MreB, the cell shape‐determining bacterial actin homologue, co‐ordinates cell wall morphogenesis in <i>Caulobacter crescentus</i>

TLDR

The bacterial actin homologue MreB is essential for maintaining rod‑shaped cells and forms longitudinal spirals in Bacillus subtilis and Escherichia coli. We hypothesize that MreB filaments act as a cytoskeleton that organizes or tracks the PBP2–peptidoglycan biosynthesis complex. Loss of MreB in Caulobacter crescentus yields lemon‑shaped cells with weakened walls, while MreB localizes as longitudinal bands or spirals that shift to mid‑cell during division in an FtsZ‑dependent manner, coordinating PBP2 band formation and associating with other penicillin‑binding proteins.

Abstract

Summary The bacterial actin homologue, MreB, is required for the maintenance of a rod‐shaped cell and has been shown to form spirals that traverse along the longitudinal axis of Bacillus subtilis and Escherichia coli cells. The depletion of MreB in Caulobacter crescentus resulted in lemon‐shaped cells that possessed defects in the integrity of the cell wall. MreB localization appeared as bands or spirals that encircled the cell along its entire length and switched to a mid‐cell location at a time that coincided with the initiation of cell division. The formation of smaller MreB spirals or bands at the mid‐cell was dependent on the presence on the cytokinetic protein, FtsZ. Penicillin‐binding protein 2 (PBP2) also formed band‐like structures perpendicular to the cell periphery that resembled, and depended upon, MreB localization. PBP2 co‐immunoprecipitated with several other penicillin‐binding proteins, suggesting that these proteins are in association in Caulobacter cells. We hypothesize that MreB filaments function as a cytoskeleton that serves as an organizer or tracking device for the PBP2–peptidoglycan biosynthesis complex.