Salmonella “syringe” ready for its close-up

Salmonella bacteria are tiny, but they wreak mighty havoc on human health, causing serious, sometimes fatal, food poisoning. In 1998, Jorge Galán, Ph.D., D.V.M., the Lucille P. Markey Professor of Microbial Pathogenesis, threw new light on Salmonella’s virulence when his research team revealed that the bacteria infects cells by forming “needle complexes,” syringe-like tubes through which Salmonella exchanges proteins with its host.

Now Galán and his colleagues have joined forces with the laboratory of Vinzenz M. Unger, Ph.D., associate professor of molecular biophysics and biochemistry, to paint a vivid three-dimensional portrait of the Salmonella syringe using a state-of-the-art technique known as cryoelectron microscopy.

In this method, an electron microscope scans samples that contain many copies of the object of interest suspended in an ice-like solid at every possible angle (background in image at right). Researchers then feed scores of images of the object seen from these myriad perspectives to powerful computers, which combine the information in the two-dimensional views to calculate the object’s three-dimensional structure.