Genetic requirements for induction of germination of spores of Bacillus subtilis by Ca(2+)-dipicolinate

Characterization of individual spores of two biological insecticides, Bacillus thuringiensis and Lysinibacillus sphaericus, in response to glutaraldehyde using single-cell optical approaches

Bacillus thuringiensis (Bt) and Lysinibacillus sphaericus (Ls) are the most widely used microbial insecticides. Both encounter unfavorable environmental factors and pesticides in the field. Here, the responses of Bt and Ls spores to glutaraldehyde were characterized using Raman spectroscopy and differential interference contrast imaging at the single-cell level. Bt spores were more sensitive to glutaraldehyde than Ls spores under prolonged exposure: <1.0% of Bt spores were viable after 10 min of 0.5% (v/v) glutaraldehyde treatment, compared to ~ 20% of Ls spores. The Raman spectra of glutaraldehyde-treated Bt and Ls spores were almost identical to those of untreated spores; however, the germination process of individual spores was significantly altered. The time to onset of germination, the period of rapid Ca2+-2,6-pyridinedicarboxylic acid (CaDPA) release, and the period of cortex hydrolysis of treated Bt spores were significantly longer than those of untreated spores, with dodecylamine germination being particularly affected. Similarly, the germination of treated Ls spores was significantly prolonged, although the prolongation was less than that of Bt spores. Although the interiors of Bt and Ls spores were undamaged and CaDPA did not leak, proteins and structures involved in spore germination could be severely damaged, resulting in slower and significantly prolonged germination. This study provides insights into the impact of glutaraldehyde on bacterial spores at the single cell level and the variability in spore response to glutaraldehyde across species and populations.

BacteSign: Building a Findable, Accessible, Interoperable, and Reusable (FAIR) Database for Universal Bacterial Identification

With the increasing incidence of diverse global bacterial outbreaks, it is important to build an immutable decentralized database that can capture regional changes in bacterial resistance with time. Herein, we investigate the use of a rapid 3D printed µbiochamber with a laser-ablated interdigitated electrode developed for biofilm analysis of Pseudomonas aeruginosa, Acinetobacter baumannii and Bacillus subtilis using electrochemical biological impedance spectroscopy (EBIS) across a 48 h spectrum, along with novel ladder-based minimum inhibitory concentration (MIC) stencil tests against oxytetracycline, kanamycin, penicillin G and streptomycin. Furthermore, in this investigation, a search query database has been built demonstrating the deterministic nature of the bacterial strains with real and imaginary impedance, phase, and capacitance, showing increased bacterial specification selectivity in the 9772.37 Hz range.

Impact of sporulation temperature on germination of Bacillus subtilis spores under optimal and adverse environmental conditions

Bacillus subtilis spores are important food spoilage agents and are occasionally involved in food poisoning. In foods that are not processed with intense heat, such bacterial spores are controlled by a combination of different hurdles, such as refrigeration, acidification, and low water activity (aw), which inhibit or delay germination and/or growth. Sporulation temperature has long been regarded as a relevant factor for the assessment of germination in chemically defined media, but little is known about its impact on food preservation environments. In this study, we compared germination dynamics of B. subtilis spores produced at optimal temperature (37 °C) with others incubated at suboptimal (20 °C) and supraoptimal (43 °C) temperatures in a variety of nutrients (rich-growth medium, L-alanine, L-valine, and AGFK) under optimal conditions as well as under food-related stresses (low aw, pH, and temperature). Spores produced at 20 °C had a lower germination rate and efficiency than those incubated at 37 °C in all the nutrients, while those sporulated at 43 °C displayed a higher germination rate and/or efficiency in response to rich-growth medium and mostly to L-alanine and AGFK under optimal environmental conditions. However, differences in germination induced by changes in sporulation temperature decreased when spores were activated by heat, mainly due to the greater benefit of heat for spores produced at 20 °C and 37 °C than at 43 °C, especially in AGFK. Non-heat-activated spores produced at 43 °C still displayed superior germination fitness under certain stresses that had considerably impaired the germination of the other two populations, such as reduced temperature and aw. Moreover, they presented lower temperature and pH boundaries for the inhibition of germination in rich-growth medium, while requiring a higher NaCl concentration threshold compared to spores obtained at optimal and suboptimal temperature. Sporulation temperature is therefore a relevant source of variability in spore germination that should be taken into account for the accurate prediction of spore behaviour under variable food preservation conditions with the aim of improving food safety and stability.

Construction of Graphene@Ag-MLF composite structure SERS platform and its differentiating performance for different foodborne bacterial spores

A new surface-enhanced Raman spectroscopy (SERS) biosensor of Graphene@Ag-MLF composite structure has been fabricated by loading AgNPs on graphene films. The response of the biosensor is  based on plasmonic sensing. The results showed that the enhancement factor of three different spores reached 107 based on the Graphene@Ag-MLF substrate. In addition, the SERS performance was stable, with good reproducibility (RSD<3%). Multivariate statistical analysis and chemometrics were used to distinguish different spores. The accumulated variance contribution rate was up to 96.35% for the top three PCs, while HCA results revealed that the spectra were differentiated completely. Based on optimal principal components, chemometrics of KNN and LS-SVM were applied to construct a model for rapid qualitative identification of different spores, of which the prediction set and training set of LS-SVM achieved 100%. Finally, based on the Graphene@Ag-MLF substrate, the LOD of three different spores was lower than 102 CFU/mL. Hence, this novel Graphene@Ag-MLF SERS substrate sensor was rapid, sensitive, and stable in detecting spores, providing strong technical support for the application of SERS technology in food safety.

Effect of novel and conventional food processing technologies on Bacillus cereus spores

This chapter provides a summary of the effect of thermal and non-thermal processing technologies on Bacillus cereus spores, a well-known pathogenic bacterium associated with foodborne illnesses. B. cereus has been frequently detected in rice, milk products, infant food, liquid eggs products and meat products all over the world. This Gram positive, rod-shaped, facultative anaerobe can produce endospores that can withstand pasteurization, UV radiation, and chemical reagents commonly used for sanitization. B. cereus spores can germinate into vegetative cells that can produce toxins. The conventional regime for eliminating spores from food is retorting which uses the application of high temperature (121 °C). However, at this temperature, there could be a significant amount of loss in the organoleptic and functional qualities of the food components, especially proteins. This leads to the research on the preventive measures against germination and if possible, to reduce the resistance before using a non-thermal technology (temperatures less than retorting-121 °C) for inactivation. This chapter reviews the development and success of several food processing technologies in their ability to inactivate B. cereus spores in food.

