Global Impacts: The Role of Microbes in Maintaining Atmospheric Balances
It may seem surprising to learn that bacteria are responsible for about half the photosynthesis on Earth. Most photosynthetic bacteria can be found freely swimming in the oceans that cover 70% of the Earth's surface. These bacteria affect key chemical balances in the Earth's atmosphere and play a crucial role in maintaining the habitability of the entire planet.
Metagenomics can help scientists gain insights into the mechanisms behind changes of energy and matter in the sea, the composition of Earth's atmosphere, and global climate.
Bacteria and the Carbon Cycle
One of the most important ways photosynthetic bacteria affect life on Earth is through their role in the global carbon cycle. Carbon is the most abundant element in living things, including humans (excluding the hydrogen and oxygen in the water that makes up the bulk of our weight). However, most of the carbon on Earth is in the form of carbon dioxide (CO2), which cannot be used by animals and most bacteria. 
Through photosynthesis, plants and certain bacteria "fix" carbon from the atmosphere, turning it into a form that is useable to many more life forms (and releasing oxygen). Through the process of fixing carbon, photosynthetic bacteria remove CO2—which is a major greenhouse gas—from the atmosphere. In this way, photosynthetic bacteria mitigate some of the effects of the release of CO2 and other greenhouse gases from human activities that most scientists believe is responsible for global warming.
Microbial "Bucket Brigades"
To achieve complex chemical transformations, no single microbe can do it alone; it takes a community. Many microbial communities, including those involved in the generation and consumption of greenhouse gases, function through a "bucket brigade" system, in which each microbe performs its own individual task, with its end product becoming the starting fuel for its neighbor. Through metagenomics, scientists can examine the genetic bases behind these complex bucket brigades and explore how genes from various organisms influence each other's activities.
The information on this Web page was derived from the National Research Council report The New Science of Metagenomics: Revealing the Secrets of Our Microbial Planet (2007) and the 20-page educational booklet derived from that report, Understanding Our Microbial Planet: The New Science of Metagenomics.
PHOTO CREDIT: Image of photosynthetic bacteria courtesy NASA.
Support for this web publication was provided by the Presidents' Circle Communication Initiative of the National Academies.
