CHEMICALLY DEFINED, SYNTHETIC MEDIA FOR SPORULATION AND FOR GERMINATION AND GROWTH OF BACILLUS SUBTILIS

Pilot-scale production of Bacillus subtilis MSCL 897 spore biomass and antifungal secondary metabolites in a low-cost medium

OBJECTIVES

Bacillus subtilis is a plant growth promoting bacterium (PGPB) that acts as a microbial fertilizer and biocontrol agent, providing benefits such as boosting crop productivity and improving nutrient content. It is able to produce secondary metabolites and endospores simultaneously, enhancing its ability to survive in unfavorable conditions and eliminate competing microorganisms. Optimizing cultivation methods to produce B. subtilis MSCL 897 spores on an industrial scale, requires a suitable medium, typically made from food industry by-products, and optimal temperature and pH levels to achieve high vegetative cell and spore densities with maximum productivity.

RESULTS

This research demonstrates successful pilot-scale (100 L bioreactor) production of a biocontrol agent B. subtilis with good spore yields (1.5 × 109 spores mL-1) and a high degree of sporulation (>80%) using a low-cost cultivation medium. Culture samples showed excellent antifungal activity (1.6-2.3 cm) against several phytopathogenic fungi. An improved methodology for inoculum preparation was investigated to ensure an optimal seed culture state prior to inoculation, promoting process batch-to-batch repeatability. Increasing the molasses concentration in the medium and operating the process in fed-batch mode with additional molasses feed, did not improve the overall spore yield, hence, process operation in batch mode with 10 g molasses L-1 is preferred. Results also showed that the product quality was not significantly impacted for up to 12 months of storage at room temperature.

CONCLUSION

An economically-feasible process for B. subtilis-based biocontrol agent production was successfully developed at the pilot scale.

Meat extract casein peptone agar - A novel culture medium for the enumeration of Bacillus endospores in commercial products

Here we propose a novel culture medium, Meat Extract Casein Peptone (MECP) agar, to support the enumeration of Bacillus endospores in commercial products. The formulation is the result of screening eight different veterinary, pharmaceutical, and industrial grade peptones for the ability to support the formation of small, well-defined Bacillus colonies on solid culture medium. The impact of agar purity, agar formulation rate, and metal cation additives were examined in prototype medium batches prepared from preferred peptone inputs. A customized plate counting assay based on the resultant MECP agar formulation was compared with standardized pour-plate and spread-plate assays (ISO 4833) and flow cytometry for the ability to accurately enumerate five Bacillus-based biostimulants and biofertilizers. Estimations of Bacillus endospore concentration generated by the customized spread-plate assay were significantly higher than those produced by ISO 4833 pour-plate and spread-plate assays for four out of the five tested products and were in better agreement with flow cytometry values; however, flow cytometry values were numerically higher than values returned by both plating methods. Both flow cytometry and plating assays based on MECP or similar culture media represent potential candidates for standardization and validation through organizations such as ISO and AOAC International for the enumeration of Bacillus-based products.

Cryptosporulation in Kurthia spp. forces a rethinking of asporogenesis in Firmicutes

Endosporulation is a complex morphophysiological process resulting in a more resistant cellular structure that is produced within the mother cell and is called endospore. Endosporulation evolved in the common ancestor of Firmicutes, but it is lost in descendant lineages classified as asporogenic. While Kurthia spp. is considered to comprise only asporogenic species, we show here that strain 11kri321, which was isolated from an oligotrophic geothermal reservoir, produces phase-bright spore-like structures. Phylogenomics of strain 11kri321 and other Kurthia strains reveals little similarity to genetic determinants of sporulation known from endosporulating Bacilli. However, morphological hallmarks of endosporulation were observed in two of the four Kurthia strains tested, resulting in spore-like structures (cryptospores). In contrast to classic endospores, these cryptospores did not protect against heat or UV damage and successive sub-culturing led to the loss of the cryptosporulating phenotype. Our findings imply that a cryptosporulation phenotype may have been prevalent and subsequently lost by laboratory culturing in other Firmicutes currently considered as asporogenic. Cryptosporulation might thus represent an ancestral but unstable and adaptive developmental state in Firmicutes that is under selection under harsh environmental conditions.

Comparative evaluation for thermostability and gastrointestinal survival of probiotic Bacillus coagulans MTCC 5856

Thermal stability (D-value and pasteurization) and gastric acid resistance of spore forming and nonspore forming probiotic strains were evaluated in this study. Bacillus coagulans MTCC 5856 spores showed highest thermal resistance (D-value 35.71 at 90 °C) when compared with other Bacillus strains and Lactobacillus species. B. coagulans strains exhibited significantly higher resistance to simulated gastric juice (pH 1.3, 1.5, and 2.0) compared to Lactobacillus strains. It also showed high resistance to cooking conditions of chapati (whole wheat flour-based flatbread) (88.94% viability) and wheat noodles (and 94.56% viability), suggesting remarkable thermal resistance during food processing. Furthermore, B. coagulans MTCC 5856 retained 73% viability after microwave cooking conditions (300 s, at 260 °C) and 98.52% in milk and juice at pasteurization temperature (420 min, at 72 °C). Thus, B. coagulans MTCC 5856 clearly demonstrated excellent resistance to gastric acid and high temperature (90 °C), thereby suggesting its extended application in functional foods (milk, fruit juices, chapati, and wheat noodles) wherein high temperature processing is involved.

