Determination of dipicolinic acid in bacterial spores by ultraviolet spectrometry of the calcium chelate

Elucidating Bacterial Spore Dynamics through Lanthanide-Enhanced Live Imaging

Identifying and distinguishing dormant and active bacterial spores are vital for biosecurity, food safety, and space exploration. Yet, there is a lack of simple, quick, and nondestructive methods to achieve this. The common Schaeffer-Fulton method is both sample-destructive and requires significant operator involvement. In this study, we employed lanthanide-beta-diketonate complexes to directly observe both dormant and germinated single spores. Staining is instantaneous and requires minimal sample processing. The complex stains areas outside the core of dormant spores, leaving the core hollow and nonfluorescent. However, upon germination, the complex enters the core, making it brightly fluorescent. This difference was noted in five bacterial species including Bacillus, Clostridium, and Clostridioides. Various lanthanides and beta-diketonates can be mixed to form a range of spore-visualizing complexes. Due to their low toxicity, these complexes allow for live imaging of single germinating spores. We demonstrate low-cost imaging using a USB microscope as well as imaging of spores in milk matrices. This method provides a valuable tool for studying bacterial spores.

Multi-Functional Silver Nanoparticles for High-Throughput Endospore Sensing

In spore-forming bacteria such as Bacillus and Clostridium, the vegetative cells form highly durable hard shells called endospores inside the bacteria to survive as the growth environment deteriorates. Because of these properties, endospores can cause food poisoning and medical accidents if they contaminate food, medicine, or other products, and it is required for technology to detect the spores at the manufacturing site. In this study, we focused on the surface-enhanced Raman scattering (SERS) method for the sensitive detection of dipicolinic acid (DPA), a molecular marker of endospores. We constructed Fe₃O₄/Ag core-shell functional silver nanoparticles that specifically bind to DPA, and investigated a method for the qualitative detection of DPA by SERS and the quantitative detection of DPA by fluorescence method using a terbium complex formed on the surface. As a result, the concentration of the functional silver nanoparticles constructed could detect spore-derived DPA by fluorescence detection method, and SERS was several tens of nM. The functionalized nanoparticles can detect DPA quantitatively and qualitatively, and are expected to be applied to detection technology in the production of food and pharmaceuticals.

A turn-on luminescence probe for highly selective detection of an anthrax biomarker

Highly selective detection of Bacillus anthrax spores has attracted worldwide attention because Bacillus anthrax spores not only are harmful to the health of human beings and animals, but also can be used as biological warfare agents. Here, we report a simple platform by mixing EuCl₃ ·6H₂ O and sodium polyacrylate in aqueous solution and further investigate its luminescence response towards Bacillus anthrax biomarker dipicolinic acid (DPA) as a turn-on luminescence probe. Importantly, our probe has good sensitivity, lower detection limit, excellent selectivity as well as great anti-interference ability due to the great luminescence enhancement of Eu³⁺ . Moreover, a test paper is constructed to realize the purpose of portable detection. These results indicate that our probe is an excellent candidate for sensing DPA.

Predicting Stability Constants for Terbium(III) Complexes with Dipicolinic Acid and 4-Substituted Dipicolinic Acid Analogues using Density Functional Theory

The relative stability constants of Tb(III) complexes exhibiting binding to a series of 4-substituted analogues of dipicolinic acid (2,6-pyridinedicarboxylic acid) (DPA) were calculated using density functional theory (DFT) with the standard thermodynamic cycle. DFT calculations showed that the strengths of the stability constants were modified by the substituents in the following (decreasing) order: -NH2 > -OH ∼ -CH2OH > -imidazole ∼ -Cl ∼ -Br ∼ -H > -F > -I, with the differences among them falling within one to two log units except for -NH2. Through population and structural analysis, we observed that the -NH2, -OH, -CH2OH, and halide substituents can donate electrons via resonance effect to the pyridine ring of DPA while inductively withdrawing electrons with different strengths, thus resulting in the different binding strengths of the 4-substituted DPAs to the Tb(III) ions. We believe that these observations possess utility not only in the ongoing development of luminescent probes for bioanalytical studies but also for more recent cross-industrial efforts to enhance reservoir surveillance capabilities using chemical tracers within the oil and gas sector.

