The Cell Wall of Escherichia coli: Early Effects of Penicillin Treatment and Deprivation of Diaminopimelic Acid

SUMMARY The morphological effects on bacterial walls of the early stages of inhibition of mucopolymer synthesis have been investigated in Escherichia coli. Inhibition was achieved in strain b by penicillin treatment and in auxotrophic strains m203 and m173–25 by deprivation of diaminopimelic acid (DAP). Only growing organisms were affected; the walls of organisms in stationary phase remained unchanged. The first effects of treatment with penicillin appear in 20 min., whereas changes in DAP-deprived auxotrophs become visible only after 40–60 min. The soft layers of the wall formed bag-like protrusions and, at the same time, wide gaps or holes developed in the proteinaceous portion of the rigid layer. Widening of these gaps was paralleled by a weakening of the rigid layer, resulting eventually in bursting of the cell, or in protective media of high osmotic strength, in the formation of spheroplasts. The initial appearance and the subsequent widening of gaps in the rigid layer, observed almost exclusively in organisms multiplying logarithmically, are taken to indicate the presence of a mechanically weak mucopolymer formed under conditions that prevent crosslinking. The discontinuities, interpreted as sites of mucopolymer synthesis, were randomly distributed over the bacterium. Their appearance at the poles of the bacteria seemed frequently to be suppressed by media of high osmotic pressure, in which plasmolysis was first seen in the polar regions. The observations suggest that morphogenesis of the protein layer is dependent on the secondary structure of the mucopolymer in newly synthesized wall areas.