Kinetics and community profiling of sulfate-reducing bacteria in organic carbon treated mine tailings
McBroom, Mark David.
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Acid rock drainage (ARD) poses a significant health and environmental hazard worldwide via the discharge of highly acidic waters and potentially toxic levels of mobile metals. This is a result of weathering and microbial oxidation of pyretic minerals present in mine tailings. Sulfate reducing bacteria (SRB), which are often indigenous to mine tailings, have demonstrated promising potential in metabolically raising effluent pH and immobilizing metals through precipitation and biomineralization. The addition of an organic carbon source has the potential of stimulating the SRB and reducing ARD at its source. Often the success of a process based on implementing endemic microbial consortia for in situ bioremediation is highly dependent on an understanding of the community structure and potential activity of microbial community members when provided a specific substrate. The goal of this research was to identify viable methodologies that can be used to select and monitor successful bioremediation treatments. Differences in microbial community structure and activity of batch cultures inoculated with tailings were observed for independent treatments of whey and lactate as carbon sources. Community response to whey treatment of bench-scale columns was also observed. Development and optimization of DNA extraction and purification methods was required for the highly contaminated tailing samples. Microbial community structure and phylogeny were identified using denaturing gradient gel electrophoresis (DGGE) and automated sequencing. The methods used in this paper were successful at identifying pre- and posttreatment community structure of endemic microbial populations. Shifts in community structure were observed in treated columns and treated batch cultures. Sulfate reduction in treated batch cultures was highly variable between samples, suggesting microheterogeneities in community structure of sampled tailings. Selection for specific phylogenies was evident with respect to carbon source treatment, culturing conditions, and sampled inocula. Variability in community structure was roughly correlated to sulfate reduction in individual organic carbon treatments. Resulting community profiles were highly dependent on methods used in obtaining, amplifying, and isolating community DNA of phylogenetically distinct populations. The success of implementing molecular techniques to observe and optimize bioremediation is ultimately dependent on the methodology used.