Fluorescence of bioaerosols: mathematical model including primary fluorescing and absorbing molecules in bacteria

This paper describes a mathematical model of fluorescent biological particles composed of bacteria, viruses, or proteins. The fluorescent and/or light absorbing molecules included in the model are amino acids (tryptophan, etc.); nucleic acids (DNA, RNA, etc.); coenzymes (nicotinamide adenine dinucleotides, flavins, and vitamins B₆ and K and variants of these); and dipicolinates. The concentrations, absorptivities, and fluorescence quantum yields are estimated from the literature, often with large uncertainties. The bioparticles in the model are spherical and homogeneous. Calculated fluorescence cross sections for particles excited at 266, 280, and 355 nm are compared with measured values from the literature for several bacteria, bacterial spores and albumins. The calculated 266- and 280-nm excited fluorescence is within a factor of 3.2 of the measurements for the vegetative cells and proteins, but overestimates the fluorescence of spores by a factor of 10 or more. This is the first reported modeling of the fluorescence of bioaerosols in which the primary fluorophores and absorbing molecules are included.

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.

Bacillus cereus spores release alanine that synergizes with inosine to promote germination

BACKGROUND

The first step of the bacterial lifecycle is the germination of bacterial spores into their vegetative form, which requires the presence of specific nutrients. In contrast to closely related Bacillus anthracis spores, Bacillus cereus spores germinate in the presence of a single germinant, inosine, yet with a significant lag period.

METHODS AND FINDINGS

We found that the initial lag period of inosine-treated germination of B. cereus spores disappeared in the presence of supernatants derived from already germinated spores. The lag period also dissipated when inosine was supplemented with the co-germinator alanine. In fact, HPLC-based analysis revealed the presence of amino acids in the supernatant of germinated B. cereus spores. The released amino acids included alanine in concentrations sufficient to promote rapid germination of inosine-treated spores. The alanine racemase inhibitor D-cycloserine enhanced germination of B. cereus spores, presumably by increasing the L-alanine concentration in the supernatant. Moreover, we found that B. cereus spores lacking the germination receptors gerI and gerQ did not germinate and release amino acids in the presence of inosine. These mutant spores, however, germinated efficiently when inosine was supplemented with alanine. Finally, removal of released amino acids in a washout experiment abrogated inosine-mediated germination of B. cereus spores.

CONCLUSIONS

We found that the single germinant inosine is able to trigger a two-tier mechanism for inosine-mediated germination of B. cereus spores: Inosine mediates the release of alanine, an essential step to complete the germination process. Therefore, B. cereus spores appear to have developed a unique quorum-sensing feedback mechanism to monitor spore density and to coordinate germination.

Spore dipicolinic acid contents used for estimating the number of endospores in sediments

Endospores are heat-resistant bacterial resting stages that can remain viable for long periods of time and may thus accumulate in sediments as a function of sediment age. The number of spores in sediments has only rarely been quantified, because of methodological problems, and consequently little is known about the quantitative contribution of endospores to the total number of prokaryotic cells. We here report on a protocol to determine the number of endospores in sediments and cultures. The method is based on the fluorimetric determination of dipicolinic acid (DPA), a spore core-specific compound, after reaction with terbium chloride. The concentration of DPA in natural samples is converted into endospore numbers using endospore-forming pure cultures as standards. Quenching of the fluorescence by sediment constituents and background fluorescence due to humic substances hampered direct determination of DPA in sediments. To overcome those interferences, DPA was extracted using ethyl acetate prior to fluorimetric measurements of DPA concentrations. The first results indicated that endospore numbers obtained with this method are orders of magnitude higher than numbers obtained by cultivation after pasteurization. In one of the explored sediment cores, endospores accounted for 3% of all stainable prokaryotic cells.