The Effect of Calcium/Magnesium Ratio on the Biomass Production of a Novel Thermoalkaliphilic Aeribacillus pallidus Strain with Highly Heat-Resistant Spores

Hot springs are fascinating extreme environments for the isolation of polyextremophilic microorganisms with extraordinary characteristics. Since polyextremophilic bacterial growth are not as high as routine bacteria, the objective of this study was to investigate the effect of some environmental factors on biomass and metabolites productions in the newly isolated strain, from Larijan hot spring in Iran. The strain was identified as Aeribacillus pallidus Lhs-10 and deposited as CCUG 72355 and IBRC-M 11202 in Sweden and Iran, respectively. This thermoalkaliphilic strain can grow best at 50 °C, pH 8 and in the presence of 25 g/l NaCl. The physiological characterization of this strain show that [Ca/Mg] ratio affect its growth and biomass production with the best results obtained at the ratio of 2.5. Moreover, lactic and acetic acids production by this strain was affected by pH, aeration, and temperature, where a metabolic shift was detected from lactate to acetate production when the culture was aerated. Besides, its spores could tolerate heating at 80, 85, 90, 95 and 98 °C for 30 min without any reduction in the initial spore population, whereas D-value was defined 50 min at 98 °C. This newly lactic acid-producing strain of A. pallidus can be a promising strain that can be used in the harsh conditions in industrial processes.

Comparison of the plant growth-promotion performance of a consortium of Bacilli inoculated as endospores or as vegetative cells

The effect of three plant growth-promoting Bacillus strains inoculated either alone or as a consortium was tested on oat (Avena sativa) growth. The bioinoculants were applied as vegetative cells or endospores at low cell densities on the seeds and their effect was tested in sterile in vitro conditions, pot experiments, and a field trial. The in vitro seed germination assay showed that both individual bacterial inocula and bacterial consortia had positive effects on seed germination. Greenhouse pot experiments with sterile and non-sterile soil showed that consortia increased the total dry biomass of oat plants as compared to single strain inoculation and uninoculated controls. However, the positive impact on plant growth was less prominent when the bioinoculated strains had to compete with native soil microbes. Finally, the field experiment demonstrated that the consortium of vegetative cells was more efficient in promoting oat growth than the endospore consortium and the uninoculated control. Moreover, both consortia successfully colonized the roots and the rhizosphere of oat plants, without modifying the overall structure of the autochthonous soil microbial communities.

Metabolic engineering of Bacillus subtilis for production of para-aminobenzoic acid - unexpected importance of carbon source is an advantage for space application

High-strength polymers, such as aramid fibres, are important materials in space technology. To obtain these materials in remote locations, such as Mars, biological production is of interest. The aromatic polymer precursor para-aminobenzoic acid (pABA) can be derived from the shikimate pathway through metabolic engineering of Bacillus subtilis, an organism suited for space synthetic biology. Our engineering strategy included repair of the defective indole-3-glycerol phosphate synthase (trpC), knockout of one chorismate mutase isozyme (aroH) and overexpression of the aminodeoxychorismate synthase (pabAB) and aminodeoxychorismate lyase (pabC) from the bacteria Corynebacterium callunae and Xenorhabdus bovienii respectively. Further, a fusion-protein enzyme (pabABC) was created for channelling of the carbon flux. Using adaptive evolution, mutants of the production strain, able to metabolize xylose, were created, to explore and compare pABA production capacity from different carbon sources. Rather than the efficiency of the substrate or performance of the biochemical pathway, the product toxicity, which was strongly dependent on the pH, appeared to be the overall limiting factor. The highest titre achieved in shake flasks was 3.22 g l-1 with a carbon yield of 12.4% [C-mol/C-mol] from an amino sugar. This promises suitability of the system for in situ resource utilization (ISRU) in space biotechnology, where feedstocks that can be derived from cyanobacterial cell lysate play a role.

The use of a chemically defined artificial diet as a tool to study Aedes aegypti physiology

Aedes aegypti mosquitoes obtain from vertebrate blood nutrients that are essential to oogenesis, such as proteins and lipids. As with all insects, mosquitoes do not synthesize cholesterol but take it from the diet. Here, we used a chemically defined artificial diet, hereafter referred to as Substitute Blood Meal (SBM), that was supplemented with cholesterol to test the nutritional role of cholesterol. SBM-fed and blood-fed mosquitoes were compared regarding several aspects of the insect physiology that are influenced by a blood meal, including egg laying, peritrophic matrix formation, gut microbiota proliferation, generation of reactive oxygen species (ROS) and expression of antioxidant genes, such as catalase and ferritin. Our results show that SBM induced a physiological response that was very similar to a regular blood meal. Depending on the nutritional life history of the mosquito since the larval stage, the presence of cholesterol in the diet increased egg development, suggesting that the teneral reserves of cholesterol in the newly hatched female are determinant of reproductive performance. We propose here the use of SBM as a tool to study other aspects of the physiology of mosquitoes, including their interaction with microbiota and pathogens.

Effect of medium components and culture conditions in Bacillus subtilis EA-CB0575 spore production

Bacillus subtilis spores have important biotechnological applications; however, achieving both, high spore cell densities and sporulation efficiencies in fermentation, is poorly reported. In this study, medium components and culture conditions were optimized with different statistical methods to increase spore production of the plant growth promoting rhizobacteria B. subtilis EA-CB0575. Key medium components were determined with Plackett-Burman (PB) design, and the optimum concentration levels of two components (glucose, MgSO4·7H2O) were optimized with a full factorial and central composite design, achieving 1.37 × 10(9) CFU/mL of spore cell density and 93.5 % of sporulation efficiency in shake flask. The optimized medium was used to determine the effect of culture conditions on spore production at bioreactor level, finding that maintaining pH control did not affect significantly spore production, while the interaction of agitation and aeration rates had a significant effect on spore cell density. The overall optimization generated a 17.2-fold increase in spore cell density (8.78 × 10(9) CFU/mL) and 1.9-fold increase in sporulation efficiency (94.2 %) compared to that of PB design. These results indicate the potential of B. subtilis EA-CB0575 to produce both, high spore cell densities and sporulation efficiencies, with very low nutrient requirements and short incubation period which can represent savings of process production.

