By characterizing motility of colonies, as well as single-filament motility of short filaments, the authors find that increasing the agar concentration of the media results in smaller colonies, and slower individual filament movement.
As depicted in some of the electron micrographs in Figure 3, the authors describe the presence of thin filaments within the sheaths surrounding the motile filaments. Is it possible that these are in fact type IV pili? How does the structure compare to other published reports of type IV pili?