The role of microorganisms in mineral weathering has long been recognized and is most often investigated through the lens of proton-promoted dissolution or nutrient scavenging by heterotrophic microorganisms. However, oxidation of Fe(II) is recognized as the rate limiting step in the weathering of Fe(II)-bearing silicate minerals, and Fe(II)-bearing minerals potentially represent a vast reservoir of metabolic energy for lithotrophic microorganisms. This study investigated the role of lithotrophic Fe(II)-oxidizing bacteria (FeOB) in the weathering of Fe(II)-bearing silicate minerals at Luquillo Critical Zone Observatory in Puerto Rico. Samples were obtained from the bedrock-saprolite interface within the Rio Icacos Watershed of the Luquillo Mountains in the summers of 2016 and 2017. Rio Icacos is underlain by the rapidly weathering Rio Blanco Quartz Diorite which contain the Fe(II)-silicate minerals biotite and hornblende. Prior studies (Buss et al., Geobiology, 2005) suggested that the flux of Fe(II) from bedrock weathering supports a lithotrophic microbial community at the bedrock-saprolite interface. As previously reported, we found a marked increase in microbial biomass (ATP) near this interface. Regolith recovered from the interface was used as inoculum for enrichment cultures with powderized quartz diotite as the sole energy source. Monitoring of the relative abundance of Fe(II) and ATP suggested growth of microorganisms coupled to the oxidation of Fe(II) in the quartz diorite. TEM and EDS revealed the accumulation of nanoparticulate Fe-oxyhydroxides on mineral surfaces only under biotic conditions. Simulated weathering experiments showed that microbially-oxidized quartz diorite had greater susceptibility to proton promoted dissolution. Shotgun metagenomic libraries from in situ and enrichment culture samples contained multiple bins related to known FeOB, including Betaproteobacteria genera, contained homologs to model extracellular Fe(II) oxidation systems. Our results provides insight into the potential role of FeOB in Fe(II)-mineral alteration and its contribution to the globally important process of rock weathering.

Extracellular electron transfer as a mechanism of biogeochemical weathering of Fe(II)-silicates by lithotropic Fe(II)-oxidizing bacteria

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.