FIG. 21.

Time course of penicillin-induced death and bacteriolysis. A simplified schematic survey is shown of the events which take place in growing control cells (A) and in staphylococci after the addition of 0.1-μg/ml penicillin (B). The critical first 90 min of treatment with this antibiotic, which include three cell cycles (generation time of staphylococci, 30 min), are illustrated; these events lead to penicillin-induced death and finally to bacteriolysis. First cell cycle. (A1 to A2) In untreated cells a normal, thin, highly organized and complete cross wall will be formed in the first division plane which contains the intact splitting system. Only after this cross wall has been completed do the murosomes of the first cross wall initiate cell separation via perforation of periodically arranged minute pores into the peripheral wall in the first division plane. After such initial step, the subsequent tearing apart of these pores initiates the separation of the two daughter cells. Reference figure, Fig. 10a. (B1 to B2) After the addition of a lethal concentration of penicillin, the staphylococci almost immediately lose the capacity to form a splitting system. Reference figure, Fig. 19a. Furthermore, the cells are now no longer capable of assembling normal, compact cross walls, but they synthesize mainly a network of fine fibrils arranged in rather thick, deformed and often incomplete defective cross walls. Nevertheless, the staphylococci try to start cell separation via murosome-induced perforation of the peripheral wall as if the first cross wall is intact and complete. However, instead of cell separation only rather large, murosome-induced cavities appear in the peripheral wall of the first division plane. Reference figure, Fig. 13f. Second cell cycle. (A3) During separation of the untreated daughter cells the formation of a new cross wall in the second division plane is initiated at a 90° angle with respect to the previous one. Reference figure, Fig. 2b. Cross wall initiation starts with a very localized, murosome-mediated wall lysis which attacks only some inner layers of the peripheral wall; cross wall assembly takes place and proceeds in this small lytic region. Reference figure, Fig. 5e. (B3) In the presence of penicillin, the second division plane is likewise initiated via a very localized, murosome-mediated wall lysis of some inner layers of the peripheral wall. Reference figure, Fig. 19c to f. However, no cross wall assembly takes place here; the cross wall material bound for the second division plane is detoured and deposited further on in the first division plane, so that the deformed, defective first cross wall becomes even thicker. Reference figure, Fig. 19e. (A4) In control cells, only after completion of the cross wall, the next cell separation is initiated via murosome-mediated perforation of the peripheral wall in the second division plane. Reference figure, Fig. 10a. (B4) Like in normal staphylococci, cell separation in the second division plane starts with murosome-mediated punching of pores into the peripheral wall in spite of the fact that in the presence of penicillin no cross wall material has been deposited at this site. Hence, due to their high internal turgor, the cells will burst and eject the murosome and a limited amount of their plasmatic constituents (aneurysm principle). This murosome-induced morphogenetic death takes place about 50 min after addition of the drug. Reference figure, Fig. 20b to f. For further details see Fig. 22. Third cell cycle. (A5) In control cells, already during the course of cell separation in the second division plane, the cross walls for the third division plane are initiated, again at a 90° angle to the previous one. Reference figure, Fig. 2a. (B5) The dead staphylococci, killed in the presence of penicillin during late stages of the second cell cycle, have lost part of their cytoplasm. This loss reduces considerably the tension of the elastic cell wall and results, therefore, in some shrinkage of the cells. The dead staphylococci preserve, however, their seemingly intact cellular integrity and, therefore, hardly differ from bacteria that are still alive. Reference figure, Fig. 23d. (A6) In control cells the cross walls for the third division planes are completed and the next cell separation is initiated (not depicted). (B6) Disintegration of the cell wall and decomposition of the cytoplasm (bacteriolysis) start only about 30 min after penicillin-induced death, leaving behind mainly large pieces of ruptured cell walls, membrane fragments, and plasmatic debris. Reference figure, Fig. 23b. Schematic drawing modified from reference 48 and supplemented and varied. For the sake of simplicity, only one murosome has been depicted at all the murosomal sites.