In situ surface-etched bacterial spore detection using dipicolinic acid-europium-silica nanoparticle bioreporters

A basic approach was optimized for the synthesis of highly selective and sensitive in situ mesoporous (MCM) type imprinted silica polymers for the detection of dipicolinic acid (DPA) using europium as a reporter. DPA is a ubiquitous biochemical marker available during the germination event of endospore-forming bacteria such as Bacillus . Additionally, an MCM-MIP (molecularly imprinted polymeric phenomena) detector and a companion MCM-non-surface-MIP detector were synthesized using europium reporters for the sensing of DPA under optimized laboratory conditions. Our results showed that the in situ molecular imprinting process enabled rapid, selective detection of DPA with high sensitivity compared to MCM-MIP (imprinted for DPA; no DPA present), MCM-Non-MIP (no imprint present), and MCM-SR-MIP (imprinted with DPA present) detectors. The lower detection limit observed for DPA concentration is 5.49 × 10(-10) mol dm(-3) for MCM-MIP. The performance of the sensor in high-salt-water conditions, under photo-bleaching, and its reusability were also evaluated. The synthesized in situ MCM-MIP material should permit the detection of DPA for field assays related to suspect bacterial sporulation events.

Residue dynamics of clopyralid and picloram in rape plant rapeseed and field soil

A new method for simultaneous analysis of clopyralid and picloram residues in rape plant, rapeseed and field soil was developed and validated. The residual dynamics and final residues of clopyralid and picloram in rape plant, rapeseed and soil were determined by high performance liquid chromtography-diode array detector (HPLC-DAD) and high performance liquid chromtography-mass spectroscopy detector (HPLC-MSD). The limit of quantification (LOQ) was established as 0.02 mg/kg for soil sample, 0.5 mg/kg for rape and rapeseed sample, respectively. It was shown that recoveries ranged from 71.3%-109.0% for clopyralid, and 84.0%-100.5% for picloram at fortified levels of 0.02-2 mg/kg. From residue trials at two geographical experimental plots in China and laboratory simulated pots, the results showed that the half-lives of clopyralid in rape and soil were 3.66-4.83 and 2.53-5.17 days, respectively, for picloram with half-lives of 5.17-10.73 and 3.45-7.11 days. For tirals applied according to the label recommended, at harvest time the final residues of clopyralid in rapeseed were below 1.82 mg/kg, while the picloram residues could not be detected in rapeseed (<LOQ).

Multiple-trap laser tweezers Raman spectroscopy for simultaneous monitoring of the biological dynamics of multiple individual cells

We report the development of a multiple-trap laser tweezers Raman spectroscopy (LTRS) array for simultaneously acquiring Raman spectra of individual cells in physiological environments. This LTRS-array technique was also combined with phase contrast and fluorescence microscopy, allowing measurement of Raman spectra, refractility, and fluorescence images of individual cells with a temporal resolution of ~5 s. As a demonstration, we used this technique to monitor multiple Bacillus cereus spores germinating in a nutrient medium for up to 90min and observed the kinetics of dipicolinic acid release and uptake of nucleic acid-binding stain molecules during spore germination.

Fluorescence lifetime and intensity of terbium-doped dipicolinic acid in water, HCl, and sodium acetate buffer solutions

The lifetimes of the individual fluorescing lines from the terbium-doped dipicolinic acid (DPA) complex have been measured and reported, for the first time to our knowledge. These lifetimes have been measured as a function of terbium and dipicolinic acid concentration, solvent pH, and solvent composition for water, HCl, and sodium acetate buffer solutions. Fluorescence lifetimes over the range from 0.75 to 1.07 ms were measured. The maximum fluorescence was obtained for distilled water solutions.

Factors contributing to heat resistance of Clostridium perfringens endospores

The endospores formed by strains of type A Clostridium perfringens that produce the C. perfringens enterotoxin (CPE) are known to be more resistant to heat and cold than strains that do not produce this toxin. The high heat resistance of these spores allows them to survive the cooking process, leading to a large number of food-poisoning cases each year. The relative importance of factors contributing to the establishment of heat resistance in this species is currently unknown. The present study examines the spores formed by both CPE(+) and CPE(-) strains for factors known to affect heat resistance in other species. We have found that the concentrations of DPA and metal ions, the size of the spore core, and the protoplast-to-sporoplast ratio are determining factors affecting heat resistance in these strains. While the overall thickness of the spore peptidoglycan was found to be consistent in all strains, the relative amounts of cortex and germ cell wall peptidoglycan also appear to play a role in the heat resistance of these strains.

