A biomarker based on the stable isotopes of nickel

Abstract

The new stable isotope systems of transition metals are increasingly used to understand and quantify the impact of primitive microbial metabolisms on the modern and ancient Earth. To date, little effort has been expended on nickel (Ni) isotopes but there are good reasons to believe that this system may be more straightforward, and useful in this respect, than some others. Here, we present Ni stable isotope data for abiotic terrestrial samples and pure cultures of methanogens. The dataset for rocks reveals little isotopic variability and provides a lithologic baseline for terrestrial Ni isotope studies. In contrast, methanogens assimilate the light isotopes, yielding residual media with a complementary heavy isotopic enrichment. Methanogenesis may have evolved during or before the Archean, when methane could have been key to Earth's early systems. Our data suggest significant potential in Ni stable isotopes for identifying and quantifying methanogenesis on the early planet. Additionally, Ni stable isotope fractionation may well prove to be the fundamental unambiguous trace metal biomarker for methanogens.biological fractionation ͉ early life ͉ methanogens ͉ trace metal L ife has had a profound impact on the surface of the Earth, with perhaps the most obvious expression being the advent of oxygenic photosynthesis leading to the evolution of an oxidised atmosphere and oceans (1, 2). However, the microorganisms and metabolisms mediating oxygenic photosynthesis probably evolved relatively late in the Archean (3-5) and other metabolisms, such as methanogenesis, likely dominated both the early history of the biosphere itself (6-8) and the surface chemistry of the planet (9, 10). For example, atmospheric methane has been suggested as the dominant greenhouse gas before 2.3 Ga, before the evolution of oxic conditions (10). This inference is based on models of solar luminosity, atmospheric photochemistry and Archean microbial ecology, but little is known about the actual timing of the evolution of methanogens or methanogenesis as a metabolism. Phylogenetic studies indicate methanogens are deeply rooted in the tree of life (6,8,11), but this approach relies on biological evidence to constrain the timing of evolutionary events.In the investigation of the history of life on Earth, isotopic and chemical biomarkers serve both to calibrate time in phylogenetic trees and to document the impact of the biosphere on the physical world. An array of tools has traditionally been harnessed, including organic molecules (12) and the isotopic composition of key bioactive elements whose surface geochemical cycles are dominated by the biosphere (13). The transition metals are a recent addition to the latter group, with Fe undergoing the most intensive study (14,15). Fe has advantages and disadvantages in this regard, as the many studies conducted on its isotope system have shown. The ubiquitous role of Fe in the biosphere makes its isotopes a key system to study, though other isotope systems such as Se (16) and Cu (17) may also be promising....

Nonspecific uptake and homeostasis drive the oceanic cadmium cycle

“…= 0.9986 ± 0.0006; ref. 8) and the growing literature for other biologically active transition metals, whereby microorganisms exhibit a general preference for the light isotopes of a given element, e.g., Mo (12), Cu (13), Zn (14), Fe (15), and Ni (16). We rule out adsorption as the cause of the light isotopic fractionation observed for Cd in cultured cells, because a subset of cells plunged into the growth medium for a short time (∼10 s) resulted in no fractionation of Cd isotopes ( Fig.…”

Assessment of international reference materials for isotope-ratio analysis (IUPAC Technical Report)

“…The majority of reports on nickel isotopes have focused on radiogenic isotope studies [191], on nutrition studies [192], and some on mass-dependent isotopic fractionation studies [193]. Recent work on methanogen biomarkers with variations in nickel isotopic composition suggests that there is more to learn from these types of experiments [194]. Whenever δ…”

“…With the advent of MC-ICP-MS, the corresponding R( Isotope-amount ratio determined using synthetic isotope mixtures. Platinum has five stable isotopes, 192 Pt, 194 Pt, 195 Pt, 196 Pt, and 198 Pt, with isotopic abundances of 0.8, 32.9, 33.8, 25.2, and 7.4 %, respectively, in naturally occurring terrestrial material, and it has one radioactive isotope, 190 Pt, with a characteristic terrestrial isotopic composition with an isotopic abundance of 0.01 %. The half-life of 190 Pt is 4.5 × 10 11 years.…”

Iron Formation: The Sedimentary Product of a Complex Interplay among Mantle, Tectonic, Oceanic, and Biospheric Processes

“…For example, the chromium isotope composition of iron formations has been explored to constrain biogeochemical cycling of chromium in Precambrian surface environments and oceans (Frei et al, 2009) in order to provide an independent secular record of the redox state of the atmosphere and oceans. Other isotope systems such as nickel (Cameron et al, 2009) have a great potential as environmental proxy and will be undoubtedly used in future investigations.…”