Studies on the biosynthesis of dipicolinic acid in spores of Bacillus cereus var. mycoides

Role of Dipicolinic Acid in Heat Resistance of Spores of Clostridium botulinum and Clostridium sporogenes PA3679 by Thermal and Pressure-assisted Thermal Processing

Dipicolinic acid (DPA) is a major constituent of spores and reportedly provides protection against inactivation by various thermal processes; however, the relationship between DPA and resistance towards pressure-assisted thermal processing is not well understood. Thermal and pressure-assisted thermal inactivation studies of Clostridium botulinum nonproteolytic strains QC-B and 610-F, proteolytic strain Giorgio-A, and thermal surrogate Clostridium sporogenes PA3679 spores suspended in ACES buffer (0.05 M, pH 7.0) were performed to determine if a relationship exists between DPA release and log reduction of spores. Thermal inactivation at 80, 83, and 87 °C for nonproteolytic strains and 101, 105, and 108 °C for the proteolytic strain and thermal surrogate were conducted. Pressure-assisted thermal inactivation for nonproteolytic strains at 83 °C/600 MPa and for the proteolytic strain and thermal surrogate at 105 °C/600 MPa were performed. Surviving spores were enumerated by 5-tube MPN method for log reductions and analyzed for released DPA by liquid chromatography-tandem mass spectrometry. The correlation between MPN log reductions, released DPA, and D-values were calculated. A positive correlation between released DPA and log reduction of spores was observed for QC-B and 610-F at 80 and 83 °C (r = 0.6073 - 0.7755; P < 0.01). At 87 °C, a positive correlation was detected for 610-F (r = 0.4242, P < 0.05) and no correlation was observed for QC-B (r = 0.1641; P > 0.05). A strong, positive correlation (r = 0.8359 - 0.9284; P < 0.05) between released DPA and log reduction of spores was observed for Giorgio-A at 101, 105, and 108 °C, and a strong, positive correlation (r = 0.8402; P < 0.05) was observed for PA3679 at 101 °C. A positive correlation (r = 0.5646 - 0.6724; P < 0.01) was observed for QC-B, 610-F, and Giorgio-A after pressure-assisted thermal treatment. No correlation (r = 02494; P > 0.05) was found for PA3679 after pressure-assisted thermal treatment. These results suggest a correlation exists between DPA release and heat resistance; however, the level of correlation varied between strains and temperatures. The findings from this research may aid in the development of spore inactivation strategies targeting the thermal resistance profiles of various strains of C. botulinum spores.

Beetroot-pigment-derived colorimetric sensor for detection of calcium dipicolinate in bacterial spores

In this proof-of-concept study, we describe the use of the main red beet pigment betanin for the quantification of calcium dipicolinate in bacterial spores, including Bacillus anthracis. In the presence of europium(III) ions, betanin is converted to a water-soluble, non-luminescent orange 1∶1 complex with a stability constant of 1.4 × 10(5) L mol(-1). The addition of calcium dipicolinate, largely found in bacterial spores, changes the color of the aqueous solution of [Eu(Bn)(+)] from orange to magenta. The limit of detection (LOD) of calcium dipicolinate is around 2.0 × 10(-6) mol L(-1) and the LOD determined for both spores, B. cereus and B. anthracis, is (1.1 ± 0.3)× 10(6) spores mL(-1). This simple, green, fast and low cost colorimetric assay was selective for calcium dipicolinate when compared to several analogous compounds. The importance of this work relies on the potential use of betalains, raw natural pigments, as colorimetric sensors for biological applications.

One-step conversion of to its using salts for GC-MSdetection of bacterial endospores

Methyl sulfate (MeSO4-) salts were explored as thermochemolysis-methylation (TCM) reagents for gas chromatographic (GC) analysis of dipicolinic acid (DPA) as its dimethyl ester (Me2DPA) from bacterial endospores. The reaction was carried out under non-pyrolytic conditions by inserting a small coiled wire filament coated with the sample and reagents directly inside a GC injection port at 290 °C. Above 10 : 1 methyl donor/DPA ratios, alkali metal salts of MeSO4- effected 80-90% conversion of DPA to Me2DPA, which was 10-20 times more active than the same amount of tetramethylammonium hydroxide (TMA-OH) at this temperature. A quaternary salt mixture consisting of 1 : 3 : 1 : 3 TMA+/Na+/OH-/MeSO4- methylated spore DPA with an average conversion of 86% (mean conversion by TMA-OH under the same conditions was 4%). Therefore, the sensitivity for detection of bacterial endospores was increased over 20-fold compared to that observed with the more commonly employed TMA-OH methylating reagent. The limit of detection by this method was 9 × 104 total spores. Mechanisms describing the observed behavior are proposed and discussed. This is the first use of MeSO4- as a TCM reagent for GC.

