The kinetics of
peptidoglycan degradation were examined under different conditions of
autolysis of Escherichia coli. With
cephaloridine- or
moenomycin-induced
autolysis, degradation did not exceed 25 to 35%, whereas in
EDTA-induced
autolysis it rapidly reached 65 to 70%. When nonautolyzing cells were fixed overnight with
glutaraldehyde, followed by an
osmium fixation, and thin sections were stained by the
phosphotungstic acid method, a dark, 15-nm-thick layer of uniform appearance and constant width occupied the whole area between the inner and outer membranes of the envelope. The stained material was tentatively identified with
peptidoglycan. Ultrastructural changes in this
phosphotungstic acid-stained periplasmic space were investigated at different time intervals after induction of
autolysis. In all cases, breakdown proceeded over the whole cell surface. During
antibiotic-induced
autolysis a progressive thinning down limited to the inner side of the layer was observed. During
EDTA-induced
autolysis, the rapid decrease in thickness correlated well with the important loss of material labeled with [3H]
diaminopimelic acid. Considering these changes and the insufficient amounts of
peptidoglycan (1.3 U/nm2) necessary to account for a regularly structured
polymer occupying the whole 15-nm layer, it was speculated that
peptidoglycan might be unevenly distributed throughout the periplasmic space.