Bacterial moving and shaking: the 11th blast meeting

Abstract

Since their inception 20 years ago, the biennial blast (Bacterial Locomotion and Signal Transduction) meetings instantly became the place to be for exchanging and sharing the latest developments in the field of bacterial motility and signalling. At the 11th edition, held last January in New Orleans, LA, researchers reported on the myriad of mechanisms involved in bacterial movement, sensing and adaptation, ranging from the molecular level to multicellular behaviour. New insights into bacterial signalling phenomena were gained, revealing previously unsuspected layers of complexity, particularly in mechanisms ensuring signal transduction fidelity and novel links to metabolic processes.

Fig. 1.

Chemotaxis signal transduction in Escherichia coli and the two-state model for chemoreceptor signalling. The activity of the chemotaxis signal transduction pathway ultimately regulates the direction of rotation of the flagellar motors by modulating the phosphorylation state of the CheY response regulator, which has increased affinity for the flagellar switch complex in the phosphorylated form. CheY is phosphorylated by activated CheA histidine kinase, which is coupled to the chemoreceptors (methyl accepting chemotaxis proteins or MCPs) via CheW. Attractant (+ATT) binding to MCPs has an inhibitory effect on the kinase activity of CheA (Kinase OFF), lowering the phospho-CheY pool, thereby promoting counterclockwise rotation (CCW) of the flagellar motors. Methylation of the cytoplasmic domains of MCPs by the CheR methyltransferase promotes the activating state of the CheA kinase (Kinase ON), increasing the pool of phospho-CheY and thus clockwise (CW) rotation of the flagella motors. Activated phospho-CheA also phosphorylates CheB, thereby promoting its methylesterase activity, allowing the MCPs to be reset to background methylation state. (Courtesy of Sandy Parkinson, University of Utah).

Fig. 2.

Model of the core unit chemotaxis signalling complex purified with Nanodisc-inserted chemoreceptors. The cartoon shows diagrammatically the stoichiometry and deduced organization of purified, kinase-activating core units of MCP/CheW/CheA, formed with Nanodisc-embedded Tar chemoreceptors, organized as trimers of dimers.

Fig. 3.

One-sample FRET technique (OS-FRET). The new OS-FRET method utilizes a fluorescent donor (D) and a novel non-fluorescent FRET acceptor NFQ1 (Q). NFQ1 is reversibly coupled to one protein and the donor is irreversibly linked to the second protein in the complex. After the first measurement in the presence of quencher and donor, reducing agent is added to quantify NFQ1 release and a second measurement is done on the same sample in the absence of FRET (Courtesy of Annette Erbse and Joe Falke, University of Colorado).

Fig. 4.

Images of coarse grain models of a bacterial chemoreceptor in a membrane. Backbone particles are shown as green spheres and phosphate head groups as brown spheres. A. Models of isolated Tsr dimers show a pronounced kink just below the HAMP domain. B. Models of the trimer of dimers show a rod-like structure and reduced kinking.

Fig. 5.

Working model of Flavobacterium johnsoniae gliding motility. Gld proteins in the cell envelope are thought to form the motor (pink) that propels adhesins, such as SprB (black) and RemA (blue), along the cell surface. Exopolysaccharides (orange) enhance motility by coating the substratum and interacting with specific adhesins. OM, outer membrane; CM, cytoplasmic membrane; PG, peptidoglycan (Courtesy of Mark McBride, University of Wisconsin).