A new chemically defined medium for the growth and sporulation of Bacillus cereus strains in anaerobiosis

A new chemically defined liquid medium, MODS, was developed for the aerobic growth and anaerobic growth and sporulation of Bacillus cereus strains. The comparison of sporulation capacity of 18 strains of B. cereus has shown effective growth and spore production in anaerobiosis..

Coatings capable of germinating and neutralizing Bacillus anthracis endospores

Endospores are formed by various bacterial families, including Bacillus and Clostridium, in response to environmental stresses as a means to survive conditions inhospitable to vegetative growth. Although metabolically inert, the endospore must interact with its environment to determine an optimal time to return to a vegetative state, a process known as germination. Germination has been shown to occur in response to a variety of chemical stimuli from specific nutrient germinants including amino acids, sugars and nucleosides. This process is known to be mediated primarily by the GerA family of spore-specific receptor proteins which initiates a signal transduction cascade that results in a return of oxidative metabolism in response to germinant receptor interactions. Herein, we report the development of a novel coating system capable of germinating B. anthracis endospores, followed by rapid killing of the vegetative bacteria by a novel incorporated amphiphilic biocide. The most effective formulation tested exhibited an ability to germinate and kill B. anthracis endospores and vegetative bacteria, respectively. The formulation reported resulted in a 90% reduction in as little as 5 min, and a 6 log reduction by 45 min.

Pulsed feedback defers cellular differentiation

In response to sudden environmental stress, B. subtilis cells can defer sporulation for multiple cell cycles using a pulsed positive feedback loop.

Environmental signals induce diverse cellular differentiation programs. In certain systems, cells defer differentiation for extended time periods after the signal appears, proliferating through multiple rounds of cell division before committing to a new fate. How can cells set a deferral time much longer than the cell cycle? Here we study Bacillus subtilis cells that respond to sudden nutrient limitation with multiple rounds of growth and division before differentiating into spores. A well-characterized genetic circuit controls the concentration and phosphorylation of the master regulator Spo0A, which rises to a critical concentration to initiate sporulation. However, it remains unclear how this circuit enables cells to defer sporulation for multiple cell cycles. Using quantitative time-lapse fluorescence microscopy of Spo0A dynamics in individual cells, we observed pulses of Spo0A phosphorylation at a characteristic cell cycle phase. Pulse amplitudes grew systematically and cell-autonomously over multiple cell cycles leading up to sporulation. This pulse growth required a key positive feedback loop involving the sporulation kinases, without which the deferral of sporulation became ultrasensitive to kinase expression. Thus, deferral is controlled by a pulsed positive feedback loop in which kinase expression is activated by pulses of Spo0A phosphorylation. This pulsed positive feedback architecture provides a more robust mechanism for setting deferral times than constitutive kinase expression. Finally, using mathematical modeling, we show how pulsing and time delays together enable “polyphasic” positive feedback, in which different parts of a feedback loop are active at different times. Polyphasic feedback can enable more accurate tuning of long deferral times. Together, these results suggest that Bacillus subtilis uses a pulsed positive feedback loop to implement a “timer” that operates over timescales much longer than a cell cycle.

How long should a cell wait to respond to an environmental change? While many pathways such as those affecting chemotaxis respond to environmental signals quickly, in other contexts a cell may want to defer its response until long after the signal's onset—sometimes waiting multiple cell cycles. How can cells create “timers” to regulate these long deferrals? We study this question in the bacterium Bacillus subtilis, which responds to stress by transforming into a dormant spore. We show that B. subtilis can defer sporulation for extended time periods by first undergoing multiple rounds of growth and proliferation, and only then sporulating. The timer for this deferral is a pulsed positive feedback loop, which ratchets up the concentration of the sporulation master-regulator Spo0A to a critical level over multiple cell cycles. Finally, using mathematical modeling, we illustrate how a novel dynamic feedback mechanism, “polyphasic positive feedback,” lets cells defer sporulation more robustly than with other circuit strategies. Developing techniques that can access pulsing and time-delay dynamics with higher time resolution will enable us to determine if this polyphasic strategy provides a general design principle for the regulation of multi-cell-cycle deferral times seen in other systems.

Requirement for Acetate and Glycine (or Serine) for Sporulation Without Growth of Bacillus subtilis

Cells of Bacillus subtilis sporulate when they are transferred, at any time of growth in nutrient sporulation medium, to a potassium-phosphate buffer containing slowly utilizable carbon sources such as l-aspartate, citrate, l-glutamate, or lactate. Transfer to buffer containing more rapidly utilizable carbon sources such as malate or glucose leads to sporulation only when the cells either had reached the end of growth or when the transfer medium also contains glycine. Acetate, which as a sole carbon source does not allow growth, also does not alone permit sporulation; however, the presence of both acetate (0.05 m) and glycine or l-serine (0.01 m) in the buffer medium allows sporulation if the cells are transferred to this medium after they have grown in the nutrient sporulation medium beyond the end of the exponential growth phase (T(0)). The development, required before transfer, does not seem to involve the end of a round of deoxyribonucleic acid duplication, as experiments with tryptophan-starved cells have indicated. Glycine or serine cannot be replaced by any of the known metabolites, which are partially derived from them. Amino acid analysis of nutrient sporulation medium showed that glycine (but not serine) is present at a concentration of 0.3 mm at the beginning of the developmental period, thus allowing, in combination with an acetyl-coenzyme A (CoA) precursor, sporulation but not growth. Acetyl-CoA is required not only for adenosine-triphosphate synthesis but also for some other reactions.