Determination of chlorinated acid herbicides in vegetation and soil by liquid chromatography/electrospray-tandem mass spectrometry

The method presented uses reversed-phase liquid chromatography with negative electrospray ionization and tandem mass spectrometry to analyze 9 chlorinated acid herbicides in soil and vegetation matrixes: clopyralid, dicamba, MCPP, MCPA, 2,4-DP, 2,4-D, triclopyr, 2,4-DB, and picloram. A 20 g portion is extracted with a basic solution and an aliquot acidified and micropartitioned with 3 mL chloroform. Vegetation samples are subjected to an additional cleanup with a mixed-mode anion exchange solid-phase extraction cartridge. Two precursor product ion transitions per analyte are measured and evaluated to provide the maximum degree of confidence in results. Average recoveries for 3 different soil types tested ranged from 72 to 107% for all compounds with the exception of 2,4-DB at 56-99%. Average recoveries for the 3 different vegetation types studied were lower and ranged from 53 to 80% for all compounds.

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.

Comparison of the properties of Bacillus subtilis spores made in liquid or on agar plates

AIMS

To compare the properties of the spores of Bacillus subtilis prepared in liquid and on plates.

METHODS AND RESULTS

The spores of B. subtilis were prepared at 37 degrees C using a nutrient exhaustion medium either in liquid or on agar plates. The levels of core water, dipicolinic acid (DPA) and small, acid-soluble spore proteins (SASP) were essentially identical in spores made in liquid or on plates. Spores prepared in liquid were killed approximately threefold more rapidly at 90 degrees C in water than the spores prepared on plates, and the spores prepared in liquid were more sensitive to nitrous acid and a diluted stable superoxidized water. Spores prepared in liquid also germinated more rapidly with several agents than those prepared on plates. Pellets of spores prepared on plates were darker than spores prepared in liquid, and spores prepared in liquid had more readily extracted coat protein. However, there were no major differences in the relative levels of individual coat proteins or the cross-linking of the coat protein GerQ in the two types of spores, although the inner membrane of spores prepared on plates had a higher ratio of anteiso- to iso-fatty acids.

CONCLUSIONS

The preparation in liquid yielded spores with some different properties than those made on agar plates. Spores made in liquid had lower resistance to heat and several chemicals, and germinated more readily with several agents. There were also differences in the composition of the inner membrane of spores prepared under these two conditions. However, there were no major differences in the levels of DPA, core water, SASP and individual coat proteins or the cross-linking of a coat protein in spores made in liquid and on plates.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work demonstrates that the preparation method can affect the resistance and germination properties of bacterial spores, even if an identical medium and temperature are used. Evidence was also obtained consistent with the role of the inner membrane in spore resistance and germination, and that some factor in addition to core water, DPA and SASP content plays a role in spore resistance to wet heat.

A highly sensitive HPLC method for determination of nanomolar concentrations of dipicolinic acid, a characteristic constituent of bacterial endospores

A high-performance liquid chromatographic method with indirect fluorescence detection has been developed for quantification of dipicolinic acid, a major constituent of bacterial endospores. After separation on a reversed-phase column, a post-column reagent of sodium acetate at 1 mol l(-1) with 50 micromol l(-1) terbium chloride was added for complexation of dipicolinic acid. Terbium monodipicolinate complexes formed were quantified by measuring the fluorescence emission maximum at 548 nm after excitation with UV light at 270 nm wavelength. Parameters of post-column complexation were optimized to achieve a detection limit of 0.5 nmol DPA l(-1), corresponding to about 10(3) Desulfosporosinus orientis endospores per ml. The method was applied to the analysis of spore contamination in tuna and for estimating the endospore numbers in marine sediments.

