High-resolution spatial order of physiological differentiation in structured biofilms of Escherichia coli

SERRA, DIEGO O.; RICHTER, ANJA M.; KLAUCK, GISELA; MIKA, FRANZISKA; HENGGE, REGINE

Miami

Conferencia; 6th ASM Conference on Biofilms; 2012

ASM Conferences; Matt Parsek & Fitnat Yildiz (Chairs).

Bacterial biofilms are multicellular structured 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. Using flagella, curli fibres and cell morphology as anatomical and physiological hallmarks in light, fluorescence and scanning electron microscopy studies, we distinguished at high resolution different physiological zones in E. coli K-12 macrocolony biofilms. Small ovoid cells embedded in a thick network of curli fibres form the outer biofilm layers. Strikingly, in this zone curli fibres encase each bacterium by forming a shell which remains compactly structured around the cell without being attached to its surface. The inner zone of the macrocolony is characterized by bistable curli expression which leads to patches and strings of cells surrounded by curli fibre shells right next to curli-free cells. The bottom zone features larger cells and a dense and tight mesh of entangled flagella, the formation of which requires flagellar motor function, suggesting a new role of flagella as an architectural element in biofilms. Cells in the outer rim growth zone produce flagella, which wrap around and tie cells together. However, only about 30-50 um away from the outer edges, patches and strings of curli-encased cells already form, which further develop into the confluent curli layer of the biofilm surface. In conclusion, our study reveals the microanatomy and microphysiology of a bacterial biofilm in unprecedented detail. It also shows bacterial curli networks to strikingly resemble Alzheimer plaques and it provides clues to understanding virulence of high curli-producing pathogenic E. coli, as is the case with the recent German O104:H4 outbreak strain.