Recovery of spores from thermophilic dairy bacilli and effects of their surface characteristics on attachment to different surfaces

Spores from four Geobacillus spp. were isolated from a milk powder manufacturing line in New Zealand. Liquid sporulation media produced spore yields of approximately 10(7) spores ml(-1); spores were purified using a two-phase system created with polyethylene glycol 4000 and 3 M phosphate buffer. The zeta potentials of the spores from the four isolates ranged from -10 to -20 mV at neutral pH, with an isoelectric point between pH 3 and 4. Through contact angle measurements, spores were found to be hydrophilic and had relative hydrophobicity values of 10 to 40%, as measured by the microbial adhesion to hexadecane assay. The most hydrophilic spore isolate with the smallest negative charge attached in the highest numbers to Thermanox and stainless steel (1 x 10(4) spores cm(-2)), with fewer spores attaching to glass (3 x 10(3) spores cm(-2)). However, spores produced by the other three strains attached in similar numbers (P > 0.05) to all substrata (approximately 1 x 10(3) spores cm(-2)), indicating that there was no simple relationship between individual physicochemical interactions and spore adherence. Therefore, surface modifications which limit the attachment of one strain may not be effective for all stains, and control regimens need to be devised with reference to the characteristics of the particular strains of concern.

Rapid differentiation and enumeration of the total, viable vegetative cell and spore content of thermophilic bacilli in milk powders with reference to Anoxybacillus flavithermus

AIMS

The development of a rapid method for the selective detection and enumeration of the total and viable vegetative cell and spore content of thermophilic bacilli in milk powder by PCR.

METHODS AND RESULTS

Quantitative PCR and microscopy indicate the presence of up to 2.9 log units more cells in milk powder than accounted for by plate counting due to the majority of cells being killed during milk processing. Two approaches for viable and dead cell differentiation of thermophilic bacilli by quantitative PCR were evaluated, these being the nucleic binding dye ethidium monoazide (EMA) and DNase I digestion. The former agent exposed to a viable culture of Anoxybacillus flavithermus caused considerable cell inactivation. In contrast, DNase I treatment had no effect on cell viability and was utilized to develop DNA extraction methods for the differential enumeration of total, viable vegetative cells and spores in milk powder. Moreover, the methods were further applied and evaluated to 41 factory powder samples taken throughout eight process runs to assess changes in numbers of vegetative cells and spores with time. DNase I treatment reduced vegetative cell numbers enumerated with PCR by up to 2.6 log units. The quantification of spores in the factory milk powders investigated indicates on average the presence of 1.2 log units more spores than determined by plate counting.

CONCLUSIONS

The method presented in this study provides the ability to selectively enumerate the total and viable cell and spore content of reconstituted milk.

SIGNIFICANCE AND IMPACT OF THE STUDY

The current study provides a tool to monitor the extent of thermophilic contamination during milk powder manufacturing 60-90 min after sampling.

Sensing of nitrogen limitation by Bacillus subtilis: comparison to enteric bacteria

Previous studies showed that Salmonella typhimurium apparently senses external nitrogen limitation as a decrease in the concentration of the internal glutamine pool. To determine whether the inverse relationship observed between doubling time and the glutamine pool size in enteric bacteria was also seen in phylogenetically distant organisms, we studied this correlation in Bacillus subtilis, a gram-positive, sporulating bacterium. We measured the sizes of the glutamine and glutamate pools for cells grown in batch culture on different nitrogen sources that yielded a range of doubling times, for cells grown in ammonia-limited continuous culture, and for mutant strains (glnA) in which the catalytic activity of glutamine synthetase was lowered. Although the glutamine pool size of B. subtilis clearly decreased under certain conditions of nitrogen limitation, particularly in continuous culture, the inverse relationship seen between glutamine pool size and doubling time in enteric bacteria was far less obvious in B. subtilis. To rule out the possibility that differences were due to the fact that B. subtilis has only a single pathway for ammonia assimilation, we disrupted the gene (gdh) that encodes the biosynthetic glutamate dehydrogenase in Salmonella. Studies of the S. typhimurium gdh strain in ammonia-limited continuous culture and of gdh glnA double-mutant strains indicated that decreases in the glutamine pool remained profound in strains with a single pathway for ammonia assimilation. Simple working hypotheses to account for the results with B. subtilis are that this organism refills an initially low glutamine pool by diminishing the utilization of glutamine for biosynthetic reactions and/or replenishes the pool by means of macromolecular degradation.

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

Levinson, Hillel S. (U.S. Army Natick Laboratories, Natick, Mass.), and Mildred T. Hyatt. Effect of sporulation medium on heat resistance, chemical composition, and germination of Bacillus megaterium spores. J. Bacteriol. 87:876-886. 1964.-Bacillus megaterium spores, grown on variously supplemented media, had varying concentrations of P, Ca, Mn, or dipicolinic acid. Supplementation with CaCl(2) yielded spores with increased heat resistance; addition of l-glutamate, l-proline, or increase of the phosphate concentration yielded spores with reduced heat resistance. Germination characteristics depended on both the sporulation medium and the germinant (glucose, l-alanine, l-leucine, or KNO(3)); pronounced differences were demonstrable with glucose and l-alanine, which trigger germination via different metabolic pathways. An increase in CaCl(2) during sporulation yielded spores with increased germination in glucose but not in l-alanine. Germination in l-alanine was optimal with spores produced on media containing 0.1 mm MnCl(2), but germination of such spores was minimal in glucose. An increase in the sporulation medium phosphate decreased the initial germination rate in glucose, but not in l-alanine. Spores produced in CaCl(2)-supplemented media had increased heat-activation requirements (increased dormancy) for germination induced by l-alanine, and decreased heat-shock requirements for glucose-induced germination. An increase of sporulation phosphate yielded spores with reduced dormancy for germination induced by l-alanine, but with unchanged dormancy on the other germinants. Spores produced with added l-glutamate had reduced dormancy for glucose-induced germination, and increased dormancy for germination induced by l-alanine. Addition of CaCl(2) or l-glutamate to the sporulation medium yielded spores with increased sensitivity to "ionic germination" (with KI). Spores from synthetic medium were incapacitated for full postgerminative development, as shown by repression of the changes in oxygen-uptake rate which accompany normal cell division.

