ENGINEERED ELECTRON TRANSFER
Tuning mineral reactivity
Can we tune the subsurface mineralogy and reactivity by engineering microbes?
Iron oxides in our subsurface can greatly aid in e.g. contaminant removal from ground water reservoirs or soils. It is hard, though, to control the determing mineral paramaters such as phase and reactivity of an already formed sediment. Dissimilatory microbes, however, readily can transform iron oxides by delivering electrons produced as part of their metabolismcan.
The rate of this reduction process is key for the final mineral phase. Another player is the bacterial associated extracellular matrices (EM) which offer preferential binding sites for nucleation and waslily can adsorb free ions. The variation in the EM and electron production rate between bacteria make it hard to predict the end-product from microbial induced transformations of existing nanoparticulate iron oxide.
Shewanella oneidensis is a naturally occurring biofilm producing metal-reducing bacterium. It transports electrons via the Mtr pathway which is a series of transmembrane intermolecular electron transfer events to extracellular solid minerals. In contrast the popular model microbe Escherichia coli lacks the Mtr pathway and is hence not able to reduce solid metals. We are using an engineered E.coli that expres the Mtr pathway to try and optimize controls on transformation by electron transport.