Comparison of two plankton species' genomes yields surprising results for scientists

An international team of researchers have for the first time studied the genetic makeup of two species of phytoplankton - tiny plants that play a key role in global photosynthesis and carbon cycling.

Washington, May 1 : An international team of researchers have for the first time studied the genetic makeup of two species of phytoplankton - tiny plants that play a key role in global photosynthesis and carbon cycling.

"Through our research we've been trying to understand Ostreococcus' role in marine ecosystems. Genomics has taught us that you can learn much more when you can do a comparison. The first genome is exciting but the second genome is even more exciting because you can suddenly compare organisms and see what each is doing differently and what they are doing the same," said Brian Palenik, a Scripps Institution of Oceanography researcher.

The international team's work, published in the online edition of Proceedings of the National Academy of Sciences, is the first comparison of the genetic makeup of two closely related eukaryotic phytoplankton and the mechanisms that make them biologically similar and distinct.

The researchers' comparison of Ostreococcus lucimarinus and Ostreococcus tauri yielded several surprising results, including the documentation of a "new" chromosome differing between the species.

The chromosome appeared somewhat different between the species, and researchers believe it may serve as a gene transfer "trash can" where foreign DNA is integrated.

Another surprising difference was the identification of a chromosome featuring the same-albeit rearranged-genes in the two species. The researchers hypothesize that this chromosome might be related to sexual functions, as the rearrangements are enough to prevent sex between the species.

"These are pretty remarkable differences that we didn't expect. We would expect the DNA to change slowly and see a small number of differences between the two species as they slowly evolve... This is the case for much of the genome. From a future applied perspective, from our comparison we are learning the tricks nature has used to 'engineer' an extremely small eukaryotic cell. This may have future applications in bioengineering," said Palenik, a professor in the Marine Biology Research Division at Scripps.

Another equally important find, researchers said, was the prominent role that the element selenium played in Ostreococcus.

"Humans require selenium in small amounts and most people have roughly 25 selenium proteins. Tiny Ostreococcus organisms were shown to have up to 21 selenium proteins, an enormous number relative to their small genome and microscopic size," said Palenik.

"This may be because selenium enzymes are some 10- to 50-times more efficient than similar enzymes that don't use selenium. Based on their size, such efficiency is important to help conserve resources such as nitrogen," he said.

"We may need to think more about how selenium helps drive the health of the oceans. It's a nutrient element that we don't understand very well and now we have evidence of a group of organisms that clearly use it intensively. We may need to think about how this is affecting primary production in the oceans," he added.

The researchers want to carry further study involving a third Ostreococcus organism, which will lead to further comparisons and evolutionary evaluations.

"Genomic comparisons are exciting because they allow us not to just document the diversity of the ocean but to start to understand the processes behind that diversity and see all of the changes in the evolution of two species," said Palenik.

ANI