EFFECT OF SPORULATION MEDIUM ON HEAT RESISTANCE, CHEMICAL COMPOSITION, AND GERMINATION OF BACILLUS MEGATERIUM SPORES

Comparison of sporulation and germination conditions for Clostridium perfringens type A and G strains

Clostridium perfringens is a spore forming, anaerobic, Gram-positive bacterium that causes a range of diseases in humans and animals. C. perfringens forms spores, structures that are derived from the vegetative cell under conditions of nutrient deprivation and that allows survival under harsh environmental conditions. To return to vegetative growth, C. perfringens spores must germinate when conditions are favorable. Previous work in analyzing C. perfringens spore germination has produced strain-specific results. Hence, we analyzed the requirements for spore formation and germination in seven different C. perfringens strains. Our data showed that C. perfringens sporulation conditions are strain-specific, but germination responses are homogenous in all strains tested. C. perfringens spores can germinate using two distinct pathways. The first germination pathway (the amino acid-only pathway or AA) requires L-alanine, L-phenylalanine, and sodium ions (Na⁺) as co-germinants. L-arginine is not a required germinant but potentiates germination. The AA pathway is inhibited by aromatic amino acids and potassium ions (K⁺). Bicarbonate (HCO₃^-), on the other hand, bypasses potassium-mediated inhibition of C. perfringens spore germination through the AA pathway. The second germination pathway (the bile salt / amino acid pathway or BA) is more promiscuous and is activated by several bile salts and amino acids. In contrast to the AA pathway, the BA pathway is insensitive to Na⁺, although it can be activated by either K⁺ or HCO₃^-. We hypothesize that some C. perfringens strains may have evolved these two distinct germination pathways to ensure spore response to different host environments.

Effect of Calcium and Manganese Supplementation on Heat Resistance of Spores of Bacillus Species Associated With Food Poisoning, Spoilage, and Fermentation

Bacterial spores often survive thermal processing used in the food industry, while heat treatment leads not only to a decrease in the nutritional and organoleptic properties of foods, but also to a delay in fermentation of fermented foods. Selective reduction of undesirable spores without such impediments is an ongoing challenge for food scientists. Thus, increased knowledge of the spore-forming bacteria is required to control them. In this study, the heat resistance results (D_100°C) of the spores of four Bacillus species were determined and compared to previous literature, and found that B. cereus has significantly lower heat resistance than the other Bacillus species, B. coagulans, B. subtilis, and B. licheniformis. Using the spores of these strains, this study also evaluated the effects of single and combined supplementation of calcium (0.00–2.00 mM) and manganese (0.00–0.50 mM) on heat resistance (D_100°C). The results revealed that the spores of B. licheniformis and B. cereus displayed the smallest heat resistance when sporulated on media rich in calcium. Conversely, B. coagulans spores and B. subtilis spores exhibited the greatest heat resistance when sporulated under calcium-rich conditions. The opposite results (stronger heat resistance for B. licheniformis spores and B. cereus spores, and smaller heat resistance for B. coagulans spores and B. subtilis spores) were obtained when the spores were formed on media poor in the minerals (particularly calcium). Based on the results, the Bacillus species were divided into two groups: B. licheniformis and B. cereus; and B. coagulans and B. subtilis. The study provides valuable insight to selectively reduce spores of undesirable Bacillus species in the food industry.

Metallo-inhibition of Mnx, a bacterial manganese multicopper oxidase complex

The manganese oxidase complex, Mnx, from Bacillus sp. PL-12 contains a multicopper oxidase (MCO) and oxidizes dissolved Mn(II) to form insoluble manganese oxide (MnO₂) mineral. Previous kinetic and spectroscopic analyses have shown that the enzyme's mechanism proceeds through an activation step that facilitates formation of a series of binuclear Mn complexes in the oxidation states II, III, and IV on the path to MnO₂ formation. We now demonstrate that the enzyme is inhibited by first-row transition metals in the order of the Irving-Williams series. Zn(II) strongly (K_i ~ 1.5 μM) inhibits both activation and turnover steps, as well as the rate of Mn(II) binding. The combined Zn(II) and Mn(II) concentration dependence establishes that the inhibition is non-competitive. This result is supported by electron paramagnetic resonance (EPR) spectroscopy, which reveals unaltered Mnx-bound Mn(II) EPR signals, both mono- and binuclear, in the presence of Zn(II). We infer that inhibitory metals bind at a site separate from the substrate sites and block the conformation change required to activate the enzyme, a case of allosteric inhibition. The likely biological role of this inhibitory site is discussed in the context of Bacillus spore physiology. While Cu(II) inhibits Mnx strongly, in accord with the Irving-Williams series, it increases Mnx activation at low concentrations, suggesting that weakly bound Cu, in addition to the four canonical MCO-Cu, may support enzyme activity, perhaps as an electron transfer agent.

