Investigation of bacterial spore structure by high resolution solid-state nuclear magnetic resonance spectroscopy and transmission electron microscopy

"Sporotan" a new fluorescent stain for identifying cryptic spores of Rhodobacter johrii

We propose a new fluorescent stain "sporotan" and staining protocol which aid in the identification of cryptic endospores which are otherwise mistaken as poly-β-hydroxyalkanoate granules.

Intracellular membranes of bacterial endospores are reservoirs for spore core membrane expansion during spore germination

Bacterial endospores are formed by certain bacteria, such as Bacillus subtilis or the pathogenic Bacillus anthracis and Clostridioides difficile, to allow survival in environmental conditions which are lethal to vegetative bacteria. The spores possess a particular architecture and molecular inventory which endow them with a remarkable resistance against desiccation, heat and radiation. Another remarkable spore feature is their rapid return to vegetative growth during spore germination and outgrowth. The underlying processes of this latter physiological and morphological transformation involve a number of different events, some of which are mechanistically not entirely understood. One of these events is the expansion of the central spore core, which contains the DNA, RNA and most spore enzymes. To date, it has been unclear how the ~1.3- to 1.6-fold expansion of the core membrane surface area that accompanies core expansion takes place, since this occurs in the absence of significant if any ATP synthesis. In the current work, we demonstrate the presence of intracellular membrane structures in spores located just below the core membrane. During spore germination these internal core membranes disappear when the core size increases, suggesting that they are integrated into the core membrane to allow core expansion. These intracellular membranes are most probably present as more or less compressed vesicles or tubules within the dormant spore core. Investigations of spores from different species suggest that these intracellular membrane structures below the core membrane are a general feature of endospore forming bacteria.

Nanomechanical Characterization of Bacillus anthracis Spores by Atomic Force Microscopy

The study of structures and properties of bacterial spores is important to understanding spore formation and biological responses to environmental stresses. While significant progress has been made over the years in elucidating the multilayer architecture of spores, the mechanical properties of the spore interior are not known. Here, we present a thermal atomic force microscopy (AFM) study of the nanomechanical properties of internal structures of Bacillus anthracis spores. We developed a nanosurgical sectioning method in which a stiff diamond AFM tip was used to cut an individual spore, exposing its internal structure, and a soft AFM tip was used to image and characterize the spore interior on the nanometer scale. We observed that the elastic modulus and adhesion force, including their thermal responses at elevated temperatures, varied significantly in different regions of the spore section. Our AFM images indicated that the peptidoglycan (PG) cortex of Bacillus anthracis spores consisted of rod-like nanometer-sized structures that are oriented in the direction perpendicular to the spore surface. Our findings may shed light on the spore architecture and properties.

IMPORTANCE

A nanosurgical AFM method was developed that can be used to probe the structure and properties of the spore interior. The previously unknown ultrastructure of the PG cortex of Bacillus anthracis spores was observed to consist of nanometer-sized rod-like structures that are oriented in the direction perpendicular to the spore surface. The variations in the nanomechanical properties of the spore section were largely correlated with its chemical composition. Different components of the spore materials showed different thermal responses at elevated temperatures.

Effects of Electrolyzed Oxidizing Water on Inactivation of Bacillus subtilis and Bacillus cereus Spores in Suspension and on Carriers

Spores of some Bacillus species are responsible for food spoilage and foodborne disease. These spores are highly resistant to various interventions and cooking processes. In this study, the sporicidal efficacy of acidic electrolyzed oxidizing (EO) water (AEW) and slightly acidic EO water (SAEW) with available chlorine concentration (ACC) of 40, 60, 80, 100, and 120 mg/L and treatment time for 1, 2, 3, 4, 5, and 6 min were tested on Bacillus subtilis and Bacillus cereus spores in suspension and on carrier with or without organics. The reduction of spore significantly increased with increasing ACC and treatment time (P < 0.05). Nondetectable level of B. cereus spore in suspension occurred within 2 min after exposure to both EO waters containing 120 mg/L ACC, while only SAEW at 120 mg/L and 2 min treatment achieved >6 log reductions of B. subtilis spore. Both types of EO water with ACC of 60 mg/L and 6 min treatment achieved a reduction of B. subtilis and B. cereus spores to nondetectable level. EO water with ACC of 80 mg/L and treatment time of 3 min on carrier test without organics addition resulted in reductions of B. subtilis spore to nondetectable level. But, addition of 0.3% organics on carrier decreased the inactivation effect of EO water. This study indicated that EO water was highly effective in inactivation of B. subtilis and B. cereus spores in suspension or on carrier, and therefore, rendered it as a promising disinfectant to be applied in food industry.

