Penicillin: reversible inhibition of forespore septum development in Bacillus megaterium cells

Effects of antibiotics on synthesis and persistence of sigma E in sporulating Bacillus subtilis

A potential regulatory link between the activation of a sporulation-specific sigma factor (sigma E) and forespore septum formation was investigated by treating Bacillus subtilis with inhibitors of protein or peptidoglycan synthesis and monitoring the consequences of these treatments on sigma E activation and septation. Western blot (immunoblot) and electron microscopic analyses revealed that both the formation of sigma E and septation were inhibited to a similar degree when either rifampin or chloramphenicol was added at different times before the second hour into sporulation but that penicillin preferentially blocked septation. We interpret these results as indicating that the syntheses of the gene products for both septation and sigma E activation occur at approximately the same time in development but that synthesis of an intact septum is unlikely to be a prerequisite for the formation of sigma E. We observed that penicillin could not only block septation but, depending on the time of its addition, could also inhibit both the activation of sigma E and the synthesis of its precursor. The basis of this effect is unknown, but it is not due to an overall disruption of protein synthesis. The incorporation of [35S] methionine by the sporulating cultures was unaffected by penicillin treatment. A time course study of the effects of rifampin and chloramphenicol treatments on sigma E levels revealed that both the synthesis of sigma E and its disappearance from sporulating cultures is inhibited by these antibiotics. This suggests that ongoing macromolecular synthesis is required for the turnover of sigma E.

Correlation of penicillin-binding protein composition with different functions of two membranes in Bacillus subtilis forespores

The distribution of penicillin-binding proteins (PBPs) within different membranes of sporulating cells of Bacillus subtilis was examined in an effort to correlate the location of individual PBPs with their proposed involvement in either cortical or vegetative peptidoglycan synthesis. The PBP composition of forespores was determined by two methods: examination of isolated forespore membranes and assay of the in vivo accessibility of the PBPs to penicillin. In both cases, it was apparent that PBP 5*, the major PBP synthesized during sporulation, was present primarily, but not exclusively, in the forespore. The membranes from mature dormant spores were prepared by either chemically stripping the integument layers of the spores, followed by lysozyme digestion, or lysozyme digestion alone of coat-defective gerE spores. PBP 5* was detected in membranes from unstripped spores but was never found in stripped ones, which suggests that the primary location of this PBP is the outer forespore membrane. This is consistent with a role for PBP 5* exclusively in cortex synthesis. In contrast, vegetative PBPs 1 and 2A were only observed in stripped spore preparations that were greatly enriched for the inner forespore membrane, which supports the proposed requirement for these PBPs early in germination. The apparent presence of PBP 3 in both membranes of the spore reinforces the suggestion that it catalyzes a step common to both cortical and vegetative peptidoglycan synthesis.

Changes in penicillin-binding proteins during sporulation of Bacillus subtilis

The penicillin-binding proteins (PBPs) of Bacillus subtilis were examined in samples collected at various times from sporulating cultures and compared with the PBPs in a presporulation sample. Large increases in vegetative PBPs 2B and 3 and the appearance of at least one new PBP (42,000 daltons) occurred at reproducible times during sporulation. In some strains a second new PBP (60,000 daltons) was also produced. By comparing the PBP activities in sporulating cells and two spo0 mutants we have classified these changes as sporulation-related events rather than the consequences of stationary-phase aging. The other vegetative PBPs (PBPs 1, 2A, 4, and 5) decreased during sporulation, but not in sufficient amount or at the appropriate time to account for the appearance of the new proteins. A possible connection between specific PBP changes and the penicillin-sensitive stages of sporulation is suggested.

Inhibition of peptidoglycan, ribonucleic acid, and protein synthesis in tolerant strains of Streptococcus mutans