Thioflavin-T does not report on electrochemical potential and memory of dormant or germinating bacterial spores

IMPORTANCE

Bacillus and Clostridium spores cause food spoilage and disease because of spores' dormancy and resistance to microbicides. However, when spores "come back to life" in germination, their resistance properties are lost. Thus, understanding the mechanisms of spore germination could facilitate the development of "germinate to eradicate" strategies. One germination feature is the memory of a pulsed germinant stimulus leading to greater germination following a second pulse. Recent observations of increases in spore binding of the potentiometric dye thioflavin-T early in their germination of spores led to the suggestion that increasing electrochemical potential is how spores "remember" germinant pulses. However, new work finds no increased thioflavin-T binding in the physiological germination of Coatless spores or of intact spores germinating with dodecylamine, even though spore memory is seen in both cases. Thus, using thioflavin-T uptake by germinating spores to assess the involvement of electrochemical potential in memory of germinant exposure, as suggested recently, is questionable.

A Family of Spore Lipoproteins Stabilizes the Germination Apparatus by Altering Inner Spore Membrane Fluidity in Bacillus subtilis Spores

Dormant bacterial spores undergo the process of germination to return to a vegetative state. In most species, germination involves the sensing of nutrient germinants, the release of various cations and a calcium-dipicolinic acid (DPA) complex, spore cortex degradation, and full rehydration of the spore core. These steps are mediated by membrane-associated proteins, and all these proteins have exposure on the outer surface of the membrane, a hydrated environment where they are potentially subject to damage during dormancy. A family of lipoproteins, including YlaJ, which is expressed from the sleB operon in some species, are present in all sequenced Bacillus and Clostridium genomes that contain sleB. B. subtilis possesses four proteins in this family, and prior studies have demonstrated two of these are required for efficient spore germination and these proteins contain a multimerization domain. Genetic studies of strains lacking all combinations of these four genes now reveal all four play roles in ensuring efficient germination, and affect multiple steps in this process. Electron microscopy does not reveal significant changes in spore morphology in strains lacking lipoproteins. Generalized polarization measurements of a membrane dye probe indicate the lipoproteins decrease spore membrane fluidity. These data suggest a model in which the lipoproteins form a macromolecular structure on the outer surface of the inner spore membrane, where they act to stabilize the membrane and potentially interact with other germination proteins, and thus stabilize the function of multiple components of the germination machinery. IMPORTANCE Bacterial spores exhibit extreme longevity and resistance to many killing agents, and are thus problematic agents of several diseases and of food spoilage. However, to cause disease or spoilage, germination of the spore and return to the vegetative state is necessary. The proteins responsible for initiation and progression of germination are thus potential targets for spore-killing processes. A family of membrane-bound lipoproteins that are conserved across most spore-forming species was studied in the model organism Bacillus subtilis. The results indicate that these proteins reduce the membrane fluidity and increase the stability of other membrane associated proteins that are required for germination. Further understanding of such protein interactions on the spore membrane surface will enhance our understanding of the germination process and its potential as a decontamination method target.

Effect of dual-frequency thermosonication, food matrix, and germinants on Alicyclobacillus acidoterrestris spore germination

The off-odors associated with spoilage of acidic beverages are linked to the germination and growth of Alicyclobacillus acidoterrestris (AAT) spores. As a consequence, we determined the influence of nutrients, non-nutrient germinants, dual-frequency thermosonication (DFTS), and food matrix on spore germination. AAT spores in orange juice (OJ), supplemented by L-alanine (L-ala), had the highest germination rate and lowest DPA content at 10 h of incubation. The formation of microscopic pores in cell membranes during DFTS caused irreversible damage in AAT spores in citrate buffer solution (CBS); however, it stimulated AAT spore germination in CBS containing L-ala. Hence, the germination potential was established in the order: L-ala > Calcium dipicolinate > asparagine, glucose, fructose, and potassium ion mixture (AGFK) > L-valine. The conductivity analysis indicated that membrane damage could be a key factor contributing to the artificial germination in CBS. AFM images revealed that after 2 h of adding L-ala, the protein content increased with increased germinated cells. TEM showed that membrane poration and coat detachment were the main pre-germination morphological changes detected after DFTS treatment. This study provides evidence that germination stimulated with DFTS might be an effective strategy for reducing A. acidoterrestris spores in fruit juices.

Post-high-pressure temperature and time - Overlooked parameters in high pressure treatment of bacterial spores

High pressure (HP) processing has high potential for bacterial spore inactivation with minimal thermal input. To advance HP germination and subsequent inactivation of spores, this study explored the physiological state of HP-treated spores using flow cytometry (FCM). Bacillus subtilis spores were treated at 550 MPa and 60 °C (very HP (vHP)) in buffer, incubated after the HP treatment, and stained for FCM analysis with SYTO16 indicating germination and propidium iodide (PI) indicating membrane damage. FCM subpopulations were analyzed depending on the HP dwell time (≤20 min), post-HP temperature (ice, 37 °C, 60 °C) and time (≤4 h), germination-relevant cortex-lytic enzymes (CLEs) and small-acid-soluble-proteins-(SASP)-degrading enzymes by using deletion strains. The effect of post-HP temperatures (ice, 37 °C) was additionally studied for moderate HP (150 MPa, 38 °C, 10 min). Post-HP incubation conditions strongly influenced the prevalence of five observed FCM subpopulations. Post-HP incubation on ice did not or only slowly shifted SYTO16-positive spores to higher SYTO16 levels. At 37 °C post-HP, this shift accelerated, and a shift to high PI intensities occurred depending on the HP dwell time. At 60 °C post-HP, the main shift was from SYTO16-positive to PI-positive subpopulations. The enzymes CwlJ and SleB, which are CLEs, seemed both necessary for PI or SYTO16 uptake, and to have different sensitivities to 550 MPa and 60 °C. Different extents of SASP degradation might explain the existence of two SYTO16-positive subpopulations. Shifts to higher SYTO16 intensities during post-HP incubation on ice or at 37 °C might rely on the activity and recovery of CLEs, SASP-degrading enzymes or their associated proteins from reversible HP-induced structural changes. These enzymes seemingly become active only during decompression or after vHP treatments (550 MPa, 60 °C). Based on our results, we provide a refined model of HP germination-inactivation of B. subtilis spores and an optimized FCM method for quantification of the safety-relevant subpopulation, i.e., vHP (550 MPa, 60 °C) superdormant spores. This study contributes to the development of mild spore inactivation processes by shedding light on overlooked parameters: post-HP incubation conditions. Post-HP conditions significantly influenced the physiological state of spores, likely due to varying enzymatic activity. This finding may explain inconsistencies in previous research and shows the importance of reporting post-HP conditions in future research. Furthermore, the addition of post-HP conditions as HP process parameter may open up new possibilities to optimize HP-based inactivation of spores for potential industrial applications in the food industry.

Sporulation, Structure Assembly, and Germination in the Soil Bacterium Bacillus thuringiensis: Survival and Success in the Environment and the Insect Host

Bacillus thuringiensis (Bt) is a rod-shaped, Gram-positive soil bacterium that belongs to the phylum Firmicutes and the genus Bacillus. It is a spore-forming bacterium. During sporulation, it produces a wide range of crystalline proteins that are toxic to different orders of insects. Sporulation, structure assembly, and germination are essential stages in the cell cycle of B. thuringiensis. The majority of studies on these issues have focused on the model organism Bacillus subtilis, followed by Bacillus cereus and Bacillus anthracis. The machinery for sporulation and germination extrapolated to B. thuringiensis. However, in the light of recent findings concerning the role of the sporulation proteins (SPoVS), the germination receptors (Gr), and the cortical enzymes in Bt, the theory strengthened that conservation in sporulation, structure assembly, and germination programs drive the survival and success of B. thuringiensis in the environment and the insect host. In the present minireview, the latter pinpointed and reviewed.