Levels of Ca2+-dipicolinic acid in individual bacillus spores determined using microfluidic Raman tweezers

Pyridine-2,6-dicarboxylic acid (dipicolinic acid [DPA]) in a 1:1 chelate with calcium ion (Ca-DPA) comprises 5 to 15% of the dry weight of spores of Bacillus species. Ca-DPA is important in spore resistance to many environmental stresses and in spore stability, and Ca-DPA levels in spore populations can vary with spore species/strains, as well as with sporulation conditions. We have measured levels of Ca-DPA in large numbers of individual spores in populations of a variety of Bacillus species and strains by using microfluidic Raman tweezers, in which a single spore is trapped in a focused laser beam and its Ca-DPA is quantitated from the intensity of the Ca-DPA-specific band at 1,017 cm(-1) in Raman spectroscopy. Conclusions from these measurements include the following: (i) Ca-DPA concentrations in the spore core are >800 mM, well above Ca-DPA solubility; (ii) SpoVA proteins may be involved in Ca-DPA uptake in sporulation; and (iii) Ca-DPA levels differ significantly among individual spores in a population, but much of this variation could be due to variations in the sizes of individual spores.

Optimizing the laser-pulse configuration for coherent Raman spectroscopy

We introduce a hybrid technique that combines the robustness of frequency-resolved coherent anti-Stokes Raman scattering (CARS) with the advantages of time-resolved CARS spectroscopy. Instantaneous coherent broadband excitation of several characteristic molecular vibrations and the subsequent probing of these vibrations by an optimally shaped time-delayed narrowband laser pulse help to suppress the nonresonant background and to retrieve the species-specific signal. We used this technique for coherent Raman spectroscopy of sodium dipicolinate powder, which is similar to calcium dipicolinate (a marker molecule for bacterial endospores, such as Bacillus subtilis and Bacillus anthracis), and we demonstrated a rapid and highly specific detection scheme that works even in the presence of multiple scattering.

Comprehensive assignment of mass spectral signatures from individual Bacillus atrophaeus spores in matrix-free laser desorption/ionization bioaerosol mass spectrometry

We have fully characterized the mass spectral signatures of individual Bacillus atrophaeus spores obtained using matrix-free laser desorption/ionization bioaerosol mass spectrometry (BAMS). Mass spectra of spores grown in unlabeled, 13C-labeled, and 15N-labeled growth media were used to determine the number of carbon and nitrogen atoms associated with each mass peak observed in mass spectra from positive and negative ions. To determine the parent ion structure associated with fragment ion peaks, the fragmentation patterns of several chemical standards were independently determined. Our results confirm prior assignments of dipicolinic acid, amino acids, and calcium complex ions made in the spore mass spectra. The identities of several previously unidentified mass peaks, key to the recognition of Bacillus spores by BAMS, have also been revealed. Specifically, a set of fragment peaks in the negative polarity is shown to be consistent with the fragmentation pattern of purine nucleobase-containing compounds. The identity of m/z = +74, a marker peak that helps discriminate B. atrophaeus from Bacillus thuringiensis spores grown in rich media is [N1C4H12]+. A probable precursor molecule for the [N1C4H12]+ ion observed in spore spectra is trimethylglycine (+N(CH3)3CH2COOH), which produces a m/z = +74 peak when ionized in the presence of dipicolinic acid. A clear assignment of all the mass peaks in the spectra from bacterial spores, as presented in this work, establishes their relationship to the spore chemical composition and facilitates the evaluation of the robustness of "marker" peaks. This is especially relevant for peaks that have been used to discriminate Bacillus spore species, B. thuringiensis and B. atrophaeus, in our previous studies.

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.

