Redox gradients, microbial biofilms and biogeochemical cycles in the Critical Zone

In Critical Zone, most microorganisms organize themselves in biofilms. These complex structures, of limited elements diffusion, are still poorly understood. The microorganisms metabolic activity and the presence of reactive groups in the extracellular matrix make them very reactive heterogeneous structures. Moreover, the low permeability to organic and inorganic molecules results in the establishment of strong physico-chemical gradients within the biofilm thickness. The goal of this PhD is to understand the redox gradients composition and organization within these structures, in particular by studying the production of extracellular reactive oxygen species by microorganisms, demonstrated by J.Diaz and C.Hansel (Nature, 2013). A biofilm high redox potential is very impactful for sensitive redox species like metals, especially for Mn, a key oxidizing agent in geosciences. Thus, to better evaluate the impact that microbial biofilms have on metal cycles is a crucial issue in biogeosciences.