2 ALTERNATIVE MECHANISMS OF CELL-SEPARATION IN STAPHYLOCOCCI - ONE LYTIC AND ONE MECHANICAL

Electron microscopy studies revealed two different mechanisms of cell separation in Staphylococcus aureus. Both mechanisms were initiated by the centrifugal lyric action (directed outward from the center) of mu rosomes, which perforated the peripheral cell wall. Thereafter, during the first type of cell separation, murosomes also lysed large parts o f the cross wall proper in the opposite, i.e., centripetal direction, forming spokelike lytic lesions (''separation scars'') next to the mos t prominent structure of the cross wall, the splitting system. This bi directional lyric action of murosomes revealed that the staphylococcal cross wall is composed of permanent and transitory parts; transitory parts constituted about one-third of the volume of the total cross wal l and seemed to be digested during cell separation. The second mechani sm of cell separation was encountered within the splitting system, whi ch has been regarded as the main control unit for lyric cell separatio n for more than 25 years. The splitting system, however, represents ma inly a mechanical aid for cell separation and becomes effective when c ell-wall autolytic activities are insufficient.