Alteration in the penicillin-binding profile of Bacillus megaterium during sporulation

Characterization of the involvement of two compensatory autolysins in mother cell lysis during sporulation of Bacillus subtilis 168

The 30-kDa sporulation-specific peptidoglycan hydrolase CwlC of Bacillus subtilis 168 was purified and characterized. It is an N-acetylmuramoyl-L-alanine amidase (amidase) that is associated with the mother cell wall of sporulating cells, and although it is secreted, it undergoes no N-terminal processing except removal of the initial methionine. It was found that mother cells of a strain insertionally inactivated in cwlC and lytC (the major vegetative amidase gene) did not lyse at the end of sporulation. Mutants with single mutations in cwlC or lytC lysed, and so the two autolysins must have mutually compensatory roles in mother cell lysis. Active CwlC and LytC are present at the time of mother cell lysis; however, reporter gene analysis revealed that lytC transcription ceases early in sporulation, and therefore the function that LytC has in mother cell lysis is performed by material remaining from presporulation expression. Autolytic enzymes similar in molecular mass to CwlC were detected in two other Bacillus species by their cross-reactivity with anti-CwlC antiserum.

Molecular analysis of three major wall-associated proteins of Bacillus subtilis 168: evidence for processing of the product of a gene encoding a 258 kDa precursor two-domain ligand-binding protein

Antisera raised to a 109 kDa wall-associated protein (WAP) of Bacillus subtilis 168 cross-reacts with two other WAPs of 220 and 58 kDa. The structural gene for the 109 kDa WAP (designated wapA) was cloned, sequenced, mapped at around 340 degrees on the B. subtilis 168 chromosome and found to encode a precursor of all three wall-bound forms (2334 amino acids and 258,329 Da). The protein has two ligand-binding domains; the N-terminal domain has three direct repeats of 102 residues with 40% identity, which are responsible for wall binding. The C-terminal domain consists of two blocks of residues with a conserved motif repeated a total of 31 times. The motif consensus sequence GXXXX(Y,F)XYDXXG is almost identical to that of the Escherichia coli rearrangement hot spot family and shows similarity to a carbohydrate-binding motif of a number of Gram-positive secreted proteins. A mutant insertionally inactivated in the wapA gene had no distinguishable phenotype apart from lacking the three WAPs. The possible role of WAPA and its two-domain relationship with other ligand-binding proteins is discussed.

Penicillin-binding proteins in beta-lactam-resistant laboratory mutants of Streptococcus pneumoniae

The increasing number of penicillin-resistant clinical strains of Streptococcus pneumoniae has raised questions about the mechanism involved. We have isolated a large number of independent, spontaneous laboratory mutants with increasing resistance against either piperacillin or cefotaxime. Both classes of mutants showed a different pathway of penicillin-binding protein (PBP) alterations, and within each group of mutants the individual PBPs appeared to have changed at different resistance levels and in different sequences. The mutations led to decreased beta-lactam affinity and possibly to a reduction in the amount of protein present in the cell, but differences in apparent molecular weight, like those reported in low- and high-level resistant pathogenic strains, were not found. Some mutants showed a high degree of cross-resistance to a variety of penicillins and cephalosporins independently of the acquired PBP alterations, indicating that different genotypes can be responsible for the same phenotypic expression of resistance.

Reduced heat resistance of mutant spores after cloning and mutagenesis of the Bacillus subtilis gene encoding penicillin-binding protein 5

Part of the gene encoding penicillin-binding protein 5 from Bacillus subtilis 168 was cloned in Escherichia coli with a synthetic oligonucleotide as a hybridization probe. The gene was designated dacA by analogy with E. coli. The nucleotide sequence was determined, and the predicted molecular mass was 45,594 daltons (412 amino acids). A comparison of the predicted amino acid sequence with that of the E. coli penicillin-binding protein 5 indicated that these enzymes showed about 25% identity. The B. subtilis dacA gene was mutated by integration of a plasmid into the structural gene by homologous recombination. A comparison of the mutant and control strains revealed that (i) the mutant lacked detectable penicillin-binding protein 5, (ii) the D-alanine carboxypeptidase activity of membranes isolated from the mutant was only 5% of that measured in membranes from the control strain, (iii) the mutant cells showed apparently normal morphology only during exponential growth, and after the end of exponential phase the cells became progressively shorter, (iv) the mutant sporulated normally except that the forespore occupied about two-thirds of the mother cell cytoplasm and, during its development, migrated towards the center of the mother cell, and (v) purified mutant spores were 10-fold less heat resistant but possessed normal refractility and morphology. Preliminary chemical analysis indicated that the structure of the cortex of the mutant was different.

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.

