Team Takes Phytoplankton Genome Research to Next Level

Scripps Marine Biologist Brian Palenik said it was “exciting” when nearly four years ago he and his colleagues decoded the first genetic blueprint of organisms that play large roles in vitally important earthly functions such as photosynthesis and global carbon cycling.

At that time, just the fact that the novel tools of genomics were being used to probe tiny phytoplankton was seen as an important milestone in furthering our understanding of ocean ecosystems.

Now, an international team of scientists led by Palenik has taken the next step. The team took two species of plankton from a genus called Ostreococcus and conducted the first comparison of their genomes. Surprising insights resulted for the one-micron-long organism.

“Genomics has taught us that you can learn much more when you can do a comparison,” said Palenik. “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.”

Since the two species were so closely related, Palenik and his colleagues were surprised by several important differences, including the discovery of a chromosome unique to one of the species. Another chromosome appeared similar, but its genes were arranged differently between the two. The researchers suspect this difference may be tied to reproduction since the slight difference is enough to prevent cross-breeding between the species.

“These are pretty remarkable differences that we didn’t expect,” said Palenik. “We would expect the DNA to change slowly and see a small number of differences between the two species as they slowly evolve.”

Even more of a revelation was the discovery of the prominent role of the chemical element selenium in Ostreococcus. While humans need selenium in small doses, Ostreococcus is chock full of the stuff in its microscopic frame.

“We may need to think more about how selenium helps drive the health of the oceans,” said Palenik. “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.”

Even more surprises may lay ahead in future research as the scientists add a third plankton genome to the comparison mix.

— Mario C. Aguilera