Partition of old murein in small patches over the entire wall of E. coli cells forced to grow as a coccoid.

With the development of a technique to visualize the ages of different portions of the sacculus, De Pedro et al. showed that the sacculus of Escherichia coli was tripartite: (i) the establish poles contained only old wall, (ii) the nascent poles (or septa) were composed entirely of new murein, and (iii) the elongating cylindrical wall was a mixture of patches of both old and new peptidoglycan. This short note presents a computer analysis of data files of work presented in the recent paper by De Pedro et al. of the growth pattern of the wall of E. coli forced to grow in a quite unusual morphology as large spheres in the presence of mecillinam. Compared with rod-shaped cells, only very small patches (spikes) of old wall were retained interspersed with new murein during the conversion to large spheroids. This subdivision appeared to be the case for both the previous wall of the poles, which are ordinarily retained intact, and the previous patches retained within the cylindrical wall. These very small patches after the conversion to spheroids were much smaller than the sidewall patches in rod-shaped cells reported previously. This implies that the mechanism that prevents the insertion of new wall into both the wall of the poles and the old wall patches of the sidewall in the presence of mecillinam is superseded by insertion throughout the old wall. The work in the De Pedro et al. paper from 2001 was done with cells of same strain as in the earlier papers with rod-shaped cells, so the results of computer analysis of the fluorescence micrographs can be critically compared.