Shifting microbial communities sustain multi-year iron reduction and methanogenesis in ferruginous sediment incubations

Abstract

19Reactive Fe(III) minerals can influence methane (CH 4 ) emissions by inhibiting microbial 20 methanogenesis or by stimulating anaerobic CH 4 oxidation. The balance between Fe(III) 21 reduction, methanogenesis, and methane oxidation in ferruginous Archean and Paleoproterozoic 22 oceans would have controlled CH 4 fluxes to the atmosphere, thereby regulating the capacity for 23 CH 4 to warm the early Earth under the Faint Young Sun. We studied CH 4 and Fe cycling in 24 anoxic incubations of ferruginous sediment from the ancient ocean analogue Lake Matano, 25 Indonesia over three successive transfers (500 days total). Iron reduction, methanogenesis, 26 methane oxidation, and microbial taxonomy were monitored in treatments amended with 27 ferrihydrite or goethite. After three dilutions, Fe(III) reduction persisted only in bottles with 28 ferrihydrite. Enhanced CH 4 production was observed in the presence of goethite, highlighting the 29 potential for reactive Fe(III)-oxides to inhibit methanogenesis. Supplementing the media with 30 hydrogen, nickel and selenium did not stimulate methanogenesis. There was limited evidence for 31 Fe(III)-dependent CH 4 oxidation, although some incubations displayed CH 4 -stimulated Fe(III)-32 reduction. 16S rRNA profiles continuously changed over the course of enrichment, with ultimate 33 dominance of unclassified members of the order Desulfuromonadales in all treatments. Microbial 34 diversity decreased markedly over the course of incubation, with subtle differences between 35 ferrihydrite and goethite amendments. These results suggest that Fe(III)-oxide mineralogy and 36

Evidence for microbial iron reduction in the methanic sediments of the oligotrophic southeastern Mediterranean continental shelf

“…Thus, a possible scenario is that Fe(III) is reduced by pyrite oxidation (Eq. 3) (Bottrell et al, 2000), which triggers the "cryptic" sulfur cycle, as observed in other marine sediments (Holmkvist et al, 2011;Brunner et al, 2016;Egger et al, 2016). In this cycle, elemental sulfur, and eventually by disproportionation also sulfide and sulfate, is produced.…”

Phylogenetic and structural diversity of aromatically dense pili from environmental metagenomes

“…The sediments were mixed with anoxic freshwater media in a 1:5 ratio in an anoxic chamber and dispensed in stoppered serum bottles, as in Bray et al . (). Cultures were amended first with goethite and later with ferrihydrite.…”

Phylogenetic and structural diversity of aromatically dense pili from environmental metagenomes

“…Two sediment cores were obtained from 590 m water depth in Lake Matano, Sulawesi Island, Indonesia in May 2010 (2°28’S, 121°20’E, in situ sediment temperature ~27°C) and stored under anoxic conditions. The sediments were mixed with anoxic freshwater media in a 1:5 ratio in an anoxic chamber and dispensed in stoppered serum bottles, as in Bray et al (2017). Cultures were amended first with goethite and later with ferrihydrite.…”