Exploring carbon cycling in selected micro-organisms exposed to terrestrial carbon sequestration
South Africa‘s economy is primarily driven by the utilization of coal to provide electricity, which results in more fossil fuels to be burnt that contributes towards global warming. The average daily temperature is estimated to rise between 1.1 to 6.4˚C by 2100. Carbon sequestration is a technology that can limit CO2 emission into the atmosphere by storing the CO2 away in oceans or the terrestrial subsurface. South Africa is focusing on geological storage at depths of 1 000 m. Limited scientific knowledge is available on the direct impact when large amounts of supercritical CO2 is injected into the subsurface. This includes the diversity of the deep subsurface microbial communities as well as their ecosystems and biogeochemical processes. The main aim of this project was to use selected deep subsurface micro-organisms (T. scotoductus, Geobacillus sp. GE-7 and Geobacillus sp. A12) and an organism that was known to grow under pressure (E. limosum) and introduce them to CCS conditions using a high pressure syringe incubator system. The identities of the selected micro-organisms were verified using molecular techniques, the genomes of these micro-organisms were retrieved and information regarding possible CO2 fixation pathways was verified using the Metacyc database collection. The CO2 fixation pathways of interest were the Calvin cycle, the reductive acetyl Co-enzyme A and the reductive citric acid cycles. Surprisingly, T. scotoductus and E. limosum were able to remain viable and metabolically active even at 100 bar and 100% CO2. This has never been previously reported in literature. However Geobacillus sp. GE-7 and Geobacillus sp. A12 could not remain viable when the pressure was increased from 2 bar to 20 bar or higher. The outcomes of this study indicate that the interactions between supercritical CO2 and the subsurface organisms should be considered as biogeochemical cycling. However, these interactions in the subsurface are still relatively unknown and the availability of interactive metabolic pathways indicate that the subsurface communities could survive and interact with this introduced substrate.