In the last decade, the application of fluorescence microscopy techniques to bacteria has revolutionized our view of bacterial cell architecture. Recent advances have conclusively shown that prokaryotic cells, like eukaryotic cells, possess a complex, highly structured and dynamic subcellular organization, where proteins are targeted with spatial and temporal precision. Furthermore, it has been shown that bacteria possess distant but genuine homologues of the three main eukaryotic cytoskeletal proteins: actin (MreB), tubulin (FtsZ) and intermediate filaments (CreS). MreB proteins undergo actin-like polymerisation and form filaments similar to F-actin (filamentous actin) in vitro. In vivo, they assemble into highly dynamic helical filamentous structures that encircle the cytoplasm; just under the cell membrane. MreB cytoskeletal structures are essential for viability and direct cell morphogenesis (determination and maintenance of cell shape) in non-spherical bacteria. They are also involved in DNA segregation, cell polarity, and probably various other processes. However, the mechanistic details and the effector proteins used by MreB proteins to fulfil these roles remain almost completely unknown. The current view is that the actin-like cytoskeletal structures may serve as 'tracks' for the movement of proteins and molecular complexes to their sites of biological action. In particular, they would control cell shape by organizing the movement and assembly of macromolecular machineries that effect both insertion and degradation of the cell wall during elongation. Indeed, the tough cell wall (CW) is the main determinant of cell shape in bacteria, and the target of many antibiotics. The two types of bacterial walls (Gram+ and Gram-) have, independently of their shape, a common primary structure: the cross-linked polymer peptidoglycan (PG). The walls of Gram+ bacteria additionally contain anionic polymers, in particular teichoic acids (TA), that like PG play a key role in maintaining shape and integrity. Although the composition of the CW and the biosynthetic pathways of PG and TA precursors are known in detail, the factors controlling overall CW synthesis and structure remain largely unknown. Expansion of the CW is complicated because it requires insertion of new material during growth and formation of a crosswall (septum) during cell division without compromising wall integrity. Other physiological changes including the extrusion of appendages such as pili and flagella, protein secretion and DNA uptake also require CW modification. These various facets of the wall metabolism require the coordinated action of a large set of enzymes capable of continuously synthesizing and hydrolyzing the bonds of the CW polymers. Despite the important roles of these enzymes, virtually nothing is known about how their activities are spatially and temporally regulated to bring about controlled wall enlargement. The aim of this project is to determine the role(s) of the actin-like MreB cytoskeleton and the factors controlling bacterial cell morphogenesis by generating and combining genetic, genomic, microscopic, biochemical, physiochemical, transcriptomics and mathematical modelling information at a number of levels. Emphasis is given to an interdisciplinary approach to tackle significant biological problems. The rod-shaped Gram+ bacterium Bacillus subtilis will be used as model organism of study, but the conservation of the protein-protein interactions and their mechanisms of action will also be analyzed in other Gram+ bacteria. The proposed research work would mainly focus on four major challenges in the field: (i) to identify and characterise targets and effectors that move along and/or are positioned by the MreB filaments; (ii) to elucidate the mechanistic details of MreBs dynamics and morphogenetic function; (iii) to elucidate how MreB proteins are spatially and temporally organized, probably using other cellular factors and (iv) to determine the structure-regulation-properties of the bacterial CW during the cell cycle, and their relation with the actin-like cytoskeleton.