Regulation of peptidoglycan hydrolases: localization, abundance, and activity

Most bacteria are surrounded by a cell wall composed of peptidoglycan (PG) that specifies shape and protects the cell from osmotic rupture. Growth, division, and morphogenesis are intimately linked to the synthesis of this exoskeleton but also its hydrolysis. The enzymes that cleave the PG meshwork require careful control to prevent aberrant hydrolysis and loss of envelope integrity. Bacteria employ diverse mechanisms to control the activity, localization, and abundance of these potentially autolytic enzymes. Here, we discuss four examples of how cells integrate these control mechanisms to finely tune cell wall hydrolysis. We highlight recent advances and exciting avenues for future investigation.

Uptake of UVc induced photoproducts of dipicolinic acid by Bacillus subtilis spores - Effects on the germination and UVc resistance of the spores

Dipicolinic acid (DPA) is a specific molecule of bacterial spores which is essential to their resistance to various stresses such as ultraviolet (UV) exposure and to their germination. DPA has a particular photochemistry that remains imperfectly understood. In particular, due to its ability to absorb UVc radiation, it is likely to form in vitro a wide variety of photoproducts (DPAp) of which only about ten have been recently identified. The photochemical reactions resulting in DPAp, especially those inside the spores, are still poorly understood. Only one of these DPAp, which probably acts as a photosensitizer of DNA upon exposure to UVc, has been identified as having an impact on spores. However, as UVc is required to form DPAp, it is difficult to decouple the overall effect of UVc exposure from the possible effects of DPAp alone. In this study, DPAp were artificially introduced into the spores of the FB122 mutant strain of Bacillus subtilis, one that does not produce DPA. These experiments revealed that some DPAp may play a positive role for the spore. These benefits are visible in an improvement in spore germination rate and kinetics, as well as in an increase in their resistance to UVc exposure.

Influence of probiotics on water quality in intensified Litopenaeus vannamei ponds under minimum-water exchange

The effects of two probiotics on NH₃ degradation, as well as the magnetic field (21.56 m tesla) on the germination and proliferation of Bacillus spores, were studied in-vitro. Additionally, the effect of these probiotics on water quality maintenance in Litopenaeus vannamei holding ponds was investigated. For 180 min, NH₃ degradation was assessed as follows: Set 1: ammonia-free tap water with NH₃; Probiotic A (5 × 10¹⁰ viable Bacillus spores/g) with NH₃; Probiotic B (multi spp. 2 × 10⁹ CFU/g) with NH₃; and Set 2: same as set 1 with 30 mg L⁻¹ OM. The magnetic field was tested on Probiotic A (3.5 × 10⁷ CFU) for 36 h in triplicate. In the presence of organic matter, both probiotics degrade NH₃. The viable Bacillus count increased within 6 h of being exposed to the magnetic field, reaching its peak after 36 h. Firstly, fifteen ponds (250,000 PL/acre) were investigated, then 360 water samples were collected from the same corresponding pond for 8 weeks, and subjected to T1: control; T2: Probiotic A (0.007 g/m³/2 weeks); T3: Probiotic B (0.03 g/m³/2 weeks). Both probiotics with TVC and NH₃ demonstrated a negative correlation, on the other hand, they showed a significant (P ≤ 0.01) improvement in DO and pH. Overall, both probiotics were able to degrade NH₃ and the magnetic field (21.56 m tesla) was efficient to improve the germination and proliferation of Bacillus spores in-vitro. Probiotics were also effective for reducing TVC and NH₃ levels by increasing dissolved oxygen and pH in pond water.

Genetic Evidence for Signal Transduction within the Bacillus subtilis GerA Germinant Receptor

Bacterial spores can rapidly exit dormancy through the process of germination. This process begins with the activation of nutrient receptors embedded in the spore membrane. The prototypical germinant receptor in Bacillus subtilis responds to l-alanine and is thought to be a complex of proteins encoded by the genes in the gerA operon: gerAA, gerAB, and gerAC. The GerAB subunit has recently been shown to function as the nutrient sensor, but beyond contributing to complex stability, no additional functions have been attributed to the other two subunits. Here, we investigate the role of GerAA. We resurrect a previously characterized allele of gerA (termed gerA*) that carries a mutation in gerAA and show that it constitutively activates germination even in the presence of a wild-type copy of gerA. Using an enrichment strategy to screen for suppressors of gerA*, we identified mutations in all three gerA genes that restore a functional receptor. Characterization of two distinct gerAB suppressors revealed that one (gerAB[E105K]) reduces the GerA complex's ability to respond to l-alanine, while another (gerAB[F259S]) disrupts the germinant signal downstream of l-alanine recognition. These data argue against models in which GerAA is directly or indirectly involved in germinant sensing. Rather, our data suggest that GerAA is responsible for transducing the nutrient signal sensed by GerAB. While the steps downstream of gerAA have yet to be uncovered, these results validate the use of a dominant-negative genetic approach in elucidating the gerA signal transduction pathway. IMPORTANCE Endospore formers are a broad group of bacteria that can enter dormancy upon starvation and exit dormancy upon sensing the return of nutrients. How dormant spores sense and respond to these nutrients is poorly understood. Here, we identify a key step in the signal transduction pathway that is activated after spores detect the amino acid l-alanine. We present a model that provides a more complete picture of this process that is critical for allowing dormant spores to germinate and resume growth.

Clostridioides difficile spore germination: initiation to DPA release

Germination by Clostridioides difficile spores is an essential step in pathogenesis. Spores are metabolically dormant forms of bacteria that resist severe conditions. Work over the last 10 years has elucidated that C. difficile spores germinate thorough a novel pathway. This review summarizes our understanding of C. difficile spore germination and the factors involved in germinant recognition, cortex degradation and DPA release.

Effect of oxygen on the germination and culturability of Bacillus atrophaeus spores

The effect of oxygen on the germination and culturability of aerobic Bacillus atrophaeus spores was investigated in this study. Under oxic or anoxic conditions, various nutritional and non-nutritional germinants were utilized to induce germination. Tb³⁺-dipicolinic acid fluorescence assay and phase-contrast microscopy were used to track the germination process. The final germination level, germination half time, and germination speed were used to define germination kinetics. Colony-forming unit enumeration was used to assess the culturability of germinated spores germinated with or without oxygen. The results show that in the absence of oxygen, the final germination level was unaffected, germination half time decreased by up to 35.0%, germination speed increased by up to 27.4%, and culturability decreased by up to 95.1%. It is suggested that oxygen affects some germinant receptor-dependent germination pathways, implying that biomolecules engaged in these pathways may be oxygen-sensitive. Furthermore, spores that have completed the germination process in either anoxic or oxic conditions may have different culturability. This research contributed to a better understanding of the fundamental mechanism of germination.

