Every time we take medicine, it is excreted via the urine reaching rivers and even drinking water at low concentrations. This happens because environmental microorganisms do not have yet the necessary molecular tools to break the complex chemical structures of medicines. However, some substances are partially or totally removed from (waste)water by microorganisms, and this thesis investigated the mechanisms underlying this process. We learned that higher medicine concentrations normally increase removal rates. Furthermore, complete ammonia-oxidizing bacteria were more successful than canonical nitrifiers in the conversion of benzimidazole fungicides. Finally, we identified gene candidates responsible for the conversion of paracetamol in wastewater treatment plants (i.e. amidases, dioxygenases). Mobile genetic elements were present near these catabolic genes, so they might be exchanged between bacteria in a similar way as antibiotic-resistant genes. In conclusion, this thesis increased our knowledge about the microbial degradation pathways of medicines, which will be useful to improve risk assessment models and guide the design of novel processes to remove medicines from water.
Ana Belén Ríos Miguel was born on July 12th 1993 in Burgos, Spain. She always enjoyed mathematics and other (natural) science courses in school, so she decided to study the Bachelor in Biotechnology at the University of Salamanca, Spain. After obtaining the Bachelor’s degree in 2015, she continued her career abroad by enrolling the Master in Microbiology at Radboud University, The Netherlands. During the two Master internships, she specialized in metabolic modeling of infectious diseases. She completed the Master’s degree in 2017 with a cum laude grade. Missing the combination of lab work and data analysis, she started a PhD in the department of Microbiology at Radboud University under the supervision of dr. Cornelia Welte and prof. dr. Mike Jetten. She investigated the microbial removal of pharmaceuticals under wastewater treatment plant conditions. The research conducted during the PhD period (2018-2022) is described in this thesis.