Characterisation of betalain patterns of differently coloured inflorescences from Gomphrena globosa L. and Bougainvillea sp. by HPLC-DAD-ESI-MSn

In the present study, the betaxanthin (bx) and betacyanin patterns of differently coloured inflorescences from Gomphrena globosa L. and Bougainvillea sp. have been investigated in detail by applying reversed phase high-performance liquid chromatography-diode array detection (HPLC-DAD) coupled with positive ion electrospray mass spectrometry. Histidine-bx was found to be the predominant betaxanthin of Gomphrena globosa inflorescences. Furthermore, arginine-bx was detected as a novel betaxanthin, which to the best of our knowledge has not been reported as a pigment that occurs naturally so far. Dopa-bx was the major betaxanthin of Bougainvillea sp., although several minor betaxanthins were also present, including lysine-bx and putrescine-bx, novel betaxanthins hitherto not observed naturally. Remarkable differences in the betacyanin patterns between the purple, red and orange varieties were observed for both Gomphrena and Bougainvillea inflorescences. Hence, both the betacyanin profiles and the relative betaxanthin:betacyanin ratios determine the broad colour palette of Gomphrena petals and Bougainvillea bracts.

Monitoring DPA Release from a Single Germinating Bacillus subtilis Endospore via Surface-Enhanced Raman Scattering Microscopy

A method for monitoring DPA release from a single germinating Bacillus subtilis endospore is reported. High S/N ratio SERS spectra were obtained with excitation power 3 mW at 647.1 nm and 1 min spectral collection times. The method is proof-of-principle for the SERS detection limit at the single spore level. This represents a 100- to 1000-fold improvement over previously reported detection limits for SERS-based measurements of DPA in endospores.

Levels of glycine betaine in growing cells and spores of Bacillus species and lack of effect of glycine betaine on dormant spore resistance

Bacteria of various Bacillus species are able to grow in media with very high osmotic strength in part due to the accumulation of low-molecular-weight osmolytes such as glycine betaine (GB). Cells of Bacillus species grown in rich and minimal media contained low levels of GB, but GB levels were 4- to 60-fold higher in cells grown in media with high salt. GB levels in Bacillus subtilis cells grown in minimal medium were increased approximately 7-fold by GB in the medium and 60-fold by GB plus high salt. GB was present in spores of Bacillus species prepared in media with or without high salt but at lower levels than in comparable growing cells. With spores prepared in media with high salt, GB levels were highest in B. subtilis spores and > or =20-fold lower in B. cereus and B. megaterium spores. Although GB levels in B. subtilis spores were elevated 15- to 30-fold by GB plus high salt in sporulation media, GB levels did not affect spore resistance. GB levels were similar in wild-type B. subtilis spores and spores that lacked major small, acid-soluble spore proteins but were much lower in spores that lacked dipicolinic acid.

Proteins and dipicolinic acid released during heat shock activation of Bacillus subtilis spores probed by optical spectroscopy

UV fluorescence and absorption spectroscopy from Bacillus subtilis spores detected proteins and dipicolinic acid (DPA) released into the supernatant after heat treatments ranging from 20 degrees to 90 degrees C. The protein and DPA concentration in the supernatant was greater with higher heat treatment temperatures, undergoing a substantial increase for T > or = 60 degrees C, and supporting the theory that spores undergo a phase transition from a glassylike to a rubberylike state at 56 degrees C. Gel electrophoresis detected several small proteins with molecular weights between 6 and 11 kDa. These proteins may be small acid-soluble spore proteins that are present in spores but break down during germination. A 30 kDa protein extracted above 60 degrees C is related to the rubber-glass phase transition.

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

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

Vibrational and microbiological study on alkaline metal picolinates and o-iodobenzoates

FT-IR and Raman experimental data were assigned to appropriate bond vibrations and used to compare the different electronic charge distributions in the aromatic rings and carboxylic anions of various lithium, sodium, potassium, rubidium and caesium o-iodobenzoates and picolinates. Then principal component analysis (PCA) was applied in order to attempt to distinguish the biological activities of these compounds according to selected band wavenumbers. The growth of the bacteria Escherichia coli and Bacillus subtilis and the yeasts Saccharomyces cerevisiae and Hansenula anomala under optimal growth conditions were measured after 24 hours of incubation by the classical plate method. The influence of the picolinates and o-iodobenzoates on the growth of these microorganisms, again after 24 hours of incubation, was also measured and compared to the effect of sodium benzoate, which was used as a reference material. In general, the o-iodobenzoates exhibited more activity against the microorganisms than the picolinates. A statistically significant linear correlation between the spectral data and the degree of influence of a given compound on microorganism growth was established. The correlation coefficients for the o-iodobenzoates were 0.696, -0.628, 0.693 and 0.755 for E. coli, B. subtilis, H. anomala and S. cerevisiae, respectively, and for the picolinates they were 0.818, 0.826, 0.821 and 0.877 for E. coli, B. subtilis, H. anomala and S. cerevisiae, respectively. Therefore, IR spectroscopy is shown to be a rapid and reliable analytical tool for preliminary estimation of the antimicrobial properties of newly synthesized compounds, that can be applied before microbial performance tests.