Effects of Calcium and Manganese on Sporulation of Bacillus Species Involved in Food Poisoning and Spoilage

Spores are resistant against many extreme conditions including the disinfection and sterilization methods used in the food industry. Selective prevention of sporulation of Bacillus species is an ongoing challenge for food scientists and fermentation technologists. This study was conducted to evaluate the effects of single and combined supplementation of calcium and manganese on sporulation of common pathogenic and food spoilage Bacillus species: B. cereus, B. licheniformis, B. subtilis and B. coagulans. Sporulation of Bacillus vegetative cells was induced on sporulation media supplemented with diverse concentrations of the minerals. Under the various mineral supplementation conditions, the degree of sporulation was quantified with colonies formed by the Bacillus spores. The results revealed that B. licheniformis and B. cereus displayed the weakest sporulation capabilities on media with minimal supplementation levels of calcium and manganese. The lowest sporulation of B. subtilis and B. coagulans was observed on media supplemented with the highest level of calcium and low levels of manganese. Depending on effect of supplementation on sporulation, the Bacillus species were divided into two distinct groups: B. licheniformis and B. cereus; and B. subtilis and B. coagulans. The information provides valuable insight to selectively reduce sporulation of Bacillus species undesirable in the food industry.

A Standard Method To Inactivate Bacillus anthracis Spores to Sterility via Gamma Irradiation

In 2015, a laboratory of the United States Department of Defense (DoD) inadvertently shipped preparations of gamma-irradiated spores of Bacillus anthracis that contained live spores. In response, a systematic evidence-based method for preparing, concentrating, irradiating, and verifying the inactivation of spore materials was developed. We demonstrate the consistency of spore preparations across multiple biological replicates and show that two different DoD institutions independently obtained comparable dose-inactivation curves for a monodisperse suspension of B. anthracis spores containing 3 × 10¹⁰ CFU. Spore preparations from three different institutions and three strain backgrounds yielded similar decimal reduction (D₁₀) values and irradiation doses required to ensure sterility (D_SAL) to the point at which the probability of detecting a viable spore is 10^-6 Furthermore, spores of a genetically tagged strain of B. anthracis strain Sterne were used to show that high densities of dead spores suppress the recovery of viable spores. Together, we present an integrated method for preparing, irradiating, and verifying the inactivation of spores of B. anthracis for use as standard reagents for testing and evaluating detection and diagnostic devices and techniques.IMPORTANCE The inadvertent shipment by a U.S. Department of Defense (DoD) laboratory of live Bacillus anthracis (anthrax) spores to U.S. and international destinations revealed the need to standardize inactivation methods for materials derived from biological select agents and toxins (BSAT) and for the development of evidence-based methods to prevent the recurrence of such an event. Following a retrospective analysis of the procedures previously employed to generate inactivated B. anthracis spores, a study was commissioned by the DoD to provide data required to support the production of inactivated spores for the biodefense community. The results of this work are presented in this publication, which details the method by which spores can be prepared, irradiated, and tested, such that the chance of finding residual living spores in any given preparation is 1/1,000,000. These irradiated spores are used to test equipment and methods for the detection of agents of biological warfare and bioterrorism.

Paramagnetism in Bacillus spores: Opportunities for novel biotechnological applications

Spores of Bacillus megaterium, Bacillus cereus, and Bacillus subtilis were found to exhibit intrinsic paramagnetic properties as a result of the accumulation of manganese ions. All three Bacillus species displayed strong yet distinctive magnetic properties arising from differences in manganese quantity and valency. Manganese ions were found to accumulate both within the spore core as well as being associated with the surface of the spore. Bacillus megaterium spores accumulated up to 1 wt.% manganese (II) within, with a further 0.6 wt.% adsorbed onto the surface. At room temperature, Bacillus spores possess average magnetic susceptibilities in the range of 10-6 to 10-5 . Three spore-related biotechnological applications-magnetic sensing, magnetic separation and metal ion adsorption-were assessed subsequently, with the latter two considered as having the most potential for development.