Cytolysis of Bacillus subtilis by Fusarium oxysporum

Growth of Fusarium oxysporum on heat-killed Bacillus subtilis cells was accompanied by the loss of bacterial cytoplasmic contents, and this 'cytolysis' could be catalysed in heat-treated bacteria by the fungal culture fluids. In electron micrographs the bacterial walls appeared undamaged, and the absence of wall-lytic enzymes was confirmed by use of isolated bacterial walls as substrate. Appearance of cytolytic activity in cultures was paralleled by the production of proteolytic activity in the cultures. Proteolysis and cytolysis had similar pH optima at 8.8-9.0. Cultures grown on casein, but not glucose, produced high cytolytic activity. Rapid cytolysis occurred when heat-treated B. subtilis cells were incubated with trypsin, subtilisin or pronase E. Viable bacteria, however, were not attacked, either by concentrated culture fluids or by the commercial protease preparations.

Inactivation of B. subtilis spores and E. coli endotoxin by ethylene oxide

Exposure of Bacillus subtilis spores to ethylene oxide (EO) showed correlation between the killing rate and the EO concentration, when the temperature was kept at 55 degrees C and the relative humidity at 100%. The co-efficient of dilution was calculated to be 0.9. The effect of EO on Escherichia coli endotoxin was investigated by the chromogenic Limulus Amebocyte Lysate (LAL) test. A solution of endotoxin was dried on glass tubes and exposed to 450 or 900 mg EO/l during 1-46 h under the same conditions as the spore inactivation. The LAL activity of the endotoxin was reduced to about 30%. The EO-treated endotoxin was tested in the rabbit pyrogen test. The summed temperature increase for three rabbits was 0.9 degrees C, while the same assay using untreated test pieces showed an increment of 3.7 degrees C. Administration of the same quantity of EO-treated and untreated endotoxin to the rabbits, as adjusted by the LAL-test, produced the same temperature increment. The addition of polymyxin B (PB) to an endotoxin solution reduced the LAL activity by 75%. Had the endotoxin been exposed to EO, thereby reducing the LAL activity by 70%, addition of PB further reduced the activity by 99%. The reaction of EO on the endotoxin reduced the LAL activity as well as the pyrogenic response and increased the affinity to PB.

On the dielectrically observable consequences of the diffusional motions of lipids and proteins in membranes. 2. Experiments with microbial cells, protoplasts and membrane vesicles

The dielectric properties of suspensions of intact cells of Methylophilus methylotrophus, Paracoccus denitrificans and Bacillus subtilis have been measured in the frequency range 1 kHz to 13 MHz. All possess a pronounced dispersion corresponding in magnitude and relaxation time to the "beta-dispersion" in a terminology defined by Schwan [Adv. Biol. Med. Phys. 5:147-209 (1957)]. The latter two strains, but not M. methylotrophus, also possess a substantial alpha-dispersion. The relaxation time of the beta-dispersion of B. subtilis is significantly lower than that of the other two strains, due to the higher internal K+ content of this Gram-positive organism. Treatment of P. denitrificans or B. subtilis with lysozyme greatly reduces the magnitude of the alpha-dispersion; in the latter case it is virtually abolished. The magnitude of both the alpha- and beta-dispersions of protoplasts of these organisms is significantly decreased by treatment with the cross-linking reagent glutaraldehyde, indicating that diffusional motions of the lipids and/or proteins in the protoplast membranes contribute to the dielectric relaxations observed in this frequency range. Such motions cannot be unrestricted, as in the "fluid mosaic" model, since the relaxation times of the lipids and proteins, if restricted by hydrodynamic forces alone, should then correspond, in protoplasts of this radius (0.4-0.5 micron), to approximately 10 Hz. Even after treatment of the (spherical) protoplasts with glutaraldehyde, the breadth of the remaining beta-dispersion is still significantly greater than (a) that of a pure Debye dispersion and (b) that to be expected solely from a classical Maxwell-Wagner-type mechanism. It is recognised that the surfaces of the protein complexes in such membranes extend significantly beyond the membrane surface as delineated by the phospholipid head-groups; such molecular granularity can in principle account for the broadened dielectric relaxations in the frequency range above 1 kHz, in terms of the impediment to genuinely tangential counterion relaxation caused by the protruding proteins themselves. The relaxation time of a previously observed, novel, low-frequency, glutaraldehyde-sensitive (mu-) dispersion in bacterial chromatophore suspensions, as well as that of their alpha-dispersion, is significantly increased by increasing the aqueous viscosity with glycerol. This finding is consistent with the view that, from a dielectric standpoint, the motions of charged proteins (and lipids) in biological membranes are rather tightly coupled to those of the adjacent ions and dipoles in the electric double layer.(ABSTRACT TRUNCATED AT 400 WORDS)

Single, chemically defined sporulation medium for Bacillus subtilis: growth, sporulation, and extracellular protease production

The composition and application of a single, chemically defined medium or growth and sporulation of Bacillus subtilis is described. At 37 degrees C cells grew with a doubling time of about 40 min; cultures attained near-maximal spore formation (70 to 80% by 12 h after the end of exponential growth and produced 1 X 10(9) to 2 X 10(9) heat-resistant free spores at 24 h. Dipicolinic acid production was completed between 7 and 11 h. Cells grown in the single, chemically defined medium excreted levels of serine and neutral proteases comparable to those excreted in nutrient broth medium.

A standardized monitor for the control of ethylene oxide sterilization cycles

The resistance of spores of B. subtilis var. niger produced in liquid synthetic medium and exposed to ethylene oxide on a nylon surface, has been shown to the almost identical to that for spores produced on a traditional solidified complex medium with exposure to the sterilant on aluminium foil. The use of short lengths of nylon tube as carriers allowed easy production and handling, with self-protection of the spore-bearing surface. Addition of a dye provided visual evidence of inoculation without affecting resistance to ethylene oxide. Such a monitor is suitable for use as a standardized biological challenge in routine ethylene oxide sterilization cycles.

