Image courtesy of NASA
Phytoplankton known as coccolithophores bloom in the Barents Sea north of Russia, their scales giving off a bright green glow.
Coccolithophores have influenced global climate for more than 200 million years and can account for 20% of total carbon fixation in some systems. Forming blooms that sometimes occupy hundreds of thousands of square kilometers, these marine phytoplankton are distinguished by their elegantly sculpted calcium carbonate exoskeletons (coccoliths) that make them visible from space. Although coccolithophores export carbon in the form of organic matter and calcite to the sea floor, they also release carbon dioxide (CO2) in the calcification process. Coccolithophores thus have a complex influence on the carbon cycle, driving either CO2 production or uptake and carbon sequestration and export to the deep ocean. To better understand these processes, researchers have sequenced the first haptophyte reference genome from the coccolithophore Emiliania huxleyi.
The genomic variability in E. huxleyi helps explain its ability to thrive in oceans from the equator to the subarctic. In addition to providing insights into its role in the global carbon cycle, the algal genome offers hints that E. huxleyi may be involved in the global sulfur cycle because it produces a compound that can influence cloud formation and therefore affect climate.
The Department of Energy Joint Genome Institute (DOE JGI) has sequenced the E. huxleyi genome and compared it with sequences from 13 other algal isolates. The large and complex E. huxleyi genome indicates that these phytoplanktondo not exist as a clearly defined species with a uniform genome. Instead, they represent a more diffuse community—a “pan genome”—with different individuals possessing a shared core of genes supplemented by different gene sets to cope with the particular challenges of a local environment. DOE JGI and its collaborators found that the core genes include those that allow E. huxleyi to survive in low levels of phosphorus and assimilate and break down nitrogen-rich compounds. This sequencing effort represents the first ever algal pan genome.
Betsy A. Read
Department of Biological Sciences, California State University–San Marcos, 92096
DOE JGI contributions were supported by the DOE Office of Science under contract no. 7DE-AC02-05CH11231.
Read, B. A., et al. “Pan genome of the phytoplankton Emiliania underpins its global distribution,” Nature 499, 209–213 (2013). [DOI: 10.1038/nature12221].
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