Visible and UV coherent Raman spectroscopy of dipicolinic acid

We use time-resolved coherent Raman spectroscopy to obtain molecule-specific signals from dipicolinic acid (DPA), which is a marker molecule for bacterial spores. We use femtosecond laser pulses in both visible and UV spectral regions and compare experimental results with theoretical predictions. By exciting vibrational coherence on more than one mode simultaneously, we observe a quantum beat signal that can be used to extract the parameters of molecular motion in DPA. The signal is enhanced when an UV probe pulse is used, because its frequency is near-resonant to the first excited electronic state of the molecule. The capability for unambiguous identification of DPA molecules will lead to a technique for real-time detection of spores.

Floral fluorescence effect

The way flowers appear to insects is crucial for pollination. Here we describe an internal light-filtering effect in the flowers of Mirabilis jalapa, in which the visible fluorescence emitted by one pigment, a yellow betaxanthin, is absorbed by another, a violet betacyanin, to create a contrasting fluorescent pattern on the flower's petals. This finding opens up new possibilities for pollinator perception as fluorescence has not previously been considered as a potential signal in flowers.

Fourier transform infrared reflectance microspectroscopy study of Bacillus subtilis engineered without dipicolinic acid: the contribution of calcium dipicolinate to the mid-infrared absorbance of Bacillus subtilis endospores

Mid-infrared spectra of spores of two strains of Bacillus subtilis, PS832 (wild-type) and FB122 (sleB spoVF), that are isogenic except for the two mutations in FB122 were obtained by Fourier transform infrared (FT-IR) reflectance microspectroscopy. The mutations in FB122 cause the spores of this strain to be devoid of dipicolinic acid (pyridine-2,6-dicarboxylic acid; DPA), a biomarker characteristic of bacterial spores. Analysis of these two strains by difference spectroscopy revealed a spectrum similar to that of calcium dipicolinate (CaDPA), a chelate salt of DPA. This difference spectrum was compared to mid-infrared spectra of both DPA and CaDPA, and was attributed to CaDPA only. This is the first report known to the authors of a genetically engineered organism being used to identify the spectral contribution of a particular cellular component.

Rapid detection of an anthrax biomarker by surface-enhanced Raman spectroscopy

A rapid detection protocol suitable for use by first-responders to detect anthrax spores using a low-cost, battery-powered, portable Raman spectrometer has been developed. Bacillus subtilis spores, harmless simulants for Bacillus anthracis, were studied using surface-enhanced Raman spectroscopy (SERS) on silver film over nanosphere (AgFON) substrates. Calcium dipicolinate (CaDPA), a biomarker for bacillus spores, was efficiently extracted by sonication in nitric acid and rapidly detected by SERS. AgFON surfaces optimized for 750 nm laser excitation have been fabricated and characterized by UV-vis diffuse reflectance spectroscopy and SERS. The SERS signal from extracted CaDPA was measured over the spore concentration range of 10(-14)-10(-12) M to determine the saturation binding capacity of the AgFON surface and to calculate the adsorption constant (Kspore=1.7 x 10(13) M(-1)). At present, an 11 min procedure is capable of achieving a limit of detection (LOD) of approximately 2.6 x 10(3) spores, below the anthrax infectious dose of 10(4) spores. The data presented herein also demonstrate that the shelf life of prefabricated AgFON substrates can be as long as 40 days prior to use. Finally, these sensing capabilities have been successfully transitioned from a laboratory spectrometer to a field-portable instrument. Using this technology, 10(4) bacillus spores were detected with a 5 s data acquisition period on a 1 month old AgFON substrate. The speed and sensitivity of this SERS sensor indicate that this technology can be used as a viable option for the field analysis of potentially harmful environmental samples.