Half of the oxygen that we breathe is produced by tiny ocean plants called phytoplankton. They form the base of the oceanic food-web and control the balance of gases in our atmosphere. The growth of phytoplankton is regulated by the availability of nutrients and in large parts of the oceans, nitrogen is the limiting nutrient. Our atmosphere is composed of 78 % nitrogen gas but this nitrogen is only available to an exclusive group of organisms called nitrogen-fixers.

Nitrogen-fixers can make their own fertilizer by converting nitrogen gas into ammonium. By doing this they support growth in the oceans. For many years large phytoplankton, which could be easily identified using a microscope, were thought to be the main nitrogen-fixing organisms in the oceans. In this talk I will present how the use of molecular methods targeting specific genes has led to fascinating discoveries of previously unknown nitrogen-fixing organisms.