Active mechanics in the growth of a bacterial cell wall

It is well known that rod-shaped bacterial cell walls---a thin shell made of a disordered peptidoglycan network---grow rapidly in length. This speed allows cells to divide several times per hour. However, fast growth requires the cell to rapidly add material to a highly pressurized (osmotically) shell without bursting. The basic mechanism for growth is actively driven dislocations plowing through the shell in the circumferential direction. These motor-driven defects introduce new material (MreB filaments) into the shell but generate stress concentrations surrounding the moving defects. Motivated by the large deformations inherent in bacterial growth, we develop a nonlinear continuum mechanics model with actively driven dislocations to describe the growth of the cell wall. Using numerical simulations, we study the interaction of stress fields that arise as these filaments are added to the existing peptidoglycan mesh. Furthermore, we investigate how the growth mechanics are affected by fluctuations in turgor pressure, and the presence of heterogeneities and defects in the cell wall that can form during an osmotic shock or antibiotic treatment.