An Up-Close View of Bacterial "Motors"

Bacteria are the most abundant form of life on Earth, and they are capable of living in diverse habitats ranging from the surface of rocks to the insides of our intestines. Over millennia, these adaptable little organisms have evolved a variety of specialized mechanisms to move themselves through their particular environments. In two recent Caltech studies, researchers used a state-of-the-art imaging technique to capture, for the first time, three-dimensional views of this tiny complicated machinery in bacteria. "Bacteria are widely considered to be 'simple' cells; however, this assumption is a reflection of our limitations, not theirs," says Grant Jensen , a professor of biophysics and biology at Caltech and an investigator with the Howard Hughes Medical Institute (HHMI). "In the past, we simply didn't have technology that could reveal the full glory of the nanomachines-huge complexes comprising many copies of a dozen or more unique proteins-that carry out sophisticated functions." Jensen and his colleagues used a technique called electron cryotomography to study the complexity of these cell motility nanomachines. The technique allows them to capture 3-D images of intact cells at macromolecular resolution-specifically, with a resolution that ranges from 2 to 5 nanometers (for comparison, a whole cell can be several thousand nanometers in diameter). First, the cells are instantaneously frozen so that water molecules do not have time to rearrange to form ice crystals; this locks the cells in place without damaging their structure.