CHANGES IN MICROBIAL GROWTH AND IRON REDUCTION DUE TO CARBON SEQUESTRATION

This experiment is the first attempt at creating a model to illustrate microbial responses to carbon sequestration. During carbon sequestration, very high amounts of anthropogenic CO₂ is pumped into confined brine aquifers in an effort to mitigate the effects of global warming. Should this CO₂ leak into the shallower subsurface, changes to the environment may be evident. In addition to acidifying the surrounding environment and changing groundwater chemistry, the presence of CO₂ may have unforeseen effects on microbial growth rates and metabolism. One question this process raises is what effect will high CO₂ pressures underground have on the subsurface ecology? In this set of experiments, we cultured the iron-reducing bacterium Shewanella oneidensis, strain MR-1 in increasing partial pressures of CO₂ in order to examine changes in growth rates and metabolism. Iron reduction was chosen in this case as a representative of microbial metabolic responses. Shewanella oneidensis, a facultative anaerobe isolated from lake sediment, was used for this experiment because it is easy to culture and because it is capable of utilizing a wide variety of electron acceptors. Shewanella was grown anaerobically in batch cultures using lactate as the electron donor and Fe-citrate as the terminal electron acceptor. The medium was heavily buffered using phosphate to withstand changes in pH due to high CO₂ pressures. Growth experiments were conducted by checking changes in optical density over a 3 day period. Cell counts were taken through DAPI staining. Rates of iron reduction were examined using ferrozine. Initial data shows that growth of Shewanella is definitely hindered by increasing CO₂ pressures, despite the fact that there was no significant drop in pH. We expect future work to show that CO₂ will interfere with the rates of iron reduction suggesting decreased respiration and metabolism. Data from this work can provide initial ideas on how microbes respond to carbon sequestration, which will later lead to an understanding on changes in subsurface microbial interactions.