Cell wall deficient (L-form) bacteria are thought to be important in various resistant, persistent or chronic infections. L-form cells are highly abnormal in size and shape and are sensitive to osmotic shock but highly resistant to antibiotics that work on the cell wall (e.g. penicillins and cephalosporins). How these unusual cells arise and how they proliferate in the absence of a wall, is poorly understood. The Errington lab recently developed a model system for studying this long standing problem in the tractable model bacterium Bacillus subtilis. A key element of L-form biology that awaits further investigation lies in how these cells revert to the walled state. This reversion or regeneration requires the resumption of cell wall synthesis and the reacquisition of the normal regular rod cell shape. Regeneration is presumably important for the resumption of disease in patients with persistent or recurrent infections. Therefore, blocking regeneration might offer a way of dealing with problem infections. A better understanding of the mechanisms of regeneration might also be important for various biotechnological applications. The aims of this proposal are as follows. First, to use state of the art imaging methods to characterise the poorly understood regeneration process. Second, to attempt to identify mutations that prevent or enhance the rate of regeneration, and characterise the genes affected, so as to understand the process better. The genes identified might provide novel targets for drugs to target persistence. Finally to explore the extent to which regeneration of L-forms can be exploited as a novel vehicle for efficient transformation or genome transplantation processes.