In situ structures of polar and lateral flagella revealed by cryo-electron tomography

Abstract

The bacterial flagellum is a sophisticated self-assembling nanomachine responsible for motility in many bacterial pathogens, including Pseudomonas aeruginosa, Vibrio spp., and Salmonella enterica. The bacterial flagellum has been studied extensively in the model systems Escherichia coli and Salmonella enterica serovar Typhimurium, yet the range of variation in flagellar structure and assembly remains incompletely understood. Here, we used cryo-electron tomography and subtomogram averaging to determine in situ structures of polar flagella in P. aeruginosa and peritrichous flagella in S. Typhimurium, revealing notable differences between these two flagellar systems. Furthermore, we observed flagellar outer membrane complexes as well as many incomplete flagellar subassemblies, which provide additional insight into mechanisms underlying flagellar assembly and loss in both P. aeruginosa and S. Typhimurium.