Behavior of Shewanella oneidensis MR-1 in a sulfur and zinc-rich medium and its applications for biosensing and biomaterials

Abstract

An increasing focus of current microbiology research is the fact that some strains of bacteria, called dissimilatory metal-reducing bacteria (DMRB), are capable of utilizing certain metallic ions as terminal electron acceptors in their metabolic processes. One strain in particular, Shewanella oneidensis MR-1, can reduce ions of iron, lead, arsenic, and uranium, among others. Under anaerobic conditions it has also been shown to reduce sulfur compounds, nitrates, and chromates. The cultivation of DMRB under controlled conditions therefore has significant implications for the low-energy, room-temperature synthesis of metal sulfide and/or metal oxide semiconductors. Furthermore, Shewanella and other DMRB can form biofilms that interact electronically with solid-phase minerals in their environment. For this reason there exists a potential to grow DMRB directly into porous substrates in order to create biosensors that are capable of producing electrical signals that provide information about metal ion concentration in water as well as a range of other water quality variables.I will highlight my recent work exploring the behavior of Shewanella oneidensis MR-1, in a medium rich in both zinc and thiosulfate ions. I have grown Shewanella bacteria in a three-electrode system and used a potentiostat to hold the system at a fixed DC voltage during cultivation while also measuring current output. After completing the cultivation step, I have used cyclic voltammetry and electrochemical impedance spectroscopy to characterize the DC and AC current-voltage dynamics of the system, which can reveal the reduction-oxidation activity of key bacterial proteins. In the second experiment, I have grown Shewanella bacteria under both aerobic and anaerobic conditions in media rich in zinc and thiosulfate ions and used scanning electron microscopy and energy dispersive microscopy to characterize the minerals that precipitate within the batches. I compare results from a minimal medium containing only the zinc and thiosulfate sources to a more traditional Shewanella medium containing various vitamins, minerals and other nutrients to support growth. I also compare the inoculated batches to sterile control batches containing no bacteria in order to infer the effect that the bacteria have on mineralization in their environment. Finally, I use confocal microscopy to explore the fluorescence behavior of the precipitates generated in both inoculated and sterile batches.