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Monday, December 12th, 2011 . 11:54 am | No Comments

Small but Mighty: Planktonic Lifegivers of the Ocean

DR. SALLIE (PENNY) CHISHOLM, Martin Professor of Environmental Studies (Civil and Environmental Engineering/Biology) at the Massachusetts Institute of Technology, USA, is one of the foremost experts on Prochlorococcus. It is the smallest photosynthetic organism in the ocean, yet it punches way above its weight in the ecosystem services it supplies us with. These cyanobacteria (also known as “blue-green algae”) synthesize life, providing oxygen and building sugars, out of nothing more than sunlight, water, carbon dioxide, and nutrients. These little heroes form the base of the food web, upon which all marine animals depend. They are widespread and the most numerous of plant-like forms of marine life, yet were only discovered belatedly, 25 years ago, because of their small size–they can barely be seen under a microscope.
Prochlorococcus cells
The scanning electron microscope image shows several Prochlorococcus cells, including one in the process of dividing © Claire Ting

Prochlorococcus comes in many different varieties (strains) or “ecotypes” (ecological “flavors”) which are specially adapted to the surrounding particular environmental conditions in terms of light, temperature, and nutrients. Viruses can infect these bacteria and are key to how Prochlorococcus can maintain such genetic diversity, enabling them to take advantage of changes in the ecosystem. To reproduce, viruses hijack the genetic material of the bacteria for their own purposes, and in the process, shuttle genes around between the bacteria, ensuring natural selection has a good genetic mixture to operate on.

On top of their essential role in ocean ecosystems, the metabolic blueprint of these ‘minimalist’ bacteria (theirs is the smallest genome that can make life from sunlight and inorganic compounds) may also prove useful in designing efficient pathways for the manufacture of biofuels or new antibiotic-like pharmaceuticals. Although some advocate fertilizing the oceans to promote the growth of other phytoplankton species so they will draw more CO2 from the atmosphere, Dr. Chisholm remains skeptical that these types of ‘geoengineering’ approaches can help solve our climate change problems without introducing yet more unintended negative side effects.

To read the full article, go to:


To listen to an interview with Dr. Chisholm, see:


Author: Lindy Weilgart, Okeanos – Foundation for the Sea

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