Biochemical changes occurring during sporulation in Bacillus species

Time-Resolved Proteomics of Germinating Spores of Bacillus cereus

Bacillus cereus is a spore-forming human pathogen that is a burden to the food chain. Dormant spores are highly resistant to harsh environmental conditions, but lose resistance after germination. In this study, we investigate the B. cereus spore proteome upon spore germination and outgrowth so as to obtain new insights into the molecular mechanisms involved. We used mass spectrometry combined with co-expression network analysis and obtained a unique global proteome view of the germination and outgrowth processes of B. cereus spores by monitoring 2211 protein changeovers. We are the first to examine germination and outgrowth models of B. cereus spores experimentally by studying the dynamics of germinant receptors, other proteins involved in spore germination and resistance, and coat and exosporium proteins. Furthermore, through the co-expression analysis of 1175 proteins identified with high quality data, germination proteome data were clustered into eight modules (termed black, blue, brown, green, red, turquoise, grey, and yellow), whose associated functions and expression profiles were investigated. Germination related proteins were clustered into blue and brown modules, the abundances of which decreased after finishing germination. In the brown and blue we identified 124 proteins that could be vital during germination. These proteins will be very interesting to study in future genetic studies regarding their function in spore revival in B. cereus.

Nocturnal production of endospores in natural populations of epulopiscium-like surgeonfish symbionts

Prior studies have described a morphologically diverse group of intestinal microorganisms associated with surgeonfish. Despite their diversity of form, 16S rRNA gene surveys and fluorescent in situ hybridizations indicate that these bacteria are low-G+C gram-positive bacteria related to Epulopiscium spp. Many of these bacteria exhibit an unusual mode of reproduction, developing multiple offspring intracellularly. Previous reports have suggested that some Epulopiscium-like symbionts produce dormant or phase-bright intracellular offspring. Close relatives of Epulopiscium, such as Metabacterium polyspora and Clostridium lentocellum, are endospore-forming bacteria, which raises the possibility that the phase-bright offspring are endospores. Structural evidence and the presence of dipicolinic acid demonstrate that phase-bright offspring of Epulopiscium-like bacteria are true endospores. In addition, endospores are formed as part of the normal daily life cycle of these bacteria. In the populations studied, mature endospores were seen only at night and the majority of cells in a given population produced one or two endospores per mother cell. Phylogenetic analyses confirmed the close relationship between the endospore-forming surgeonfish symbionts characterized here and previously described Epulopiscium spp. The broad distribution of endospore formation among the Epulopiscium phylogenetic group raises the possibility that sporulation is a characteristic of the group. We speculate that spore formation in Epulopiscium-like symbionts may be important for dispersal and may also enhance survival in the changing conditions of the fish intestinal tract.

Serological studies on the formation of protein parasporal inclusions in Bacillus thuringiensis

A strain of Bacillus thuringiensis has been isolated, and methods have been developed for separation of the crystalline, parasporal inclusions in a pure form. Normal sporulation with concomitant crystal formation takes place when cells are incubated under suitable conditions in a nutrient free medium. Serological techniques have been used to study the origin and development of the crystals. Rabbit antisera have been prepared to a vegetative cell extract, suspensions of crystals, and a solution of crystal protein (obtained by alkali treatment of crystals). Tests have been carried out mainly by the Ouchterlony gel plate technique. Crystal protein solutions were found to be more active than suspensions of intact crystals both in reaction with, and in neutralization of, the crystal antibodies. Antisera to the vegetative cell extract gave no reaction with crystal protein. Ultrasonic extracts of cells taken before or during crystal formation gave no reaction with the crystal antibodies. Tests with alkali extracts of disrupted cells showed that the crystal antigen is absent in vegetative cells but arises during sporulation. The appearance of the antigen can be correlated with the formation and growth of the crystals as followed by examination of disrupted cell preparations under the electron microscope. It can be concluded that the crystalline protein inclusions do not arise from precursors in the same antigenic state.

