Treponema pallidum

Which of the following best describes a key characteristic of the organism which is the causal agent of syphilis?

1: Treponema pallidum, a rectangular-shaped bacterium
2: Treponema pallidum, a rod-shaped bacterium
3: Treponema pallidum, a spiral-shaped bacterium
4: Treponema pallidum, a needle-shaped bacterium