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Tiny algae could play big environmental role

(Download Image) Credits: 3D reconstruction: A.Z. Worden, T. Deerinck, M. Terada, J. Obiyashi and M. Ellisman (MBARI and NCMIR). Background: Flavio Robles (Lawrence Berkeley National Laboratory). A 3D reconstruction of an electron tomographic slice (0.5 microns thick) of one of the smallest known eukaryotic algae, Micromonas.

Scientists from two-dozen research organizations led by the Department of Energy (DOE) Joint Genome Institute (JGI) and the Monterey Bay Aquarium Research Institute (MBARI) have decoded genomes of two algal strains, highlighting the genes enabling them to capture carbon and maintain its delicate balance in the oceans.

These findings, from a team led by Alexandra Worden of MBARI and published in the April 10 edition of the journal Science will illuminate cellular processes related to algae-derived biofuels being pursued by DOE scientists.

The study sampled two geographically diverse isolates of the photosynthetic algal genus Micromonas — one from the South Pacific, the other from the English Channel. The analysis identified approximately 10,000 genes in each, compressed into genomes totaling about 22 million nucleotides.

"Yet, surprisingly, they are far more diverse than we originally thought," Worden said. "These two picoeukaryotes, often considered to be the same species, only share about 90 percent of their genes."

To put this in perspective, humans and some primates have about 98 percent of their genes in common. Worden said that the algae's divergent gene complement may cause them to access and respond to the environment differently.  "This also means that as the environment changes, these different populations will be subject to different effects, and we don't know whether they will respond in a similar fashion."

She said that their apparently broad physiological range (exemplified by their expansive geographical range) may result in increased resilience as compared to closely related species, enabling them to survive environmental change better than organisms with a narrower geographic range.  Testing the hypotheses developed through cataloging their respective inventory of genes, Worden said, will go a long way towards understanding their biology and ecology.

Algae were blazing the pathway of photosynthesis long before plants colonized land — so the results bear significantly on terrestrial plant research as well.

"Genome sequencing of Micromonas and the subsequent comparative analysis with other algae previously sequenced by JGI and Genoscope [France], have proven immensely powerful for elucidating the basic 'toolkit' of genes integral not only to the effective carbon cycling capabilities of green algae, but to those they have in common with land plants," DOE JGI Director Eddy Rubin said.

Tiny Micromonas , less than two microns in diameter, or roughly a 50th of the width of a human hair, are one of the few globally distributed marine algal species thriving throughout the world's oceans from the tropics to the poles. They capture CO 2 , sunlight, water and nutrients, and produce carbohydrates and oxygen. Their productivity — which provides food resources within marine food webs — as well as their knack for capturing carbon, and influencing the carbon flux that may have a bearing on climate change, make these algae a keen target of study.

For the complete article, see the JGI Website.

April 10, 2009

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David Gilbert
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