ACTIVATION OF BACTERIAL ENDOSPORES

Mini-review: effect of temperature on microbial reductive dehalogenation of chlorinated ethenes: a review

Temperature is a key factor affecting microbial activity and ecology. An increase in temperature generally increases rates of microbial processes up to a certain threshold, above which rates decline rapidly. In the subsurface, temperature of groundwater is usually stable and related to the annual average temperature at the surface. However, anthropogenic activities related to the use of the subsurface, e.g. for thermal heat management, foremost heat storage, will affect the temperature of groundwater locally. This mini-review intends to summarize the current knowledge on reductive dehalogenation activities of the chlorinated ethenes, common urban groundwater contaminants, at different temperatures. This includes an overview of activity and dehalogenation extent at different temperatures in laboratory isolates and enrichment cultures, the effect of shifts in temperature in micro- and mesocosm studies as well as observed biotransformation at different natural and induced temperatures at contaminated field sites. Furthermore, we address indirect effects on biotransformation, e.g. changes in fermentation, methanogenesis and sulfate reduction as competing or synergetic microbial processes. Finally, we address the current gaps in knowledge regarding bioremediation of chlorinated ethenes, microbial community shifts and bottlenecks for active combination with thermal energy storage, and necessities for bioaugmentation and/or natural re-populations after exposure to high temperature.

Heat activation and inactivation of bacterial spores. Is there an overlap?

Heat activation at a sublethal temperature is widely applied to promote Bacillus species spore germination. This treatment also has potential to be employed in food processing to eliminate undesired bacterial spores by enhancing their germination, and then inactivating the less heat resistant germinated spores at a milder temperature. However, incorrect heat treatment could also generate heat damage in spores, and lead to more heterogeneous spore germination. Here, the heat activation and heat damage profile of Bacillus subtilis spores was determined by testing spore germination and outgrowth at both population and single spore levels. The heat treatments used were 40-80°C, and for 0-300 min. The results were as follows. 1) Heat activation at 40-70°C promoted L-valine and L-asparagine-glucose-fructose-potassium (AGFK) induced germination in a time dependent manner. 2) The optimal heat activation temperatures for AGFK and L-valine germination via the GerB plus GerK or GerA germinant receptors were 65 and 50-65°C, respectively. 3) Heat inactivation of dormant spores appeared at 70°C, and the heat damage of molecules essential for germination and growth began at 70 and 65°C, respectively. 4) Heat treatment at 75°C resulted in both activation of germination and damage to the germination apparatus, and 80°C treatment caused more pronounced heat damage. 5) For the spores that should withstand adverse environmental temperatures in nature, heat activation seems functional for a subsequent optimal germination process, while heat damage affected both germination and outgrowth. Importance Bacterial spores are thermal resistant structures that can thus survive preservation strategies and revive through the process of spore germination. The more heat resistant spores are the more heterogeneous they germinate upon adding germinants. Upon germination spores can cause food spoilage and cause food intoxication. Here we provide new information on both heat activation and inactivation regimes and their effects on the (heterogeneity of) spore germination.

Effect of Temperature on Acetate Mineralization Kinetics and Microbial Community Composition in a Hydrocarbon-Affected Microbial Community During a Shift From Oxic to Sulfidogenic Conditions

