The origin of the rotation of one end of a cell relative to the other end during growth of gram-positive rods.
The Gram-positive rod wall elongates by an inside-to-outside mechanism of linking new peptidoglycan on the inside and the cracking, by autolysis, of old wall on the outside. During this process the peptidoglycan experiences stress in different directions in different levels of the wall. The stress that develops in a rod-shaped cell if the wall was uniform in physical properties throughout its thickness is twice as great in the hoop direction as in the axial direction. This leads to splitting in the direction of the longitudinal axis. However, the older, partially split, more peripheral wall is stressed in the direction of the elongating cell axis and thus favors circumferential cracks. It is suggested that these processes combine to form a system of helical cracks, grooves, or crevasses. The stable system of grooves would have the same handedness, fairly constant pitch and elongate as the cell grows. Their continuing development would result in the rotation of one end of the cell relative to the other even in cells with no spiral or apparent helical character. Such rotation has been experimentally observed with Bacillus subtilis. The proposed mechanism for rotation during growth may account, in part, for the formation of helical coils of bundles of filamentous organisms (macrofibers), the morphology of spirilla and vibroids, and for the shapes of some mutant and some antibiotic-treated organisms. Rotation due to generation of helical cracks as the result of the biophysics of the growth process as proposed here, is an alternative to the proposal by Mendelson (1976, Helical growth of Bacillus subtilis: a new model for cell growth. Proc. natn. Acad. Sci. U.S.A. 73, 1740-1744) that rotation is due to the laying down of nascent peptidoglycan in a helical pattern.
Koch
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Department of Biology, Indiana University, Bloomington 47405.
D001407:Bacillus / Q000254:growth & development* / Q000502:physiology; D001412:Bacillus subtilis / Q000254:growth & development; D002473:Cell Wall / Q000502:physiology; D012399:Rotation; D013314:Stress, Mechanical