Cell lysis in 168/s and in an autolytic-deficient mutant, FJ6, was studied by following the release of wall material liberated by the two known autolysins, an -acetylmuramoyl-L-alanine amidase and an endo-β--acetylglucosaminidase. Lysing organisms were examined in thin sections by electron microscopy and measurements were made both of the location and size of holes produced by autolysin action and of peripheral wall thickness. In strain 168/s the initial site of lysis involved solubilization of the cross-wall and of one or both poles distal to the division site. Subsequently, the cylindrical wall was degraded through perforations at an increasing number of sites. Specific sites of autolysis, at the cross-wall and at one pole, were also observed in organisms prefixed with formaldehyde in a buffer of low ionic strength, although these effects were not observed in strain FJ6. In strain 168/s the bulk of the autolysin appeared to be located at the cross-wall and at one distal pole. The peripheral wall was reduced in thickness in autolysing cells, although it was uncertain whether the reduction was due to autolytic attack at the outer surface, to contraction of the wall in the suspending buffer or to shrinkage during preparation for electron microscopy. Lysis of strain FJ6 involved the initial breakdown of the cytoplasmic membrane and leakage of cellular contents through a limited number of sites along the wall. In contrast, lysis in MB21, the parental strain of FJ6, was similar to that described for strain 168/s.


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