N2 fixation was key to the expansion of life on Earth, but which organisms fixed N2 and if Mo-nitrogenase was functional in the low Mo early ocean is unknown. Here, the authors show that purple sulfur bacteria fix N2 using Mo-nitrogenase in a Proterozoic ocean analogue, despite low Mo conditions.
- Miriam Philippi
- Katharina Kitzinger
- Marcel M. M. Kuypers