Exposure of exponentially growing cultures of Streptococcus mutans strains FA-1 and GS-5 to various concentrations of benzylpenicillin (Pen G) resulted in inhibition of turbidity increases at low concentrations (0.02 to 0.04 mug/ml). However, in contrast to some other streptococcal species, growth inhibition was not accompanied by cellular lysis or by a rapid loss of viability. In both strains, synthesis of insoluble cell wall peptidoglycan was very sensitive to Pen G inhibition and responded in a dose-dependent manner to concentrations of about 0.2 and 0.5 mug/ml for strains GS-5 and FA-1, respectively. Higher Pen G concentrations failed to inhibit further either growth or insoluble peptidoglycan assembly. Somewhat surprisingly, Pen G also inhibited both ribonucleic acid (RNA) and protein syntheses, each in a dose-dependent manner. Compared with inhibition of peptidoglycan synthesis, inhibition of RNA and protein syntheses by Pen G was less rapid and less extensive. Maximum amounts of radiolabeled Pen G were specifically bound to intact cells upon exposure to about 0.2 and 0.5 mug/ml of Pen G for strains GS-5 and FA-1, respectively, concentrations consistent with those that resulted in maximum or near-maximum inhibitions of the synthesis of cellular peptidoglycan, RNA, and protein. Five polypeptide bands that had a very high affinity for [(14)C]Pen G were detected in a crude cell envelope preparation of strain FA-1. After exposure of cultures of strain FA-1 to the effects of saturating concentrations of the drug for up to 3 h, addition of penicillinase was followed by recovery of growth after a lag. The length of the lag before regrowth depended on both Pen G concentration and time of exposure. On the basis of these and other observations, it is proposed that the secondary inhibitions of cellular RNA or protein synthesis, or both, are involved in the tolerance of these organisms to lysis and killing by Pen G and other inhibitors of insoluble peptidoglycan assembly.

Requirement for peptidoglycan synthesis during sporulation of Bacillus subtilis

Cultures of Bacillus subtilis were treated during sporulation with antibiotics (bacitracin and vancomycin) that affect peptidoglycan synthesis. The cells were resistant to the effects of the antibiotics only when the drugs were added about 2 h after the beginning of sporulation. This was about 1 h later than the escape time of a temperature-sensitive sporulation mutant that is unable to complete prespore septation. Similar experiments were done with a mutant temperature sensitive for peptidoglycan synthesis. This showed an escape curve similar to that shown by the antibiotics. When sporulating cells were treated with antibiotics, they produced alkaline phosphatase earlier than normal. Enzyme production was unaffected by inhibition of deoxyribonucleic acid synthesis but was inhibited by chloramphenicol. Sporulation mutants that are unable to make alkaline phosphatase under normal conditions were able to make it in the presence of bacitracin. The alkaline phosphatase made under these conditions was under "sporulation-type" control since its synthesis was repressible by casein hydrolysate and unaffected by inorganic phosphate. When cells were treated with bacitracin in the growth medium as well as in the sporulation medium, alkaline phosphatase synthesis was at the same level as in an untreated control. A number of other antibiotics and surfactants were tested for the ability to cause premature production of the phosphatase of those tested, only taurodeoxycholate whowed this behavior. Moreover, incubation of cells with taurodeoxycholate in the growth medium as well as in the sporulation medium prevented premature enzyme production.

Effect of cephapirin on formation of D-alanine carboxypeptidase in growing Bacillus subtilis cells

Cephapirin was utilized to examine the interaction of beta-lactam antibiotics with growing Bacillus subtilis cells and the biological effects simultaneously produced. Saturation binding and quantitative cell death were observed at the cephapirin concentration of 0.1 mug/ml. Cephapirin bound to all penicillin-binding proteins except the d-alanine carboxypeptidase. A specific [(14)C]benzylpenicillin-binding assay was developed for the d-alanine carboxypeptidase. At the lowest saturating concentration of antibiotic (0.1 mug/ml), cephapirin inhibited formation of the d-alanine carboxypeptidase. Upon incubation with cephapirin, 18% of the membranous d-alanine carboxypeptidase was released into the media. The data suggest that beta-lactam antibiotics may affect the formation of bacterial cytoplasmic membranes in addition to their effect on cell wall synthesis.

Accessibility of the (14C)benzylpenicillin binding proteins in membranes of sporulating bacilli

Triton X-100 treatment or freeze-thawing damages the membranes of sporulating or vegetative cells as seen by protein leakage from cells. A 40% increase in the specific [(14)C]benzylpenicillin-binding capacity of detergent-treated or frozen sporulating cells was observed. Neither freezing nor Triton X-100 treatment of vegetative cells produced a detectable effect on their [(14)C]benzylpenicillin-binding capacity. These data indicate the presence of penicillin-binding sites in intact sporulating bacilli not accessible to penicillin in routine binding assays. The chemical specificity of [(14)C]benzylpenicillin binding to detergent-treated sporulating cells is similar to that observed with untreated vegetative or sporulating cells.