Layered Distribution, According to Age, Within the Cell Wall of Bacillus Subtilis

When soluble autolytic activity was added to growing cultures of a mutant possessing a reduced rate of cell wall turnover, there was a delay of more than one generation before solubilization of new cell wall began, in contrast to the immediate increase in the rate of solubilization of old cell wall. A similar delay was found before turnover of new cell wall occurred in the parent, in agreement with a previous report (Mauck et al., 1971). When sodium lauryl sulfate-inactivated cell walls were prepared, the great bulk of the wall formed a uniformly susceptible substrate to added autolytic activity. The immediate solubilization of new wall eliminates insusceptibility to autolytic enzyme as an explanation for the failure to be turned over. There were, however, major differences in the rate of solubilization of wall of different ages. During solubilization of the initial 30% of the cell wall preparation, wall two generations old was solubilized at least seven times faster than wall one-half a generation old. This result is interpreted in terms of differences in accessibility. The cell wall is seen as consisting of a series of layers, the age of which increases with the distance from the membrane, such that wall newly synthesized on the membrane passes out through the thickness of the cell wall layer during subsequent growth and only becomes susceptible to turnover as it reaches the outer surface, largely in the form of a layer, more than one generation after incorporation.