Microbial diversity featuring silica mobilization in non-thermal subsurface environments

Silicon is among the most common elements of the Earth's crust. The role of microbes in silica mobilization is well known for hydrothermal environments, but non-hydrothermal quartz-dominated ecological niches have been poorly investigated. Here we present evidences of quartz amorphization resulting in a wide variety of silica deposits from the world's largest quartz-sandstone cave. Constant temperatures and neutral/acidic pH conditions imply a key role of microbes in quartz polymerization, triggering an increase of pH, releasing inorganic cations and metals, and supplying nucleation sites for silica precipitation. Illumina-MiSeq analysis describes the microbial populations differentiation through the process, controlled by hydrological settings, cave location, and nutrient availability. This discovery shows that amorphous silica can form in subsurface environments through mediation of microbes, with implications for understanding silica dominated niches as those of Precambrian stromatolites.