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.
I. A renewed view on the complex community of nitrite oxidizing bacteria derived from sewage
It is well known that Nitrospira is the key organism of nitrite oxidation in wastewater treatment plants. Nevertheless, physiology of such bacteria is not investigated in detail, since they are hard to maintain in the lab. However, our findings verify that environmental variables decide in terms of niche separation and vice versa, novel NOB can be obtained by a directed cultivation approach using competitive conditions. We successfully cultivated novel species of Nitrospira and Nitrotoga to extend the set of reference organisms for phenotypic and genomic investigations. Selected physiological characteristics were compared in order to understand the driving forces for shaping diversity of nitrite oxidizers.
II. Application of marine microalgae for management of heterotrophic and nitrifying bacterial communities in recirculating aquaculture plants for larvae (MiBiFisch)
Recirculation aquaculture systems gain increasing attention worldwide with minimum ecological impact for the production of aquatic food. To maintain the water quality, purification is performed in biofiltration systems, which are attractive habitats for microbial communities. Communities of nitrifying and probiotic bacteria are supposed to reduce colonization of carrier elements with heterotrophic and pathogenic bacteria, since they compete for oxygen, ammonia, other nutrients and surfaces. The goal of this project is to develop a product suitable to prevent proliferation of pathogenic bacteria and to establish nitrifying biofilms for larval rearing systems.
Our cooperation partners are coworkers at the GMA (Gesellschaft für Marine Aquakultur, Büsum) and BlueBioTech (Mikroalgen Biotechnologie, Büsum).