Dormant spores sense amino acids through the B subunits of their germination receptors

Bacteria from the orders Bacillales and Clostridiales differentiate into stress-resistant spores that can remain dormant for years, yet rapidly germinate upon nutrient sensing. How spores monitor nutrients is poorly understood but in most cases requires putative membrane receptors. The prototypical receptor from Bacillus subtilis consists of three proteins (GerAA, GerAB, GerAC) required for germination in response to L-alanine. GerAB belongs to the Amino Acid-Polyamine-Organocation superfamily of transporters. Using evolutionary co-variation analysis, we provide evidence that GerAB adopts a structure similar to an L-alanine transporter from this superfamily. We show that mutations in gerAB predicted to disrupt the ligand-binding pocket impair germination, while mutations predicted to function in L-alanine recognition enable spores to respond to L-leucine or L-serine. Finally, substitutions of bulkier residues at these positions cause constitutive germination. These data suggest that GerAB is the L-alanine sensor and that B subunits in this broadly conserved family function in nutrient detection.

Viability, Sublethal Injury, and Release of Cellular Components From Alicyclobacillus acidoterrestris Spores and Cells After the Application of Physical Treatments, Natural Extracts, or Their Components

Alicyclobacillus acidoterrestris is a spoiling microorganism regarded as one of the most important causes of spoilage of fruit juices and acidic products. In this paper, four strains of A. acidoterrestris (type strain-DSM 3922; two wild strains isolated from soil-C8 and C24; wild strain isolated from a spoiled pear juice CB1) were treated through natural extracts/active compounds from essential oils (EOs), and physical treatments were used to assess their susceptibility and the presence of sublethal injury. The characterization of damage was also performed. The results suggest that it is possible to control A. acidoterrestris through alternative approaches, although the effect relied upon the age of spores. In addition to the mere antimicrobial effect, some treatments could cause a sublethal injury on spores. Lemon extract was the most effective treatment for both the antimicrobial effect and the sublethal injury, as evidenced by the release of proteins, and calcium dipicolinate [dipicolinic acid (DPA)] by fresh spores and only DPA (with an exception for C8) by old spores. A sublethal injury with protein release was also found for physical treatments [US (ultrasound) or heating]. For the first time, this paper reports on the existence of a sublethal injury for A. acidoterrestris, and this evidence could also be a challenge, because injured microorganisms could restore their metabolism, or an opportunity to design new preserving treatments.

Bacillus spore germination at moderate high pressure: A review on underlying mechanisms, influencing factors, and its comparison with nutrient germination

Spore-forming bacteria are resistant to stress conditions owing to their ability to form highly resistant dormant spores. These spores can survive adverse environmental conditions in nature, as well as decontamination processes in the food and related industries. Bacterial spores may return to their vegetative state through a process called germination. As spore germination is critical for the loss of resistance, outgrowth, and development of pathogenicity and spoilage potential, the germination pathway has piqued the interest of the scientific community. The inhibition and induction of germination have critical applications in the food industry. Targeted germination can aid in decreasing the resistance of spores and allow the application of milder inactivation procedures. This germination-inactivation strategy allows better maintenance of important food quality attributes. Different stimuli are reported to trigger germination. Among those, isostatic high pressure (HP) has gained increasing attention due to its potential applications in industrial processes. However, pressure-mediated spore germination is extremely heterogeneous as some spores germinate rapidly, while others exhibit slow germination or do not undergo germination at all. The successful and safe implementation of the germination-inactivation strategy, however, depends on the germination of all spores. Therefore, there is a need to elucidate the mechanisms of HP-mediated germination. This work aimed to critically review the current state of knowledge on Bacillus spore germination at a moderate HP of 50-300 MPa. In this review, the germination mechanism, heterogeneity, and influencing factors have been outlined along with knowledge gaps.

Pressure and Temperature Combined With Microbial Supernatant Effectively Inactivate Bacillus subtilis Spores

Spores from the Bacillus species pose a challenge to the food industry because of their ubiquitous nature and extreme resistance. Accumulated evidence indicates that it is effective to induce spore germination homogenously before killing them. However, it is difficult to obtain and apply exogenous germination factors, which will affect food composition. Therefore, this study screened endogenous germinants from microorganisms by assessing the effect of Escherichia coli, Bacillus subtilis, Saccharomyces cerevisiae, Lactiplantibacillus plantarum, and Streptococcus thermophilus cultures (cell-free) on B. subtilis spore germination. The results showed that the supernatants from these five microorganisms induced spore germination instead of sediments. Moreover, the supernatants of E. coli, B. subtilis, and S. cerevisiae exhibited higher germination rates than L. plantarum and S. thermophilus, and the induction effects were concentration-dependent. Furthermore, plate counting confirmed that the microbial supernatants induced the lowest spore germination ratio on strains B. subtilis FB85 [germination receptors (GRs) mutant] but not strains B. subtilis PB705 (PrkC mutant). In addition, B. subtilis and S. cerevisiae supernatants, combined with pressure and temperature, were effective in spore inactivation. The findings suggested that microbial supernatants may include agents that induce spore germination and may be used for spore inactivation.

Isolation, stability, and characteristics of high-pressure superdormant Bacillus subtilis spores

Bacterial spores are a major challenge in industrial decontamination processes owing to their extreme resistance. High-pressure (HP) of 150 MPa at 37 °C can trigger the germination of spores, making them lose their extreme resistance. Once their resistance is lost, germinated spores can easily be inactivated by a mild decontamination step. The implementation of this gentle germination-inactivation strategy is hindered by the presence of a subpopulation of so-called high-pressure superdormant (HPSD) spores, which resist germination or germinate only very slowly in response to HP. It is essential to understand the properties of HPSD spores and the underlying causes of superdormancy to tackle superdormant spores and further develop germination-inactivation strategies involving HP. This study investigated factors influencing the prevalence of HPSD spores and successfully isolated them by combining buoyant density centrifugation and fluorescence-activated cell sorting, which allowed further characterisation of HPSD spores for the first time. The prevalence of HPSD spores was shown to be strongly dependent on the HP dwell time, with increasing treatment times reducing their prevalence. Spore mutants lacking major germinant receptors further showed a highly increased prevalence of HPSD spores; 93% of the spores remained dormant even after a prolonged HP dwell time of 40 min. In contrast to nutrient germination, sublethal heat treatment of 75 °C for 30 min prior to pressure treatment did not induce spore activation and increase germination. The isolated HPSD spores did not show visible structural differences compared to the initial dormant spores when investigated with transmission electron microscopy. Re-sporulated HPSD spores showed similar germination capacity compared to the initial dormant spores, indicating that HPSD spores are most likely not genetically different from the rest of the population. Moreover, the majority of HPSD spores germinated when exposed a second time to the same germination treatment; however, the germination capacity was lower than that of the initial population. The fact that the majority of spores lost superdormancy when exposed a second time to the same trigger makes it unlikely that there is one factor that determines whether a spore germinates with a certain HP treatment or not. Instead, it seems possible that there are other reversible or cumulative causes. This study investigated the factors influencing spore HP superdormancy to improve the understanding of HPSD spores with regard to their stability, germination capacity, and potential underlying causes of spore HP superdormancy. This knowledge will contribute to the development of HP-based germination-inactivation strategies for gentle but effective spore control.