Cell wall teichoic acid as a reserve phosphate source in Bacillus subtilis

Although exponential growth of Bacillus subtilis 168 in a phosphate-limited medium halted with the exhaustion of inorganic phosphate, the bacteria continued to grow at a slower rate for a further 3 to 4 h at 37 degrees C. This postexponential growth in the absence of an exogenous phosphate supply was accompanied by a loss of teichoic acid from the cell walls of the bacteria. Quantitative analysis of walls and culture fluids showed that the phosphate loss from the walls could not be accounted for by an increase in phosphate-containing compounds in the medium, which implied that the cells were using their own wall teichoic acids to supply phosphate necessary for growth. Addition of exogenous teichoic acid to phosphate-starved cultures resulted in stimulation of growth and in the simultaneous disappearance of teichoic acid phosphate from the medium. It is proposed that teichoic acids, which can contain more than 30% of the total phosphorus of exponential-phase cells, can be used as a reserve phosphate source when the bacteria are starved for inorganic phosphate.

Regulation of lactate dehydrogenase synthesis in Bacillus subtilis

The regulation of lactate dehydrogenase in Bacillus subtilis was determined under a variety of growth conditions and in mutants blocked in the citric acid cycle. The synthesis of lactate dehydrogenase increased sharply concomitantly upon the exhaustion of glucose from the medium and the onset of the stationary phase. The synthesis of lactate dehydrogenase may be under catabolite repression control. Studies with mutants blocked in the citric acid cycle showed that lactate dehydrogenase is regulated independently of either the oxidative or reductase branches of the cycle. Certain citric acid cycle mutants, e.g., aconitase or succinate dehydrogenase, exhibited very low levels of lactate dehydrogenase while others, e.g., malate dehydrogenase or isocitrate dehydrogenase, showed normal levels. A stage O sporulation mutant expressed levels of lactate dehydrogenase more than one thousand-fold higher than the low group of citric acid cycle mutants. The induction of lactate dehydrogenase was shown to be independent of the accumulation of its substrate, pyruvate.

Evidence that spo0A mutations are recessive in spo0A-/spo0A+ merodiploid strains of Bacillus subtilis

The spo0A locus contains two types of closely linked mutations that block sporulation at stage 0: spo0A mutations (the most pleiotropic of the stage 0 markers) and spo0C mutations. It was previously thought that spo0A mutations were dominant in merodiploids of Bacillus subtilis, whereas spo0C mutations were recessive. We have shown that spo0A mutations were recessive when spo0A-/spo0A+ merodiploids were made in the genetic backgrounds of strains that were resistant to antibiotic produced by the wild-type strain. Reinvestigation of cultures of spo0A-/spo0A+ merodiploids constructed in the antibiotic-sensitive spo0A strain showed that they contained the spo0A allele at a low frequency, and they produced very few haploid Spo- segregants. These facts indicated that the cultures contained mostly homogenotic (spo0A+/spo0A+) cells. The reason for the poor survival of the spo0A-/spo0A+ merodiploids in the genetic background of the antibiotic-sensitive strain was not clear, but several possible explanations were given. It may have been related to the diploid state of other genes in the same merodiploid cells. The previous indication that spo0A mutations were dominant seems to have been based on the properties of a rare class of Spo- segregants that were probably selected in the presence of antibiotic.

Specificity of the weak binding between the phage SPO1 transcription-inhibitory protein, TF1, and SPO1 DNA

The interaction of the phage SPO1 protein transcription factor 1 (TF1), with DNA has been analyzed by membrane filter binding and by sedimentation methods. Substantially specific binding of TF1 to helical SPO1 DNA can be demonstrated by nitrocellulose filter-binding assays at relatively low ionic strength (0.08). However, TF1-DNA complexes dissociate and reequilibrate relatively rapidly and this makes filter-binding assays unsuitable for quantitative measurements of binding equilibra. Accordingly, the sedimentation properties of TF1-DNA complexes have been explored and a short-column centrifugation assay has been elaborated for quantitative measurements. Preferential binding of TF1 to the hydroxymethyluracil-containing SPO1 DNA has also been demonstrated by short-column centrifugation. TF1 binds relatively weakly and somewhat cooperatively to SPO1 DNA at many sites; TF1-DNA complexes dissociate and reequilibrate rapidly. At 20 degrees C in 0.01 M phosphate, pH 7.5, 0.15 KC1, one molecule of TF1 can bind to approximately every 60 nucleotide pairs of SPO1 DNA.

Role of sugar uptake and metabolic intermediates on catabolite repression in Bacillus subtilis

Many phosphorylated intermediates exert catabolite repression on the enzyme acetoin dehydrogenase in Bacillus subtilis. This was shown with strains that are blocked at different positions in central metabolism when they receive sugars that cannot be metabolized past enzymatic block(s). In the case of sorbitol, transport events were not involved in catabolite repression, for this sugar cannot repress acetoin dehydrogenase in a strain lacking sorbitol dehydrogenase but otherwise able to take up sorbitol. The presence of glucose did not markedly influence the uptake of acetoin.

[Relations between catabolite repression and sporulation in Bacillus subtilis (author's transl)]

Acetoin dehydrogenase can be catabolite repressed by numerous sources of carbon. The following results point out that the catabolite repression of this enzyme and the inhibition of sporulation are mediated by the same mechanism: 1. Mutants, able to synthesize acetoin dehydrogenase in the presence of glucose, sporulate in glucose medium at a higher rate than the standard strain. 2. The catabolite repressing effect of a compound and its ability to inhibit sporulation are in a direct relation to each other. 3. The limitation of inorganic phosphate in the growth medium, which is known to favour sporulation, counteracts the catabolite repressing effect of glucose.

