Figure 2

Environmental and biological factors that promote the E. coli K-12 corona formation or else preclude this formation. (A) The colony (A-1) produced the E. coli’s corona when it was inoculated with a toothpick that punctured the 0.6% ABE semisolid agar and contacted the Petri dish’s plastic surface. The colony (A-2) by contrast did not generate a corona when the bacterial inoculation was carried out with a drop containing 5 μl of a stationary culture grown in LB medium of MG1655 strain deposited carefully on semisolid agar surface (B-C) The flagella-driven swimming interstitial/internal motility abolished the corona formation. Typical 14-old-day macrocolony swimming colony of E. coli K-12 MG1655 strain (B) View from the top (C) Reverse view (D) Corona developed on a plastic surface, but not on a glass surface (E). ( F) A typical 14-old-day macrocolony of E.coli K-12 W3110 strain (G) Appearance of the same colony when the external colony was removed (H-I) E. coli’s corona developed inside semisolid 1.0% ABE agar concentration. (H) View from the top (I) Reverse view. (J-K) The enlarged box region in (H-I) showing the corona at × 40 (J) and ×100 (K) magnifications. The closed white arrowheads indicate the situation of corona. The open white arrowheads indicated the coronal root. Scale bars: (A-G), 0.5 cm; (H-I) 0.25 cm; (J) 300 μm; (K) 100 μm.