Aquifer thermal energy storage (ATES) allows for the seasonal storage and extraction of heat in the subsurface thus reducing reliance on fossil fuels and supporting decarbonization of the heating and cooling sector. However, the impacts of higher temperatures toward biodiversity and ecosystem services in the subsurface environment remain unclear. Here, we conducted a laboratory microcosm study comprising a hydrocarbon-degrading microbial community from a sulfidic hydrocarbon-contaminated aquifer spiked with ¹³C-labeled acetate and incubated at temperatures between 12 and 80°C to evaluate (i) the extent and rates of acetate mineralization and (ii) the resultant temperature-induced shifts in the microbial community structure. We observed biphasic mineralization curves at 12, 25, 38, and 45°C, arising from immediate and fast aerobic mineralization due to an initial oxygen exposure, followed by slower mineralization at sulfidogenic conditions. At 60°C and several replicates at 45°C, acetate was only aerobically mineralized. At 80°C, no mineralization was observed within 178 days. Rates of acetate mineralization coupled to sulfate reduction at 25 and 38°C were six times faster than at 12°C. Distinct microbial communities developed in oxic and strictly anoxic phases of mineralization as well as at different temperatures. Members of the Alphaproteobacteria were dominant in the oxic mineralization phase at 12–38°C, succeeded by a more diverse community in the anoxic phase composed of Deltaproteobacteria, Clostridia, Spirochaetia, Gammaproteobacteria and Anaerolinea, with varying abundances dependent on the temperature. In the oxic phases at 45 and 60°C, phylotypes affiliated to spore-forming Bacilli developed. In conclusion, temperatures up to 38°C allowed aerobic and anaerobic acetate mineralization albeit at varying rates, while mineralization occurred mainly aerobically between 45 and 60°C; thermophilic sulfate reducers being active at temperatures > 45°C were not detected. Hence, temperature may affect dissolved organic carbon mineralization rates in ATES while the variability in the microbial community composition during the transition from micro-oxic to sulfidogenic conditions highlights the crucial role of electron acceptor availability when combining ATES with bioremediation.

Effect of antibiotic to induce Clostridioides difficile-susceptibility and infectious strain in a mouse model of Clostridioides difficile infection and recurrence

The anaerobic bacterium Clostridioides difficile is the leading cause of antibiotic-associated diarrhea that can culminate in life-threating colitis. During the C. difficile infection (CDI), C. difficile produces toxins that generate the clinical symptoms of the disease, and produce spores, which persist in the host during antibiotic treatment and can cause recurrent CDI (R-CDI). In this work, we aimed to compare three antibiotic regimens in the susceptibility of mice to CDI and R-CDI (i.e., antibiotic cocktail followed by clindamycin, 5 days of cefoperazone and 10 days of cefoperazone) with three different C. difficile isolates (i.e., strains 630; R20291, and VPI 10463). We observed that the severity of the clinical symptoms of CDI and R-CDI was dependent on the antibiotic treatment used to induce C. difficile-susceptibility, and that the three strains generated a different onset to diarrhea and weight loss in mice that were administrated with the same antibiotic treatment and which differed in comparison to the effect previously reported by other research groups. Our results suggest that, in our experimental conditions, in those animals treated with antibiotic cocktail followed by clindamycin, infection with strain R20291 had the highest diarrhea manifestation in comparison to strains 630 and VPI 10463. In animals treated with cefoperazone for 5 days, infection with strains R20291 or 630 had the highest diarrhea manifestation in comparison to VPI 10463, while in animals treated with cefoperazone for 10 days, infection with strain R20291 or VPI 10463, but not 630, had the highest diarrhea manifestation.

Understanding the Effects of High Pressure on Bacterial Spores Using Synchrotron Infrared Spectroscopy

Bacterial spores are extremely resistant life-forms that play an important role in food spoilage and foodborne disease. The return of spores to a vegetative cell state is a three-step process, these being activation, germination, and emergence. High-pressure (HP) processing is known to induce germination in part of the spore population and even to inactivate a high number of Bacillus spores when combined with other mild treatments such as the addition of nisin. The aim of the present work was to investigate the mechanisms involved in the sensitization of spores to nisin following HP treatment at ambient temperature or with moderate heating leading to a heterogeneous spore response. Bacillus subtilis spores were subjected to HP treatment at 500 MPa at 20 and 50°C. The physiological state of different subpopulations was characterized. Then Fourier transform infrared (FTIR) microspectroscopy coupled to a synchrotron infrared source was used to explore the heterogeneity of the biochemical signatures of the spores after the same HP treatments. Our results confirm that HP at 50°C induces the germination of a large proportion of the spore population. HP treatment at 20°C generated a subpopulation of ungerminated spores reversibly sensitized to the presence of nisin in their growth medium. Regarding infrared spectra of individual spores, spores treated by HP at 50°C and germinated spores had similar spectral signatures involving the same structural properties. However, after HP was performed at 20°C, two groups of spores were distinguished; one of these groups was clearly identified as germinated spores. The second group displayed a unique spectral signature, with shifts in the spectral bands corresponding to changes in membrane fluidity. Besides, spores spectra in the amide region could be divided into several groups close to spectral properties of dormant, germinated, or inactivated spores. The part of the spectra corresponding to α-helix and β-sheet-structures contribute mainly to the spectral variation between spores treated by HP at 20°C and other populations. These changes in the lipid and amide regions could be the signature of reversible changes linked to spore activation.