Two-dimensional multiwavelength fluorescence spectra of dipicolinic acid and calcium dipicolinate

Dipicolinic acid (DPA) and the Ca2+ complex of DPA (CaDPA) are major chemical components of bacterial spores. With fluorescence being considered for the detection and identification of spores, it is important to understand the optical properties of the major components of the spores. We report in some detail on the room-temperature fluorescence excitation and emission spectra of DPA and its calcium ion complex and provide a comparison of the excitation-emission spectrum in a dry, wet paste and aqueous form. DPA solutions have weak, if any, fluorescence, with increased fluorescence when the DPA is dry. After exposure to a broad source UV light of the DPA, wet or dry, we observe a large increase in fluorescence with a maximum intensity emission peak at around 440 nm for excitation light with a wavelength of around 360 nm. There is a slight blueshift in the absorption spectra of UV-exposed DPA from the unexposed DPA solution. CaDPA in solution shows a slight fluorescence with increased fluorescence in the dry form, and a substantial increase of fluorescence was observed after UV exposure with an emission peak of around 410 nm for excitation around 305 nm. The detailed excitation-emission spectra are necessary for better interpretation of the fluorescence spectra of bacterial spores where DPA is a major chemical component.

Potentiometric sensor for dipicolinic acid

A potentiometric chemosensor for selective determination of dipicolinic acid (2,6-pyridinedicarboxylic acid, DPA) was developed based on the surface imprinting technique coupled with a nanoscale transducer: an indium tin oxide (ITO)-coated glass plate. The sensor fabrication conditions, optimal recognition condition, as well as selectivity, sensitivity, and stability of the DPA sensor have been investigated. The DPA sensor could recognize DPA from 3,5-pyridinedicarboxylic acid. Potentiometric measurements demonstrated selective detection of DPA in a concentration range of 1.5 x 10(-6) to 0.0194 M. The response time of DPA sensor for 4 x 10(-4) M DPA was 25 s. The potentiometric response of the DPA sensor to DPA is at 90% of its initial magnitude after 550 times measurement. The viability of such a modified ITO electrode in the presence of other inorganic, organic, and biological materials was probed.

Changes in the luminescence between dried and wet bacillus spores

Fluorescence has been suggested as a method with which to detect and identify bacterial spores. To better understand the nature of the fluorescence signal, we observed the intrinsic steady-state fluorescence and phosphorescence spectra of Bacillus globigii (BG) in both dried and aqueous forms. In vitro, dried, and suspension forms of BG were measured at room temperature in 300-600-nm excitation wavelengths. Also, the phosphorescence of dry BG spores was measured at room temperature at 300-600-nm excitation wavelengths. The wet BG spores exhibited a strong maximum in their fluorescence spectrum, with the peak excitation wavelength near 300 nm and emission wavelength near 400 nm. When the BG was dried, this peak shifted to an approximately 450-nm excitation maximum and an 500-nm emission maximum. The difference between the wet and the dry spore fluorescence spectra cannot be explained by the phosphorescence of the dry spores. Other changes must take place when the spores are wet to account for the large changes observed in the spectrum.

Determination of spore concentration in Bacillus thuringiensis through the analysis of dipicolinate by capillary zone electrophoresis

A new capillary zone electrophoresis (CZE) method for the analysis of dipicolinic acid, a specific component found in spores but not in vegetative cells, was used to determine spore concentration in Bacillus thuringiensis according to the relationship between the spore concentration and the content of dipicolinate. The quantitative relationship was established by using purified spores. Electrolyte conditions that affected the separation efficiency of dipicolinate and the reproducibility were investigated. With 10 mM phosphate, 10 mM ethylenediaminetetraacetic acid and 0.25 mM tetradecyltrimethylammonium bromide at pH 6.2 as the carrier electrolyte, dipicolinate can be determined within 8 min at an applied voltage of -25 kV (anode at detector) and a capillary temperature of 25 degrees C. The method has a high separation efficiency with which the number of theoretical plates is above 300,000 plates m(-1). The relative standard deviations for migration time and peak area are less than 0.5% and 2.0%, respectively. The detection limit for dipicolinate was 10 ng ml(-1), which corresponds to 7.2 x 10(5) spores ml(-1). The method was used to determine spores in fermentation broths, and the results obtained agreed well with the values obtained by plate counting.

