Upward mobility and alternative lifestyles: a report from the 10th biennial meeting on Bacterial Locomotion and Signal Transduction

Abstract

This past January, in Cuernavaca Mexico, a conglomerate of scientists met to discuss the contemporary view of Bacterial Locomotion and Signal Transduction (BLAST). The BLAST meetings represent a field that has its roots in chemotaxis and the flagellum-based motility but now encompass all types of cellular movement and signalling. The topics varied from the interactions between molecules to the interactions between species. We heard about 3D reconstructions of transmembrane chemoreceptors within cells, new biophysical methods for understanding cellular engines, intricate phosphorelays, elaborate gene networks, new messenger molecules and emerging behaviours within complex populations of cells. At BLAST X we gained an appreciation for the lifestyle choices bacteria make, how they get to where they are going and the molecular mechanisms that underlie their decisions. Herein we review the highlights of the meeting.

Figure 1

The two-state model of chemoreceptor signaling. Methyl-accepting chemotaxis proteins (MCPs) or chemoreceptors regulate the activity of the signal-transducing histidine kinase CheA, which is coupled to MCPs through CheW. The MCP receptors can be viewed as having two activity states, one that is inhibitory with respect to the kinase and one that is activating. Attractant binding promotes the inhibitory state (and ultimately counter clockwise (CCW) rotation of the flagellar motor), whereas cytoplasmic methylation favors the activating state (and ultimately clockwise (CW) flagellar rotation). Action by the CheR methyltransferase, is countered by the CheB methylesterase, which itself is regulated by CheA through phosphorylation. In this way, kinase activity is used to reset the receptor state equilibrium as the bacteria swim up a gradient of ligand. Courtesy of Sandy Parkinson.

Figure 2

Wild-type chemoreceptor array architecture in Caulobacter crescentus (A) tomographic slice perpendicular to the chemoreceptor array. The base plate composed of CheA-CheW (white arrows) is visible running parallel to the inner membrane, at a distance of 31nm. Thin pillar-like densities connecting the base plate with the inner membrane are evident. (B) Slice through the tomogram parallel to the membranes directly above the base plate. The hexagonal lattice of the chemoreceptor array is visible. A power spectrum confirms this and demonstrates a center-to-center spacing of 12nm (inset). (C) Manually segmented three-dimensional surface representation of a unit cell of the region where the base plate and the chemoreceptor tips connect. Averaging and six-fold symmetry were applied. (D) Model for the arrangement of the receptors superimposed upon tomographic data. The dimensions and symmetry of the bottom half of the trimers-of-dimers from the crystal structure (PDB ID 1QU7) fit well in each intersection of the observed hexagonal lattice. SL: S-Layer, OM: outer membrane, IM: inner membrane. Scale bars: A and B: 50 nm, D: 5nm. Courtesy of Ariane Briegel and Grant Jensen.

Figure 3

Electron tomography reconstructions of Tsr chemoreceptors overexpressed in whole cells. The chemoreceptor structures fall into two classes: one that is contracted in regions beneath the cytoplasmic membrane that map to the location of the HAMP domain (left) and another that is expanded (right). The proportion of molecules in the expanded state increases when attractant is added, whereas the proportion of molecules in the contracted state increases when modifications are made to the receptor to mimic methylation. The receptors are shown on a background of the hexagonal lattices they form at the poles of cells. Courtesy of Cezar Khursigara and Sriram Subramaniam.

Figure 4

Model for the Red four component TCS mechanism controlling progression through the M. xanthus developmental program. Left panel: Developmental progression is repressed when RedC histidine protein kinase (HPK) phosphorylates the receiver (REC) domain of RedF, a stand-alone response regulator. Right panel: Development proceeds when RedC instead phosphorylates the first REC domain of RedD, a dual receiver response regulator. The phosphoryl group is then transferred to the HPK-like protein, RedE, and RedE acts as a phosphatase on RedF. Courtesy of Penelope Higgs.

Figure 5

The Predataxis behavior of M. xanthus. When eating E. coli, M. xanthus forms an unusual rippling structure that results from the coordinated reversals of predatory cells. Courtesy of John Kirby.

Figure 6

Differentiation within a B. subtilis biofilm. Fluorescent markers for cells expressing genes associated with flagella (blue), the extracellular matrix (red) and sporulation factors (yellow) localize to different positions of the colony, shown here in thin crosssection, with aerial structures above and solid substrate below. Courtesy of Hera Vlamakis and Roberto Kolter.