Deciphering the dual chemotaxis strategy of bacteria in porous media

Chemotaxis of bacterial swimmers that move in a run-and-turn pattern is well studied in uniform bulk fluid. It is primarily based on modulating the run time in dependence on the swimming direction with respect to the source of chemoattractant (run time bias). Here, we provide evidence that the lophotrichously flagellated soil bacterium Pseudomonas putida may also perform chemotaxis in porous media where the free path length is severely restricted. Besides the classical run time bias, we identify a second chemotactic strategy: the change in swimming direction upon a turn event is adjusted, so that the direction of the next run phase is biased towards the source of chemoattractant (turn angle bias). Agent based simulations, based on the experimentally observed statistical properties of the swimming pattern, indicate that turn angle bias is the predominant chemotaxis strategy of bacteria in porous environments.