Effect of sporulation medium and its divalent cation content on the heat and high pressure resistance of Clostridium botulinum type E spores

Clostridium (C.) botulinum type E belongs to the non-proteolytic physiological C. botulinum group II and produces the highly potent Botulinum neurotoxin E (BoNT/E) even at refrigerated temperatures. As C. botulinum type E spores are highly prevalent in aquatic environments, seafood and fishery products are commonly associated with this organism. Hydrostatic high pressure (HHP) treatments, or treatments combining HHP with elevated temperatures (HHPT), can be used to improve traditional preservation methods and increase food safety, quality and durability. In this study, we assessed the effect of different sporulation media and cation concentration on the heat resistance, HHP resistance, and HHPT resistance of spores from three C. botulinum type E strains. SFE (sediment fish extract) sporulation media yielded the most resistant spores, whereas, in M140 media, the least resistant spores were produced. Furthermore our results indicate that the divalent cation content (Ca(2+), Mg(2+) and Mn(2+)) plays a role in the differential development of C. botulinum type E spore resistance to heat, HHP and HHPT in different media. Calcium cations confer heat and HPPT resistance to spores, while high amounts of magnesium cations appear to have a negative effect. Manganese cations in low concentrations are important for the development resistance to HPP and HPPT treatments, but not heat alone. This study provides valuable information on the nature of non-proteolytic C. botulinum type E spores grown in different media. The data provided here can be useful to the food industry and to researchers when considering spore properties in food safety risk assessment and the experimental design of future inactivation studies.

Effect of radioprotective agents in sporulation medium on Bacillus subtilis spore resistance to hydrogen peroxide, wet heat and germicidal and environmentally relevant UV radiation

AIMS

To determine the effects of cysteine, cystine, proline and thioproline as sporulation medium supplements on Bacillus subtilis spore resistance to hydrogen peroxide (H(2)O(2)), wet heat, and germicidal 254 nm and simulated environmental UV radiation.

METHODS AND RESULTS

Bacillus subtilis spores were prepared in a chemically defined liquid medium, with and without supplementation of cysteine, cystine, proline or thioproline. Spores produced with thioproline, cysteine or cystine were more resistant to environmentally relevant UV radiation at 280-400 and 320-400 nm, while proline supplementation had no effect. Spores prepared with cysteine, cystine or thioproline were also more resistant to H(2)O(2) but not to wet heat or 254-nm UV radiation. The increases in spore resistance attributed to the sporulation supplements were eliminated if spores were chemically decoated.

CONCLUSIONS

Supplementation of sporulation medium with cysteine, cystine or thioproline increases spore resistance to solar UV radiation reaching the Earth's surface and to H(2)O(2). These effects were eliminated if the spores were decoated, indicating that alterations in coat proteins by different sporulation conditions can affect spore resistance to some agents.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides further evidence that the composition of the sporulation medium can have significant effects on B. subtilis spore resistance to UV radiation and H(2)O(2). This knowledge provides further insight into factors influencing spore resistance and inactivation.

Effects of minerals on sporulation and heat resistance of Clostridium sporogenes

In this study, various mineral supplements, such as chloride salts (CaCl2, MgCl2, MnCl2, FeCl2 and KCl) supplying cations and calcium salts (CaCl2, CaCO3, CaSO4, Ca(OH)2 and CaHPO4) supplying anions, were tested if they could stimulate the sporulation of Clostridium sporogenes, a surrogate microorganism for C. botulinum. Of the cations tested, the addition of CaCl2 showed a slightly, but not significantly, greater increase in spore levels within 3 weeks of incubation, compared to that of the other cations. The optimum concentration of CaCl2 was 0.5%, which yielded nearly 10(4) CFU/ml of spores. Of the anions tested, CaCO3 promoted sporulation within one week, which was the most effective compound for promoting rapid sporulation among the minerals tested. CaSO4 produced a pattern of sporulation similar to that of CaCl2. While CaHPO4 resulted in the maximum production of spores after 4 weeks, Ca(OH)2 failed to induce sporulation. With an optimized concentration of 0.5% CaCO3, the spore yield was approximately 10(5) CFU/ml. The spores prepared in sporulation medium with CaCO3 (pH 5.0) had slightly, but not significantly, higher D values than those produced with CaCl2 (pH 5.0) at temperatures ranging from 113 to 121 degrees C. However, no significant differences were observed in Z values (both 10.76 degrees C). In a large scale spore production, D(121 degrees C) values of the spore crops prepared with CaCl2 and CaCO3 and resuspended in phosphate buffer (pH 7.0) were found to be both 0.92 min. In conclusion, our data suggest that CaCO3 is highly effective in reducing sporulation time as well as enhancing heat resistance.