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.

Conservation of the "Outside-in" Germination Pathway in Paraclostridium bifermentans

Clostridium difficile spore germination is initiated in response to certain bile acids and amino acids (e.g., glycine). Though the amino acid-recognizing germinant receptor is unknown, the bile acid germinant receptor is the germination-specific, subtilisin-like pseudoprotease, CspC. In C. difficile the CspB, CspA, and CspC proteins are involved in spore germination. Of these, only CspB is predicted to have catalytic activity because the residues important for catalysis are mutated in the cspA and cspC sequence. The CspB, CspA, and CspC proteins are likely localized to the outer layers of the spore (e.g., the cortex or the coat layers) and not the inner membrane where the Ger-type germinant receptors are located. In C. difficile, germination proceeds in an “outside-in” direction, instead of the “‘inside-out” direction observed during the germination of Bacillus subtilis spores. During C. difficile spore germination, cortex fragments are released prior to the release of 2,4-dipicolinic acid (DPA) from the spore core. This is opposite to what occurs during B. subtilis spore germination. To understand if the mechanism C. difficile spore germination is unique or if spores from other organisms germinate in a similar fashion, we analyzed the germination of Paraclostridium bifermentans spores. We find that P. bifermentans spores release cortex fragments prior to DPA during germination and the DPA release from the P. bifermentans spore core can be blocked by high concentrations of osmolytes. Moreover, we find that P. bifermentans spores do not respond to steroid-like compounds (unlike the related C. difficile and P. sordellii organisms), indicating that the mere presence of the Csp proteins does permit germination in response to steroid compounds. Our findings indicate that the “outside in” mechanism of spore germination observed in C. difficile can be found in other bacteria suggesting that this mechanism is a novel pathway for endospore germination.

Selection of inactivation medium for fungal spores in clinical wastes by supercritical carbon dioxide

The present study aimed to select the best medium for inactivation of Aspergillus fumigatus, Aspergillus spp. in section Nigri, A. niger, A. terreus var. terreus, A. tubingensis, Penicillium waksmanii, P. simplicissimum, and Aspergillus sp. strain no. 145 spores in clinical wastes by using supercritical carbon dioxide (SC-CO₂). There were three types of solutions used including normal saline, seawater, distilled water, and physiological saline with 1% of methanol; each solution was tested at 5, 10, and 20 mL of the water contents. The experiments were conducted at the optimum operating parameters of supercritical carbon dioxide (30 MPa, 75 °C, 90 min). The results showed that the inactivation rate was more effective in distilled water with the presence of 1% methanol (6 log reductions). Meanwhile, the seawater decreases inactivation rate more than normal saline (4.5 vs. 5.1 log reduction). On the other hand, the experiments performed with different volumes of distilled water (5, 10, and 20 mL) indicated that A. niger spores were completely inactivated with 10 mL of distilled water. The inactivation rate of fungal spores decreased from 6 to 4.5 log as the amount of distilled water increased from 10 to 20 mL. The analysis for the spore morphology of A. fumigatus and Aspergillus spp. in section Nigri using scanning electron microscopy (SEM) has revealed the role of temperature and pressure in the SC-CO₂ in the destruction of the cell walls of the spores. It can be concluded that the distilled water represent the best medium for inactivation of fungal spores in the clinical solid wastes by SC-CO₂.

