Biophysics of pole formation of gram-positive rods.

During pole formation in Bacillus subtilis the inner and outer surfaces of the nascent pole are enlarged by almost exactly the same extent. This means that the stress is almost uniformly distributed throughout the polar wall. This differs from the situation in the cylindrical side wall, where most of the stress is exerted in the outer portions of the intact wall. Because the stress is shared more uniformly, the maximum strain in any part of the polar wall is reduced, compared with the maximum strain within the side wall. The lowered stress may account, in part, for the resistance of the polar wall to hydrolysis by autolytic enzymes under certain conditions. The shape of the newly completed pole is significantly different from the spherical shape that the hydrostatic pressure would tend to produce. It does, however, achieve the shape that maximizes the polar volume under the restrictions arising due to expansion along the circumference not being possible near the junction of cylindrical and polar wall.