Heat activation/shock temperatures for Bacillus anthracis spores and the issue of spore plate counts versus true numbers of spores

Assessing true numbers of viable anthrax spores is complex. Optimal heat activation conditions vary with species, media and germinants. Published time/temperature combinations for Bacillus anthracis spores range from 60 degrees C for <or=90 min to boiling for 1 min. Results presented here indicate that temperatures are best kept to <or=70 degrees C and holding times need not exceed 15-30 min. Under conditions of 60 degrees C for 90 min, 62-23 degrees C for 15 min and 70 degrees C for 15 or 30 min, although the ratio of heated:unheated counts ranged from <1 to >1, post-heating counts were less than their pre-heating counterparts on between 71% and 88% of occasions. A high probability was found of viable spore counts differing significantly from counts determined microscopically, with differences of almost 1 log possible. Viable counts were lower than microscopic counts in 15 of 18 tests.

Differentiation of spores of Bacillus subtilis grown in different media by elemental characterization using time-of-flight secondary ion mass spectrometry

We demonstrate the use of time-of-flight secondary ion mass spectrometry (TOF-SIMS) in a forensics application to distinguish Bacillus subtilis spores grown in various media based on the elemental signatures of the spores. Triplicate cultures grown in each of four different media were analyzed to obtain TOF-SIMS signatures comprised of 16 elemental intensities. Analysis of variance was unable to distinguish growth medium types based on 40Ca-normalized signatures of any single normalized element. Principal component analysis proved successful in separating the spores into groups consistent with the media in which they were prepared. Confusion matrices constructed using nearest-neighbor classification of the PCA scores confirmed the predictive utility of TOF-SIMS elemental signatures in identifying sporulation medium. Theoretical calculations based on the number and density of spores in an analysis area indicate an analytical sample size of about 1 ng, making this technique an attractive method for bioforensics applications.

EFFECT OF SUGARS AND OTHER CARBON COMPOUNDS ON GERMINATION AND POSTGERMINATIVE DEVELOPMENT OF BACILLUS MEGATERIUM SPORES

Hyatt, Mildred T. (Pioneering Research Division. U.S. Army Natick Laboratories, Natick, Mass.), and Hillel S. Levinson. Effect of sugars and other carbon compounds on germination and postgerminative development of Bacillus megaterium spores. J. Bacteriol. 88:1403-1415. 1964.-A total of 77 carbon-containing compounds were tested for their ability to support germination and postgerminative development of Bacillus megaterium spores. The only effective germination agents were certain of the hexose sugars and their derivatives. With unheated spores, only d-glucose, d-mannose, 2-deoxy-d-glucose, d-glucosamine, and N-acetyl-d-glucosamine (all at 25 mm) supported appreciable germination (ca. 25%). Heat-shock at 60 C for 10 min increased germination and decreased the concentration of sugar required for germination, so that these compounds, at 2.5 mm, supported 40 to 60% germination. Higher concentrations (25 mm) of other compounds, d-fructose, l-sorbose, d-allose, d-altrose, 2-hydroxyethyl-d-glucose, and beta-methyl-d-glucoside, were required for appreciable germination of heated spores. Glucose or mannose contamination accounted for the germination apparently induced by certain other sugars. Ionic contamination did not appear to contribute to the germination induced by d-glucose, d-fructose, 2-deoxy-d-glucose, or l-sorbose. There was no clear-cut evidence for a multiplicity of metabolic pathways in the triggering of B. megaterium spore germination by various sugars. Postgerminative development of germinated spores was supported by a wider variety of carbon compounds, including some pentoses and hexoses, many oligosaccharides, sugar derivatives, some alcohols, and some of the tricarboxylic acid cycle intermediates. Compounds effective for germination were not necessarily utilizable for growth, and vice versa. Oxygen consumption rates reflected the progress and extent of postgerminative development on the various carbon compounds. Utilization of glucose during postgerminative development was followed, and the concentration requirements were determined.

