Fig. 3

The role of rpoN1 in bacterial motility of P. citrulli. a Twitching motility of the wild type (WT), ΔrpoN1, ΔpilA, and complemented strains ΔrpoN1-C and ΔpilA-C of P. citrulli. The strains were spread on NA plates containing 1.0% agar. After 72 h, the colonies were photographed and observed using a stereoscope. b Transmission electron microscopy verified the presence of pili. Pili were observed in the wild type (WT) strain and the complemented strains ΔrpoN1-C and ΔpilA-C, while no pili were observed in the ΔrpoN1 and ΔpilA strains. Solid arrows represent type IV pili, and dashed arrows represent the polar flagellum. Bars = 500 nm. c Swarming motility of the WT, ΔrpoN1, ΔpilA, and complemented strains ΔrpoN1-C and ΔpilA-C of P. citrulli. The strains were added dropwise to 0.6% (w/v) semisolid medium plates and incubated at 28°C for 48 h. d Swimming motility of the WT, ΔrpoN1, and complemented strains ΔrpoN1-C of P. citrulli. The strains were added dropwise to 0.3% (w/v) semisolid medium plates at 28°C for 48 h. e The expression levels of the flagella-related genes flhA, flgM, fliC, fliE, fliH, fliI, fliJ, and fliK in the wild-type and ΔrpoN1 strains were measured by qRT-PCR. The values represent the average of three independent experiments. Asterisks indicate significant differences between the samples (* P < 0.05, ** P < 0.01, and *** P < 0.001)