Medium effects on the photophysical properties of terbium(III) complexes with pyridine-2,6-dicarboxylate

Emission quantum yields and excited-state lifetimes of mono-, bis- and tris-complexes of terbium(III) with pyridine-2,6-dicarboxylate (DPA) have been measured for aqueous solutions as a function of pH and in the presence of six different anions: bromide, chloride, sulfate, perchlorate, acetate and nitrate. The state of ligation of the terbium ion had a more dramatic effect on photophysical properties of the complexes in comparison with the alteration of other medium parameters. An increase in the number of DPA ligands, coordinated with Tb3+ (from zero to three) resulted in an increase in the emission quantum yield from 0.06 to approximately 0.4, with concurrent prolongation of the excited-state lifetime from 0.5 to approximately 2 ms. It was determined that both an increase in the non-radiative decay rates and a decrease in the values of the radiative decay rate constants, contribute to the luminescence quenching that was detected when the number of DPA ligands was decreased and/or the media acidified. The purpose of this investigation is to aid in the establishment of optimal conditions for conducting terbium(III)-based emission assays for DPA, which is found in the coats of endospores.

Spectrally resolved absolute fluorescence cross sections for bacillus spores

Absolute fluorescence cross sections for Bacillus subtilis and B. cereus bacterial spores as both aqueous suspensions and aerosols were measured at a number of excitation wavelengths between 228 and 303 nm. The fluorescence was spectrally resolved at each excitation wavelength. We found that the optimum excitation wavelength for spore fluorescence is between 270 and 280 nm. The fluorescence cross section for aqueous suspensions is four times larger than for dry aerosols when measured under similar conditions. Measurements on wet aerosols showed an increase in fluorescence cross section over dry aerosols, indicating an enhancement of the fluorescence when the bacterial spores are wet. Mie scattering cross sections at 90 degrees to the direction of the incident radiation and extinction cross sections as a function of wavelength for B. subtilis suspensions and fluorescence cross sections for tryptophan are also reported.

Acetonema longum gen. nov. sp. nov., an H2/CO2 acetogenic bacterium from the termite, Pterotermes occidentis

A previously undescribed, H2-oxidizing CO2-reducing acetogenic bacterium was isolated from gut contents of the wood-feeding termite, Pterotermes occidentis. Cells of representative strain APO-1 were strictly anaerobic. Gram-negative, endospore-forming motile rods which measured 0.30-0.40 x 6-60 microm. Cells were catalase positive, oxidase negative, and had 51.5 mol percent G + C in their DNA. Optimum conditions for growth on H2 + CO2 were at 30-33 degrees C and pH (initial) 7.8, and under these conditions cells formed acetate according to the equation: 4 H2 + 2 CO2----CH3COOH + 2 H2O. Other energy sources supporting good growth of strain APO-1 included glucose, ribose, and various organic acids. Acetate and butyrate were major fermentation products from most organic compounds tested, however propionate, succinate, and 1,2-propanediol were also formed from some substrates. Based on comparative analysis of 16S rRNA nucleotide sequences, strain APO-1 was related, to but distinct from, members of the genus Sporomusa. Moreover, physiological and morphological differences between strain APO-1 and the six known species of Sporomusa were significant. Consequently, it is proposed herewith that a new genus, Acetonema, be established with strain APO-1 as the type strain of the new species, Acetonema longum. A. longum may contribute to the nutrition of P. occidentis by forming acetate, propionate and butyrate, compounds which are important carbon and energy sources for termites.

High-resolution solid-state 13C nuclear magnetic resonance of bacterial spores: identification of the alpha-carbon signal of dipicolinic acid

Natural-abundance solid-state 13C nuclear magnetic resonance spectra were obtained for bacterial spores for the first time by using the technique of cross-polarization magic-angle-spinning nuclear magnetic resonance spectroscopy. A resonance at about 150 ppm, detectable in spore samples having a Mn content of less than 0.05%, was consistent with an identification as the alpha-carbon signal of calcium dipicolinate; this signal was missing from a spore sample treated with acid to release dipicolinate and from a spore coat preparation. Carbohydrate peaks were particularly intense in spores and coat preparations of Bacillus macerans. Signals ascribable to beta-hydroxybutyrate were prominent in a B. cereus sample.