Germination-Arrest Bacillus subtilis Spores as An Oral Delivery Vehicle of Grass Carp Reovirus (GCRV) Vp7 Antigen Augment Protective Immunity in Grass Carp (Ctenopharyngodon idella)

Oral vaccination is a practical method for the active immunization of farmed fish in the matter of animal welfare and handling costs. However, it always shows insufficient protective immunity, mainly due to antigen degradation in the gastrointestinal tract (GIT). Bacillus subtilis spores have been shown to be able to protect surface-display heterologous antigens against degradation. Neverthless, the spores can germinate in GIT, which causes loss of the antigens with spore coat disassembly. Here, we developed a novel surface display system using the B. subtilis spore coat proteins CotB and CotC as anchors for the heterogenous antigen, and the germination-controlling genes cwlJ and sleB as the ectopic integration sites for the fusion genes. Using this display system, we engineered germination-arrest spores displaying the model antigen Vp7 of grass carp reovirus (GCRV) on their surface. Oral vaccination of the engineered spores could confer immune protection against GCRV in grass carp (Ctenopharyngodon idella) via eliciting adaptive humoral and cellular immune responses. Most importantly, the germination-arrest spores were shown to significantly augment immunogenicity and protection above the engineered spores based on the existing surface display system. Therefore, the presently reported antigen expression strategy opens new and promising avenues for developing oral vaccines for the immunization of farmed fish species.

Bacillus spores: a review of their properties and inactivation processing technologies

Many factors determine the resistance properties of a Bacillus spore to heat, chemical and physical processing, including thick proteinaceous coats, peptidoglycan cortex and low water content, high levels of dipicolinic acid (DPA), and divalent cations in the spore core. Recently, attention has been focused on non-thermal inactivation methods based on high pressure, ultrasonic, high voltage electric fields and cold plasmas for inactivating Bacillus spores associated with deterioration in quality and safety. The important chemical sporicides are glutaraldehyde, chorine-releasing agents, peroxygens, and ethylene oxide. Some food-grade antimicrobial agents exhibit sporostatic and sporicidal activities, such as protamine, polylysine, sodium lactate, essential oils. Surfactants with hydrophilic and hydrophobic properties have been reported to have inactivation activity against spores. The combined treatment of physical and chemical treatment such as heating, UHP (ultra high pressure), PEF (pulsed electric field), UV (ultraviolet), IPL (intense pulsed light) and natural antimicrobial agents can act synergistically and effectively to kill Bacillus spores in the food industry.

Bioluminescence dynamics in single germinating bacterial spores reveal metabolic heterogeneity

Spore-forming bacteria modulate their metabolic rate by over five orders of magnitude as they transition between dormant spores and vegetative cells and thus represent an extreme case of phenotypic variation. During environmental changes in nutrient availability, clonal populations of spore-forming bacteria exhibit individual differences in cell fate, the timing of phenotypic transitions and gene expression. One potential source of this variability is metabolic heterogeneity, but this has not yet been measured, as existing single-cell methods are not easily applicable to spores due to their small size and strong autofluorescence. Here, we use the bacterial bioluminescence system and a highly sensitive microscope to measure metabolic dynamics in thousands of B. subtilis spores as they germinate. We observe and quantitate large variations in the bioluminescence dynamics across individual spores that can be decomposed into contributions from variability in germination timing, the amount of endogenously produced luminescence substrate and the intracellular reducing power. This work shows that quantitative measurement of spore metabolism is possible and thus it opens avenues for future study of the thermodynamic nature of dormant states.

The molecular dynamics of bacterial spore and the role of calcium dipicolinate in core properties at the sub-nanosecond time-scale

Bacterial spores are among the most resistant forms of life on Earth. Their exceptional resistance properties rely on various strategies, among them the core singular structure, organization and hydration. By using elastic incoherent neutron scattering, we probed the dynamics of Bacillus subtilis spores to determine whether core macromolecular motions at the sub-nanosecond timescale could also contribute to their resistance to physical stresses. In addition, in order to better specify the role of the various spore components, we used different mutants lacking essential structure such as the coat (PS4150 mutant), or the calcium dipicolinic acid complex (CaDPA) located in the core (FB122 mutant). PS4150 allows to better probe the core’s dynamics, as proteins of the coat represent an important part of spore proteins, and FB122 gives information about the role of the large CaDPA depot for the mobility of core’s components. We show that core’s macromolecular mobility is not particularly constrained at the sub-nanosecond timescale in spite of its low water content as some dynamical characteristics as force constants are very close to those of vegetative bacteria such as Escherichia coli or to those of fully hydrated proteins. Although the force constants of the coatless mutant are similar to the wild-type’s ones, it has lower mean square displacements (MSDs) at high Q showing that core macromolecules are somewhat more constrained than the rest of spore components. However, no behavior reflecting the glassy state regularly evoked in the literature could be drawn from our data. As hydration and macromolecules’ mobility are highly correlated, the previous assumption, that core low water content might explain spores’ exceptional resistance properties seems unlikely. Thus, we confirm recent theories, suggesting that core water is mostly as free as bulk water and proteins/macromolecules are fully hydrated. The germination of spores leads to a much less stable system with a force constant of 0.1 N/m and MSDs ~2.5 times higher at low Q than in the dormant state. DPA has also an influence on core mobility with a slightly lower force constant for the DPA-less mutant than for the wild-type, and MSDs that are ~ 1.8 times higher on average than for the wild-type at low Q. At high Q, germinated and DPA-less spores were very similar to the wild-type ones, showing that DPA and core compact structure might influence large amplitude motions rather than local dynamics of macromolecules.

DNA Damage Kills Bacterial Spores and Cells Exposed to 222-Nanometer UV Radiation

