Metagenomics of Globally Important Eukaryotic Phytoplankton

Elements likely contributing to success include high gene density and genes potentially involved in defense and nutrient uptake.

The Science

Global CO2 fixation is divided equally among terrestrial and marine ecosystems, each accounting for ~50 billion tons of carbon per year. Tiny “pico” phytoplankton are responsible for much of the CO2 capture in marine ecosystems; however, the genomes of only six of these organisms have been sequenced. In a new study published this month in the Proceedings of the National Academy of Sciences (USA), members of the prymnesiophyte phytoplankton lineage sequenced at the DOE Joint Genome Institute. Because most of these tiny organisms cannot be grown in culture, metagenomic approaches (the study of genetic material recovered directly from environmental samples) were used to analyze cells from subtropical North Atlantic waters. The organisms analyzed have composite genomes with strong evolutionary derivations from different sources. This lineage is thought to be responsible for 25% of the global picophytoplankton biomass whose abundance varies in different biogeographical areas. Changes in ocean temperatures associated with global climate processes could lead to changes in the abundance of these important organisms, with as yet poorly characterized consequences. This study shows the value of culture-independent metagenomic analyses for characterizing the marine microbiome with the potential for exploring its impacts on climate change processes.

Summary

Among eukaryotes, four major phytoplankton lineages are responsible for marine photosynthesis; prymnesiophytes, alveolates, stramenopiles, and prasinophytes. Contributions by individual taxa, however, are not well known, and genomes have been analyzed from only the latter two lineages. Prevalence of putative Ni-containing superoxide dismutases (SODs), instead of Fe-containing SODs, seems to be a common adaptation among eukaryotic phytoplankton for reducing Fe quotas in low-Fe modern oceans. Highly mosaic gene repertoires, although compositionally distinct for each major eukaryotic lineage, now seem to be an underlying facet of successful marine phytoplankton.

Principal Investigator

Alexandra Worden
Monterey Bay Aquarium and Research Institute

BER Program Manager

Ramana Madupu

U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]

References

Cuveliera, M.L., Allen, A. E., A. Monier, J. P. McCrow, M. Messié, S. G. Tringe, T. Woyke, R. M. Welsh, T. Ishoey, J.-H. Lee, B. J. Binder, C. L. DuPont, M. Latasa, C. Guigand, K. R. Buck, J. Hilton, M. Thiagarajan, E. Caler, B. Read, R. S. Lasken, F. P. Chavez, and A. W. Worden. 2010. “Targeted Metagenomics and Ecology of Globally Important Uncultured Eukaryotic Phytoplankton,” Proceedings of the National Academy of Sciences (USA) 107, 14679–84.