To colonize surfaces, bacteria must adhere and proliferate. How those terms compete to shape the foundations of biofilm is barely understood. When bacteria grow between a coverslip and a gel pad, they form microcolonies, which develop initially in a plane before terraces establish at their centre. In this configuration, we developed methods to probe adhesion at the scale of the microcolony and at the single cell level. We evidenced that adhesion is stronger at the old pole. During surface colonization, cell elongation is able to rupture the adhesive bonds of surrounding bacteria regardless of their position in the microcolony. However, the shape of microcolonies depends on the level of adhesion and the transition from 2D expansion to 3D growth is linearly corrleated to the strength of adhesive bonds. Finally, we showed that the microcolony of P. aeruginosa adapts its morphogenesis to maximize cell-cell contacts rather than cell-environment interactions when iron becomes scarce in the environment. In this case, reducing the surface of exchange with the environment allows to limit the loss of secreted molecules required to efficiently fetch extracelllular iron at very low concentration.
Lunch @ 11:45, seminar 12-1:00