PD Dr. Eva Spieck
Biological oxidation of ammonia to nitrite and further to nitrate has an immense impact for the functioning of the nitrogen cycle in natural and man-made ecosystems. We are interested in studying the diversity of nitrifying microorganisms in moderate and extreme environments by using cultivation-dependent and molecular methods.
Our main topic is the selective enrichment of novel nitrite oxidizing bacteria and one hot spot of so far unknown representatives are geothermal settings. Recently, we successfully isolated a typical member of such habitats, subsequently named Nitrospira calida. In addition, we characterized the moderately thermophilic ammonia oxidizing archaeon ‘Candidatus Nitrososphaera gargensis’, originating from Garga hot spring in Siberia by genome sequencing.
In 2007, we described a novel cold-adapted betaproteobacterium existing in permafrost-affected soils in the Siberian Arctic as ‘Candidatus Nitrotoga arctica’. This nitrite oxidizer is found in co-existence with other genera such as Nitrospira and Nitrobacter also in activated sludge.
In sewage-derived experiments, we could show that the nitrite oxidizing community is mainly influenced by nitrite and temperature. By the use of several new Nitrospira isolates, we could uncover ecological niche separation in dependence on various environmental factors.
Nitrifying biofilms are also relevant for biofiltration in aquaculture plants, were ammonia and nitrite oxidizers are covering carrier elements. Our goal is to investigate nitrification efficiency with regard to N-load and operational parameters.
In kinetic experiments, the substrate affinity of nitrite oxidizers was analyzed and it was shown that the Km value for nitrite of Nitrospira and Nitrotoga is clearly lower in comparison to Nitrobacter, which otherwise revealed the highest maximum activity Vmax.