Dr. Gordon Southam
Bacteria-Metal Interactions in the Natural Environment
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Position: Professor Office: BGS 1078 Phone: 519 661-3197 Fax: 519 661-3198 Email:gsoutham@uwo.ca Web site: http://www.uwo.ca/earth/people/faculty/southam.html |
Research
BACTERIA-METAL INTERACTIONS IN THE NATURAL ENVIRONMENT
My research focuses on the vital roles that bacteria play in the weathering of rocks, the formation of soils and sediments, and the genesis of authigenic minerals. Current and future research initiatives encompass the two main categories of interactions between metals and bacterial cell surfaces: metal solubilisation, which is most conspicuous in acid mine drainage (AMD) systems, and metal precipitation, which can occur through a variety of mechanisms. Present economic and environmental concerns have increased awareness of the impact of microorganisms on metals and have directed my attention to the following areas:
Mineral specific attachment of Thiobacillus spp. T. ferrooxidans and T. thiooxidans have the ability to out compete each other in the colonisation of metal sulphides and elemental sulphur, respectively. My research has implicated lipopolysaccharide in the mineral specific attachment of Thiobacillus spp. to metal sulphides and elemental sulphur. I am also gaining insight into the ecology of thiobacilli by investigating the role of nanoenvironments in the colonisation of these minerals in natural systems at neutral pH.
Fundamental aspects of mineral precipitation. Bacteria have the capacity to precipitate more toxic heavy metals cations than can be explained by a their net negative surface charge. This non-stoichiometric process is of fundamental significance in understanding the trace element geochemistry of aquatic systems. I am planning to examine the kinetics of this phenomenon and its relationship to the nucleation of minerals on bacterial surfaces.
Bioremediation of AMD. The bioremediation of AMD by dissimilatory sulphate reducing bacteria results in the formation of amorphous metal sulphides. Since amorphous sulphides are extremely labile, diagenesis to more stable, crystalline mineral forms is required for long-term disposal. While sulphide mineral diagenesis has been described in anaerobic systems, the underlying mechanism is not understood. Recent in vitro studies in my laboratory have demonstrated that crystalline metal suphides result from anaerobic bacterial diagenesis. I am planning to examine the relationship between the kinetics of sulphate reduction, bacterial biomass formation and sulphide mineral diagenesis in industry-scale bioremediation processes for the treatment of AMD.
Placer gold formation. The physical model for the formation of large gold nuggets does not account for the growth of nuggets two orders of magnitude larger than the host material from which they are formed. I have shown that labile bacterial organics have the capacity to solubilize elemental gold leading to the precipitation of crystalline octahedral gold. I am currently extending this experimental model into natural systems through the examination placer and lateritic weathering environments.
The field of geomicrobiology is rapidly expanding as bacteriological processes are being discovered that explain anomalies previously considered belonging to the realm of geochemistry. I intend to continue to contribute to the fundamental understanding of these underlying processes and to link them to industrial applications for the bioremediation of inorganic pollution.
