Colleen Hansel, Harvard University
The activity of a physiologically diverse range of microorganisms is largely responsible for the formation of secondary minerals within the environment. Minerals produced by microbes are typically nanoparticulate, disordered, and poorly crystalline leading to enhanced reactivities relative to synthetic analogs. These microbially derived nanoparticles can therefore exert a significant force on the transport of contaminants, bioavailability of nutrients, and cycling of carbon. At times, mineral formation is a consequence of enzyme-catalyzed redox transformations that allow for energy conservation by the organism, such as the enzymatic reduction of soluble uranium to the mineral uraninite. In many cases, however, mineral formation is not a direct consequence of enzymatic activity and thus does not provide a known benefit to the organism. For instance, mineralization of iron and manganese is oftentimes a result of coupled biotic-abiotic processes, whereby microbes produce reactive metabolites that abiotically induce metal redox transformations leading to the nucleation and precipitation of minerals on organic templates also produced by the organism. Formation of nanoparticles in the environment, therefore, relies on a synergistic relationship between biology and chemistry, yet we are far from realizing the full potential of microorganisms to drive mineral cycling. Identifying the geochemical and biochemical pathways leading to microbial nanoparticle formation, the thermodynamic and kinetic constraints on these pathways, the fate and environmental impact of nanoparticles, and the steps necessary to translate this knowledge to environmental remediation and biotechnology are outstanding challenges in the field of mineral biogeochemistry.
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