In bacteria, the though external cell wall and the intracellular actin-like (MreB) cytoskeleton are major determinants of cell shape. The biosynthetic pathways and chemical composition of the cell wall, a three dimensional polymer network that is one of the most prominent targets for antibiotics, are well understood. However, despite decades of study, little is known about the complex cell wall ultrastructure and the molecular mechanisms that control cell wall morphogenesis in time and space. In rod-shaped bacteria, MreB homologues assemble into dynamic structures thought to control shape by serving as organizers for the movement and assembly of macromolecular machineries that effect sidewall elongation. However, the mechanistic details used by the MreB cytoskeleton to fulfil this role remain to be elucidated. Furthermore, development of high-resolution microscopy techniques has led to new breakthroughs this year, published by our lab and others, which are shaking the model developed over the last decade and re-questioning the MreB “actin cytoskeleton” designation.The aim of this project is to combine powerful genetic, biochemical, genomic and systems biology approaches available in the model bacterium Bacillus subtilis with modern high-resolution light microscopic techniques to study the dynamics and mechanistic details of the MreB cytoskeleton and of CW assembly. Parameters measured by the different approaches will be combined to quantitatively describe the features of bacterial cell morphogenesis.