E. coli's Chemotaxis Network
Cells arrange their components—proteins, lipids, and nucleic acids—in organized and reproducible ways to optimize the activities of these components and, therefore, to improve cell efficiency and survival. Eukaryotic cells have a complex arrangement of subcellular structures such as membrane-bound organelles and cytoskeletal transport systems. However, subcellular organization is also important in prokaryotic cells, including rod-shaped bacteria like Escherichia coli, most of which lack such well-developed systems of organelles and motor proteins for transporting cellular cargoes. In fact, it has remained somewhat mysterious how bacteria are able to organize and spatially segregate their interiors.
To understand how chemotaxis receptor clusters form and what controls their size and density, photoactivated localization microscopy (PALM) is used to visualize individual chemoreceptors in single E. coli cells. From these high-resolution images (like the one shown above) it is apparent that receptors are not actively distributed or attached to specific locations in cells. Instead, random receptor diffusion and receptor–receptor interactions are sufficient to generate the observed complex, ordered pattern. This simple mechanism, termed stochastic self-assembly, may prove to be widespread in both prokaryotic and eukaryotic cells.
Image courtesy of Derek Greenfield and Ann L. McEvoy, University of California, Berkeley.