Effect of nuclear motion on the absorption spectrum of dipicolinic acid

Using semiclassical electron-radiation-ion dynamics, the authors have examined the effect of nuclear motion, resulting from both finite temperature and the response to a radiation field, on the line broadening of the excitation profile of 2,6-pyridinedicarboxylic acid (dipicolinic acid). With nuclei fixed, there is a relatively small broadening associated with the finite time duration of an applied laser pulse. When the nuclei are allowed to move, the excitation spectrum exhibits a much larger broadening, and is also reduced in height and shifted toward lower frequencies. In both cases, the excitation is due to well-defined pi to pi* transitions. The further inclusion of thermal motion at room temperature broadens the linewidth considerably because of variations in the molecular geometry: Transitions that had zero or negligible transition probabilities in the ground state geometry are weakly excited at room temperature.

Electron microscopy of spores of Bacillus megaterium with special reference to the effects of fixation and thin sectioning

Resting spores of Bacillus megaterium appear uniformly opaque and undifferentiated under the electron microscope. Germinated spores and spores which have lost their dipicolinic acid underwent characteristic changes in structure. Spores fixed with KMnO₄ lose their dipicolinic acid. Spores fixed with OsO₄ under certain conditions retain their dipicolinic acid. When conventional sectioning procedures are used with either method of fixation, abnormal spore structure is produced as a result of the solution of cellular constitutents. Dry sections of unfixed spores embedded in methacrylate reveal the spore structure in a more normal state. Indirect evidence has been obtained for the existence of a penetration barrier at or near the outer edge of the cortex.

Chemical composition and heat resistance of some aerobic bacterial spores

Walker, Homer W. (Iowa State University of Science and Technology, Ames), Jack R. Matches, and John C. Ayres. Chemical composition and heat resistance of some aerobic bacterial spores. J. Bacteriol. 82:960-966. 1961.-Analyses of spores of Bacillus species for nitrogen, carbohydrate, dipicolinic acid, and phosphorus showed little correlation with heat resistance. However, as the molar concentration of magnesium increased in relation to dipicolinic acid and calcium concentrations, heat resistance generally decreased. Analyses of several batches of spores indicated that this relationship between calcium, magnesium, and dipicolinic acid did not always hold true. Therefore, while these materials apparently play an important role, other factors need to be included before a full explanation of thermal stability of spores can be made.

RAPID METHODS OF STAINING BACTERIAL SPORES AT ROOM TEMPERATURE

Lechtman, M. D. (University of Southern California, Los Angeles), J. W. Bartholomew, A. Phillips, and M. Russo. Rapid methods of staining bacterial spores at room temperature. J. Bacteriol. 89:848-854. 1965.-Spores of Bacillus subtilis var. niger were stained in 2 min at room temperature, after suitable pretreatment, with a dye reagent composed of 2% crystal violet in 1% phenol and 26% ethanol. Pretreatments included heat fixation to 260 C, mechanical rupture, and hydrolysis at room temperature in 44 n H(3)PO(4) for 5 min, 33.4 n H(3)PO(4) for 10 min, 12 n HCl for 5 sec, 6 n HCl for 2 min, 12 n HNO(3) for 5 sec, and 6 n HNO(3) for 60 sec. Acid hydrolysis at 60 C enabled the lowering of both acid concentration and time: 33.4 n H(3)PO(4) for 15 sec, 25.9 n H(3)PO(4) for 60 sec, 2 n HCl for 30 sec, 1 n HCl for 30 sec, 2 n HNO(3) for 15 sec, and 1 n HNO(3) for 30 sec. After acid treatment, 1 n NaOH was used as a neutralization agent. The cytological manifestations of these pretreatments, examined in an electron microscope after replication, showed definite degradation of spore coats, which probably explains the increase in dye permeability. The pretreatments were evaluated for use in a differential staining procedure for spores and vegetative cells. They were found to be too drastic in that they resulted in replacement of the primary dye by the 0.25% safranine counter stain in both vegetative cells and endospores. Less drastic pretreatments, such as 6 n HNO(3) for 10 sec at room temperature, gave good differential stains, but failed to stain some free spores. The staining techniques above were evaluated with six species of Bacillus and were found to apply to all.

