...forwarded for your information, Martin Cylic-di-GMP signalling and high resolution spatial order in macrocolony biofilms of E. coli Professor Regine Hengge, from Freie Universität in Berlin, leads this lunchtime seminar Date: 19 Nov 2012 Time: 12:30 - 13:30 Venue: G34, Sir Alexander Fleming Building Campus: South Kensington Campus Speaker: Professor Regine Hengge Contact: Kylie Glasgow Abstract Bacterial macrocolonies represent structured biofilms that can produce wrinkled, ring- or radiation-like patterns, whose formation depends on motility and an extracellular matrix of adhesins, amyloid fibres (e.g. curli) and polysaccharides (e.g. cellulose). While flagella are synthesized by postexponentially growing rod-shaped E. coli cells, curli fibres and cellulose are produced during entry into stationary phase, with starving cells becoming smaller and ovoid. This transition is under exquisite control of the general stress sigma factor RpoS and the ubiquitous bacterial second messenger cyclic-di-GMP (2). The latter is produced by diguanylate cyclases (DGC, with GGDEF domains) and is degraded by specific phosphodiesterases (PDE, with EAL or HD-GYP domains). c-di-GMP controls a variety of targets, including transcription and the activities of enzymes and complex cellular structures. Many bacterial species possess multiple GGDEF/EAL proteins (29 in E. coli K-12), which has led to the concept of temporal and functional sequestration of locally acting c-di-GMP control modules (1). The presentation will focus on a cascade of two distinct c-di-GMP control modules. C-di-GMP synthesized by the first of these modules antagonizes an inhibitor of the second one, which constitutes a locally acting signaling complex of a DGC, the inhibitor and a c-di-GMP-binding transcription factor. This protein complex controls the expression of the biofilm regulator CsgD, which in turn regulates the biosynthesis of curli fibres and cellulose. Using fluorescence and scanning EM, it was found that this cascade is active in the top layer of a macrocolony biofilm, where small starved cells are literally encased in a thick network of curli fibres. By contrast, the bottom of the biofilm is formed by still growing cells surrounded by a tight mesh of entangled flagella, the formation of which requires flagellar motor function. The inner regions of the biofilm show heterogeneous curli expression. Cells in the outer rim growth zone produce flagella, which rap around and tie cells together. Overall, this study reveals the microanatomy of a bacterial biofilm and the underlying regulatory networks in unprecedented detail. 1. Hengge, R. 2009. Principles of cyclic-di-GMP signaling. Nature Rev. Microbiol. 7:263-273. 2. Hengge, R. 2011. The general stress response in Gram-negative bacteria, p. 251-289. In G. Storz and R. Hengge (ed.), Bacterial Stress Responses. ASM Press, Washington, D.C.