A fundamental question in biology that remains to be understood is how cell shapes are geneticallyencoded and enzymatically generated. Spheres and rods are among the most common shapes adopted bywalled bacteria. The bacterial cell wall, formed by peptidoglycan, largely determines cell shape. When bacteriareproduce by binary fission (division), the shapes of the two daughter cells are already determined by theirmother cell. For this reason, it is difficult to explore the origin of cell shape using healthy bacterial cells. Takingadvantage of a sphere-to-rod morphological transition during the germination of the bacterium Myxococcusxanthus, we propose to explore the mechanisms underlying the generation and maintenance of rod-like cellshapes. Cells of M. xanthus change back and forth between rods and spheres at different life stages. Rod-shaped vegetative cells thoroughly degrade their walls and shrink into uniformly sized spherical cells that thenmature into spores. Unlike endospore formation in Bacillus species, whole M. xanthus cells convert to spores.As the spores of M. xanthus germinate, cells rebuild their walls and reestablish rod shape without preexistingtemplates. This unique morphological transition provides a rare opportunity to visualize de novo cell wallsynthesis (CWS) and bacterial morphogenesis. To understand the mechanism of morphogenesis in M.xanthus, we propose three specific aims. First, to reveal the mechanism of de novo CWS during germination,we will test the hypothesis that a defined pattern of cell wall growth is required for the establishment of rodshape. Second, to elucidate the mechanism by which the MreB cytoskeleton supports rod shape duringgermination, we will test the hypothesis that MreB determines rod shape by guiding the motion of the CWSmachinery. Third, to reveal the mechanism by which cell polarity regulates CWS and rod shape in germinatingspores, we will test the hypothesis that the establishment of cell polarity is necessary for the sphere-to-rodtransition. Because the peptidoglycan cell wall is widely conserved among bacteria, we expect that our resultswith M. xanthus will reveal fundamental mechanisms of morphogenesis, which is difficult to study in otherbacteria.
