Figure 5.

A thermodynamic model of bacterial distribution at the water-air interface. (a) System surface energy, G, as a function of the relative position, z₀, of an E. coli (EC, blue) or L. innocua cell (LI, red). z₀ is defined as the vertical coordinate of the center of the cell with regard to the water level, z, normalized by the radius of the cell, R. (b) and (c): enlarged view of the energy curves at the ‘escape-to-water’ point (z₀ = −1) for L. innocua (red box) and E. coli (blue box), respectively. ∆G_w is the energy barrier a cell needs to overcome to escape into the bulk water phase from the equilibrium position, z_min. (d) Schematic illustration of various positions of a cell relative to the interface. The equilibrium position for L. innocua (z₀ = −0.9) is highlighted by the red dashed square.