Influence of transition metals added during sporulation on heat resistance of Clostridium botulinum 113B spores

Sporulation of Clostridium botulinum 113B in a complex medium supplemented with certain transition metals (Fe, Mn, Cu, or Zn) at 0.01 to 1.0 mM gave spores that were increased two to sevenfold in their contents of the added metals. The contents of calcium, magnesium, and other metals in the purified spores were relatively unchanged. Inclusion of sodium citrate (3 g/liter) in the medium enhanced metal accumulation and gave consistency in the transition metal contents of independent spore crops. In citrate-supplemented media, C. botulinum formed spores with very high contents of Zn (approximately 1% of the dry weight). Spores containing an increased content of Fe (0.1 to 0.2%) were more susceptible to thermal killing than were native spores or spores containing increased Zn or Mn. The spores formed with added Fe or Cu also appeared less able to repair heat-induced injuries than the spores with added Mn or Zn. Fe-increased spores appeared to germinate and outgrow at a higher frequency than did native and Mn-increased spores. This study shows that C. botulinum spores can be sensitized to increased thermal destruction by incorporation of Fe in the spores.

Factors influencing the resistance of biological monitors to ethylene oxide

The resistance of bacterial spore monitors is markedly influenced by the environmental conditions existing during development of spores and, subsequently, in the preparation and evaluation of the monitor. Sporulation medium, suspending medium, pasteurization and storage conditions influence resistance of spores of Bacillus subtilis var. niger to ethylene oxide, but incubation temperature and age of sporulating culture appear to be unimportant. The conditions under which the spore suspension is dried on the supporting medium of the monitor exerts a major influence on resistance. Spores exposed to ethylene oxide are abnormally susceptible to damage by shaking with Ballotini, a method frequently used to recover spores from monitors. Nutritional conditions, pH and temperature of incubation influence the ability of survivors to form colonies on solidified media.

Clear, defined medium for the sporulation of Clostridium perfringens

A new, defined medium for the sporulation of Clostridium perfringens is presented. Sporulation levels exceeding 10(6) to 10(7) heat-resistant spores per ml were obtained for seven strains: PS49, PS52, FD-1, T-65, NCTC strains 8798, 8238, and 10240. In the presence of theophylline, a methylxanthine, higher levels of heat-resistant spores were attained for strains PS49, PS52, FD-1, ant T-65; photomicrographs demonstrated a higher fraction of sporulating cells when these strains were grown in the presence of methylxanthines. Use of washed, highly diluted (less than 100 cells) inocula resulted in no reduction in spore yield. Strain KA3 grew well but sporulated poorly on this medium. The medium was clear and free of precipitate when small amounts (100 microgram/ml) of methylxanthine were incorporated.

Fatty acids of vegetative cells and spores of Bacillus licheniformis

Lipids were extracted from vegetative cells and spores of Bacillus licheniformis. Vegetative cells were grown in nutrient broth and spores on nutrient agar. Total lipid approximated 2.89% of the dry weight of vegetative cells and 2.09% of the dry weight of spores. The fatty acids were prepared as methyl esters and analyzed by gas chromatography and mass spectrometry. There were six fatty acids in concentrations greater than 5% of the total lipid in both spores and vegetative cells, but only palmitic acid was common to both. Fatty acids from vegetative cells in quantities of 5% or more of the total lipid material were lauric, myristic, palmitic, palmitoleic, and linoleic acids. Fatty acids from spores in concentrations greater than 5% of the total lipid were isopentadecylic, palmitic, Carbon-17 iso, and three other long or branched chain fatty acids which were not identified. Spores contained more long and branched chain fatty acids with odd numbers of carbon atoms than did vegetative cells.

Formation of dry-heat resistant Bacillus subtilis var. niger spores as influenced by the composition of the sporulation medium

Bacillus subtilis var. niger spores were produced on 20 different media. The spore yield from each medium and the dry-heat resistance at 160 C of the different spore populations were determined. The yield varied with a factor of 10(6) and the variation in D 160-value was about 10-fold (less than 20 S-190 S). A "synthetic" medium producing a high yield of spores with high dry-heat resistance was formulated. The concentrations of glucose, sucrose and calcium were found to be critical.

