Self-Organization of the Escherichia Coli Chemotaxis Network Imaged with Super-Resolution Light Microscopy

The Escherichia coli chemotaxis network is a model system for signal transduction and processing. Chemotaxis receptors assemble into large clusters containing tens of thousands of proteins which have been observed at cell poles and future division sites. Despite extensive study, it remains unclear how chemotaxis clusters form, what controls cluster size and density, and how the cellular location of clusters is robustly maintained in growing and dividing cells. Here, we use a super-resolution optical technique called photoactivated localization microscopy (PALM) to map the cellular locations of three proteins central to bacterial chemotaxis (the Tar receptor, CheY, and CheW) with a precision of 15 nm. We find that cluster sizes are approximately exponentially distributed, with no characteristic cluster size. One-third of receptors are part of smaller lateral clusters that have not been previously observed. Analysis of the relative cellular locations of 1.1 million individual proteins (from 326 cells) suggests that clusters form via stochastic self-assembly. The super-resolution PALM maps of E. coli receptors support a growing collection of evidence that stochastic self-assembly can create and maintain periodic structures in biological membranes, without direct cytoskeletal involvement or active transport.View Large Image | View Hi-Res Image | Download PowerPoint Slide