Authors: Miriam Philippi, Katharina Kitzinger, Jasmine S. Berg, Bernhard Tschitschko, Abiel T. Kidane, Sten Littmann, Hannah K. Marchant, Nicola Storelli, Lenny H. E. Winkel, Carsten J. Schubert, Wiebke Mohr, Marcel M. M. Kuypers
Published: 2021-08-06
DOI: 10.1038/s41467-021-25000-z
Source: Full article
AbstractBiological N2fixation was key to the expansion of life on early Earth. The N2-fixing microorganisms and the nitrogenase type used in the Proterozoic are unknown, although it has been proposed that the canonical molybdenum-nitrogenase was not used due to low molybdenum availability. We investigate N2fixation in Lake Cadagno, an analogue system to the sulfidic Proterozoic continental margins, using a combination of biogeochemical, molecular and single cell techniques. In Lake Cadagno, purple sulfur bacteria (PSB) are responsible for high N2fixation rates, to our knowledge providing the first direct evidence for PSB in situ N2fixation. Surprisingly, no alternative nitrogenases are detectable, and N2fixation is exclusively catalyzed by molybdenum-nitrogenase. Our results show that molybdenum-nitrogenase is functional at low molybdenum conditions in situ and that in contrast to previous beliefs, PSB may have driven N2fixation in the Proterozoic ocean.