Germinability of coat-lacking spores of Bacillus megaterium

Upon treatment with acid, the germinability of both intact and coat-lacking spores of Bacillus megaterium ATCC 19213 exhibited similar features. Namely, when the spores previously germinated by alanine in the presence of phosphate buffer were converted to H-spores by treatment with nitric acid, germination proceeded at a very low speed in a same germination medium. When H-spores converted to Ca-spores by treatment with calcium acetate and subsequently germinated, germination proceeded at a speed higher than that of native spores and occurred even in the absence of buffer. These results suggest that the site of exchangeable cations concerned with germinability must not exist in the coat.

Determination of dipicolinic acid in bacterial spores by derivative spectroscopy

Dipicolinic acid was extracted from approximately 0.1 mg spores or 0.5 ml of sporulating culture with 20 mM HCl for 10 min at 100 degrees C. The suspension was diluted with 5 mM Ca2+, 100 mM Tris, pH 7.6, centrifuged, and the first derivative of the uv absorbance spectrum recorded from 275 nm to 285 nm. DPA concentration was determined from the difference between the maximum at 276.6 nm and the minimum at 280 nm. The use of the difference between two first derivative values removed possible interference from sloping baselines. Turbidity, nucleic acids, and bacteriological media did not interfere. Analysis time for four extracts was 4 min using a spectrophotometer reading at 0.1-nm intervals. Dipicolinate at 0.1 mM gave 0.184 absorbance/nm at 25 degrees C. The coefficient of variation was 1.5%, and the detection limit 1 microM.

Liquid Chromatographic Determination of Dipicolinic Acid from Bacterial Spores

Dipicolinic acid was determined by reverse-phase liquid chromatography. Elution was with 0.2 M potassium phosphate, pH 1.8, containing 1.5% tert -amyl alcohol or higher concentrations of lower alcohols or acetonitrile. The normal analytical range was 50 to 1,000 μM, which is equivalent to 0.1 to 1 mg of spores per ml with a relative standard error of 2 to 4% and a detection limit of <100 pmol. Dipicolinic acid was fully extracted from spores by heating at pH 1.8 for 10 min at 100°C. Sporulating cultures may be analyzed in less than 20 min without separation of cells from media. Liquid chromatography was also used to detect dipicolinic acid in more complex substrates, e.g., guinea pig feces containing Metabacterium polyspora spores and canned food. Dipicolinic acid could be detected in unspoiled canned salmon containing <10 6 added Bacillus cereus spores per g.

Transcriptional control of peptidoglycan precursor synthesis during sporulation in Bacillus sphaericus

Synthesis of enzymes functional in the synthesis of nucleotide precursors of peptidoglycan ceases upon initiation of sporulation in Bacillus sphaericus. During sporulation, two periods of synthesis of these enzymes occur. The first starts at spore septum formation and is conincident with forespore engulfment; it involves the synthesis of those enzymes required for making the precursor of vegetative-type peptidoglycan, including L-lysyl ligase but no mesodiaminopimelyl ligase. The second period occurs shortly before the appearance of cortex. It involves the synthesis of diaminopimelyl ligase and the other enzymes needed for making the precursor of cortical peptidoglycan, but not lysyl ligase. Both events are a consequence of derepression at the level of transcription. Neither period of synthesis occurs in asporogenous mutants whose morphological block is at the point of spore septum formation.

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.

Photoreactivation, photoproduct formation, and deoxyribonucleic acid state in ultraviolet-irradiated sporulating cultures of Bacillus cereus

