional light on how this diatom species uses fats, or lipids, that it is known to store in huge amounts.

"Learning the actual pathways they use to metabolize their fats helps explain the ability of diatoms to withstand long periods with little sunlight even to overwinter and then start growing really rapidly once they return to sunlight," she says.

Three or four microns in width as many as 70 could fit in the width of a human hair Thalassiosira pseudonana is among the smallest diatoms. Like its brethren, it is encased by a frustule, a rigid cell wall delicately marked with pores in patterns distinctive enough for scientists to tell the species apart. Another new finding reported in Science concerns the unusual way the diatom metabolizes silicon to form its characteristically ornate silica frustule.

"Diatoms can manipulate silica in ways that nanotechnologists can only dream about. If we understood how they can design and build their patterned frustule as part of their biology, perhaps this could be adapted by humans," Rokhsar says.

Scientists on the project, which includes 46 researchers from 26 institutions, also considered the evolutionary implications revealed by the genomic work. The research provided direct genetic confirmation of a hypothesis that diatoms evolved when a heterotroph, a single-cell microbe, engulfed what scientists say was likely a kind of red alga. The two became one organism, an
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Contact: Sandra Hines
shines@u.washington.edu
206-543-2580
University of Washington
30-Sep-2004

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