Marine Microbial Ecosystems: Not as Simple as Once Thought

Low abundance microbes may do more than their share of carbon cycling in the ocean.

Image © 2003 National Academy of Sciences, USA
Transmission electron micrograph of a section ofProchlorococcus marinus SS120 from Bryant, D. (2003) The Beauty in Small Things Revealed. PNAS 100: 9647-9649.

The Science

New research addresses a long-held assumption that the size of a microbial population in the marine community corresponds to its level of activity in terms of carbon uptake, growth rate, etc., thus determining its impact on global biogeochemical cycles.

The Impact

The study found that marine ecosystem functioning is likely to be more complex and dynamic than previously thought. These conclusions have significant implications for understanding the role of the oceans in the global carbon cycle.


The tiny cyanobacterium Prochlorococcus is among the most abundant and important in the oceans, and distinct variants (“ecotypes”) exist at different water depths. An estimated 100 million cells of this unicellular organism can be found in a single liter of seawater. These cyanobacteria help remove some 10 billion tons of carbon from the atmosphere each year. Researchers, including scientists at the DOE Joint Genome Institute (DOE JGI), studied the activity levels of several ecotypes of Prochlorococcus at several locations in the Pacific and Atlantic Oceans. The results suggest that the theory does not fully explain the link between abundance levels and activity. In their article the authors state: “Our results suggest that low abundance microbes may be disproportionately active in certain environments and that some of the most abundant may have low metabolic activity.” “We observed uncoupling of abundance and specific activity of Prochlorococcus in the Sargasso Sea depth profile, which highlights deficiencies in our understanding of marine microbial ecology and population structure.”


Dr. Zackary I. Johnson
Duke University


Basic Research: DOE Office of Science, Office of Biological and Environmental Research


Hunt, D.E., Y Lin, M. J. Church, D. M. Karl, S G. Tringe, L. K. Izzo, and Z. I. Johnson (2012) “The relationship between abundance and specific activity of 2 bacterioplankton in open ocean surface waters”, Appl. Environ. Microbiol.. [DOI: 10.1128/AEM.02155-12]

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