Chemical and morphological studies of bacterial spore formation. II. Spore and parasporal protein formation in Bacillus cereus var. alesti

The development of both the spore and parasporal protein crystal of Bacillus cereus var. alesti was followed using chemical and cytological techniques. The changes which led to the formation of the fore-spore were similar to those already described for Bacillus cereus. However, adjacent to the developing fore-spore a small inclusion became discernible in phase contrast. This protein inclusion during its growth was differentiated from the chromatin and lipid-containing inclusions by sequential staining techniques. During spore and crystal formation no net synthesis of either nucleic acid was detected. Tracer studies with radioactive phosphorus confirmed that the spore chromatin was derived from that in the vegetative cell. These same studies also indicated that a turnover of ribonucleic acid occurred during the sporulation process. During their formation both the spore and crystal incorporated methionine-³⁵S from the medium and from cellular material into a bound form. Sequential extractions with alkali and with alkaline-thioglycollate reagent revealed that the solubility characteristics of the mature crystal were possibly related to the presence of intermolecular disulphide bonds which developed after the major synthesis of the crystal was complete. The synthetic nature of sporogenesis and crystal formation is discussed with reference to the concept of "endotrophic" sporulation.

Chemical and morphological studies of bacterial spore formation. IV. The development of spore refractility

From the stage of a completed membranous forespore to that of a fully ripened free spore, synchronously sporulating cells of a variant Bacillus cereus were studied by cytological and chemical methods. Particular attention was paid to the development of the three spore layers—cortex, coat, and exosporium—in relation to the forespore membrane. First, the cortex is laid down between the recently described (5) double layers of the forespore membrane. Then when the cortex is ⅓ fully formed, the spore coat and exosporium are laid down peripheral to the outer membrane layer covering the cortex. As these latter layers appear, the spores, previously dense by dark phase contrast, gradually "whiten" or show an increase in refractive index. With this whitening, calcium uptake commences, closely followed by the synthesis of dipicolinic acid and the process is terminated, an hour later, with the formation of a fully refractile spore. In calcium-deficient media, final refractility is lessened and dipicolinic acid is formed only in amounts proportional to the available calcium. If calcium is withheld during the period of uptake beyond a critical point, sporulating cells lose the ability to assimilate calcium and to form normal amounts of dipicolinic acid. The resulting deficient spores are liberated from the sporangia but are unstable in water suspensions. Unlike ripe spores, they do not react violently to acid hydrolysis and, in thin sections, their cytoplasmic granules continue to stain with lead solutions.

KINETICS OF DRY RUPTURE OF BACTERIAL SPORES IN THE PRESENCE OF SALT

Sacks, L. E. (U.S. Department of Agriculture, Albany, Calif.), Peter B. Percell, Richard S. Thomas, and Glen F. Bailey. Kinetics of dry rupture of bacterial spores in the presence of salt. J. Bacteriol. 87:952-960. 1964.-The kinetics of breaking spores in the dry state by use of an excess of sodium chloride and a steel ball in a shaking device were investigated. Under most conditions, disruption is a first-order process. The disruption-rate constant varies directly with the weight of the ball and inversely with the weight of the capsule contents (spores plus salt). Different spore batches differ somewhat in susceptibility to dry rupture. The dry-rupture process is highly reproducible and it is relatively simple to obtain preparations in which exactly 50%, or 90%, of the spores are broken. The procedure is uniquely suited to the disruption of small (5 to 20 mg) samples, but 150 mg of spores have been handled with conventional equipment. Apparently, the chief function of the salt is to separate the spores from one another with a relatively hard, energy-nonabsorbing matrix, preventing aggregation and consequent cushioning of the ball's impact. However, under certain conditions (small ball, high salt, large crystals) appreciable breakage results from collisions of spores with the salt crystals. The minimal salt-spore ratio for efficient breakage depends on the spore batch, but is usually greater than 3:1. Fine glass beads or inorganic salts other than sodium chloride will also serve as the matrix. Electron micrographs of the spores in various stages of disruption are shown, as are electron micrographs of the spore coats of Bacillus macerans, B. megaterium, B. cereus, B. coagulans, and Clostridium bifermentans. Prolonged agitation disintegrates spore coats. The spore coats of B. macerans exhibit a characteristic ribbed structure, previously detected only by carbon replicas of intact spores. Possible application to other biological materials is considered.

