Professor Geoffrey Gadd
1. Metal and mineral transformations by microorganisms
Microorganisms are intimately involved in soil processes that affect contaminant bioavailability. The balance between metal mobilization and immobilization varies depending on the organisms involved, their environment and physico-chemical conditions. For metal (and metal radionuclide) contaminants, mobilization can arise from leaching mechanisms, and complexation by metabolites. Immobilization can result from sorption, transport and intracellular sequestration or precipitation as organic and inorganic compounds. However, there is a lack of detailed information on the relative importance of these processes in terrestrial systems, the nature of the communities involved, or their significance both in engineered soil remediation solutions and in natural attenuation of contaminated sites. An understanding of microbial determination of metal bioavailability is essential for any attempts at remediation. Although prokaryotes (bacteria and archaea) dominate microbial communities under anaerobic conditions, fungi are ubiquitous in aerobic soils and often dominate the microbiota in low pH and metal-polluted systems. Fungi often have the largest biomass of all organisms present while their symbiotic association (mycorrhiza) with over 80% of terrestrial plant species has profound consequences for geochemical processes in the soil and root environment. However, fungal importance in geochemical activities has often been underestimated. In terrestrial environments, fungi promote rock weathering and contribute to the dissolution of mineral aggregates in soil through excretion of H+, organic acids and other ligands, or through redox transformations of mineral constituents. Fungi also play an active or passive role in mineral formation through precipitation of secondary minerals, e.g. oxalates, and through the nucleation of crystalline material onto cell walls that can result in the formation of biogenic micro-fabrics within mineral substrates. Such interactions between fungi and minerals are of importance to biogeochemical cycles including those of C, N, S and P.
This PhD project therefore seeks to assess and characterize key fungal processes which affect the bioavailability of metals in the terrestrial environment, and will employ a range of chemical, biochemical and molecular techniques. In addition, the project will provide training in methodologies and approaches of direct relevance to bioremediation and environmental management.
Applications are invited from graduates who possess a good Honours degree (2.1 or above) in microbiology, environmental chemistry, or biology, or other relevant discipline to work in an active multi-disciplinary and internationally-acclaimed research environment. Experience of molecular methods in microbiology and biological chemistry would be advantageous. Only UK residents are eligible for this research-council funded position.
References
1. Fomina, M., Hillier, S., Charnock, J.M., Melville, K., Alexander, I.J. and Gadd, G.M. (2005). Role of oxalic acid over-excretion in toxic metal mineral transformations by Beauveria caledonica. Applied and Environmental Microbiology 71, 371-381.
2. Gadd, G.M., Semple, K. and Lappin-Scott, H. (eds) (2005) Microorganisms in Earth Systems – Advances in Geomicrobiology, Cambridge University Press, Cambridge .
3. Gleeson, D.B., Clipson, N.J.W., Melville, K. , Gadd, G.M. and McDermott, F.P. (2005). Mineralogical control of fungal community structure in a weathered pegmatitic granite. Microbial Ecology 50, 360-368.
4. Gleeson, D.B., Kennedy , N.M. , Clipson, N.J.W., Melville, K. , Gadd, G.M. and McDermott, F.P. (2006). Mineralogical influences on bacterial community structure on a weathered pegmatitic granite. Microbial Ecology51, 526-534.
5. Hockin, S. and Gadd, G.M. (2003). Linked redox-precipitation of sulfur and selenium under anaerobic conditions by sulfate-reducing bacterial biofilms. Applied and Environmental Microbiology69, 7063-7072.
6. Hockin, S. and Gadd, G.M. (2006). Removal of selenate from sulphate-containing media by sulphate-reducing bacterial biofilms. Environmental Microbiology 8, 816-826.
2. Mathematical Modelling of Fungal Growth in Terrestrial Systems (joint with Dr Fordyce Davidson, Division of Mathematics)
Filamentous fungi are of fundamental importance in terrestrial ecosystems, playing important roles in decomposition, nutrient cycling, plant symbiosis and pathogenesis. They also have significant potential in several areas of environmental biotechnology such as biocontrol and bioremediation. Most species of fungi form a mycelium, i.e. a dense, interconnected network of tubes called hyphae. In all of these contexts, the fungi are growing in an environment exhibiting spatial and temporal heterogeneity. The complexity of their growth habit combined with this environmental heterogeneity, means that the role of fungi in this context is very difficult to investigate by experimental methods alone. Mathematical modelling is now proving to be a very powerful and successful complimentary tool. The mathematical models we have developed over recent years fall into two broad categories: continuum models and discrete models. The former usually comprise systems of ordinary or partial differential equations in which the variables represent the density of, e.g. fungal biomass or a substrate (an energy source such as carbon). We have developed and analysed complex models of this type, which have allowed us to address key question regarding the way in which the fungal networks grows and functions in heterogeneous environments.
This project aims to develop our mathematical modelling approach in conjunction with experimentation, to characterise fungal growth in key terrestrial systems, e.g. soil, rock and mineral substrata, especially in relation to effects of fungal colonisation and biotransformation of mineral-based substrata. These will include rocks and building materials such as stone and concrete. Specific objectives of the project will be to develop and analyse multi-substrate continuum models to better understand the complex biochemical interactions of specific classes of fungi with mineral substrata. This will lead to the development of a discrete model with which the physical and chemical interactions of the developing fungal network with the structure of the substratum will be more fully investigated.
References
1. Boswell, G.P., Jacobs, H., Davidson, F.A., Gadd, G.M. and Ritz, K. (2002). A positive numerical scheme for a mixed-type partial differential equation model for fungal growth. Applied Mathematics and Computation 138, 321-340.
2. Boswell, G.P., Jacobs, H., Davidson, F.A., Gadd, G.M. and Ritz, K. (2002). Functional consequences of nutrient translocation in mycelial fungi. Journal of Theoretical Biology217, 459-477.
3. Boswell, G.P., Jacobs, H., Ritz, K., Gadd, G.M. and Davidson, F.A (2003). A mathematical approach to studying fungal mycelia. Mycologist 17 , 165-171.
4. Boswell G.P., Jacobs H., Davidson F.A., Gadd G.M. and Ritz K. (2003). Growth and function of fungal mycelia in heterogeneous environments. Bulletin of Mathematical Biology 65, 447-477.
5. Burford, E.P., Fomina, M. and Gadd, G.M. (2003). Fungal involvement in bioweathering and biotransformation of rocks and minerals. Mineralogical Magazine 67, 1127-1155.