The release of dipicolinic acid during heating and its relation to the heat destruction of Bacillus stearothermophilus spores

The rates of dipicolinic acid (Dpa) release and the rates of death were studied for spores of five strains of Bacillus stearothermophilus. It was observed that a highly significant relationship exists between the rate of Dpa release and rate of spore death for the four out of five strains tested and for all test temperatures. At 115 degrees C the rate of Dpa release was found to be faster than the rate of death, equal at 120 degrees C and slower at 125 degrees C. The role of Dpa in heat resistance was considered and a theory is proposed to explain the mechanism by which the heat resistance of bacterial spores is overcome.

Relationship between butirosin biosynthesis and sporulation in Bacillus circulans

The relationship between butirosin biosynthesis and certain biochemical characteristics related to sporulation in a strain of Bacillus circulans NRRL B-3313 was examined. The cellular content of dipicolinic acid increased while the amount of poly-beta-hydroxybutyrate decreased with changes in antibiotic productivity. Oligosporogenous mutants failed to synthesize the antibiotic and to degrade poly-beta-hydroxybutyrate. These observations suggest that spore formation may be related to antibiotic production in this strain of B. circulans.

Role of chelation and water binding of calcium in dormancy and heat resistance of bacterial endospores

The possible relationship between the water binding by bacterial endospores and their dormancy and heat resistances has been examined in terms of the coordination characteristics of the spore-bound calcium. Stabilities of the calcium complexes of typical cytoplasmic and structural spore components were determined by potentiometric equilibrium pH measurements in model systems consisting of DPA, glycine, alanine, glutamic acid, alanyl-glutamic acid, triglycine, and tetraglycine. The Ca++-form and H+-form spores of Clostridium botulinum 33A were investigated in vivo with respect to their water sorption and heat-resistance characteristics. The results suggest that the complexing of calcium and Ca(II)-DPA may be biologically significant for spore resistance and dormancy at the following three levels: (1) complexing with spore cytoplasmic pool constituents consistent with the idea of a metal-chelate cross-linked cytoplasm or spore cement stabilizing the essential biological macromolecules, (2) complexing with structural components of the spore as indicated by the interaction with model peptides, and (3) coordination with water to produce an apparently dehydrated environment in the spore as evident from the much greater water-sorption capacity of the Ca++-form spores vs the much smaller water sorption of the H+-form spores. Interestingly enough, DPA itself, in the absence of metal ion, showed some interaction with di-, tri-, and tetrapeptides and a weak but detectable interaction with amino acids. Although the exact mode of the DPA-peptide interaction is not clear, it is attractive to speculate about its possible involvement in the control of spore dormancy and resistance.

Rapid determination of dipicolinic acid in the spores of Clostridium species by gas-liquid chromatography

A gas-liquid chromatographic procedure has been developed to quantitate dipicolinic acid in bacterial spores. The culture, washed from a plate, was hydrolyzed with acid containing the internal standard, pyridine-2,4-dicarboxylate, and then extracted into methyl isobutyl ketone. The internal standard and dipicolinic acid were then extracted into a small volume of trimethylphenylammonium hydroxide. Injection of the resultant quaternary ammonium salts into a gas chromatograph yielded, via thermal decomposition, the methyl ester derivatives of the dipicolinic acid and the internal standard. The amount of dipicolinic acid in the sample was determined from a standard curve. The method was sensitive to 100 ng of dipicolinic acid per sample and was 1,000 to 5,000 times more sensitive than the commonly used methods. Preparation of the sample required less than 1.5 h and less than 15 min of the analyst's time.

Minimal requirements for commitment to sporulation in Bacillus megaterium

Commitment to sporulation was examined by means of both endotrophic sporulation and rejuvenation experiments. In both cases, a point of commitment to the completion of sporulation occurred at stage II. With 2 x 10(8) cells/ml, the process by which commitment occurred required 0.5 mm Mg(2+), 10.0 mm phosphate, and an energy source (minimum of 5.0 mm acetate). For completion of sporulation and formation of normal, heat-resistant refractile spores, 0.3 mm Ca(2+) was required. Except for this Ca(2+) requirement, the completion of sporulation after commitment was independent of the nature of the surrounding medium. Some aspects of the utilization of these required substances were examined.

