Viability and metal reduction of Shewanella oneidensis MR-1 under CO ₂ stress: Implications for ecological effects of CO₂ leakage from geologic CO₂ sequestration

To study potential ecological impacts of CO₂ leakage to shallow groundwater and soil/sediments from geologic CO₂ sequestration (GCS) sites, this work investigated the viability and metal reduction of Shewanella oneidensis MR-1 under CO₂ stress. While MR-1 could grow under high-pressure nitrogen gas (500 psi), the mix of 1% CO₂ with N ₂ at total pressures of 15 or 150 psi significantly suppressed the growth of MR-1, compared to the N₂ control. When CO₂ partial pressures were over 15 psi, the growth of MR-1 stopped. The reduced bacterial viability was consistent with the pH decrease and cellular membrane damage under high pressure CO₂. After exposure to 150 psi CO ₂ for 5 h, no viable cells survived, the cellular contents were released, and microscopy images confirmed significant cell structure deformation. However, after a relatively short exposure (25 min) to 150 psi CO₂, MR-1 could fully recover their growth within 24 h after the stress was removed, and the reduction of MnO₂ by MR-1 was observed right after the stress was removed. Furthermore, MR-1 survived better if the cells were aggregated rather than suspended, or if pH buffering minerals, such as calcite, were present. To predict the cell viability under different CO ₂ pressures and exposure times, a two-parameter mathematical model was developed.