Figure 2

Biofilm formation of S. meliloti strains on glass surfaces in response to iron availability. A) Confocal Laser Scanning Microscopy (CLSM) images showing the architecture of 3-day-old biofilms developed by GFP-labelled Rm1021 and GR4 cells on chambered cover glass slides after growth in MM containing different concentrations of FeCl₃. Bars, 15 μm. B) CLSM images showing the thickness (represented by the xz plane) of 3- and 10-day-old biofilms developed by Rm1021 and its derivative mutant strains on chambered cover glass slides in response to low (22 μM FeCl₃) and high (220 μM FeCl₃) iron availability. C) CLSM images showing the thickness (represented by the xz plane) of 3-, 6-, and 10-day-old biofilms developed by GR4 and GR4FDCSS. The mean thickness (± SD) of biofilms formed by the different strains under the two iron conditions is shown in parenthesis below the representative CLSM image. Values having different letters are significantly different from each other (Tukey’s test, P < 0.05). Lowercase letters indicate statistical differences between the thickness of the wild type strain and its derivative mutant biofilms developed under the same conditions. Capital letters are used to indicate the statistical differences observed in the biofilms developed under the different conditions by each strain. Structured biofilms developed in MM containing 220 μM of FeCl₃ are indicated with an asterisk (*). Each experiment was repeated three times.