Acetoin degradation in Bacillus subtilis by direct oxidative cleavage

Acetate and acetaldehyde can be detected as products of the oxidative dissimilation of acetoin in Bacillus subtilis extracts. They arise as the result of the direct cleavage of acetoin without a previous oxidation to diacetyl. This can be deduced from the following observations: (a) no diacetyl was detected in acetoin dissimilation experiments in vitro and (b) methylacetoin, an acetoin analogue which can not be oxidized to the diketone, also undergoes oxidative splitting, yielding acetone and acetate. The splitting reaction requires thiamine pyrophosphate as a cofactor, suggesting that the oxidative step occurs, as known for similar reactions, by the electron transfer from hydroxyethylthiamine pyrophosphate to a proper acceptor, which in vitro can be replaced by dichlorophenolindophenol. In vivo the final product of the oxidation of hydroxyethylthiamine pyrophosphate is activated acetate. A mutant which lacks acetoin-cleaving activity can not reutilize the acetoin accumulated after growth in glucose. This corroborates the actual importance of the cleavage reaction for acetoin dissimilation. The enzyme diacetylmethylcarbinol synthase, thought to be responsible for the formation of diacetylmethylcarbinol from diacetyl, probably is identical to the enzyme catalyzing the cleavage of acetoin.

Pleiotropic effects of suppressor mutations in Bacillus subtilis

Isogenic strains of Bacillus subtilis carrying sup-1 (26), sup-3 (10), or their wild-type alleles were constructed in three genetic backgrounds. The patterns of suppression at 37 and 43.5 C, identity of mapping site, effects of the suppressor genes on growth rate, sporulation, and production of altered enzymes were examined. The similarity of the suppression pattern by sup-1 and sup-3 suggests that the suppressors are of the same type. They do not, however, represent mutations in the same gene, since, based on differences in temperature sensitivity of phage mutants in suppressor-containing hosts, sup-1 and sup-3 insert different amino acids and can coexist within the same cell. The ability to produce slow-migrating forms of enzymes of the type described in the accompanying paper was co-transferred with either of the suppressor genes during transformation, was lost on reversion of the suppressor mutations, and was independent of the genetic background. Similarly, transformation and reversion studies indicate that the additional pleiotropic properties such as slow growth rate and inability to attain competence or to yield plaques with phi105C4, which are characteristic of the Okubo sup-1 strain (HA101B) but not its early sporulation defect, result from the presence of the suppressor mutation. The possible mechanisms by which altered enzyme forms and the additional pleiotropic effects are produced in suppressor strains are discussed. In addition, a newly recognized suppressor phenotype is described and partially characterized.

Accumulation of messenger ribonucleic acid specific for extracellular protease in Bacillus subtilis 168

Production of extracellular protease by Bacillus subtilis 168 in a medium containing low concentrations of amino acids is essentially linear, whereas in a medium containing high levels of amino acids the time course of production is biphasic. Cells harvested from the growth medium are capable of secreting enzyme for 30 min in the presence of rifampin, but the appearance of the enzyme is sensitive to chloramphenicol and pactamycin. The protease messenger ribonucleic acid (mRNA), nevertheless, appears to have a short half-life typical of bacterial messengers, and this indicates that these cells contain a relatively large pool of protease-specific mRNA. This pattern of results is identical to that observed previously with B. amyloliquefaciens. Because it has now been found in two distinct organisms, it is concluded that the accumulation of mRNA for extracellular protease, supported by rapid transcription, is a biologically meaningful phenomenon related to extracellular enzyme synthesis rather than aberrant behavior due to a transcriptional control mutation.

Mapping of asporogenous mutations of Bacillus subtilis: a minimum estimate of the number of sporeulation operons

Sporulation-specific mutations in Bacillus subtilis have been mapped by transduction and transformation. The mutations caused blocks at stages 0, II, III, and IV of sporulation; more than one phenotype was found for each of these stages. On the basis of the criteria used to define a sporulation operon, a minimum estimate could be made of the number of operons activated during sporulation. Nine operons were identified for stage 0, eight for stage II, five for stage III, and six for stage IV. It is probable that several of these 28 operons are activated in groups so that the number of steps in the dependent sequence of sporulation events should turn out to be less than the number of operons.

Binding of radioactive benzylpenicillin to asporogenous mutants of Bacillus subtilis during postexponential growth

The specific penicillin binding capacity of a postexponential culture of Staphylococcus aureus remains constant, but that of a sporulating Bacillus subtilis culture fluctuates dramatically. An initial decrease in binding capacity during presporulation events is followed by two distinct intervals of enhanced specific binding capacity during the postlogarithmic growth of a sporulating B. subtilis culture. The first peak of enhanced binding occurs during septation, when enzymes for germ cell wall formation are present; and the second peak coincides with cortical biosynthesis. The specific postlogarithmic binding capacities of a number of Spo(-) mutants of B. subtilis were examined to ascertain if specific asporogenous mutations altered the binding pattern observed with the wild-type organism. Four distinct postexponential binding patterns were recognized: (i) a low, constant binding capacity resembling the binding pattern of S. aureus, (ii) a decrease in binding capacity with no subsequent significant peaks, (iii) a decrease in binding capacity followed by a single peak corresponding to the first peak seen with the wild type, (iv) a pattern similar to the wild type. The fourth pattern was observed in a mutant blocked during stage III of sporogenesis which produced forespores that never became refractile. Mutations blocking either one or both periods of enhanced postlogarithmic binding were interspersed throughout a linkage group of spore genes next to lys-2 on the B. subtilis chomosome.

