Photoferrotrophy forms Fe(III) oxides dominated by acicular goethite in an anoxic, siderite-buffered system
Year: 2026
Type: article
Abstract: Ancient Fe(II)-oxidising photoautotrophic bacteria may have facilitated the precipitation of iron- and silica-rich chemical sediments known as Banded Iron Formations (BIFs). BIFs contain a diverse assemblage of iron oxides, carbonates and silicates, which are thought to have originated from the diagenesis of one or more primary seawater precipitates. While the identity and Fe redox state of these mineral precursors remain poorly understood, a compelling hypothesis suggests that the precipitation and transformation of mixed-valence phases such as green rust might have been a key component of BIF deposition. However, it remains unknown whether photoferrotrophy in an anoxic and Fe(II) aq -rich environment can produce such mixed-valence minerals. To test whether green rust can be produced by iron-oxidising phototrophs (photoferrotrophs) thought to play a role in BIF deposition, we cultured photoferrotrophs in an environment constantly buffered by Fe(II) from the dissolution of the Fe(II)-mineral siderite (FeCO 3 ). Here we show that the photoferrotroph Rhodopseudomonas palustris TIE-1 produces Fe(III) oxyhydroxides dominated by goethite (α-FeO(OH)) even when provided with a constant excess of Fe(II) aq . Fe(III) aq was formed extracellularly and rapidly hydrolysed, probably precipitating as metastable ferrihydrite, which then transformed into goethite following Fe(II) aq -catalysed recrystallisation. Given the prevailing circumneutral pH levels, we speculate that high [Fe(III) aq ] around microbial cells prevented the formation of mixed-valence phases. Our results showing that Fe(III) minerals precipitated from solutions even with an excess of Fe(II) aq indicate that an oxidative mechanism influences the identity of primary precipitates by dictating local chemical conditions at the site of Fe(II) oxidation. Further investigation is needed to understand conditions promoting the formation of Fe(II,III) phases in conditions representative of Earth’s ancient oceans.
Source: Geo-Bio Interfaces
Authors: Alice Zhou, Benjamin Klein, Jena E. Johnson
Institution: University of Michigan
Language: English
Field: Energy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,550
OpenAlex ID: W7165865946
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