Adrián Martínez Bonilla from the Institute for Sanitary Engineering, Water Quality and Solid Waste Management of the University of Stuttgart, will give the Pretty Porous Science Lecture #74 on the topic "Role of endolithic microorganisms in nitrate turnover within the Ammer river catchment".
Date: 16 April 2026
Time: 4 pm
Title: "Role of endolithic microorganisms in nitrate turnover within the Ammer river catchment"
Location: Multi Media Lab, University of Stuttgart, Pfaffenwaldring 61, 70569 Stuttgart
Abstract
The application of nitrogen fertiliser is the main cause of NO3- contamination in groundwater. Concentrations above 50 mg/L have frequently been observed in the recharge zone of the Ammer River catchment in south-west Germany. However, the anoxic groundwater in the confined part of the aquifer usually contains around 1 mg/L of NO3-. This attenuation is thought to be caused by microorganisms which can conduct denitrification, thus decreasing the NO3- concentration in the aquifer. To study this process, we carried out exploratory drilling in the transitional zone of the catchment and retrieved Muschelkalk cores. The cores were used i) to identify potential electron donors, ii) to analyse the endolithic microbial community and iii) to enrich key denitrifying microorganisms.
We have reported the presence of different electron donors in the subsurface of the area, like pyrite (FeS2), H2 and CH4. Furthermore, we analysed the composition of the microbial communities from the groundwater and the endolithic community using 16S rRNA gene metabarcoding and enriched microorganisms that could be involved in the denitrification that takes place in the aquifer. This includes microorganisms capable of coupling NO3- reduction with oxidation of Fe(II), reduced S species, H2, CH4 and organic matter.
However, it is still unknown whether the denitrification is conducted by the planktonic community found in the groundwater or by the microorganisms associated with the porous rock matrix. To address this question, we have designed diffusion cells containing synthetic rock discs that have a mineral composition and porosity similar to that of the rock matrix found in the aquifer. These cells will be used to determine whether NO3- reducing Fe(II) oxidizing (NRFeOx) microorganisms enriched from the aquifer can colonise the porous, FeS2-containing synthetic rock matrix and use minerals as electron donors for NO3- reduction.
About Adrián Martínez Bonilla
Adrian Martinez Bonilla studied a Bachelor's degree in Biochemistry and a Master's degree in Microbiology at Universidad Autónoma de Madrid (Spain), where he also obtained his PhD in Microbiology in 2025. His PhD research focused on studying anaerobic Fe(II) oxidation by microorganisms from the deep subsurface of the Iberian Pyrite Belt and how this relates with Rio Tinto's extreme characteristics. Then he started as a postdoctoral researcher in the Department of Environmental Microbiology at ISWA, Stuttgart University, studying the microorganisms involved in nitrate reduction in the aquifer of the ‘Bronnbachquelle’ catchment.