The engine of the ocean - powered by bacteria

Posted By News On July 5, 2017 - 12:34pm
The engine of the ocean - powered by bacteria

No one has started selling probiotics for the environment yet, but a new study may give Natural Resources Defense Council just the evidence it needs. The ocean has a "microbiome", and those microbiological interactions keep the ‘engine’ of the ocean running.

Two abundant types of microorganism in the ocean - phototrophic and heterotrophic bacteria – collaborate to recycle carbon from the atmosphere into energy to feed the ecosystem. This is contrary to the popular belief that marine phototrophs and heterotrophs compete with each other to consume the scarce nutrients found in seawater.

Phototrophic bacteria use light to ‘fix’ carbon dioxide from the air, and convert this into organic matter – which leaks out, and is consumed by heterotrophs, which in turn release nutrients back to the ecosystem so the phototrophic bacteria can continue to do their job: photosynthesise and fix more carbon.

Graphical depiction of phototrophic and heterotrophic bacteria in the ocean. Credit: University of Warwick

This interaction keeps the level of nutrients in the ocean balanced and keeps a healthy base that ultimately sustains the entire marine food web. Half of the planet’s primary production and half of the oxygen we breathe rely on this system to work efficiently. The speed at which these nutrients are circulated will define the rate at which the oceans will continue to buffer against carbon dioxide in the atmosphere, which is a major greenhouse gas.

The researchers observed this interaction by growing pure cultures of each bacteria in the laboratory, and putting them together in natural seawater and doing nutrient and molecular analyses over a long timeframe.

Surprisingly, both microorganisms reached a stable state where the phototrophic and heterotrophic bacteria were seen to be mutually benefiting each other – with the phototrophs consuming inorganic nutrients and light to fix carbon, and the heterotrophs using the leaked organic carbon as a source of carbon and energy and returning inorganic nutrients to the phototroph. 

The authors also make the obligatory reference to saying their work may better predict how seas will react to climate change.

Citation: Joseph A. Christie-Oleza, Despoina Sousoni, Matthew Lloyd, Jean Armengaud & David J. Scanlan, Nutrient recycling facilitates long-term stability of marine microbial phototroph–heterotroph interactions, Nature Microbiology