Bacterial spore detection and analysis using hyperpolarized 129Xe chemical exchange saturation transfer (Hyper-CEST) NMR

Previously, we reported hyperpolarized ¹²⁹Xe chemical exchange saturation transfer (Hyper-CEST) NMR techniques for the ultrasensitive (i.e., 1 picomolar) detection of xenon host molecules known as cryptophane. Here, we demonstrate a more general role for Hyper-CEST NMR as a spectroscopic method for probing nanoporous structures, without the requirement for cryptophane or engineered xenon-binding sites. Hyper-CEST ¹²⁹Xe NMR spectroscopy was employed to detect Bacillus anthracis and Bacillus subtilis spores in solution, and interrogate the layers that comprise their structures. ¹²⁹Xe-spore samples were selectively irradiated with radiofrequency pulses; the depolarized ¹²⁹Xe returned to aqueous solution and depleted the ¹²⁹Xe-water signal, providing measurable contrast. Removal of the outermost spore layers in B. anthracis and B. subtilis (the exosporium and coat, respectively) enhanced ¹²⁹Xe exchange with the spore interior. Notably, the spores were invisible to hyperpolarized ¹²⁹Xe NMR direct detection methods, highlighting the lack of high-affinity xenon-binding sites, and the potential for extending Hyper-CEST NMR structural analysis to other biological and synthetic nanoporous structures.

Characterization of Bacillus mojavensis KJS-3 for industrial applications

One of the strains of the Bacillus mojavensis group, Bacillus mojavensis KJS-3 (B. mojavensis KJS-3), which has been demonstrated to play a role in protecting plants against diseases as a bacterial endophyte and in reducing the accumulation of mycotoxins generated by an endophytic fungus, was recently discovered in food waste. In this study, the identification and characterization of B. mojavensis KJS-3 was performed via TEM analysis, API-zym test, API 50 CHB test, assays of catalase and oxidase activity, lactic acid production, stability under various conditions, antibiotic susceptibility, and cellular fatty acid composition. The overall results of this study demonstrate that B. mojavensis KJS-3 may have great potential as a probiotic product, as this bacterium is quite stable in somewhat harsh environments. B. mojavensis KJS-3 was positive on oxidase and catalase tests, and the conversion rate of glucose to lactic acid was 58.9%. Finally, anteiso-C(15:0) (43.10%) was identified as the major fatty acid.

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.

Glassy state in Bacillus subtilis spores analyzed by differential scanning calorimetry

Thermal properties of dried spores of Bacillus subtilis, investigated by differential scanning calorimetry (DSC), were studied. A reversible heat capacity shift ascribable to glass-rubber transition was observed at 90-115 degrees C. The transition was found to be a pressure-inhibited volume-activated event. The decoated spores and the extracted peptidoglycan material exhibited glass transition, suggesting that the cortex could be involved in the event. Furthermore, the glass transition was evident when spores were treated with strong acid, and when the isogenic strain PS578 was scanned, indicating that core integrity and core components are not involved in the occurrence of the event. These results suggest that in the dried B. subtilis spores an amorphous biomaterial, possibly the cortex peptidoglycan, is present as a glass.

Effect of microwave radiation on Bacillus subtilis spores

AIMS

To compare the killing efficacy and the effects exerted by microwaves and conventional heating on structural and molecular components of Bacillus subtilis spores.

METHODS AND RESULTS

A microwave waveguide applicator was developed to generate a uniform and measurable distribution of the microwave electric-field amplitude. The applicator enabled the killing efficacy exerted by microwaves on B. subtilis spores to be evaluated in comparison with conventional heating at the same temperature value. The two treatments produced a similar kinetics of spore survival, while remarkably different effects on spore structures were seen. The cortex layer of the spores subjected to conductive heating was 10 times wider than that of the untreated spores; in contrast, the cortex of irradiated spores did not change. In addition, the heated spores were found to release appreciable amounts of dipicolinic acid (DPA) upon treatment, while extracellular DPA was completely undetectable in supernatants of the irradiated spores. These observations suggest that microwave radiation may promote the formation of stable complexes between DPA and other spore components (i.e. calcium ions); thus, making any release of DPA from irradiated spores undetectable. Indeed, while a decrease in measurable DPA concentrations was not produced by microwave radiation on pure DPA solutions, a significant lowering in DPA concentration was detected when this molecule was exposed to microwaves in the presence of either calcium ions or spore suspensions.

CONCLUSIONS

Microwaves are as effective as conductive heating in killing B. subtilis spores, but the microwave E-field induces changes in the structural and/or molecular components of spores that differ from those attributable only to heat.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides information on the effect of microwaves on B. subtilis spore components.

MALDI-TOF-MS analysis of bacterial spores: wet heat-treatment as a new releasing technique for biomarkers and the influence of different experimental parameters and microbiological handling

Short wet heat-treatment is presented as a new technique to release high-mass biomarkers to obtain strain-specific fingerprints of intact bacterial spores by matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). Wet heat-treatment was applied for several minutes (3-30) by two techniques using either a screw-cap tube submerged in a glycerol bath at 120 degrees C or an Eppendorff-tube submerged in a water bath at 100 degrees C. Both techniques turned out to be successful for releasing high-mass biomarkers. The influence of different experimental parameters and microbiological handling on the peak pattern of the released high-mass biomarkers was studied. While the sporulation medium, the applied washing procedure, and the choice of matrix crucially influenced the peak pattern, other parameters like storage conditions were found to be insignificant. A protocol of optimized experimental conditions for MALDI-MS of wet heat-treated spores is presented.