Photoreactivation of ultraviolet-irradiated Bacillus cereus T declined markedly during the development of stage IV forespores. During ultraviolet irradiation of a culture containing early and late stage IV forespores, both vegetative- and spore-type photoproducts were formed. The formation of vegetative-type photoproducts (mainly thymine dimers) decreased to nearly half during late stage IV, remaining constant until lysis of the mother cells began, when it fell to zero. Spore-type photoproducts were first observed during late stage IV and increased with the increase in numbers of late stage IV forespores. The occurrence of spore-type photoproducts preceded the development of refractile forespores by about 1 h. At stage III the nuclear material occupied a central position, and the ribosomes were at the periphery of the forespore protoplast. During stage IV the deoxyribonucleic acid (DNA) occurred in a peripheral position, and bundles of fibers ("transition" DNA) could be seen. By stage V, all of the DNA appeared to be of the spore type and was peripheral, and the forespore protoplast center was packed with ribosomes. Forespore stages II, III, and IV were classified by light and electron microscopy. The curve for electron microscope classifications preceded that for light microscope classifications by approximately one stage. The formation of spore-type photoproducts preceded differentiation of DNA by about 1 h, the latter coinciding with the development of refractility. Spore-type photoproducts have been associated with DNA in the A state, and the progressive change of the forespore DNA into this state is discussed in relation to the spore differentiation process.

Use of ultraviolet radiation to locate dipicolinic acid in Bacillus cereus spores

A novel method is described that allows a direct determination of the location of a portion of the dipicolinic acid (DPA) in spores. Ultraviolet (UV) irradiation is shown to cause cross-linkage of DPA to spore proteins which have the characteristics of membrane proteins. We suggest that DPA resides in the inner forespore membrane (IFSM) and spore cytoplasm (i.e., the spore protoplast). Only that portion of the DPA in the vicinity of the IFSM appeared to form UV-induced DPA-protein adducts.

Development of ultraviolet resistance in sporulating Bacillus cereus T

Ultraviolet (UV) resistance patterns of sporulating Bacillus cereus were determined. Six different categories of UV resistance were discernible as the organism progressed from exponential growth to the free, mature spore. Light microscope observations allowed the assignment of certain sporulation stages to specific UV resistance categories. Marked changes in UV resistance were associated with stages III, mid-IV, and post-IV of sporulation. Dipicolinic acid was shown to sensitize forespores to UV radiation. Mechanisms invoked to explain the different UV categories are discussed.

Cell wall polymers of Bacillus sphaericus 9602. II. Synthesis of the first enzyme unique to cortex synthesis during sporulation

The cell wall peptidoglycan of vegetative cells of Bacillus sphaericus 9602 contains l-lysine and d-isoasparagine and is devoid of diaminopimelic acid (Dap), whereas the peptidoglycan of its spore cortex is devoid of l-lysine and d-isoasparagine and contains meso-Dap. These two structures have a common biosynthetic precursor, uridine-diphospho-N-acetylmuramyl-l- alanyl-d-glutamic acid, which accepts either l-lysine or meso-Dap, the latter reaction being the first unique to the synthesis of the spore cortex peptidoglycan. l-lysine-adding activity decays at the end of vegetative growth to a level which is maintained until Dap-adding activity appears, when it declines rapidly again. Dap-adding activity is not detectable in refractile spores, in vegetative cells, or in sporulating cells until about 4 hr after the end of vegetative growth, when it increases rapidly for about 1.5 hr in a process dependent on continued protein and ribonucleic acid (RNA) synthesis. This process apparently involves transcription and translation during this period of a "sporulation-specific" gene whose product is essential for and unique to sporulation. It is closely followed by the acquirement of refractility. Another sporulation-specific gene, that for dipicolinate synthase, is apparently transcribed and translated in an overlapping period commencing about 0.5 hr later, although dipicolinate does not accumulate rapidly until 1.5 hr later, when about 75% of the cells are already refractile. Inhibition of protein synthesis with chloramphenicol or of RNA synthesis with streptolydigin inhibited accumulation of these enzymes in sporulating cells; this inhibition could be reversed by washing out the antibiotics after 1.5 hr. Sporulation recommenced with an unaltered sequence of events but with poorer synchrony. There was no evidence for a messenger RNA for either enzyme of lifetime greater than a small fraction of the period of enzyme accumulation, although dilution with 10 volumes of fresh medium failed to prevent synthesis of Dap-adding enzyme in cells which had become terminally swollen, a process preceding enzyme synthesis by about 1.5 hr. The synthesis of this enzyme in B. sphaericus is apparently dependent on programmed transcription of the appropriate gene.