FIG 3.

Cellulose is necessary for growth at the air-liquid interface (ALI) and results in bioconvection. Shown are bright-field images of ancestral P. fluorescens SBW25 (a) and SBW25 ΔwssA–J (cellulose-negative mutant) (b) taken at four time intervals. Complete movies are available as Movies S1, S2, S6, and S7 at figshare (https://figshare.com/projects/Causes_and_consequences_of_cellulose_production_by_Pseudomonas_fluorescens_SBW25_at_the_air-liquid_interface/59630). Images above the line show growth at the ALI captured using camera 3; images below the line are from camera 1 (Fig. 1). At 0 h, the medium is inoculated with ∼10⁴ cells · ml⁻¹. By 19 h, the ancestral cellulose-producing genotype has formed a thin white pellicle at the ALI (visible by both cameras 1 and 3). No pellicle formation is seen in the cellulose-negative mutant, but growth is evident in the broth phase. By 26 h, in cultures of the cellulose-producing ancestral type, plumes characteristic of bioconvection stream from the ALI (pointed at by the black arrow). No evidence of mat formation or streaming is seen in SBW25 ΔwssA–J. By 40 h, streaming has largely ceased in the ancestral type, although growth is still apparent at the ALI. Scale bars are 5 mm. Contrast has been adjusted to highlight salient features.