Aerotaxis in Sinorhizobium meliloti, a soil bacterium

The legume family needs the help of soil bacteria to fix the atmospheric nitrogen they need to grow. In order to do so, such bacteria, called rhizobia, are swimming towards the plants by following the chemical gradient created by their roots. One of the most common member of the rhizobia family, Sinorhizobium meliloti, is displaying this chemotactic behaviour as well as an aerotactic one. To study and compare this not yet referenced aerotaxis to the already found chemotaxis, we made a few experimental set-ups. The first one consists of a sealed chamber containing S. meliloti, in which we insert an air bubble. The second one is a capillary filled with bacteria, sealed at one end and closed with PDMS at the other. In these experiments, we notice the formation of a profile of motile bacteria peaked at the interface with the air bubble or the PDMS. We also uses microfluidic devices to control the oxygen gradient in which the bacteria are swimming. The characterization of the swimming behaviour in presence of oxygen will help us understand the motility of S. meliloti in situ, and thus could lead us to some culture optimizations.