Long and short range heterogeneity of production of amyloid curli fibres and cellulose is essential for morphogenesis of Escherichia coli macrocolony biofilms

SERRA, DIEGO O.; HENGGE, REGINE

Marburg/Lahn

Congreso; VAAM-Jahrestagung 2015; 2015

Vereinigung für Allgemeine und Angewandte Mikrobiologie (VAAM).

Introduction. In E. coli macrocolonies the emergence of elaborated structures, such as ridges and wrinkles, relies on a precise spatial distribution of flagella, amyloid curli fibers and cellulose. Over a long range, this spatial matrix distribution is based on E. coli differentiating into different physiological layers in response to nutrient gradients building up in the biofilm: vegetatively growing cells entangled by flagella in the bottom layer (i.e., close to the nutrient-providing agar) and starving stationary-phase cells producing cellulose and curli fibers in the top layer. Objectives. This study aims at investigating how heterogeneity of matrix synthesis occurs over very short distances inside macrocolonies and how does it impact macrocolony microarchitecture. Methods. Heterogeneity of matrix synthesis inside biofilms of E. coli strains W3110 and AR3110 and derivative mutants was examined by combining macrocolony cryo-sectioning, specific labelling of matrix components and fluorescence and SEM microscopy. Results. We found that the lower zone of the stationary-phase macrocolony layer represents a highly heterogeneous transition area with cells that have switched to stationary phase and the production of mainly cellulose being located immediately adjacent to ?naked?, elongated and flagellated cells. Importantly, we found that YciR, a trigger enzyme with c-di-GMP degrading phosphodiesterase activity which acts as a central switching device in the control of csgD expression, is a key player in generating this heterogeneity. A knockout mutation in yciR resulted in confluent and homogeneous distribution of cellulose and curli in the entire stationary phase zone. At the macroscopic level this translated into large, rigid and extremely flat macrocolonies with scared breaks at the surface, thus reflecting extreme cohesiveness but reduced elasticity of the macrocolony. Conclusion. Overall, these results highlight that heterogeneity in matrix synthesis is essential for the development of complex morphological patterns in macrocolony biofilms.