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What diversity lies in a millimeter of ocean water?

A team of scientists at the Massachusetts Institute of Technology (MIT) has reported that Prochlorococcus, a tiny and extremely abundant photosynthetic marine bacterium, occurs in nature as many diverse subpopulations. The diversity of this species apparently accounts for its ability to flourish and persist in a wide range of ocean conditions.

Prochlorococcus is perhaps one of the most abundant and widely distributed marine producers. The finding that every sample of seawater contains a very large range of genetically distinct subpopulations of the bacterium provides a potential explanation for its abundance. If the subpopulations are each adapted to proliferate under different environmental conditions, there could be implications for the organisms' ability to survive when conditions change.

Prochlorococcus was discovered by MIT researcher Sallie Chisholm. It is now recognized as perhaps the most abundant of the marine primary producers in the ocean, occurring in up to and over 100,000 cells per milliliter. Since its discovery it has been the primary focus of research in the Chisholm laboratory.

The abundant producer is now a model system for understanding the diversity of marine phytoplankton. By examining the genetics of single cells, researchers can document the diversity of coexisting subpopulations. The MIT findings will recast how researchers think about species, diversity and the ability of microorganisms to adapt to a wider range of environmental conditions including those driven by global climate change.

Images (1 of )

  • artist's illustration of the prochloroccocus bacteria in a drop of seawater
  • the prochlorococcus bacteria shows up as faint green dots under bright field microscopy
An artist's illustration of Prochlorococcus diversity in a drop of seawater.
Carly Sanker, MIT
Prochlorococcus seen as faint green dots under bright-field microscopy.
Jessie Thompson, MIT

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