Membrane particles from Escherichia coli and Bacillus subtilis, containing penicillin-binding proteins and enriched for chromosomal-origin DNA

Rapid-sedimenting DNA-membrane complexes were obtained from both Bacillus subtilis and Escherichia coli by a method involving gentle lysis followed by restriction enzyme digestion and sucrose gradient fractionation. These complexes were substantially enriched in chromosomal origin DNA, and in B. subtilis, the complexes were enriched in penicillin-binding proteins relative to that of the total membrane. Such complexes may represent procaryotic membrane domains which are topographically and functionally distinct.

The association of penicillin-binding proteins with cell elongation and septum formation in Bacillus megaterium

Analysis of the penicillin-binding proteins in the membranes from germinated spores of Bacillus megaterium and a filamentous mutant indicated that (a) no specific synthesis of any penicillin-binding protein occurred before or during two relatively synchronous cell divisions, (b) penicillin-binding proteins 1, 3a and 3b may be involved in cell elongation and (c) filamentation of the mutant may be due to a decrease in the concentration of penicillin-binding protein 1.

The sporulation-specific penicillin-binding protein 5a from Bacillus subtilis is a DD-carboxypeptidase in vitro

The sporulation-specific penicillin-binding protein 5a was purified from Bacillus subtilis and shown to possess dd-carboxypeptidase activity in vitro.

Regulation of penicillin-binding protein activity: description of a methicillin-inducible penicillin-binding protein in Staphylococcus aureus

The penicillin-binding proteins (PBPs) of two methicillin-resistant strains of Staphylococcus aureus (R2 and R1) were analyzed in cells grown in the absence and in the presence of methicillin. Under the former condition, strain R2 showed the typical PBP pattern of beta-lactam-susceptible strains, while strain R1 showed a markedly increased amount of PBP-3. Under the latter condition, on the other hand, a novel PBP (PBP-2a) located between PBP-2 and -3 was detected in strain R2, while strain R1 appeared to synthesize an even greater amount of PBP-3, in respect to untreated cells. Both R2 PBP-2a and R1 PBP-3 showed a very low affinity for methicillin, which was consistent with the MICs for the respective strains.

Restoration of vegetative penicillin-binding proteins during germination and outgrowth of Bacillus subtilis spores: relationship of individual proteins to specific cell cycle events

The order in which the vegetative penicillin-binding proteins (PBPs) are first synthesized and the rate of their return to normal levels during germination and outgrowth of Bacillus subtilis spores were determined. The rate of synthesis of most of the PBPs was much faster than that of the majority of other membrane proteins, which is consistent with the involvement of PBPs in biosynthesis of the rapidly expanding peptidoglycan. The pattern of PBP changes that occurred during the cell cycle, including sporulation, suggests a likely role for PBP 2A in cell elongation and a unique requirement for PBP 2B during both symmetric and asymmetric septum formation. PBP 3 is the only PBP that appears to be equally necessary for vegetative and cortical peptidoglycan synthesis.

The interaction of nocardicin A with the penicillin-binding proteins of Bacillus megaterium KM

The inhibition of elongation of Bacillus megaterium KM growing in the presence of low concentrations of nocardicin A resulted in the production of osmotically stable, actively dividing coccal-shaped cells. Saturation of penicillin-binding proteins 3a and 3b with nocardicin A in vivo at these concentrations was correlated with the inhibition of cell elongation. Analysis of the DD-carboxypeptidase activity of isolated vegetative membranes of B. megaterium KM in vitro indicated that penicillin-binding protein 4 is not a DD-carboxypeptidase under the assay conditions used. Penicillin-binding proteins were analysed by two-dimensional gel electrophoresis and the suitability of lysozyme treatment of cells as a method of membrane preparation was investigated with regard to the detection of proteins with highly labile penicillin-binding activities in vitro.

Stability and synthesis of the penicillin-binding proteins during sporulation

The penicillin-binding proteins (PBPs) of Bacillus subtilis were examined after incubation of vegetative and sporulating cultures with chloramphenicol, an inhibitor of protein synthesis. The results indicate that the sporulation-specific increases in vegetative PBPs 2B and 3 and the appearance of two new PBPs, 4* and 5*, depend on concurrent protein synthesis, which is most likely to be de novo synthesis of the PBPs rather than synthesis of an activator or processing enzyme. It was also learned that in vivo the PBPs differ in their individual stabilities, which helps to explain some of the quantitative changes that occur in the PBP profile during sporulation. All the membrane-bound PBPs, except possibly PBP 1, were found to be stable in the presence of crude extracts of sporulating cells that contained proteolytic activity.

Identification of penicillin-binding protein 5a of Bacillus megaterium KM as a DD-carboxypeptidase

Measurement of the stabilities of DD-carboxypeptidase activity and the penicillin-binding activity of proteins 5 and 5a in membranes isolated from vegetative cells and stage-V forespores suggests that the unique sporulation-specific protein 5a may be a penicillin-sensitive DD-carboxypeptidase.