Elucidating microbial and abiotic iron and silica mineral precipitation relevant for Banded Iron Formations (BIFs) in column experiments

• Applicant: Professor Dr. Andreas Kappler
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 534725971

Banded iron formations (BIFs) are sediments precipitated in Precambrian oceans. Their composition and mineralogy have been used as paleo-proxies for the composition of early Earth's oceans, biosphere and atmosphere. It is widely accepted that planktonic bacteria played a key role in the oxidation of Fe2+ to form the precursor minerals of BIFs, i.e. ferric oxyhydroxides (ferrihydrite). Two types of microbes were important. The oldest were photoferrotrophs, i.e. anoxygenic Fe(II)-oxidizing phototrophs using Fe2+ as electron donor in photosynthesis. At some stage in Earth’s history, they were replaced by cyanobacteria because the O2 they produced was toxic to the photoferrotrophs. Although research over the past twenty years has shed significant insights into the mechanisms by which microbes facilitated BIF precipitation, it remains unknown how the microbial communities might have interacted, and when the transition from a photoferrotroph-dominated to a cyanobacteria-dominated water column took place. This project aims to fill this gap, investigating the interaction of these communities in BIF formation, with an emphasis on co-incubating the main planktonic microbial communities in large mesocosms. This project will use column bioreactors designed to simulate the dynamic early Earth ocean conditions. Column bioreactors permit monitoring of conditions, including temperature, oxygen levels, metal concentration and speciation, and the presence of specific microbial communities, in addition to collecting sediments for mineral characterization. This facilitates a systematic exploration of the biogeochemical processes involved and characterization of the interactions between different microbes. The experiments will initially involve individual inoculations of the cyanobacteria Synechococcus sp. PCC 7002 and the photoferrotrophs Chlorobium sp. strain N1, followed by a joint inoculation to study their interactions and collective influence on iron cycling. Analytical techniques such as flow cytometry, fluorescent microscopy, SEM, ICP-MS, XRD, and Mössbauer spectroscopy will facilitate monitoring microbial, Si and Fe distributions, mineral precipitation, and cell-mineral aggregate morphologies. Additionally, we propose the application of Scanning-Transmission Electron Microscopy and synchrotron-based cryo-Transmission soft-X-ray Microscopy for characterization of microbe-metal interactions, especially the biomineralization processes involved, and the role of these microbes in shaping the early Earth’s iron cycle. Temperature cycles will be employed to determine whether seasonal changes in ocean temperature were responsible for causing the alternating precipitation of Fe and Si minerals. The novelty of this research is that it offers a comprehensive, multi-disciplinary, and technologically advanced approach to understanding BIF genesis, aiming to fill critical knowledge gaps in our understanding of early Earth conditions and the development of early life.

• DFG Programme: Research Grants