FIG. 8.

Formation and positioning of the murosomes. A highly speculative attempt to reconstruct the formation and localization of staphylococcal murosomes, which are derivatives of the cytoplasmic membrane. (A) The primary wall. A part of the primary wall (prW) is depicted. (B-1) Formation of the secondary wall. By apposition growth the secondary wall (scW) is placed beneath the primary wall. The cytoplasmic membrane (CM) is indicated beneath the primary wall. Sandwiched between the wall and the membrane is the so-called membrane-wall interlayer (MWI). (B and B-2) Murosome morphogenesis. The murosomes (MuS) seem to originate from a local invagination of the cytoplasmic membrane followed by evagination of the membrane-wall interlayer (B and B-2). It is not clear, however, whether the secondary wall is formed before genesis of the murosomes (B-1 to B-2) or whether it is synthesized only after the murosomes are formed (B to C). Moreover, it cannot be excluded that murosomes and secondary wall originate synchronously. The surface of the murosomes is covered with particles which seem to originate from the membrane-wall interlayer. Reference figure, Fig. 6g and h. (C) Positioning of the murosomes. At this stage the murosomes are found to be anchored beneath the primary wall within the secondary wall material. The murosomes are always considered to be placed directly above the site where the next cross wall formation will be initiated. If murosome positioning takes place only after formation of the secondary wall (B-1 to B-2) the murosomes must be assumed to be capable of penetrating into the secondary wall (B-2 to C). Reference figure, Fig. 6c.