When the bacterial surface structure in the extreme polar region CYC202 purchase (the outer

surface of the funnel shape) was examined by scanning electron microscopy, it looked smooth (as a ring structure), in contrast to the surface of the spiral body, which had a capsular wrinkle-like structure, as shown in Figure 4d. A unique structure in the flagellate polar region was also observed for C. coli, which has polar cup-like structures (32.5 ± 5.8 nm thick [n = 42]) (Fig. 5a); these cup-like structures ares located inside (and adjacent to) the inner membrane, similarly to C. jejuni. In the C. coli strain (M5) the pole structures spontaneously separate as small round particles with a flagellum from the bacterial spiral bodies (Fig. 5b); these small particles are 0.25 ± 0.05 μm (n = 32). They are distinct from coccoids (much larger round cells [0.63 ± 0.12 μm, n = 68]) with two flagella), which appear in the tip areas of bacterial colonies (Fig. 5c, d, f). In contrast to C. jejuni and C. coli (with a single flagellum at each pole), C. fetus has a single flagellum at only one pole, as shown in Figure 6a, although dividing (long) C. fetus cells have a single flagellum at each pole Dorsomorphin (Fig. 6a). C. fetus has, albeit rarely, two flagella

at one pole (Fig. 6a). In C. fetus, the cup-like structures appear to be composed of two parallel membranes (Fig. 6b); the cup-like structures are 31.0 ± 5.9 nm thick, including the inner membrane (n = 51). C. fetus has temperature-dependent motility, similar to the motility of C. jejuni (Fig. 6c); the swimming speed at 37 or 42°C being >100 μm/s. Campylobacter lari is very similar to C. jejuni (and C. coli) in terms of polar flagellation, cup-like structures and high-speed and temperature-dependent motility (Fig. 6a–c); the cup-like structures are 29.8 ± 6.2 nm thick, including the inner membrane (n = 35) and the swimming speed at 37 or 42°C >100 μm/s. In this study, we demonstrated that C. jejuni swims much faster at 37–42°C

(>100 μm/s) than do curved rods, including H. pylori and V. cholerae, and non-curved rods, including V. parahaemolyticus, S. enterica, E. coli and P. mirabilis. C. jejuni is a motile bacterium with one of the highest swimming speeds (>100 μm/s) reported, to our knowledge. The extremely high motility of C. jejuni might be associated with its structure in the flagellate polar region (characterized by cup-like G protein-coupled receptor kinase structures, funnel shaped with tubular structures and less dense space) as shown in Figure 7. The bacterial polar structures occasionally separate from the bacterial spiral bodies, forming small round particles with a single flagellum. By contrast, we found no polar cup-like structures in H. pylori (a spiral-shaped bacterium), V. cholerae O1 (biotypes Classical and El Tor) and O139 (comma-shaped bacteria), or non-curved rods such as V. parahaemolyticus, S. enterica, E. coli, and P. mirabilis (data not shown), indicating that these polar cup-like structures are unique to Campylobacter species.