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. 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 and growth rate, thus determining its impact on global biogeochemical cycles. Researchers, including scientists at the U.S. Department of Energy’s Joint Genome Institute, studied the activity levels of several Prochlorococcus ecotypes 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.” They conclude that marine ecosystem functioning is likely to be more complex and dynamic than previously thought. This finding has significant implications for understanding the role of the oceans in the global carbon cycle.
Reference: 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 Two Bacterioplankton in Open Ocean Surface Waters,” Applied Environmental Microbiology, DOI: 10.1128/AEM.02155-12. (Reference link).
Contact: Dan Drell, SC-23.2, (301) 903-4742
SC-33.2 Biological Systems Science Division, BER
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