Department of Applied Environmental Science, Stockholm University, Sweden e-mail: email@example.com
Microbial mobilization of Fe and other trace elements in fresh waters: the role of siderophores produced by P. fluorescens
The titel abowe is the titel of my PhD projekt plan and I was accepted as a graduate student 1 feb 2005.
The main focus of the study is on the natural microbiological cycling of metals in potential water reservoirs such as lakes and groundwater. The objective of the experiments (Kalinowski et al 2006, Edberg 2007 and Edberg et al manuscript) presented here was to examine the chelating properties of siderophores produced by Pseudomonas fluorescens cultivated in presence of acid leached ore from the former uranium mine in Ranstad. The properties were examined with respect to metal mobilisation and the detection of free as well as metal complexed siderophore.
Iron is an essential element for numerous metabolic processes, e.g. nitrogen fixation and photosynthesis, in terrestrial and aquatic organisms, including bacteria, fungi and cyanobacteria. Due to the low solubility of Fe in nature, microorganisms produce Fe specific ligands, siderophores, to obtain this essential element. Even though, siderophores primarily are produced to obtain iron they have also been shown to bind other metals with high affinity. They have been shown to bind for eg; molybdenum, gallium, aluminum, lanthanides and actinides, which has led to the suggestion to use siderophores for bioremediation of metal contaminated soil. In the former uranium mine Ranstad, southern Sweden there are still problems with leaching of metals in spite of extensive clean up actions. It has been hypothesised that microbial processes could contribute to the metal leaching.
In two studies we have demonstrated that bacteria can promote metal mobilization, direct by ligand production and indirect by influencing pH. The bacteria; Pseudomonas fluorescens mobilise Fe, Ni and to some extent U from the ore. There is some difference in the light treatment indicating different chelating properties. The siderophore analysis indicates production of more than one siderophore with pyoverdine produced later in the stationary phase. We could also detect and estimate the amount of Fe-siderophore complexes. This shows that biomobilisation of metals could be of importance in mining areas and should be considered.
A study it planned to examine the production of bacterial ligands and the diversity of bacteria in lakes in the area close to the former uranium mine in Ranstad. The aim is to study chemistry and ligands as well as the microbial diversity in order to se if lignads produced by bacteria could influence the geochemistry of metals originating from the open pit mine or the covered piles of tailings.
Kalinowski, B.E, Johnsson, A, Ödegaard-Jensen, A, Arlinger, J, Edberg, F, Pedersen K. (2006). Microbial Mobilization of Uranium from Shale Mine Waste, Geomicrobiology Journal 23: 157-164. Edberg. F.(2007) Microbial mobilisation of Fe and other trace elements in fresh waters: the role of siderophores produced by Pseudomonas fluorescens. Licentiate Thesis, Department of Applied Environmental Scence, Stockholm University. Edberg, F., Kalinowski, B.E., Holm, K., Ek, J. Pyoverdine Production and Metal Mobilisation by Pseudomonas fluorescens. manuscript