In this Project, started in 2017, we are carrying out a comprehensive study of the complex interactions taking place in aqueous acidic solutions between dissolved metals and microbial cells inhabiting deep anoxic zones. These interactions can lead to biomineral formation and affect to the geochemical behavior of many different trace metals. We are also trying to identify adaptive mechanisms by the acidophiles to cope with extremely high salinity and metal concentrations existing in these habitats, and their possible implications for geomicrobiology and biotechnology (e.g., biomining, bioleaching). The project is funded by the Spanish Ministry of Economy and Competitiveness through its National Program of Research, Development and Innovation. The main methods used are Scanning Transmission Electron Microscopy, Cryo-Electron Microscopy, High-Resolution Transmission Electron Microscopy, Metagenomics, Metatranscriptomic, Electron Energy-Loss Spectroscopy, Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy, Bioreactors, Anaerobic Microbiology, Synchrotron X-Ray Diffraction, Biomolecular Analyses.