-aminobutyric acid as a required germinant for mutant spores of Bacillus megaterium

Germinated spores of Bacillus megaterium QM B1551 were irradiated with ultraviolet light, and spore-forming survivors were screened for germination requirements. Spore strains which failed to germinate in a variety of defined solutions germinative for spores of the parent strain were obtained. Mutant spores germinated readily in solutions containing yeast extract or one of numerous complex preparations. gamma-Aminobutyric acid, obtained from yeast extract by column chromatography, was shown to be required for germination by the mutant spores. gamma-Aminobutyric acid and l-alanine at final concentrations of 1 mm each, in solutions of KI (40 mm), equaled the potency of yeast extract (1 mg/ml) in the germination of the mutant spores. One of several other amino acids could be substituted, though less effectively, for l-alanine. alpha-Aminobutyric acid, beta-aminobutyric acid, beta-alanine, and 5-aminovaleric acid were ineffective substitutes for gamma-aminobutyric acid in mutant spore germination.

Binding of radioactive benzylpenicillin to sporulating Bacillus cultures: chemistry and fluctuations in specific binding capacity

The chemistry of the binding of (14)C-benzylpenicillin to sporulating cultures of Bacillus megaterium and B. subtilis is similar to that in a 4-hr vegetative culture of Staphylococcus aureus. Unlabeled penicillins prevent the binding of (14)C-benzylpenicillin, but benzylpenicilloic acid and benzylpenilloic acid do not. Bound antibiotic can be removed from cells with neutral hydroxylamine at 25 C. Sporulating cultures display two intervals of enhanced binding, whereas binding to stationaryphase S. aureus cells remains constant. The first period of increased binding activity occurs during formation of the spore septum or cell wall primordium development, and the second coincides with cortex biosynthesis.

Protease activities during the course of sporulation on Bacillus subtilis

Three proteolytic enzymes have been isolated from sporulating cultures of Bacillus subtilis. These activities were, respectively, a protease inhibited by ethylenediaminetetraacetic acid (EDTA) but not phenylmethylsulfonyl fluoride (PMSF), a protease active on both protein and ester substrates, and an ester-active enzyme with low activity on proteins. The latter two enzymes were inhibited by PMSF but not by EDTA. The specific activity of each was determined both intra- and extra-cellularly during growth and sporulation in a single-defined medium. All three enzymes were shown to exhibit a rapid increase in specific activity at a time coinciding with the appearance of refractile bodies in cells.

Sporulation in Bacillus subtilis 168. Comparison of alkaline phosphatase from sporulating and vegetative cells

1. The purification of the ;vegetative' alkaline phosphatase of Bacillus subtilis 168 was simplified by ionic elution of the enzyme from intact cells. 2. The enzyme has a molecular weight of about 70000 and treatment of the enzyme with 10mm-hydrochloric acid or 6.0m-guanidine hydrochloride, beta-mercaptoethanol (0.1m) gives rise to enzymically inactive subunits. 3. The amino acid composition of the enzyme was determined. The N-terminal residue determined by the DNS chloride method is glycine. 4. The properties of this enzyme were compared with the ;sporulation' alkaline phosphatase of the same strain. 5. Although the ;sporulation' enzyme differs from the ;vegetative' enzyme in its physiology of appearance and apparent mRNA stability, an examination of properties of the enzymes revealed no differences. 6. The enzyme from both cell forms is bound to the particulate fraction of cell extracts, but can be solubilized by high concentrations of magnesium chloride; removal of the magnesium chloride, by dialysis, results in precipitation of both enzymes. Both enzymes can be removed from intact cells by ionic elution. 7. The ;vegetative' and ;sporulation' enzymes have identical pH optima, K(m) and K(i) values and electrophoretic mobilities in cellulose acetate. 8. Their half-life is 28min at 65 degrees C and their Q(10) is 1.25. 9. The molecular size determined by gel filtration on Sephadex G-100 is about 69000. 10. ;Vegetative' and ;sporulation' forms gave precipitin lines that were continuous and non-spurred when tested against antiserum prepared against the ;vegetative' enzyme. 11. The ;sporulation' alkaline phosphatase appears to be associated with stage II of sporulation and appears to be induced by something specifically concerned in sporulation and not by phosphate starvation.

Some features of the bacterial membrane studied with the aid of a new fractionation technique

Membranes of Bacillus megaterium and other bacteria were bound to crystals of cadmium lauroylsarcosinate and were resolved into nine lipoprotein fractions by elution with potassium chloride and sodium deoxycholate solutions. The fractions differed widely in protein/lipid ratio. Some major protein species were probably common to all the fractions, but the phospholipid composition showed some variation. Electron-microscopic examination after negative staining revealed that material in certain fractions was in the form of particles of diameter about 12nm, and other fractions consisted of amorphous aggregates. The composition of the membrane in terms of the nine fractions was influenced markedly by the conditions of culture of the bacteria. Radioactive-labelling experiments suggested that some fractions served as precursors of others, and one fraction appeared to contain the attachment points of the DNA.

Selection of cells transformed to prototrophy for sporulation markers

A method is presented for reproducible quantitative selection of recombinants for spore markers in transformation analysis.

Sporulation of Bacillus subtilis in continuous culture

Sporulation of Bacillus subtilis 168 was studied in chemostat cultures. Sporulation occurred at high frequency under limitation of growth by glucose or the nitrogen source in minimal medium, whereas rates of sporulation were low for Mg(2+), phosphate, citrate, or tryptophan limitation. Sporulation was found at all growth rates tested, and the incidence of spores increased with decrease in growth rate of the culture. Within the range of growth rates up to the maximum obtainable with the defined medium, no threshold effect of growth rate on sporulation was observed. By studying transient states, it was possible to determine the time taken for the appearance of a refractile spore after initiation of a cell to sporulation. Under conditions of glucose limitation, cells were found to be committed to sporulation as soon as they were initiated. In nitrogen-limited cultures, however, a partial relief of nitrogen limitation prevented the development of spores during the first hour after initiation. The results of experiments with multistep changes in dilution rate of a chemostat culture indicate that initiation to sporulation is probably restricted to a particular point in the cell division cycle.