"Iron minerals are ubiquitously present in the environment. Their formation is linked to the global C and N cycle and they control the fate of nutrients, metals, and greenhouse gases. My recent work, published in international journals including Nature Geoscience, showed that Fe(II)-oxidizing bacteria form Fe(III) minerals and suggested that such bacteria were involved in the deposition of Precambrian Banded Iron Formations, the world’s largest iron mineral deposits. Three neutrophilic microbial groups contribute to Fe(III) mineral formation: microaerophiles, phototrophs and nitrate-reducing Fe(II)-oxidizers. However, as previous studies have always solely focused on only one particular Fe(II) metabolism, the contribution of the different Fe(II)-oxidizing groups to overall Fe(III) mineral formation in nature and the competition among them for Fe(II) within Fe(II)-oxidizing communities is still unknown. I propose to use an innovative and holistic approach to study for the first time the abundance, activity and spatial distribution of all three Fe(II)-oxidizing bacterial groups in one habitat in different environments. Quantification of microbial activity and both nutrient and metal sorption under varying geochemical conditions will allow us to study competition among the Fe(II)-oxidizing groups and evaluate the ecological importance of microbial Fe(III) mineral formation in both early Earth and modern environments. This requires an interdisciplinary frontier research effort at the scale of an ERC grant integrating microbiology, biogeochemistry and mineralogy. Central to this is the cultivation and characterization of Fe(II)-oxidizing bacteria and their mineral products, a research area spearheaded by my group. This frontier research will define the role of microbial iron mineral formation in modern and ancient Earth systems, open doors to new biotechnology applications and advance the search for life on the Fe-rich planet Mars."