TRACE METAL REQUIREMENTS FOR SPORULATION OF BACILLUS MEGATERIUM

Kolodziej, Bruno J. (Northwestern University, Evanston, Ill.), and Ralph A. Slepecky. Trace metal requirements for sporulation of Bacillus megaterium. J. Bacteriol. 88:821-830. 1964.-A sucrose-mineral salts medium was purified for the purpose of definitively re-examining the trace metal cations associated with the sporulation of Bacillus megaterium. Two heretofore unknown requirements for copper (0.013 mug/ml of cupric ion) and molybdenum (27.2 mug/ml of molybdate ion) were uncovered. In the purified copper-supplemented medium, sporulation levels of other metals were determined as follows: iron, 0.5 mug/ml of ferrous ion; zinc, 1.1 mug/ml of zinc ion; manganese, 0.037 mug/ml of manganous ion; and calcium, 0.9 mug/ml of calcium ion. The approximate time during which the various metals were required was determined with iron, zinc, calcium, and manganese. A molybdenum substitution for copper, iron, or zinc was noted. The copper requirement was shown for the sporulation of B. cereus var. mycoides and var. albolactis, suggesting that this may be a general requirement for sporulation. The specific functions of metal ions in sporulation are not known, but they probably act as activators of the various enzyme systems necessary for sporulation.

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.

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

A precursor of the spore-lytic enzyme of Clostridium perfringens was extracted with alkali from dormant spores of the organism. The enzyme precursor was activated by incubating it with germinated spores which had been treated with alkali. The activation was greatly enhanced by the addition of 3-phosphoglycerate, suggesting that the conversion of precursor to active enzyme depends on endogenous energy-producing metabolism during germination.

Possible involvement of beta-lactamase in sporulation in Bacillus cereus

Nonreverting beta-lactamase-negative strains were isolated from the beta-lactamase-constitutive strain, Bacillus cereus 569 H. These strains differed from both beta-lactamase-inducible and -constitutive strains not only in failure to produce beta-lactamase but also in failure to autolyze on aging, delayed sporulation, and failure to release free spores from sporangia when produced. The addition of B. cereus beta-lactamase of 15% purity to a final concentration of 10 IU/ml stimulates sporulation and particularly the release of free spores in culture from sporangia of strain 569 (inducible wild-type), 569/H (constitutive mutant of 569), and HPen(-), a nonreverting beta-lactamase strain isolated from 569/H in this laboratory. Cultures of HPen(-) did not release free spores without this treatment. Similar stimulation of sporulation and spore release by beta-lactamase from B. cereus were observed in another beta-lactamase-negative strain derived from 569/H as well as in certain sporogeny mutants of B. subtilis. The beta-lactamase preparation used in these experiments was free of peptidases, proteases, and autolysins capable of solubilizing wall from vegetative cells. These results, taken with our previous finding that a soluble peptidoglycan inducer becomes available in cultures of B. cereus only at sporulation and that normal derepression of beta-lactamase accompanies normal sporulation, suggest that beta-lactamase in B. cereus may be involved in peptidoglycan metabolism during sporulation and possibly the breakdown of sporangial wall with the concomitant release of mature spores.

Derepression of beta-lactamase (penicillinase in Bacillus cereus by peptidoglycans

In Bacillus cereus 569 a cellular inducer of beta-lactamase was isolated which has the same constituents and basic structure as the soluble peptidoglycan found in sporulation, extracts from spores, and germination extracts, and which was previously called "spore-peptide." The material has been extensively purified and characterized. Two acid-soluble, high-molecular-weight peptidoglycan fractions containing muramic acid, glucosamine, diaminopimelic acid, d-aspartate, and d- and l-alanine, -lysine, -glycine, and -glutamate, distinguishable on the basis of size and different amino acid to amino sugar ratios, have been found to be responsible for the observed induction. Both fractions are capable of inducing high levels of beta-lactamase in concentrations lower than those of benzyl penicillin required for optimal induction. Several experiments also suggest that it is the accumulation of such soluble peptidoglycan in penicillin-treated cells which leads to induction of beta-lactamase and not the penicillin itself. The "spore-peptide" inducer becomes available during sporulation, and endogenous derepression of beta-lactamase activity occurs simultaneously. Such derepression also occurs in a strain of B. cereus very sensitive to penicillin and in which both uninduced as well as "spore-peptide"-induced beta-lactamase is a small fraction of that produced by the typical penicillinase producer. These results suggest that beta-lactamase in B. cereus functions in cell wall metabolism during sporulation.