Bacterial flagellar motor PL-ring disassembly subcomplexes are widespread and ancient

Area of Science:

• Microbiology
• Cellular Biology
• Evolutionary Biology

Background:

• The bacterial flagellum is a complex nanomachine essential for motility.
• Understanding flagellar evolution provides insights into cellular evolution.
• A P- and L-ring subcomplex remains after flagellum disassembly in some bacteria.

Purpose of the Study:

• To investigate the persistence of the P- and L-ring subcomplex in additional bacterial species.
• To determine if the persistence of this subcomplex is an ancient and conserved trait.
• To hypothesize a functional role for the persistent P- and L-rings.

Main Methods:

• Cryo-electron tomography was used to image nine additional bacterial species.
• Bioinformatic analyses were performed on P- and L-ring genes.
• Comparative genomics was employed to assess gene transfer events.

Main Results:

• The P- and L-ring subcomplex was observed to persist after flagellum disassembly in multiple phyla beyond Gammaproteobacteria.
• Bioinformatic analyses did not reveal recent horizontal gene transfer for P- and L-ring genes.
• The persistence of the P- and L-ring subcomplex appears to be an ancient and conserved feature.

Conclusions:

• The P- and L-ring subcomplex is a conserved remnant of the flagellar motor across diverse bacterial phyla.
• Its persistence suggests an ancient evolutionary origin and conserved function.
• A potential function is to seal the outer membrane following flagellar motor disassembly.