(A-G) Glucose represses corona formation independently of the regulatory activity of the cAMP-CRP complex. (A) A typical 14-old-day biofilm macrocolony of E.coli K-12 strain grown over 0.6% ABE semisolid agar with Luria Bertani medium supplemented with 0.5% of D-(+)-glucose does not produce a corona (B-C) Circular cellular formation surrounding the inoculation point does not produce coronal flares or spikes (B) × 40 (C) ×100 (D) × 400 magnifications (E) Individual elongated cells 5–10 μm long, typical "swarm" cells [24,25], removed from macrocolony and observed under optical microscope at × 1000 augmentation (F-G) Corona generated by a E.coli K-12 Δcrp mutant strain (GS0549) lacking CRP protein. (G) Enlargement of the boxed region in F. Scale bars: (A) 0.25 cm (B) 400 μm (C) 200 μm (D) 40 μm (E) 20 μm (F) 350 μm (G) 150 μm. (H-I) Corona formation in relation to the canonical "core" transcriptional network that controls switching between motility and biofilm formation. In E. coli K-12, the transition from a planktonic/foraging lifestyle to biofilming behaviour is regulated by two inversely controlled transcriptional feedforward cascades, the FlhDC + σ70/σF "flagellar" cascade and the σS/MlrA/CsgD cascade (adapted from references [17,22,28]). Remarkably, while CRP in conjunction with the small RNA McsA has a dual role in the control of both cascades (forming a coherent feedforward loop (FFL) in order to regulate the expression of flhDC and an incoherent FFL to control csgD expression, ) apparently it plays no role in E. coli’s corona formation at all. Arrowheads indicate positive regulation; perpendicular lines indicate negative regulation. Scale bar: (I) 800 μm.
Gómez-Gómez and Amils BMC Research Notes 2014 7:108 doi:10.1186/1756-0500-7-108