Isotopic evidence for biological nitrogen fixation by molybdenum-nitrogenase from 3.2 Gyr.

Title	Isotopic evidence for biological nitrogen fixation by molybdenum-nitrogenase from 3.2 Gyr.
Authors	Eva E Stüeken, Roger Buick, Bradley M Guy, Matthew C Koehler
Magazine	Nature
Date	04/30/2015
DOI	10.1038/nature14180
Introduction	Nitrogen is a vital nutrient required by all living organisms, necessitating its accessibility since the origin of life. While abiotic mechanisms such as hydrothermal reduction, photochemical reactions, or lightning could have transformed atmospheric N2 into usable fixed nitrogen species such as NH4(+), HCN, or NOx, these early Earth sources were likely limited, restricting the primordial biosphere's scale. The emergence of nitrogenase, an enzyme that converts atmospheric N2 into organic NH4(+), marked a significant advancement in life's diversification, though its exact timeline remains unclear. This study provides nitrogen isotope ratios, averaging 0.0 ± 1.2‰, from marine and fluvial sedimentary rocks dating back 3.2 to 2.75 billion years. These isotopic signatures are inconsistent with abiotic formation and strongly indicate biological nitrogen fixation, most plausibly facilitated by molybdenum-based nitrogenase, which avoids the substantial negative fractionations associated with other nitrogenase types. Our findings establish a minimum age of 3.2 billion years for the onset of biological nitrogen fixation and imply that molybdenum was present and bioavailable in the mid-Archaean ocean long before the Great Oxidation Event.
Quote	Eva E Stüeken, Roger Buick and Bradley M Guy et al. Isotopic evidence for biological nitrogen fixation by molybdenum-nitrogenase from 3.2 Gyr. Nature. 2015. Vol. 520(7549). DOI: 10.1038/nature14180
Element	Molybdenum (Mo) , Nitrogen (N)
Materials	Chemical Compounds
Industry	Agriculture , Research & Laboratory