DNA outside of cells may account for the largest fraction of total DNA in many environments such as the oceans and their sediments. This cell-free DNA (cfDNA) can either be dissolved, complexed or adsorbed onto particles and minerals and is the product of active or passive release from organisms. Depending on environmental conditions, cfDNA may persist undamaged for thousands of years and therefore provides an archive of genetic information that can be used to reconstruct past changes in biodiversity. Furthermore, cfDNA might be the source of genetic material that quickly spreads through biota via horizontal gene transfer, hence contributing to the speed of adaptation and therefore evolutionary plasticity. Despite the significance of cfDNA, there was no method available to isolate and purify it from environmental samples without contamination by DNA released from cells. To overcome this challenge, we developed a non-disruptive, non-invasive and targeted method for ‘fishing’ cfDNA from water samples based on a modified CRISPR/Cas system developed in our laboratory. The student will use cultures of various different aquatic microbes (e.g. bacteria, microalgae, fungi) which will grow under different condition to see if and when they actively or passively release DNA. Furthermore, the student will sample natural aquatic environments including lakes, rivers and different oceans to isolate and sequence cell-free phylogenetic marker genes (16/18S) and selected cell-free functional genes (e.g. hydrolases). To compare these results to DNA from inside cells, the student will isolate cells from the same samples, extract their DNA and sequence the same genes targeted for cfDNA. Thus, this study will incept the field of environmental genomics of cfDNA and will provide first insights into the biodiversity of cfDNA vs cell-bound environmental DNA from diverse aquatic environments. Consequently, the student will benfit from working with a cutting-edge method that potentially produces transformative research in a highly collaborative environment as demonstrated by the multidisciplinary nature of the supervisory team. We are looking for an enthusiastic student with expertise in either of the following areas of research: molecular biology/ecology, evolution, bioinformatics.