Aerotactic response of bacteria: experimental characterization at the bacteria scale and population scale

Many environmental bacteria use their flagellar motility to find optimal regions for their development, they bias their swimming in response to chemical signals. The drift velocity associated to this response is proportional to the local concentration gradient of the signals and the chemotactic sensitivity coefficient. Although studied for many years, the dependence of this sensitivity coefficient with concentration is still debated. In our study, suspensions of Burkholderia contaminans are placed in a capillary sealed at one end and permeable to oxygen at the other end. The oxygen consumption of the bacteria in the capillary produces a gradient in which the bacteria move. By monitoring the concentration and velocity of bacteria, as well as the oxygen concentration along the capillary using encapsulated Ruthenium dye, we uncover the aerotactic sensitivity dependence on the oxygen concentration. In addition to this macroscopic approach, we also determine this cell sensitivity from modulation of the run-time distribution with swimming direction. Our multiscale approach sheds new light on the different theoretical models that have emerged from the Keller-Segel equations over the past fifty years.