This study examined the microbicidal activity of 222-nm UV radiation (UV₂₂₂), which is potentially a safer alternative to the 254-nm UV radiation (UV₂₅₄) that is often used for surface decontamination. Spores and/or growing and stationary-phase cells of Bacillus cereus, Bacillus subtilis, Bacillus thuringiensis, Staphylococcus aureus, and Clostridioides difficile and a herpesvirus were all killed or inactivated by UV₂₂₂ and at lower fluences than with UV₂₅₄B. subtilis spores and cells lacking the major DNA repair protein RecA were more sensitive to UV₂₂₂, as were spores lacking their DNA-protective proteins, the α/β-type small, acid-soluble spore proteins. The spore cores' large amount of Ca²⁺-dipicolinic acid (∼25% of the core dry weight) also protected B. subtilis and C. difficile spores against UV₂₂₂, while spores' proteinaceous coat may have given some slight protection against UV₂₂₂ Survivors among B. subtilis spores treated with UV₂₂₂ acquired a large number of mutations, and this radiation generated known mutagenic photoproducts in spore and cell DNA, primarily cyclobutane-type pyrimidine dimers in growing cells and an α-thyminyl-thymine adduct termed the spore photoproduct (SP) in spores. Notably, the loss of a key SP repair protein markedly decreased spore UV₂₂₂ resistance. UV₂₂₂-treated B. subtilis spores germinated relatively normally, and the generation of colonies from these germinated spores was not salt sensitive. The latter two findings suggest that UV₂₂₂ does not kill spores by general protein damage, and thus, the new results are consistent with the notion that DNA damage is responsible for the killing of spores and cells by UV₂₂₂IMPORTANCE Spores of a variety of bacteria are resistant to common decontamination agents, and many of them are major causes of food spoilage and some serious human diseases, including anthrax caused by spores of Bacillus anthracis Consequently, there is an ongoing need for efficient methods for spore eradication, in particular methods that have minimal deleterious effects on people or the environment. UV radiation at 254 nm (UV₂₅₄) is sporicidal and commonly used for surface decontamination but can cause deleterious effects in humans. Recent work, however, suggests that 222-nm UV (UV₂₂₂) may be less harmful to people than UV₂₅₄ yet may still kill bacteria and at lower fluences than UV₂₅₄ The present work has identified the damage by UV₂₂₂ that leads to the killing of growing cells and spores of some bacteria, many of which are human pathogens, and UV₂₂₂ also inactivates a herpesvirus.

Optimization of Sporulation and Germination Conditions of Functional Bacteria for Concrete Crack-Healing and Evaluation of their Repair Capacity

While microbial spore production and germination of bacteria have been widely studied for their applications in animal husbandry, aquatic products, medicine, and food, few studies have investigated their use for the crack-healing of concrete. To effectively heal the cracks in concrete, studies suggest that the rate of sporulation and the germination of bacteria should be sufficiently high. This study investigates the effects of different carbon sources, nitrogen sources, Mn²⁺ concentrations, and external culture conditions on the sporulation rate and analyzes the effects of the pH value, heat activation, germinants, various cations, and nutrients on the germination of spores. Bacillus cohnii (B. cohnii) is chosen as the bacterium to be mixed in concrete because of its alkalophilic nature. The mineralization activity of spores after germination and the crack-healing capacity of concrete are studied. The optimal culture medium and the optimum external conditions for spore production are obtained. The total cell count and sporulation rate of bacteria obtained on this medium are 3.14 × 10⁹ CFU/mL and 92.6%, respectively, under the optimum external conditions. The optimal pH value for the spore germination of B. cohnii is 9.7. While the cation Na⁺ strongly stimulates the germination of B. cohnii spores, other cations (such as K⁺, NH₄⁺, and Ca²⁺) do not stimulate spore germination. The optimal concentration of Na⁺ is 200 mM. The germination rate of spores in the control group concrete specimen (room temperature 24°C) was more than 50%, thus suggesting that B. cohnii bacteria can be used in the self-healing of concrete cracks. The mineralization activity test proves that the spores of B. cohnii have a mineralizing function after germination, and the crystals produced by microbial-induced carbonate precipitation (MICP) are of pure calcite. When the crack width of the concrete specimen with spores of B. cohnii is less than 1.2 mm, it can be completely repaired after 28 days of healing.

SwsB and SafA Are Required for CwlJ-Dependent Spore Germination in Bacillus subtilis

When Bacillus subtilis spores detect nutrients, they exit dormancy through the processes of germination and outgrowth. A key step in germination is the activation of two functionally redundant cell wall hydrolases (SleB and CwlJ) that degrade the specialized cortex peptidoglycan that surrounds the spore. How these enzymes are regulated remains poorly understood. To identify additional factors that affect their activity, we used transposon sequencing to screen for synthetic germination defects in spores lacking SleB or CwlJ. Other than the previously characterized protein YpeB, no additional factors were found to be specifically required for SleB activity. In contrast, our screen identified SafA and YlxY (renamed SwsB) in addition to the known factors GerQ and CotE as proteins required for CwlJ function. SafA is a member of the spore's proteinaceous coat and we show that, like GerQ and CotE, it is required for accumulation and retention of CwlJ in the dormant spore. SwsB is broadly conserved among spore formers, and we show that it is required for CwlJ to efficiently degrade the cortex during germination. Intriguingly, SwsB resembles polysaccharide deacetylases, and its putative catalytic residues are required for its role in germination. However, we find no chemical signature of its activity on the spore cortex or in vitro While the precise, mechanistic role of SwsB remains unknown, we explore and discuss potential activities.IMPORTANCE Spore formation in Bacillus subtilis has been studied for over half a century, and virtually every step in this developmental process has been characterized in molecular detail. In contrast, how spores exit dormancy remains less well understood. A key step in germination is the degradation of the specialized cell wall surrounding the spore called the cortex. Two enzymes (SleB and CwlJ) specifically target this protective layer, but how they are regulated and whether additional factors promote their activity are unknown. Here, we identified the coat protein SafA and a conserved but uncharacterized protein YlxY as additional factors required for CwlJ-dependent degradation of the cortex. Our analysis provides a more complete picture of this essential step in the exit from dormancy.

Nutrient germination improves DNA recovery from industrial Bacillus subtilis endospores during qPCR enumeration assays

Growth-independent microbial enumeration methods such as quantitative PCR require the efficient extraction of genomic DNA from targeted cells. Bacillus endospores are popular inclusions in commercial products due to their hardiness and metabolic dormancy; however, this hardiness is known to render Bacillus endospores resistant to traditional DNA isolation techniques. Metagenomic studies have sought to address this resistance through nutrient-based germination of bacterial endospores in environmental samples. In the present study, we sought to apply this technique to the enumeration of microbial products using an industrial strain of Bacillus subtilis as a model organism. Germination was induced through incubation of axenic spore suspensions in an AGFK-based rich medium. Total spore count, dipicolinic acid release and OD₆₀₀ absorbance were monitored over time to track the progression of spore populations through the stages of germination and outgrowth. Aerobic plate counts and flow cytometry were used to monitor cell populations for proliferation during the incubation period. Finally, quantitative PCR with taxon-specific primers was used to examine DNA recovery as a function of time. Results show that customized germination protocols, once appropriately validated for the species and product matrix under consideration, can result in more efficient DNA extraction and thus lower limits of detection for qPCR assays targeting industrial Bacillus endospores in microbial products.

Sporulation and Germination in Clostridial Pathogens

As obligate anaerobes, clostridial pathogens depend on their metabolically dormant, oxygen-tolerant spore form to transmit disease. However, the molecular mechanisms by which those spores germinate to initiate infection and then form new spores to transmit infection remain poorly understood. While sporulation and germination have been well characterized in Bacillus subtilis and Bacillus anthracis, striking differences in the regulation of these processes have been observed between the bacilli and the clostridia, with even some conserved proteins exhibiting differences in their requirements and functions. Here, we review our current understanding of how clostridial pathogens, specifically Clostridium perfringens, Clostridium botulinum, and Clostridioides difficile, induce sporulation in response to environmental cues, assemble resistant spores, and germinate metabolically dormant spores in response to environmental cues. We also discuss the direct relationship between toxin production and spore formation in these pathogens.

