Rachel Foster

PhD Max Planck Institute for Marine Microbiology Natural sciences Year of admission: 2013

A symbiotic relationship in the oceans
The majority of algae living in the oceans consist of diatoms. They thrive and can “bloom” thanks to cyanobacteria that help them to capture nitrogen from the atmosphere. Rachel Foster studies this symbiotic relationship, that affects the cycles of both nitrogen and carbon.

Hundreds of millions of years ago, ancient cyanobacteria started to live in symbiosis with other single-cell organisms, which used the ability of cyanobacteria to extract energy from sunlight. The collaboration became so strong and essential that in the end, the organisms became fused. We can see the result of this partnership in modern plants: plants’ chloroplasts, where photosynthesis takes place, are the remains of cyanobacteria.

A similar fusion seems to have developed between marine diatoms and modern cyanobacteria, which can fix nitrogen. They convert atmospheric nitrogen gas to biologically available ammonium. Rachel Foster, a scientist at Max Planck Institute for Marine Microbiology, in Bremen, Germany, studies this collaboration between the ocean’s diatoms and cyanobacteria and has shown, for example, that diatoms seem to control the metabolism of the cyanobacteria.

As a Wallenberg Academy Fellow, she will move to Stockholm University where she will continue to investigate this important symbiosis. Apart from affecting the cycle of nitrogen, the interaction also has an impact on the turn-over of carbon. When the algae die, they fall to the ocean floor, taking carbon with them to be buried in the sediments, which functions as a “carbon sink”. 

Photo: Sean McNamara