| Wetland plants are adapted to anoxic conditions as they prevail under waterlogged conditions. By the formation of aerenchyma these plants are able to maintain oxic conditions in their root system as well as in some parts of in the so-called rhizosphere outside the roots. By doing so, the plants favour chemical and microbial oxidation processes and hence interfere with all kind of geochemical cycles in the otherwise anoxic environment. The presence of plaques of oxidised iron around the roots of wetland plants indicate an active iron cycling in the rhizosphere. Although the role of iron-oxidising bacteria in the deposition of iron around the roots of wetland plants is more and more recognised, hardly anything is known yet about the biotic and abiotic constraints of this microbial activity under natural conditions. Iron-oxidising bacteria have to compete with other oxygen-consuming processes, both microbial and chemical. The nature of the oxidised rhizosphere is very complex with respect the fluxes of oxygen and oxidised and reduced compounds. Therefore unravelling the role of microbial activity in iron deposition requires a combination of field and model studies, as well as the collaboration between microbial ecologists and geochemists. In this project relevant iron-oxidising bacteria will be enriched and isolated in pure culture from the iron plaques of wetland plants from three contrasting iron-rich locations in freshwater and brackish environments. The isolated strains will be identified by genetic and biochemical tools and their distribution in nature will be studied by application of molecular probes. Their activity will be studied in model systems in the laboratory, among which oxygen-limited chemostats, artificial root systems and gnotobiotic plant systems. Special emphasis will be given to the competitive abilities of iron-oxidising bacteria under oxygen-limited conditions in comparison to chemical and other oxygen-consuming microbial processes. |
