Visualizing Bacterial Cell Walls and Biofilms

T he surfaces of microbial cells are perhaps their most important structure because they are in immediate contact with the external environment. Microbial cell walls admit nutrients and release wastes, and yet they must resist internal turgor pressure and environmental insults and maintain cellular shape. Walls also help cells adhere to other surfaces and provide space for specialized structures such as flagella, pili, spinae, capsules, S-layers, and exopolymeric substances (EPS). Delving into the native architecture of gramnegative and gram-positive bacterial surfaces traditionally depended on electron microscopy, which uses high vacuums and high electron accelerating voltages. These requirements usually ensure that only dry specimens can be imaged, yet living cells and their structures rely on water and its astounding ability to interact with and configure molecular ingredients. However, advances in cryo-transmission electron microscopy (cryoTEM) are helping to overcome this difficulty because they allow investigators to examine native, hydrated structures in bacteria and their associated biofilms.