Doctoral Degrees (Microbial, Biochemical and Food Biotechnology)
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Browsing Doctoral Degrees (Microbial, Biochemical and Food Biotechnology) by Subject "Aluminium toxicity"
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Item Open Access Geological carbon sequestration and its influence on subsurface microbial diversity an metabolic carbon cycling(University of the Free State, 2015-08) Erasmus, Mariana; Van Heerden, E.; Litthauer, D.; Onstott, T. C.; Phelps, T. J.; Surridge, T.English: Climate change is a reality and is a consequence of too high levels of greenhouse gases being emitted into the atmosphere, especially CO2. This is happening mainly due to the burning of fossil fuels, but other human or industrial activities are also contributing. These additional emissions are responsible for the greenhouse effect, resulting in an increase in the global average temperature of the Earth's atmosphere. Industrialization and the rise in population levels around the world has increased the demand for energy and by meeting that demand more emissions are being released into the atmosphere and are responsible for an atmospheric increase of CO2 from 280 ppm around 1850 to 400 ppm today. This is creating long term, harmful conditions on the Earth, influencing the economy, the ecology, and human health. As an attempt to manage the carbon resources more efficiently, South Africa will be storing anthropogenic CO2 in geological formations. Within these deep subsurface environments, considered for carbon sequestration, highly diverse microbial communities can be found and the metabolic activities of these microorganisms are closely tied to the geochemical and mineralogical processes occurring within the subsurface. Therefore, to determine possible influences that the CO2 could have on the diversity and metabolic carbon cycling of these subsurface microorganisms, consideration was given to the interaction between the sequestered CO2 and the subsurface biome, as well as the geological environments. In order to possibly understand how these subsurface biomes will operate in situ, the biogeochemistry for a study site, similar to proposed sites for carbon sequestration in South Africa, was characterized comprehensively. The subsurface biome from the study site, used for this research, was found to contain microorganisms belonging to the Archaeal, the Bacterial, and the Eukaryal domains, but was dominated by the Bacteria, specifically the Proteobacteria. A specifically designed, continuous high pressure bioreactor was used to evaluate the influence of the stored CO2 on the subsurface microbial diversity and metabolic carbon cycling, by mimicking carbon sequestration conditions. Due to the extreme conditions of the deep subsurface, most of these microorganisms have to grow and survive in extreme energy limiting conditions, making them likely to be inactive or to display exceptionally low metabolic activities. Even though this research indicated that in most of the conditions tested the microorganisms were not able to multiply or to produce detectable amounts of expected metabolic products; they surprisingly remained viable. The most likely reason for this was due to the presence of biofilm formations which the microorganisms used as a possible protection mechanism towards resisting the harsh conditions they were subjected to. Ultimately, this indicated that viability might be more important, than specific diversity changes or biomass yields for carbon cycling studies in the deep subsurface. A considerable decrease in the diversity was observed after the biome was subjected to carbon sequestration conditions. Only groups from the Bacteria and Archaea were able to survive these conditions, but no Eukarya could be detected. Transcriptome data obtained for the subsurface biome indicated that gene products from sulphur metabolism, nitrogen metabolism, and carbon metabolism were present and diversity analyses of the bioreactor confirmed that microorganisms, utilizing these metabolisms, remained viable after six weeks under carbon sequestration conditions. These conditions, mainly due to the acidic environment created by the dissolved CO2, allowed for significant leaching of metals from the sandstone, especially aluminium and iron, creating more stressful conditions, thus restricting the growth of the subsurface biome even more. This could result in substantial impacts on the carbon cycling occurring in the deep subsurface, and should therefore be considered during carbon sequestration.