Isolation, characterization, and mapping of Bacillus subtilis 168 germination mutants

After mutagenesis with nitrosoguanidine, germination mutants of Bacillus subtilis 168 were selected by killing, with heat, spores that germinated at 42 C and collecting survivors at 30 C. The germination properties of nine mutants variously affected in amino acid biosynthesis and sugar utilization were studied in detail. They were divided into two groups: (i) Ger-ALA mutants, failed to germinate in 10 mM L-alanine but germinated in complex media (some of these mutants were temperature sensitive); (ii) Ger-PAB mutants, germinated poorly, even in complex media, suggesting that they were blocked in important germination functions. All the mutants failed to germinate in L-alpha-amino-n-butyrate or L-valine (including temperature-sensitive mutants only at the restrictive temperature) showing that there is a step necessary for germination affected by all three acids. The mutants had normal growth rates, indicating that the defective gene products were specific for germination functions. These defects were not identified. Eight of the mutants were mapped by transduction with phage PBS-1. The recombinants were scored either by observations, by microscopy of phase darkening of the spores, or by a plate test involving the reduction of tetrazolium by heated colonies of spores. Five of the mutations, of at least three phenotypes, were between thr-5 and cysB3 away from all the sporulation markers that have been previously mapped. A linked ald (alanine dehydrogenase) locus was on the other side of thr-5. The other Ger markers were located in at least two additional positions. Auxotrophic strains that were used for mapping germinated normally, but germination of the Ger mutants differed slightly in different genetic backgrounds.

Germination of Bacillus megaterium spores after various extraction procedures

The initiation of germination of Bacillus megaterium QM B1551 spores, grown in supplemented nutrient broth, has been studied. The initiation properties depend on buffer concentrations and the particular batch of spores. Initiation in l-alanine, KBr, calcium dipicolinate, or in buffer alone increases as a function of the spore age; whereas initiation in glucose, l-leucine, or l-proline remains relatively constant. Extraction of spores with alkali, sodium dodecyl sulfate-dithiothreitol, or lithium diiodosalicylate removes variable amounts of dipicolinic acid, hexosamine, and protein. These extracted spores are still capable of initiation and, in some cases, initiation is stimulated. However, extraction of spores with 8 M urea-10% mercaptoethanol inhibits subsequent initiation.

Inhibition of Bacillus megaterium by a trimethylamine oxide-associated browning reaction product

Heated combinations of trimethylamine oxide (TMAO) and culture media (tryptone, glucose, yeast extract broth or a defined minimal medium), or heated TMAO and glucose, contained substance(s) that inhibited growth of Bacillus megaterium. Inhibition was expressed primarily as an increase of the lag phase of growth; the logarithmic growth rate was comparable to control cultures. The addition of unheated TMAO to the culture media had no effect on growth. Results suggested that TMAO was decomposed during heating and that dimethylamine, one of the degradation products, reacted with glucose by a Maillard-Amadori reaction to produce the inhibitory substance(s).

Correlation between spore structure and spore properties in Bacillus megaterium

The spores of six strains of Bacillus megaterium were divided into two distinct groups on the basis of germination. Three of the strains germinated in a mixture of l-alanine and inosine (AL type spores), and three strains germinated in a mixture of glucose and potassium nitrate (GN type spores); recriprocal germination in the respective solutions did not occur. The AL spores and the GN spores were morphologically distinct. Other differences between the two spore groups included germination inhibition characteristics, dipicolinic acid content, hexosamine content, phosphorus and magnesium content, spore coat features, ion exchange properties, and heat resistance. A correlation appears to exist between spore morphology and certain other spore properties in strains of B. megaterium.

Separation of two functional roles of L-alanine in the initiation of Bacillus subtilis spore germination

Spores of the standard transformable Marburg strain of Bacillus subtilis can be initiated to germinate by l-alanine alone. We isolated mutants which required for this process, in addition to l-alanine, the combination of d-glucose + d-fructose + K(+) or NH(4) (+) ions. In place of fructose, autoclaved or caramelized glucose could be used. Even the standard type strain required the addition of these three agents when d-alanine was present or when the temperature was raised. These findings show that l-alanine normally performs two functions during initiation, one of which is absent in the mutants or is blocked by d-alanine or elevated temperature. One of our mutants was not absolutely dependent on the addition of external l-alanine, because it could be initiated at a reduced rate by the sole addition of glucose + K(+) or NH(4) (+). When K(+) or NH(4) (+) was replaced by Na(+), the initiation rate was greatly reduced. The divalent metal ions Mg(++), Mn(++), and Ca(++) could not satisfy the cation requirement.

