Modes of bacterial cell wall synthesis: combining localization analysis and protein‐protein interactions

Abstract

In rod‐shaped bacteria, a complex of morphogenetic proteins coordinates cell wall biosynthesis during both lateral growth and division. One subset of these proteins (MreBCD) guides lateral synthesis whereas another group (FtsZQW, etc.) coordinates septum formation. We have found that FtsW, an integral membrane protein in Caulobacter crescentus, plays a novel dual role in both processes by interacting with critical components and regulators of peptidoglycan (PG) synthesis. Localization studies show that MreB actin cables collapse to irregular foci along the cell length upon FtsW ablation. This is mirrored by nearly identical changes in nascent PG synthesis, as measured by PG‐precursor labeling. Lateral patterns of PG synthesis, however, were uninterrupted by depletion of the essential cell division protein, FtsZ. Additionally, FtsW interacts with MreB actin and other morphogenetic complex components as inferred by two‐hybrid analysis. Our studies indicate that cell elongation may occur through two distinct modes of PG synthesis: (1) evenly distributed lateral synthesis directed by FtsW, and (2) new synthesis emanating from concentrated foci, directed by FtsZ. We hypothesize that FtsW and FtsZ interact with morphogenetic proteins in distinct functional ways, resulting in two discrete mechanisms of cell wall growth.