On the ecology of dissimilatory nitrate reduction to ammonium

The anthropogenic nitrogen inputs in the environment exceed the input by natural processes and impact the global nitrogen cycle considerably . Human meddling in the N-cycle occurs mainly in agricultural ecosystems. Loss of nitrogen from the agricultural soils, other than crop harvest, can have polluting effects on other environments. The three main processes through which the losses occur are ammonia volatilization, the production of gaseous nitrogen compounds and leaching of nitrate , contributing to acid rain, ozone depletion and eutrophication respectively. To reduce N-pollution and improve mitigation strategies, we need to expand our understanding of the metabolic and environmental controls of the nitrogen cycle processes. This thesis focuses on the microbial competition for nitrate between two dissimilatory nitrate reduction processes in the nitrogen cycle, as the different end-products entail important biogeochemical consequences for nitrogen retention in aquatic ecosystems such as wastewater treatment plants, as well as the successful operation of wastewater treatment systems. Nitrate can be reduced to nitrogen gas in the denitrification process, removing the nitrogen from the environment, which is desired for alleviation of eutrophication or treatment of waste water. Alternatively, in the process of dissimilatory nitrate reduction to ammonium (DNRA), ammonium is the end product, and the nitrogen is conserved in the environment, which can be beneficial in fertilizer management.