Fossil evidence of iron-oxidizing chemolithotrophy linked to phosphogenesis in the wake of the Great Oxidation Event

Abstract

The oxygenation of Earth's atmosphere allowed for the diversification of metabolisms to include those that rely on oxygen and its derivatives. For example, chemolithotrophic oxidation of sulfide and iron both require oxygen or nitrate as terminal electron acceptors. A growing number of oxygen-utilizing chemolithotrophs are known to accumulate intracellular polyphosphate as an energy reserve that allows them to adapt to the fluctuating redox conditions in their distinctive-gradient habitats. Polyphosphate is also thought to play an important role in the formation of phosphatic mineral deposits. Here we present fossil evidence of iron-oxidizing bacteria preserved as filamentous iron oxides within phosphatic Paleoproterozoic stromatolites. The filaments include twisted stalks similar to those produced by modern iron-oxidizing bacteria that are known to metabolize polyphosphate and inhabit steep redox gradients. Fossil iron-oxidizing bacteria preserved within some of the oldest known phosphorites serve as indicators of O 2 -Fe(II) gradients that may have supported microbially mediated phosphogenesis via polyphosphate metabolism and/or an active iron redox pump.

Nanoscale petrographic and geochemical insights on the origin of the Palaeoproterozoic stromatolitic phosphorites from Aravalli Supergroup, India

“…A similar range of δ 13 C org values measured in situ on cyanobacteria‐like Proterozoic microfossils have been interpreted similarly (Williford et al ., ). This does not exclude possible contributions from some phototrophic Fe(II)‐oxidizing bacteria (Crosby et al ., ), which are known to live in the photic zone of modern rift lakes (Crowe et al ., ). There is also the likely possibility that anoxygenic phototrophic micro‐organisms participated in the formation of these stromatolites, as they have been reported from modern stromatolites (Papineau et al ., ; Bosak et al ., ; Goh et al ., ; Birgel et al ., ).…”

The role of microaerophilic Fe‐oxidizing micro‐organisms in producing banded iron formations

“…Indeed, stalk-like morphologies have been observed in the rock record (Hofmann & Farmer, 2000;Little et al, 2004;Slack et al, 2007), although stalks have not yet been observed in BIFs. However, stalks may be preserved in special cases, in particular when quickly encased in silica, carbonate, or phosphate, for example, in association with stromatolites (Crosby et al, 2014). However, stalks may be preserved in special cases, in particular when quickly encased in silica, carbonate, or phosphate, for example, in association with stromatolites (Crosby et al, 2014).…”

Metatranscriptomic insights into polyphosphate metabolism in marine sediments

“…In a similar manner, large marine sulfur-oxidizing bacteria in the family Beggiatoaceae also store poly-P, and have been shown to hydrolyze their poly-P stores upon exposure to anoxic or sulfidic conditions (Schulz and Schulz, 2005; Brock and Schulz-Vogt, 2011). Poly-P hydrolysis by large sulfur-oxidizing bacteria has been implicated in phosphate mineral formation in seasonally anoxic upwelling zones through the supersaturation of sediment pore waters, and might constitute an important sink in the global P cycle, both in modern sediments (Schulz and Schulz, 2005;Goldhammer et al, 2010;Brock and Schulz-Vogt, 2011) and in the past (Bailey et al, 2013;Crosby et al, 2014).However, marine microbial communities are diverse, and beyond studies of large sulfuroxidizing bacteria, little is known about the diversity and activity of poly-P utilizing microbes in marine sediments that experience fluctuating redox conditions. Therefore, we used a metatranscriptomic approach to compare the expression of poly-Prelated genes in sediments that were experimentally exposed to anoxic and oxygenated conditions.…”