Evaporation from bare soils is a key hydrological process. This macroscopic phenomenon is governed at the microscale by capillary flows along water films between the top of the soil and the water at depth. The stability of these films is crucial to efficient drying and is highly sensitive to the physico-chemistry of the soil such as the surface tension at air-water interfaces. In soil, bacteria abound, with billions of bacteria per gram of top soil. Many of them release surfactants in their surroundings which can strongly decrease the surface tension at air-water interfaces and change the contact angle. To date, however, little is known about the potential impact of these bacteria on drying dynamics. How do surfactants accumulate at drying interfaces? Does bacterial behavior, in particular motility by swimming, modify this accumulation dynamics? What are the consequences on the interface behavior inside the soil pores? The aim of this internship is to work with an original experimental setup designed to follow the deformation of a single air-water interface which is put under evaporative forcing in the presence of surfactants. More precisely, the trainee will try to shed light on how bacterial motility could change the distribution of surfactants in the bulk and at the air-water interface. To do so, the trainee will combine direct observations of the air-water interface with individual bacteria tracking in a microfluidic chip which is put under evaporative forcing.