In this example, we hypothesized that P. aeruginosa can exploit the distinctive motilities on surface by some specific mechanisms. To validate this hypothesis and elucidate the underlying mechanisms, first, we analyzed the TFP-mediated motilities of over ten thousand P. aeruginosa cells within various nutrient conditions. We find that the motilities can always be classified into four types, as shown in figure 1. By further using combination of genetic manipulation, fluorescent microscopy and Monte Carlo simulation, second, we demonstrate that 1) these distinctive TFP-mediated motilities are dominated by the expression and the subcellular localization of a protein (FimX) which contains several functional domains, as shown in figure 2; 2) the expression and the subcellular localization of FimX can respond to nutrient conditions, thus leading the cell to search more nutrients on surface when the nutrients are limited, or to form microcolonies when the nutrients are sufficient, as shwon in figure 3. This simple strategy enables P. aeruginosa to adapt to different surface conditions. 

Surface motility and adaptability
Figure 1Distinctive TFP-mediated motilities in P.aeruginosa. (A) Unipolar-attached crawling cell: Bright field image (A1); Time series of v_(∥,lead) (t) (A2) or v_(⊥,lead) (t) (A4) or tilt angle (A6); Histogram of v_(∥,lead) (t) (A3) or v_(⊥,lead) (t) (A5) or tilt angle (A7). (B) Bipolar-attached crawling cell: Bright field image (B1); Time series of v_(∥,lead) (t) (B2) or v_(⊥,lead) (t) (B4) or tilt angle (B6); Histogram of v_(∥,lead) (t) (B3) or v_(⊥,lead) (t) (B5) or tilt angle (B7). (C) Bipolar-attached wiggling cell: Bright field image (C1); Time series of v_(∥,lead) (t) (C2) or v_(⊥,lead) (t) (C4); Histogram of v_(∥,lead) (t) (C3) or v_(⊥,lead) (t) (C5). (D) Bipolar-attached stalling cell: Bright field image (D1); Time series of v_(∥,lead) (t) (D2) or v_(⊥,lead) (t) (D4); Histogram of v_(∥,lead) (t) (D3) or v_(⊥,lead) (t) (D5); (E) ∆fliC∆pilA cell: Bright field image (E1); Time series of v_(∥,lead) (t) (E2) or v_(⊥,lead) (t) (E4); Histogram of v_(∥,lead) (t) (E3) or v_(⊥,lead) (t) (E5); (F) Switching of crawling to walking, or walking to crawling in a unipolar-attached cell: Bright field image of crawling (F1), crawling to walking (F2-F3), walking (F4), walking to crawling (F5 -F6), crawling (F7); Time series of tilt angle. Where the yellow lines in the bright images represent trajectories of leading pole, v_(∥,lead) (t) or v_(⊥,lead) (t) represent the component that arise from decomposing of the instantaneous velocities (v_lead (t)) at leading pole along or normal to the axis of cell body, the red lines in A3, A5, B3, B5, C3, C5, D3, D5, E3, E5 represent the fitting curves by using a Cauchy-Lorentz distribution. All bright images are set in a unified scale with a 2μm bar, as shown in A1.

Figure 2Expression and subcellular localization of FimX dominate the TFP-mediated motilities in P.aeruginosa. Expression and subcellular localization of FimX in a bipolar-attached crawling cell (A), or a bipolar-attached wigging cell (B), or a unipolar-attached crawling cell (C), or a bipolar-attached stalling cell (D), where A1, B1, C1, D1 show their images that was overlapping by the bright-field and the fluorescent images, A2 and B2 show time series of the symmetry factor (β). A3, B3, C2 and D2 show time series of the fluorescent intensities of RFP-tagged FimX. Relationship between k_MSD and v_(∥,lead,m) (E) in the whole population of (∆fliM) cells, where the olive, red, magenta and blue symbols represent the date stemming from the type-I, II, III and IV respectively, the solid line with various colors represent the simulation curve with various β or γ. β dependence of <v_(∥,lead,m)> (F) or <k_MSD> (G) in (fimXpDimer2-FimX) cells, where symbols represent the average of v_(∥,lead,m), error bars represent the standard error, solid lines with various colors represent the simulation curve. β and γ dependence of <k_MSD> (H) or <v_(∥,lead,m)> (I), where colors represents <k_MSD> or <v_(∥,lead,m)>, solid lines represent the boundaries of these distinctive motility types. All images are set in a unified scale with a 2μm bar, as shown in A1. 

Figure 3P.aeruginosa exploit the distinctive TFP-mediated motilities to adapt to surfaces. Expression and subcellular distribution of FimX in nutrient limited or sufficient conditions: starvation of iron (A), supplement with additional 0.1% BSA (B), where A1 or B1 shows their images that was overlapping by the bright-field and fluorescent images, A2 or B2 shows the histogram of β, A3 or B3 shows the histogram of fluorescent intensity. β and γ dependence of searching (C) or clustering efficiency (D), where colors represent the efficiency, solid lines represent the boundaries of these distinctive motility types. Sub-population of these distinctive TFP-mediated motility types in different nutrient conditions (E). All images are set in a unified scale with a 2μm bar, as shown in A1.

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