Fine structure of Bacillus megaterium during microcycle sporogenesis

Ultrathin sections were prepared from cultures of Bacillus megaterium QM B1551 undergoing microcycle sporogenesis (initial spore to primary cell to second-stage spore without intervening cell division) on a chemically defined medium. The cytoplasmic core of the dormant spore was surrounded by plasma membrane, cell-wall primordium, cortex, outer cortical layer, and spore coats. Early in the cycle, the coat opened at the germinal groove, the cortex swelled, ribosomes and a chromatinic area associated with large mesosomes (which may later be incorporated into the expanding plasma membrane) appeared in the core, and the cell wall became defined at the site of the cell wall primordium. Poly-beta-hydroxybutyrate granules began to appear in the primary cell at about 3 hr. By 7 hr, the forespore of the second-stage spore was delineated by typical double membranes. Between 7 and 12 hr, second-stage cell-wall primordium and cortex developed between the separating forespore membranes. The inner membrane became the plasma membrane of the second-stage spore, and the outer membrane eventually disintegrated within the second-stage spore cortex. A densely staining double layer (spore-coat primordium) developed external to the outer forespore membrane. The inner spore coat and the outer cortical layer of the second-stage spore developed from this primordium. The outer part of the spore coat, probably of sporangial origin, was laid down on the external surface of the inner spore coat. By 12 hr, second-stage spores were almost mature. By 20 hr, the mature endospores, with a thickened outer coat, were often still enclosed by degenerate primary cell wall and by the outer cortical layer and spore coat of the initial spore.

Metabolic requirements for microcycle sporogenesis of Bacillus megaterium

Spores of Bacillus megaterium QM B1551 germinated, elongated, and resporulated (microcycle sporogenesis) in simple chemically defined media which permitted no cell division. The second-stage spores thus produced were heat-stable and required heat activation for germination. The original amount of spore deoxyribonucleic acid tripled before completion of the cycle. Acetate and a small amount of a tricarboxylic acid cycle intermediate were the minimal organic metabolic requirements for microcycle sporogenesis. During this cycle, germinated cells oxidized acetate only after a delay, whether or not glucose was initially present. Spores that were germinated in the absence of a carbon source first oxidized an endogenous substrate, and then developed the ability to oxidize acetate.

Changes in spores of Bacillus megaterium treated with thioglycolate at a low pH and restoration of germinability and heat resistance by cations

Spores of Bacillus megaterium QM B1551 treated with thioglycolate (0.4 m, pH 2.6) at 50 C for 30 min remained refractile, but they became stainable, lysozymesensitive, and nonviable, and they lost dipicolinic acid (DPA). The loss of DPA and of viability were functions of the time and temperature of exposure to thioglycolate. Spores treated with thioglycolate at a lower temperature and for a shorter time (30 C, 5 min) retained DPA, viability, and nonstainability. Although these spores also retained their resistance to gamma radiation and to lysozyme, they lost thermo-resistance. Their percentage of germination over a 2-hr period in glucose was markedly reduced. Germinability and heat resistance were restored by exogenous cations, suggesting that the thioglycolate treatment (30 C, 5 min) resulted in the loss of spore ions essential for normal germination in glucose and for heat resistance.

Sequence of events during Bacillus megaterim spore germination

Levinson, Hillel S. (U.S. Army Natick Laboratories, Natick, Mass.), and Mildred T. Hyatt. Sequence of events during Bacillus megaterium spore germination. J. Bacteriol. 91:1811-1818. 1966.-An integrated investigation of the sequence of events during the germination of Bacillus megaterium spores produced on three different media-Liver "B" (LB), synthetic, and Arret and Kirshbaum (A-K)-is reported. Heat-activated spores were germinated in a mixture of glucose and l-alanine. For studies of dipicolinic acid (DPA) release and increase in stainability and phase-darkening, germination levels were stabilized by the addition of 2 mm HgCl(2). Heat resistance was measured by conventional plating techniques and by a new microscopic method. The sequence (50% completion time) of LB spore germination events was: loss of resistance to heat and to toxic chemicals (3.0 min); DPA loss (4.7 min); stainability and Klett-measured loss of turbidity (5.5 min); phase-darkening (7.0 min); and Beckman DU-measured loss of turbidity (7.2 min). The time difference between 50% completion of stainability and complete phase darkening was 1.5 min, in excellent agreement with the microgermination time of 1.49 min as determined by observation of spores darkening under phase optics. Alteration of the sporulation medium modified the 50% completion times of these germination events, and, in some cases, their sequence. In the A-K spores, the rates of loss of heat resistance and DPA were substantially higher than those of the other germination events, whereas in spores produced in the LB and synthetic media all germination events followed an approximately parallel time course. This is discussed from the point of view of spore population heterogeneity and germination mechanisms.