Coordinative binding of divalent cations with ligands related to bacterial spores. Equilibrium studies

It has been repeatedly postulated that the high heat resistance of bacterial spores is due to stabilization of biopolymers in the spore interior by a solid deposit of protective cement consisting of coordination complexes of ligands with divalent metal ions. This report presents data on metal-binding characteristics of some of the ligands related to spores as determined by means of potentiometric equilibrium measurements under conditions of temperature and ionic strength (t = 25.0 degrees C; mu = 1.0 KNO(3)) identical with those reported earlier by the authors in order to facilitate correlation by using comparable data. The spore ligands investigated in this study included 2,6-pyridinedicarboxylic acid (DPA), alpha,epsilon-diaminopimelic acid, D-glutamic acid, and D-alanine in a ratio of 1:1 with metal ions which are known to play a role in heat resistance of spores. Stability constants of the chelates of these spore ligands with metal ions such as Ca(II), Mg(II), Cu(II), Ni(II), Zn(II), Co(II), and Mn(II) have been determined. In general the metal chelates of DPA exhibited the greatest stability. On the basis of a consideration of the stability data together with the known configurations of the ligand and the coordination requirements of the metal ions, possible structures indicating the coordinate binding of the spore ligands with the metal ions are presented. All the metal chelates except those of Ca(II) were found to undergo hydrolysis and separation of solid phase in the pH range 7-8.5. The relatively greater hydrolytic stability of Ca(II) chelates and the high affinity of DPA for metal ions appear to be of biological significance insofar as these two spore components are more widely associated with the heat resistance of bacterial spores.

Comparisons of cells, refractile bodies, and spores of Bacillus popilliae

Spores of Bacillus popilliae from infected larvae and refractile bodies produced in a Trypticase-barbiturate medium were similar but distinct from vegetative cells of this organism in protein, nucleic acid, and enzyme composition. The spores and refractile bodies were found to have catalase activity, some of which was heat-resistant. This enzyme was not found in the vegetative cells. The spores contained dipicolinic acid, but the refractile bodies did not. The latter were similar to cells in having considerably higher levels of phosphate extractable with cold trichloroacetic acid and of poly-beta-hydroxybutyrate than had the spores. Electron microscopy demonstrated conclusively that the refractile bodies are distinctly different from either cells or spores of B. popilliae. The possibility that these bodies are formed as a result of an aborted sporulation process is discussed.

Dipicolinic acid synthesis in Penicillium citreo-viride

Hodson, Phillip H. (University of Texas, Austin), and J. W. Foster. Dipicolinic acid synthesis in Penicillium citreo-viride. J. Bacteriol. 91:562-569. 1966.-Dipicolinic acid (DPA) accumulation in culture filtrates of the mold Penicillium citreo-viride was studied in surface and submerged cultures. Good DPA yields were obtained in suspensions of washed, submerged mycelium in the presence of a carbon and a nitrogen source but in the absence of other minerals essential for growth. Fumaric acid was the only other acid formed in significant amounts. Glucose and glycerol were superior to various salts of organic acids as carbon sources, and certain amino acids were excellent nitrogen sources. l-Leucine, l-norvaline, l-tyrosine, and l-histidine were superior to urea, NH(4)Cl, or NaNO(3) as nitrogen precursors for DPA production. d-Norvaline was useless for DPA production. Glycerol-2-C(14) and -1-C(14), C(14)O(2), and l-leucine-C(14), l-tyrosine-C(14), and l-histidine-C(14) were tested as precursors in conjunction with suitable carbon and nitrogen sources. The DPA was decarboxylated chemically, and the distribution of C(14) was determined in the pyridine-C and in the carboxyl-C. The data are consistent with Martin and Foster's suggestion for bacteria that the DPA molecule is formed by a condensation of C(3) plus C(4) precursors, the resulting 2-keto, 6-aminopimelic acid derivate undergoing ring closure to form a heterocyclic precursor of DPA. The C(14)O(2) experiments indicate that oxaloacetate is formed by beta-carboxylation of pyruvate, this in turn probably becoming aspartic acid beta-semialdehyde, the C(4) compound which condenses with a second pyruvate. The enhancement of DPA formation by l-norvaline, l-leucine, and l-histidine is not ascribable to their functioning either as a source of nitrogen or carbon. l-Tyrosine, in a glycerol medium, contributed nearly 40% of the DPA carbon. The mechanism of biosynthesis of C(7) straight-chain and cyclic compounds is discussed.

CHANGES IN THERMORESISTANCE OF CLOSTRIDIUM ROSEUM AS RELATED TO THE INTRACELLULAR CONTENT OF CALCIUM AND DIPICOLINIC ACID

The cellular content of calcium and dipicolinic acid was determined quantitatively throughout the sporulation and germination processes of Clostridium, roseum. Cell counts were made throughout both processes to relate the changes in the thermoresistant population with the changes in cellular calcium and DPA. Calcium accumulation and DPA biosynthesis occurred early in sporogenesis and preceded the transition of the vegetative cells to thermoresistant spores. Calcium accumulation preceded both DPA biosynthesis and thermoresistance. During germination 80% of the cells became thermosensitive within 15 minutes after heat shock; however, the loss of calcium and DPA from the cells proceeded at a much slower rate. Approximately 2 hours of incubation were required for completion of the germination transition and the onset of cell division.

