A Microfluidic Platform to Investigate Microbial Precipitation of Metal Oxides in Porous Media.

Microorganisms commonly precipitate metal oxide nanoparticles in soils, sediments, and other environmentally relevant porous media. However, the formation and reactivity of manganese (Mn) and iron (Fe) oxides remain poorly characterized in physically complex environments. While laboratory systems can incorporate porous media as a substrate, they require destructive sampling and are not readily amenable to pore-scale analyses. The dynamic yet inaccessible nature of porous media, therefore, requires the ability to resolve microbially mediated mineral precipitation in situ and in real time. To close this gap, a microfluidic platform is developed to evaluate microbial precipitation of metal oxides in a model pore space. This platform is validated with the Mn-oxidizing bacterium Pseudomonas putida GB-1. Biofilm development and associated Mn oxide precipitation are visualized under continuous flow with time-lapse color brightfield microscopy. An image subtraction algorithm is then combined with endpoint mass measurements to estimate the rate of Mn oxide precipitation. This approach provides a tool to systematically test how microbial precipitation of metal oxides varies in response to changing physical and chemical conditions.