Figure 6. Role of Cle proteins in C. crescentus surface attachment.

(a) Cle proteins promote rapid surface attachment under flow. C. crescentus wild-type and mutant strains were assayed as indicated in (b). The efficiency of rapid surface attachment of newborn SW progeny was determined as the relative area covered by microcolonies emerging from a single mother cell after 15 hr incubation. Box plots mark the median (horizontal black lines), the lower and upper quartiles (red and blue boxes) and the extreme values (whiskers). P values obtained with a 2-tailed T-test were < 0.05 for ΔcleC and ΔcleE, whereas the ΔcleA,ΔcleB and ΔcleD mutants were statistically not significant. (b) Experimental setup for microfluidics experiments shown in (a). The direction of medium flow in the microfluidic channels is indicated by blue arrows. The position of holdfast (red), pili and flagella are indicated. Newborn wild type SW cells are able to sense surface exposure and rapidly synthesize a holdfast before cell separation and remain attached downstream of their mother cells (Hug et al., 2017). (c) Experimental setup for experiments shown in (d). Dividing C. crescentus cells were trapped in narrow quasi-2D chambers that offer immediate surface contact in the absence of flow. Holdfast was visualized using Oregon-green labeled wheat germ agglutinin lectin. Time-lapse imaging at four frames per minute allowed the determination of the time elapsed from separation of individual SW cells and the first detection of their newly secreted holdfast (Hug et al., 2017). (d) Timing of holdfast appearance after separation from mother cells. Dots represent individual cells of C. crescentus wild type and mutants as indicated. Horizontal black lines mark the average values. Values for ΔcleA-E and fliMID57WA mutants were significantly different from both WT and motBD33N with P values with a 2-tailed T-test < 0.01.