Influence of exchangeable ions on germinability of bacterial spores

Rode, L. J. (The University of Texas, Austin), and J. W. Foster. Influence of exchangeable ions on germinability of bacterial spores. J. Bacteriol. 91:1582-1588. 1966.-Native spores of Bacillus megaterium Texas, and H-spores produced by titration of native spores to pH 4 with mineral acid, did not germinate in a solution of alanine and inosine unless a strong electrolyte was present. Ca-spores prepared from either H-spores or native spores did germinate efficiently in the same solution without a strong electrolyte. Of several other bivalent cations tested, only strontium and barium could substitute for calcium in conditioning spores for subsequent germination in the absence of an electrolyte. Variable responses were obtained with different metal ion forms of 62 unidentified soil isolates and several stock species of Bacillus. Although the pattern of response was not uniform in all organisms, ions played a crucial role in the germinability of the great majority of strains tested.

Endotrophic calcium, strontium, and barium spores of Bacillus megaterium and Bacillus cereus

Foerster, Harold F. (The University of Texas, Austin), and J. W. Foster. Endotrophic calcium, strontium, and barium spores of Bacillus megaterium and Bacillus cereus. J. Bacteriol. 91:1333-1345. 1966.-Spores were produced by washed vegetative cells suspended in deionized water supplemented with CaCl(2), SrCl(2), or BaCl(2). Normal, refractile spores were produced in each case; a portion of the barium spores lost refractility and darkened. Thin-section electron micrographs revealed no apparent anatomical differences among the three types of spores. Analyses revealed that the different spore types were enriched specifically in the metal to which they were exposed during sporogenesis. The calcium content of the strontium and the barium spores was very small. From binary equimolar mixtures of the metal salts, endotrophic spores accumulated both metals to nearly the same extent. Viability of the barium spores was considerably less than that of the other two types. Strontium and barium spores were heat-resistant; however, calcium was essential for maximal heat resistance. Significant differences existed in the rates of germination; calcium spores germinated fastest, strontium spores were slower, and barium spores were slowest. Calcium-barium and calcium-strontium spores germinated readily. Endotrophic calcium and strontium spores germinated without the prior heat activation essential for growth spores. Chemical germination of the different metal-type spores with n-dodecylamine took place at the same relative rates as physiological germination. Heat-induced release of dipicolinic acid occurred much faster with barium and strontium spores than with calcium spores. The washed "coat fraction" from disrupted spores contained little of the spore calcium but most of the spore barium. The metal in this fraction was released by dilute acid. The demineralized coats reabsorbed calcium and barium at neutral pH.

RESPONSES OF BACILLUS SUBTILIS SPORES TO IONIC ENVIRONMENTS DURING SPORULATION AND GERMINATION

Fleming , H. P. (University of Illinois, Urbana), and Z. John Ordal . Responses of Bacillus subtilis spores to ionic environments during sporulation and germination. J. Bacteriol. 88: 1529–1537. 1964.—The ionic environments of germination and sporulation menstrua had a prominent influence on characteristics of Bacillus subtilis spores. There was a synergistic effect for l -alanine and inorganic ions on spore germination. The maximal rate of germination in solutions of l -alanine was dependent on ionic concentration and species. Germination was negligible in l -alanine at low ionic strength but increased as the ionic strength was increased up to about 10 −1 m with a variety of salts. Phosphate was the most active ion tested, and divalent cations were the least active in supporting germination in l -alanine. Germination progressed slowly at 45 C in sodium chloride or sodium phosphate alone but not in CaCl 2 alone. Germination rates in l -alanine were retarded at high ionic strengths (μ in the range of 0.1 to 1.0). Inhibitory effects of high concentrations of certain divalent cations on germination were related to the binding abilities of these metals. High concentrations of NaCl (10 −1 to 1.0 m ) in the sporulation medium resulted in lowered heat resistance and germination rate of the resulting spores. The addition of calcium (5 × 10 −2 m CaCl 2 ) to the sporulation medium relieved the repression of NaCl on germination and caused the spores to have a greater heat resistance. Calcium and dipicolinic acid (DPA) contents of the spores were unaffected by NaCl in the sporulation medium. The calcium, but not the DPA, content of spores increased as a result of supplementing the sporulation medium with calcium. Possible roles of ions in the germination of spores are discussed.