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H4 - Redox gradients in natural and technical urban water systems: population structure and physiological properties

Doctoral student: Niranjan Mukherjee

Supervisors: Prof. Dr. Ulrich Szewzyk, Dr. Burga Braun, Prof. Dr. Mark Gessner, Dr. Peter Casper


A redox gradient is the formation of different redox couples along a certain depth in natural and technical urban water-sediment systems due to the depletion of oxygen. In this project, redox gradients in the hyporheic zone or the surface water-groundwater interface are being studied (Fig. 1). This zone is known to have diverse redox conditions such as oxic, suboxic and anoxic (Schaper et al. 2019) and harbours correspondingly diverse microbial communities.

All over the world, demographic changes resulted in an increasing demand and consumption of pharmaceuticals and as a consequence, pharmaceutical residues released by wastewater treatment plants pose a threat to environmental processes (Ebele et al. 2017) mainly in urban water systems. As traces of pharmaceuticals have been detected in all parts of the water cycle, and even in drinking-water, the removal of these compounds is therefore of major concern. To study the degradation potential of the bacterial community of the hyporheic zone, iopromide, an iodinated X-ray contrast medium, has been chosen as it biotically transforms under oxic and anoxic conditions (El-Athman et al. 2019, Redeker et al. 2018, Schulz et al. 2008).

Figure 1 Redox gradient and associated microbial processes in the hyporheic zone (modified from Winter et al. 1998)


The aim of this project is to explore microbial community structures and functional profiles of gradient biofilms of the hyporheic sediment and lab-scale sediment reactors. The biological degradation process and dissipation potentials of iopromide in lab-scale reactors containing natural sediment cores, should be enhanced. To achieve this aim, it has to be determined, if the pollutant-degrading bacteria can live on trace pollutants alone or if they require co-substrates or partner organisms to maintain their energy metabolism. Significant interactions like syntrophy and co-metabolism between organisms for determining degradation efficiency can then be identified.


Sediment cores from the hyporheic zone are setup in a laboratory reactor under defined conditions (Fig. 2). Synthetic fresh water medium spiked with iopromide is used as a medium for the bioreactors. The formation of redox gradient is measured with dissolved oxygen, nitrate, sulphate, iron and manganese in pore water samples taken from ports vertically along the side of the column. The dissipation of iopromide and its transformation products are analysed by HPLC. On equilibration of the column, sediment cores will be removed and sliced. To get insights into the population structure and the functional aspects of the gradient microbial communities, sediments samples from different depth will be analysed.

Figure 2 Experimental setup of bioreactor containing sediment from hyporheic zone of river Erpe

Analysis of the bacterial population structure in different layers of the sediment cores will be performed using Illumina® Sequencing. Monitoring the abundance of specific bacteria according to the dissipation of pollutants will be done by quantification of bacterial genes by real-time polymerase chain reaction. For visualization of the distribution and localization of bacteria on sediment particles fluorescence in-situ hybridisation will be used in combination with confocal laser scanning microscopy. 

The second stage of the project would involve stimulating the growth of iron- and manganese- oxidizing bacteria within the above setup (Fig. 2) by simple addition of iron and manganese and evaluating the dissipation of iopromide in the presence of these bacteria.

Finally, it would be interesting to evaluate the influence of the WWTP effluent on the microbial population characteristics of the hyporheic zone sediment downstream. Using liquid chromatography Orbitrap mass spectrometry, microbial pathways for transformation can be identified.



Ebele, A. J., Abou-Elwafa Abdallah, M., & Harrad, S. (2017). Pharmaceuticals and personal care products (PPCPs) in the freshwater aquatic environment. Emerging Contaminants, 3(1), 1–16. doi.org/10.1016/j.emcon.2016.12.004

El-Athman, F., Adrian, L., Jekel, M., & Putschew, A. (2019). Abiotic reductive deiodination of iodinated organic compounds and X-ray contrast media catalyzed by free corrinoids. Chemosphere, 221, 212–218. doi.org/10.1016/j.chemosphere.2019.01.003

Redeker, M., Wick, A., Meermann, B., & Ternes, T. A. (2018). Anaerobic Transformation of the Iodinated X-ray Contrast Medium Iopromide, Its Aerobic Transformation Products, and Transfer to Further Iodinated X-ray Contrast Media. Environmental Science & Technology, 52(15), 8309–8320. doi.org/10.1021/acs.est.8b01140

Schaper, J. L., Posselt, M., Bouchez, C., Jaeger, A., Nuetzmann, G., Putschew, A., … Lewandowski, J. (2019). Fate of Trace Organic Compounds in the Hyporheic Zone: Influence of Retardation, the Benthic Biolayer, and Organic Carbon. Environmental Science & Technology, 53(8), 4224–4234. doi.org/10.1021/acs.est.8b06231

Schulz, M., Löffler, D., Wagner, M., & Ternes, T. A. (2008). Transformation of the X-ray Contrast Medium Iopromide In Soil and Biological Wastewater Treatment. Environmental Science & Technology, 42(19), 7207–7217. doi.org/10.1021/es800789r

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