Accumulation and Release of Rare Earth Ions by Spores of Bacillus Species and the Location of These Ions in Spores

Two rare earth ions, Tb³⁺ and Dy³⁺, were incorporated into spores of Bacillus species in ≤5 min at neutral pH to 100 to 200 nmol per mg of dry spores, which is equivalent to 2 to 3% of the spore dry weight. The uptake of these ions had, at most, minimal effects on spore wet heat resistance or germination, and the ions were all released upon germination, probably by complex formation with the huge depot of dipicolinic acid (DPA) released when spores germinate. Adsorbed Tb³⁺/Dy³⁺ were also released by exogenous DPA within a few minutes and faster than in spore germination. The accumulation of Tb³⁺/Dy³⁺ was not reduced in Bacillus subtilis spores by several types of coat defects, significant modification of the spore cortex peptidoglycan structure, specific loss of components of the outer spore crust layer, or the absence of DPA in the spore core. All of these findings are consistent with Tb³⁺/Dy³⁺ being accumulated in spores' outer layers, and this was confirmed by transmission electron microscopy. However, the identity of the outer spore components binding the Tb³⁺/Dy³⁺ is not clear. These findings provide new information on the adsorption of rare earth ions by Bacillus spores and suggest this adsorption might have applications in capturing rare earth ions from the environment.IMPORTANCE Biosorption of rare earth ions by growing cells of Bacillus species has been well studied and has attracted attention for possible hydrometallurgy applications. However, the interaction of spores from Bacillus species with rare earth ions has not been well studied. We investigated here the adsorption and/or desorption of two rare earth ions, Tb³⁺ and Dy³⁺, by Bacillus spores, the location of the adsorbed ions, and the spore properties after ion accumulation. The significant adsorption of rare earth ions on the surfaces of Bacillus spores and the ions' rapid release by a chelator could allow the development of these spores as a biosorbent to recover rare earth ions from the environment.

Mechanisms of enhanced bacterial endospore inactivation during sterilization by ohmic heating

During ohmic heating, the electric field may additionally inactivate bacterial endospores. However, the exact mechanism of action is unclear. Thus, a mechanistic study was carried out, investigating the possible target of electric fields inside the spore. Bacillus subtilis spores were heated by conventional and ohmic heating in a capillary system under almost identical thermal conditions. Wild-type (PS533) spores were used, as well as isogenic mutants lacking certain components known for their contribution to spores' heat resistance: small-acid soluble proteins (SASP) protecting DNA (PS578); the coat covering the spore (PS3328); and the spore germination enzyme SleB (FB122(+)). Treatment-dependent release of the spore core's depot of dipicolinic acid (DPA) was further evaluated. Up to 2.4 log₁₀ additional inactivation of PS533 could be achieved by ohmic heating, compared to conventional heating. The difference varied for the mutants, with a decreasing difference indicating a decreased effect of the electric field and vice versa. In particular, mutant spores lacking SASPs showed a behavior more similar to thermal inactivation alone. The combination of heat and electric field was shown to be necessary for enhanced spore inactivation. Thus, it is hypothesized that either the heat treatment makes the spore susceptible to the electric field, or vice versa.

Biochemical and mutational analysis of spore cortex-lytic enzymes in the food spoiler Bacillus licheniformis

Bacillus licheniformis is frequently associated with food spoilage due to its ability to form highly resistant endospores. The present study reveals that B. licheniformis spore peptidoglycan shares a similar structure to spores of other species of Bacillus. Two enzymatic activities associated with depolymerisation of the cortical peptidoglycan, which represents a crucial step in spore germination, were detected by muropeptide analysis. These include lytic transglycosylase and N-acetylglucosaminidase activity, with non-lytic epimerase activity also being detected. The role of various putative cortex-lytic enzymes that account for the aforementioned activity was investigated by mutational analysis. These analyses indicate that SleB is the major lysin involved in cortex depolymerisation in B. licheniformis spores, with CwlJ and SleL having lesser roles. Collectively, the results of this work indicate that B. licheniformis spores employ a similar approach for cortical depolymerisation during germination as spores of other Bacillus species.

Bacillus subtilis Spore Resistance to Simulated Mars Surface Conditions

In a Mars exploration scenario, knowing if and how highly resistant Bacillus subtilis spores would survive on the Martian surface is crucial to design planetary protection measures and avoid false positives in life-detection experiments. Therefore, in this study a systematic screening was performed to determine whether B. subtilis spores could survive an average day on Mars. For that, spores from two comprehensive sets of isogenic B. subtilis mutant strains, defective in DNA protection or repair genes, were exposed to 24 h of simulated Martian atmospheric environment with or without 8 h of Martian UV radiation [M(+)UV and M(-)UV, respectively]. When exposed to M(+)UV, spore survival was dependent on: (1) core dehydration maintenance, (2) protection of DNA by α/β-type small acid soluble proteins (SASP), and (3) removal and repair of the major UV photoproduct (SP) in spore DNA. In turn, when exposed to M(-)UV, spore survival was mainly dependent on protection by the multilayered spore coat, and DNA double-strand breaks represent the main lesion accumulated. Bacillus subtilis spores were able to survive for at least a limited time in a simulated Martian environment, both with or without solar UV radiation. Moreover, M(-)UV-treated spores exhibited survival rates significantly higher than the M(+)UV-treated spores. This suggests that on a real Martian surface, radiation shielding of spores (e.g., by dust, rocks, or spacecraft surface irregularities) might significantly extend survival rates. Mutagenesis were strongly dependent on the functionality of all structural components with small acid-soluble spore proteins, coat layers and dipicolinic acid as key protectants and efficiency DNA damage removal by AP endonucleases (ExoA and Nfo), non-homologous end joining (NHEJ), mismatch repair (MMR) and error-prone translesion synthesis (TLS). Thus, future efforts should focus on: (1) determining the DNA damage in wild-type spores exposed to M(+/-)UV and (2) assessing spore survival and viability with shielding of spores via Mars regolith and other relevant materials.

Mechanism of inactivation of Bacillus subtilis spores by high pressure CO2 at high temperature

Spores of wild-type Bacillus subtilis and some isogenic mutant strains were treated by high pressure CO₂ (HPCD) at high temperature (HT) (HPCD + HT) at 20 MPa and 84-86 °C for 0-60 min, and centrifuged on a high density solution to obtain pelleted spores that retained CaDPA and light spores that lost CaDPA. All treated spores were analyzed for viability, and tested for germination, outgrowth, core protein damage, mutagenesis and inner membrane (IM) properties. The results showed that (i) with HPCD + HT treated spores, most pelleted spores and all light spores were dead; ii) a significant amount of dead HPCD + HT-treated spores that retained CaDPA germinated, but outgrowth was blocked; (iii) minimal mutants were generated in survivors of HPCD + HT treatment; (iv) the GFP fluorescence decrease in HPCD + HT-treated spores with high GFP levels was slower than spore inactivation; (v) the IM of HPCD + HT-treated spores that retained CaDPA lost its ability to retain CaDPA at 85 °C, and almost all of these spores' outgrowth in high salt was blocked; and (vi) HPCD + HT-treated spores that retained CaDPA germinated with l-valine or AGFK were almost all stained with propidium iodide. These results indicated that HPCD + HT inactivated B. subtilis spores by damaging spores' IM, thus blocking spore outgrowth after germination.