Lipids in the inner membrane of dormant spores of Bacillus species are largely immobile

Bacterial spores of various Bacillus species are impermeable or exhibit low permeability to many compounds that readily penetrate germinated spores, including methylamine. We now show that a lipid probe in the inner membrane of dormant spores of Bacillus megaterium and Bacillus subtilis is largely immobile, as measured by fluorescence redistribution after photobleaching, but becomes free to diffuse laterally upon spore germination. The lipid immobility in and the slow permeation of methylamine through the inner membrane of dormant spores may be due to a significant (1.3- to 1.6-fold) apparent reduction of the membrane surface area in the dormant spore relative to that in the germinated spore, but is not due to the dormant spore's high levels of dipicolinic acid and divalent cations.

A soluble protein is immobile in dormant spores of Bacillus subtilis but is mobile in germinated spores: implications for spore dormancy

Fluorescence redistribution after photobleaching has been used to show that a cytoplasmic GFP fusion is immobile in dormant spores of Bacillus subtilis but becomes freely mobile in germinated spores in which cytoplasmic water content has increased approximately 2-fold. The GFP immobility in dormant spores is not due to the high levels of dipicolinic acid in the spore cytoplasm, because GFP was also immobile in germinated cwlD spores that had excreted their dipicolinic acid but where cytoplasmic water content had only increased to a level similar to that in dormant spores of several other Bacillus species. The immobility of a normally mobile protein in dormant wild-type spores and germinated cwlD spores is consistent with the lack of metabolism and enzymatic activity in these spores and suggests that protein immobility, presumably due to low water content, is a major reason for the metabolic dormancy of spores of Bacillus species.

Thermal properties of bacterial spores and biopolymers

Differential scanning calorimetry (DSC) measurements of dormant bacterial spores is traditionally associated with an endothermic transition at around 50 degrees C. This endothermic transition was described as an indicator for two main physico-chemical states in spores. These were a glassy state in the dormant spore core as a model for spore dormancy and a heat-activated state that generally facilitates spore resuscitation. The idea of a glassy state in dormant spores is based on the observation that a similar transition as in dormant spores was observed in low moisture biopolymers that are in a glassy state. Thermal properties of spores of Bacillus subtilis and B. cereus in a dormant and germinated, resuscitated state and of an outer and an inner coatless spore mutant of B. subtilis were investigated. Biopolymers with low moisture (<15%) and high moisture (>30%) contents such as maize starch, pectin, RNA and DNA were further studied. Critical evaluation of results revealed that the low temperature transition in dormant spores has some similarities to those observed in glassy biopolymers, but also to those of fully hydrated proteins and therefore does not necessarily indicate a glassy low moisture state. Its origin can also be attributed to the outer spore coats and it occurred at a lower temperature and for a shorter duration to be of significance for thermal heat activation of spores.

Physiological and mathematical aspects in setting criteria for decontamination of foods by physical means

In heat processing, microbial inactivation is traditionally described as log-linear. As a general rule, the relation between rate of inactivation and temperature is also described as a log-linear relation. The model is also sometimes applied in pressure and in pulsed electric field (PEF) processing. The model has proven its value by the excellent safety record of the last 80 years, but there are many deviations from log-linearity. This could lead to either over-processing or under-processing resulting in safety problems or, more likely, spoilage problems. As there is a need for minimal processing, accurate information of the inactivation kinetics is badly needed. To predict inactivation more precisely, models have been developed that can cope with deviations of linearity. As extremely low probabilities of survival must be predicted, extrapolation is almost always necessary. However, extrapolation is hardly possible without knowledge of the nature of nonlinearity. Therefore, knowledge of the physiology of inactivation is necessary. This paper discusses the physiology of denaturation by heat, high pressure and pulse electric field. After discussion of the physiological aspects, the various aspects of the development of inactivation models will be addressed. Both general and more specific aspects are discussed such as choice of test strains, effect of the culture conditions, conditions during processing and recovery conditions and mathematical modelling of inactivation. In addition to lethal inactivation, attention will be paid to sublethal inactivation because of its relevance to food preservation. Finally, the principles of quantitative microbiological risk assessment are briefly mentioned to show how appropriate inactivation criteria can be set.

FAST CARS: engineering a laser spectroscopic technique for rapid identification of bacterial spores

Airborne contaminants, e.g., bacterial spores, are usually analyzed by time-consuming microscopic, chemical, and biological assays. Current research into real-time laser spectroscopic detectors of such contaminants is based on e.g., resonance fluorescence. The present approach derives from recent experiments in which atoms and molecules are prepared by one (or more) coherent laser(s) and probed by another set of lasers. However, generating and using maximally coherent oscillation in macromolecules having an enormous number of degrees of freedom is challenging. In particular, the short dephasing times and rapid internal conversion rates are major obstacles. However, adiabatic fast passage techniques and the ability to generate combs of phase-coherent femtosecond pulses provide tools for the generation and utilization of maximal quantum coherence in large molecules and biopolymers. We call this technique FAST CARS (femtosecond adaptive spectroscopic techniques for coherent anti-Stokes Raman spectroscopy), and the present article proposes and analyses ways in which it could be used to rapidly identify preselected molecules in real time.