Energy-dependent activation of spore-lytic enzyme precursor by germinated spores of Clostridium perfringens

Physiological role of carbon dioxide in spore germination of Clostridium perfringens S40

Germination of Clostridium perfringens is known to be triggered by nutrients such as l-alanine and inosine, and facilitated by CO2, however the role of CO2 has not been fully understood. During the studies of the germination-specific protease GSP, we found that CO2 could be replaced by bicarbonate or weakly acidic pH (pH 6.0-6.5). We also found that the spores obtained from the C. perfringens S40 overproducing GSP could germinate without CO2. Moreover, the spores could germinate in the absence of nutrients, when the spores were incubated with bicarbonate or under weakly acidic pH. GSP, which might consist of three homologous proteases, CspA, CspB, and CspC, is one of the key enzymes involved in the spore germination, and converts the pre-mature form of the spore cortex-lytic enzyme, SleC, to the mature form. Maturation of SleC in the spores obtained from the mother strain of C. perfringens S40 requires nutrients plus bicarbonate or weakly acidic pH. In contrast, mature SleC was found in the spores obtained from the cells overpoducing GSP, when the spores were treated by nutrients, bicarbonate or weakly acidic pH. Each nutrients, bicarbonate and weakly acidic pH can trigger the germination of the spores obtained from C. perfringens cells overproducing GSP.

Molecular characterization of a germination-specific muramidase from Clostridium perfringens S40 spores and nucleotide sequence of the corresponding gene

The exudate of fully germinated spores of Clostridium perfringens S40 in 0.15 M KCI-50 mM potassium phosphate (pH 7.0) was found to contain another spore-lytic enzyme in addition to the germination-specific amidase previously characterized (S. Miyata, R. Moriyama, N. Miyahara, and S. Makino, Microbiology 141:2643-2650, 1995). The lytic enzyme was purified to homogeneity by anion-exchange chromatography and shown to be a muramidase which requires divalent cations (Ca2+, Mg2+, or Mn2+) for its activity. The enzyme was inactivated by sulfhydryl reagents, and sodium thioglycolate reversed the inactivation by Hg2+. The muramidase hydrolyzed isolated spore cortical fragments from a variety of wild-type organisms but had minimal activity on decoated spores and isolated cell walls. However, the enzyme was not capable of digesting isolated cortical fragments from spores of Bacillus subtilis ADD1, which lacks muramic acid delta-lactam in its cortical peptidoglycan. This indicates that the enzyme recognizes the delta-lactam residue peculiar to spore peptidoglycan, suggesting an involvement of the enzyme in spore germination. Immunochemical studies indicated that the muramidase in its mature form is localized on the exterior of the cortex layer in the dormant spore. A gene encoding the muramidase, sleM, was cloned into Escherichia coli, and the nucleotide sequence was determined. The gene encoded a protein of 321 amino acids with a deduced molecular weight of 36,358. The deduced amino acid sequence of the sleM gene indicated that the enzyme is produced in a mature form. It was suggested that the muramidase belongs to a separate group within the lysozyme family typified by the fungus Chalaropsis lysozyme. A possible mechanism for cortex degradation in C. perfringens S40 spores is discussed.

Pulling the trigger: the mechanism of bacterial spore germination

In spite of displaying the most extreme dormancy and resistance properties known among living systems, bacterial endospores retain an alert environment-sensing mechanism that can respond within seconds to the presence of specific germinants. This germination response is triggered in the absence of both germinant and germinant-stimulated metabolism. Genes coding for components of the sensing mechanism in spores of Bacillus subtilis have been cloned and sequenced. However, the molecular mechanism whereby these receptors interact with germinants to initiate the germination response is unknown. Recent evidence has suggested that in spores of Bacillus megaterium KM, proteolytic activation of an autolytic enzyme constitutes part of the germination trigger reaction.

Germination-specific cortex-lytic enzyme is activated during triggering of Bacillus megaterium KM spore germination

Antibodies were raised against purified germination-specific cortex-lytic enzyme (GSLE) from spores of Bacillus megaterium KM which neutralized the ability of GSLE to germinate permeabilized spores. Western blotting of dormant spore and vegetative cell fractions separated by SDS-PAGE demonstrated that GSLE is spore-specific and that greater than 90% of the GSLE is associated with the dormant spore cortex peptidoglycan as a phosphorylated 63kD pro-form, which could only be visualized after lysozyme digestion of the peptidoglycan. During germination, the 63kD pro-form of GSLE is processed to release the active enzyme, which had an apparent molecular weight of 30kD. Inhibitor studies demonstrated that GSLE activation occurs as part of the commitment reaction and thus represents the first-identified enzymatic event to occur during germination triggering. Proteins that cross-react with anti-GSLE sera are present in spore fractions of other species.

Purification and properties of a germination-specific cortex-lytic enzyme from spores of Bacillus megaterium KM

Two peptidoglycan-lytic enzyme activities were isolated from spores of Bacillus megaterium KM. Surface-bound lytic enzyme was extracted from dormant spores and hydrolysed a variety of peptidoglycan substrates including isolated spore cortex, but did not cause refractility changes in permeabilized spores. Germination-specific lytic enzyme activity appeared early in germination and had minimal activity on isolated peptidoglycan substrates, but caused refractility changes in permeabilized spores of several Bacillus isolated peptidoglycan substrates, but caused refractility changes in permeabilized spores of several Bacillus species. The germination-specific lytic enzyme was shown to be a heat-sensitive 29 kDa protein with maximal activity at pH 6.5. It catalysed post-commitment muramic acid delta-lactam synthesis and displayed an inhibitor profile similar to that for post-commitment A600 loss. The relationship of the germination-specific enzyme to a recently proposed model of spore germination is discussed.