Superdormant Spores as a Hurdle for Gentle Germination-Inactivation Based Spore Control Strategies

Bacterial spore control strategies based on the germination-inactivation principle can lower the thermal load needed to inactivate bacterial spores and thus preserve food quality better. However, the success of this strategy highly depends on the germination of spores, and a subpopulation of spores that fail to germinate or germinate extremely slowly hinders the application of this strategy. This subpopulation of spores is termed 'superdormant (SD) spores.' Depending on the source of the germination stimulus, SD spores are categorized as nutrient-SD spores, Ca2+-dipicolinic acid SD spores, dodecylamine-SD spores, and high pressure SD spores. In recent decades, research has been done to isolate these different groups of SD spores and unravel the cause of their germination deficiency as well as their germination capacities. This review summarizes the challenges caused by SD spores, their isolation and characterization, the underlying mechanisms of their germination deficiency, and the future research directions needed to tackle this topic in further depth.

Fluoride movement into and out of Bacillus spores and growing cells and effects of fluoride accumulation on spore properties

AIMS

To investigate effects of fluoride ion (F^- ) on, and kinetics of its movement into and out of, spores and growing cells of Bacillus species.

METHODS AND RESULTS

Effects of F^- on Bacillus cell growth, spore germination and outgrowth and heat resistance were investigated, as well as F^- movement into and out of spores using ¹⁹ F-NMR. F^- inhibited Bacillus subtilis spore germination and outgrowth, and YhdU, now named FluC, was crucial to prevent F^- accumulation in growing cells and to minimize F^- inhibition of spore germination. Dormant wild-type, yhdU and coat defective B. subtilis spores, and Bacillus cereus spores incubated in 40 mmol l^-1 NaF for 48 h accumulated 2-2·6 mol l^-1  F^- and its movement into Bacillus spores was highest at low pH. Bacillus subtilis spores lacking Ca-dipicolinic acid accumulated higher F^- levels than wild-type spores.

CONCLUSIONS

These results are consistent with F^- incorporation into the dormant spore core, and as HF and/or NaF, but not CaF₂ . YhdU played no significant role in F^- uptake or efflux in dormant spores, but assisted in F^- export early in spore germination.

SIGNIFICANCE AND IMPACT OF STUDY

This knowledge provides new insight into effects of F^- on Bacillus cells and spores and how this anion moves into, and out of spores.

Role of DNA Repair and Protective Components in Bacillus subtilis Spore Resistance to Inactivation by 400-nm-Wavelength Blue Light

The high intrinsic decontamination resistance of Firmicutes spores is important medically (disease) and commercially (food spoilage). Effective methods of spore eradication would be of considerable interest in the health care and medical product industries, particularly if the decontamination method effectively killed spores while remaining benign to both humans and sensitive equipment. Intense blue light at a ∼400 nm wavelength is one such treatment that has drawn significant interest. This work has determined the resistance of spores to blue light in an extensive panel of Bacillus subtilis strains, including wild-type strains and mutants that (i) lack protective components such as the spore coat and its pigment(s) or the DNA protective α/β-type small, acid-soluble spore proteins (SASP); (ii) have an elevated spore core water content; or (iii) lack enzymes involved in DNA repair, including those for homologous recombination and nonhomologous end joining (HR and NHEJ), apurinic/apyrimidinic endonucleases, nucleotide and base excision repair (NER and BER), translesion synthesis (TLS) by Y-family DNA polymerases, and spore photoproduct (SP) removal by SP lyase (SPL). The most important factors in spore blue light resistance were determined to be spore coats/pigmentation, α/β-type SASP, NER, BER, TLS, and SP repair. A major conclusion from this work is that blue light kills spores by DNA damage, and the results in this work indicate at least some of the specific DNA damage. It appears that high-intensity blue light could be a significant addition to the agents used to kill bacterial spores in applied settings.IMPORTANCE Effective methods of spore inactivation would be of considerable interest in the health care and medical products industries, particularly if the decontamination method effectively killed spores while remaining benign to both humans and sensitive equipment. Intense blue light radiation is one such treatment that has drawn significant interest. In this work, all known spore-protective features, as well as universal and spore-specific DNA repair mechanisms, were tested in a systematic fashion for their contribution to the resistance of spores to blue light radiation.

Updates to Clostridium difficile Spore Germination

Germination of Clostridium difficile spores is a crucial early requirement for colonization of the gastrointestinal tract. Likewise, C. difficile cannot cause disease pathologies unless its spores germinate into metabolically active, toxin-producing cells. Recent advances in our understanding of C. difficile spore germination mechanisms indicate that this process is both complex and unique. This review defines unique aspects of the germination pathways of C. difficile and compares them to those of two other well-studied organisms, Bacillus anthracis and Clostridium perfringensC. difficile germination is unique, as C. difficile does not contain any orthologs of the traditional GerA-type germinant receptor complexes and is the only known sporeformer to require bile salts in order to germinate. While recent advances describing C. difficile germination mechanisms have been made on several fronts, major gaps in our understanding of C. difficile germination signaling remain. This review provides an updated, in-depth summary of advances in understanding of C. difficile germination and potential avenues for the development of therapeutics, and discusses the major discrepancies between current models of germination and areas of ongoing investigation.

The orphan germinant receptor protein GerXAO (but not GerX3b) is essential for L-alanine induced germination in Clostridium botulinum Group II

Clostridium botulinum is an anaerobic spore forming bacterium that produces the potent botulinum neurotoxin that causes a severe and fatal neuro-paralytic disease of humans and animals (botulism). C. botulinum Group II is a psychrotrophic saccharolytic bacterium that forms spores of moderate heat resistance and is a particular hazard in minimally heated chilled foods. Spore germination is a fundamental process that allows the spore to transition to a vegetative cell and typically involves a germinant receptor (GR) that responds to environmental signals. Analysis of C. botulinum Group II genomes shows they contain a single GR cluster (gerX3b), and an additional single gerA subunit (gerXAO). Spores of C. botulinum Group II strain Eklund 17B germinated in response to the addition of L-alanine, but did not germinate following the addition of exogenous Ca²⁺-DPA. Insertional inactivation experiments in this strain unexpectedly revealed that the orphan GR GerXAO is essential for L-alanine stimulated germination. GerX3bA and GerX3bC affected the germination rate but were unable to induce germination in the absence of GerXAO. No role could be identified for GerX3bB. This is the first study to identify the functional germination receptor of C. botulinum Group II.