Research Stay Abroad at the Princeton University (USA) by SFB 1313 Doctoral Researcher Christoph Lohrmann

Christoph Lohrmann from the Institute for Computational Physics (ICP) of the University of Stuttgart is a associated doctoral researcher (research project C01) and member of the SFB 1313 Integrated Research Training Group "Interface-Driven Multi-Field Processes in Porous Media". He visited the Princeton University (USA) from February to May 2023.

I met Sujit Datta at the InterPore conference where we connected and established a collaboration for research concerning the swimming behaviour of bacteria in complex environments like tightly confining porous media. The research stay was planned to happen in 2021 but due to the pandemic it was delayed so much that the original project was finished by the time Princeton reopened its visiting program. New projects were quickly found though, so I could start my work at Princeton University.

The first project includes the chemotactic motion of bacteria, that is, their ability to sense chemical gradients and swim along them. For example, they drift towards Oxygen or nutrients, but swim away from toxins. Run-and-tumble bacteria like E. Coli have two strategies to induce this drift: They can prolong the run phase when swimming up the gradient and also decrease the (average) tumbling angle. I performed particle-based simulations of chemotactic bacteria^in porous media to assess the efficiency of both strategies. The numerical algorithms for the two strategies reproduce the experimentally observed drift towards the source of a nutrient, with a smaller drift velocity at smaller porosities. The main finding is that run length variation always outperforms tumble angle variation for all geometries.

The second project investigates a different complex environment for bacteria, namely one where bacteriophages are present. These viruses are passively diffusing entities that can attach to, infect, and kill bacteria. I simulated the hydrodynamics of bacterial swimming to assess the influence of motility on the rate of infection. The main finding is that the inclusion of hydrodynamics in the model is crucial for the estimation of encounter rates. Models without this level of detail significantly overestimate the infection rate and consequently the evolutionary cost of swimming.

Doing research and living in Princeton was a great experience. The university is a beautiful place with historic buildings on a park-like campus that houses world class research facilities and staff that provide a stimulating scientific environment. But what made the stay truly memorable were the many connections and friendships formed at the Datta lab and the graduate college. A special shout-out goes to Sujit Datta, the Datta lab patio lunch crew, and the CBE G1 cohort for welcoming me with open arms and making Princeton a home away from home.