Cell Biology

Growing Through a Wall

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Science  26 Sep 2008:
Vol. 321, Issue 5897, pp. 1742
DOI: 10.1126/science.321.5897.1742d

In bacteria, the cell wall must be firm enough to define cell shape and allow a high internal osmotic pressure, while at the same time sufficiently dynamic to allow cell growth and division. Hayhurst et al. provide insight into how the cell wall in the rod-shaped organism, Bacillus subtilis, is structurally organized to achieve these functions. The main structural component of the cell wall is peptidoglycan, comprising glycan strands cross-linked by peptides. Atomic force microscopy (AFM) on purified glycan revealed individual strands up to 5 μm long (5000 disaccharides). Fluorescence microscopy in whole cells showed that B. subtilis displays very few terminal N-acetyl glucosamine (GlcNAc) residues and that internal peptidoglycan-associated GlcNAc residues exhibit a pattern suggestive of a helical structure. AFM imaging of B. subtilis peptidoglycan sacculi revealed little indication of structural features on the outer surface, probably because surface layers are hydrolyzed during cell wall turnover. However, the inner surface exhibited 50-nm-wide cables running across the short axis of the cell with cross striations consistent with a helical structure. The authors suggest that during biosynthesis, glycan strands are polymerized and cross-linked and then coiled to form the inner-surface cables. New helices are likely inserted into the cell wall by being cross-linked between two existing cables, while the external surface is cleaved to allow cell growth. — VV

Proc. Natl. Acad. Sci. U.S.A. 105, 14600 (2008).

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