Microarchitecture and physiological differentiation in Escherichia coli biofilms: spatial distribution and functions of amyloid curli fibres, cellulose and flagella

SERRA, DIEGO O.; RICHTER, ANJA M.; HENGGE, REGINE

Stockholm

Conferencia; 60th Nobel Conference on Biofilm formation, its clinical impact and potential treatment; 2013

Karolinska Institutet; Ute Römling (Chair).

Bacterial biofilms are multicellular communities, whose formation depends on motility and an extracellular matrix of adhesins, amyloid fibres and exopolysaccharides. Escherichia coli produces flagella during the post-exponential phase, when nutrients become limiting, but the rod-shaped cells still grow. Upon entry into stationary phase, cells stop producing flagella, become ovoid and multiple stress resistant and generate amyloid curli fibres and the exopolysaccharide cellulose. Using flagella, curli fibres, cellulose and cell morphology as ´anatomical´ hallmarks in fluorescence and scanning electron microscopy, different architectural patterns and physiological zones were distinguished at high resolution in macrocolonies of W3110, a cellulose-negative K-12 strain, and AR3110, a W3110 derivative with restored capacity to produce cellulose. Macromorphologically, W3110 biofilms are characterized by an elaborated pattern of small wrinkles and rings. At the microscale, the wrinkle and ring surface consist of small ovoid, i.e. highly starved, cells literally encased in a curli network. Inner zones are characterized by heterogeneous curli expression, while the bottom and the outer rim growth zone features large flagellated cells. Unlike W3110 biofilms, cellulose-containing AR3110 macrocolonies are only about 60 micrometer thin, large and exhibit radial ridge-like structures formed by vertical buckling of the biofilm. At cellular resolution, we observe a sharp two-layer architecture. The upper surface layer of flat sectors and ridges contains small ovoid bacteria encased in a compact network of curli and cellulose, while in the lower layer the scenario changes sharply with cells being rod-shaped and flagellated. In summary, our study reveals the dramatic impact of variation in the matrix components on microarchitecture and microphysiology of E. coli biofilms at an unprecedented high resolution.