BIOCHEMICAL CHANGES OCCURRING DURING SPORULATION OF BACILLUS CEREUS T II

Gollakota , K. G. (University of Illinois, Urbana) and H. Orin Halvorson . Biochemical changes occurring during sporulation of Bacillus cereus T. II. Effect of esters of organic acids on sporulation. J. Bacteriol. 85: 1386–1393. 1963.—Sporulation of Bacillus cereus T in yeast extract-glucose-minerals medium was specifically inhibited by α-picolinic acid (APA), if the acid was added before the pH of the culture began to rise. The effects of APA could be reversed by aspartic acid or asparagine, among the amino acids, and by intermediates of the tricarboxylic acid cycle, with the exception of α-ketoglutarate and fumarate. Formate, malonate, and certain other organic acids also possessed this ability. Succinate was the best reversing agent. Fluoroacetic acid (FAA) also inhibited sporulation, but had no effect on vegetative growth or germination of spores of B. cereus T. Unlike APA, FAA inhibited sporulation even when added after the pH of the culture had started to rise. Bisulfite was similar to FAA in its effects on sporulation. With the exception of pyruvate, acetate, aspartate, and malate, most of the compounds reversing the effects of APA also overcame the effects of FAA or bisulfite on sporulation. Esters of some of the acids reversing the effects of the above inhibitors were studied for their action on germination, growth, and sporulation. Ethyl pyruvate prevented germination of the spores, slowed down growth, and inhibited sporulation. Ethyl malonate and ethyl succinate inhibited only sporulation. All the above inhibitors prevented the synthesis of dipicolinic acid (DPA) also. When B. cereus T was grown in the absence of glucose (in extracted yeast extract-minerals medium), the above inhibitors had no effect on sporulation. Ethyl oxamate permitted sporulation, but the spores produced were heat-sensitive. Ethyl pimelate caused lysis when added before the pH of the culture began to rise. When added after the pH of the culture began to rise, it also permitted sporulation, and the spores were sensitive to heat. (These heat-sensitive spores were refractile and dormant, and did not stain with crystal violet. However, they germinated normally, losing refractibility and became stainable.) The effect of ethyl oxamate and ethyl pimelate could be overcome by DPA. APA, FAA, ethyl malonate, and ethyl succinate also inhibit the sporulation of a number of other bacilli.

THE CONVERSION OF 2,6-DIAMINOPIMELIC ACID-1,7-C14TO LYSINE-1-C14BY CERTAIN BACTERIA

When 2,6-diaminopimelicacid-1,7-C14was added to growing cultures of Bacillus megaterium, Staphlococcus aureus, and Escherichia coli, 8–9% of added carbon-14 appeared in the cellular lysine. Similar experiments with Proteus vulgaris, Streptomyces griseus, Aspergillus flavus, and Lactobacillus arabinosus resulted in less than 0.3% of the added carbon-14 being incorporated into the cellular lysine. Leuconostoc mesenteroides converted 0.6% of the added DAP-1,7-C14to lysine-1-C14.Over 90% of the carbon-14 in cell lysine from B. megaterium and L. mesenteroides was found in the carboxyl carbon. This was interpreted as indicating a direct decarboxylation of DAP-1,7-C14to lysine-1-C14. About 70% of the carbon-14 in the lysine from cells of S. aureus and E. coli was found in the carboxyl carbon, thus suggesting that some lysine comes from sources other than 2,6-diaminopimelic acid.Those organisms that actively decarboxylated DAP-1,7-C14to form lysine-C14also synthesized DAP and excreted it into the culture medium during growth.

Calcium reversal of the heat susceptibility and dipicolinate deficiency of spores formed "endotrophically" in water

Spores of Bacillus cereus strain terminalis formed "endotrophically" by transferring granular vegetative cells to distilled water were found to be relatively susceptible to heat and deficient in dipicolinic acid. Calcium ions alone, added in low concentration shortly after the cells were placed in water, could completely relieve these abnormalities. Although the water-formed spores were sensitive to heat, they were as fully resistant as normal spores to gamma radiation or phenol.

Biochemical changes occurring during sporulation in Bacillus species

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