Production and analysis of a Bacillus subtilis biofilm comprised of vegetative cells and spores using a modified colony biofilm model

Bacillus subtilis is a spore-forming soil bacterium that is capable of producing robust biofilms. Sporulation can occur in B. subtilis biofilms and it is possible that the spores embedded in the protective matrix could present a significant challenge to disinfecting agents or processes. This article describes a method for the growth and quantification of a reproducible B. subtilis ATCC 35021 biofilm comprised of vegetative cells and spores using a modified colony biofilm model. In this method, membranes were inoculated and incubated for a total of 8 days to promote biofilm formation and subsequent sporulation within the biofilm. Representative samples were taken over the course of the incubation period to evaluate the biofilms using enumerative, microscopic, and spectrometric methods. At various time points, the total numbers of cells and spores were quantified. A Congo red agar (CRA) method was utilized to detect the TasA matrix protein, a primary component of the B. subtilis biofilm matrix. The presence of TasA was also confirmed using mass spectrometry. The biofilm morphologies were correlated to the enumeration data with a variety of correlative imaging techniques: confocal microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). At the end of the incubation period, the biofilm contained >7 logs total colony forming units with spores comprising approximately 10% of the biofilm. The biofilm generated using this method allows researchers to use a new, more robust challenge for efficacy testing of chemical and physical antimicrobial treatments such as antibiotics, disinfectants, or heat.

Improving culture media for the isolation of Clostridium difficile from compost

This study was to optimize the detection methods for Clostridium difficile from the animal manure-based composts. Both autoclaved and unautoclaved dairy composts were inoculated with a 12-h old suspension of a non-toxigenic C. difficile strain (ATCC 43593) and then plated on selected agar for vegetative cells and endospores. Six types of enrichment broths supplemented with taurocholate and l-cysteine were assessed for detecting a low level of artificially inoculated C. difficile (ca. 5 spores/g) from dairy composts. The efficacy of selected enrichment broths was further evaluated by isolating C. difficile from 29 commercial compost samples. Our results revealed that using heat-shock was more effective than using ethanol-shock for inducing endospore germination, and the highest endospore count (p < 0.05) was yielded at 60 °C for 25 min. C. difficile agar base, supplemented with 0.1% l-cysteine, 7% defibrinated horse blood, and cycloserine-cefoxitin (CDA-CYS-H-CC agar) was the best medium (p < 0.05) for recovering vegetative cells from compost. C. difficile endospore populations from both types of composts enumerated on both CDA-CYS-H-CC agar supplemented with 0.1% sodium taurocholate (CDA-CYS-H-CC-T agar) and brain heart infusion agar supplemented with 0.5% yeast extract, 0.1% l-cysteine, cycloserine-cefoxitin, and 0.1% sodium taurocholate (BHIA-YE-CYS-CC-T agar) media were not significantly different from each other (p > 0.05). Overall, enrichment of inoculated compost samples in broths containing moxalactam-norfloxacin (MN) produced significantly higher (p < 0.05) spore counts than in non-selective broths or broths supplemented with CC. Enrichment in BHIB-YE-CYS-MN-T broth followed by culturing on an agar containing 7% horse blood and 0.1% taurocholate provided a more sensitive and selective combination of media for detecting a low population of C. difficile from environmental samples with high background microflora.

Evolution with a seed bank: The population genetic consequences of microbial dormancy

Dormancy is a bet‐hedging strategy that allows organisms to persist through conditions that are suboptimal for growth and reproduction by entering a reversible state of reduced metabolic activity. Dormancy allows a population to maintain a reservoir of genetic and phenotypic diversity (i.e., a seed bank) that can contribute to the long‐term survival of a population. This strategy can be potentially adaptive and has long been of interest to ecologists and evolutionary biologists. However, comparatively little is known about how dormancy influences the fundamental evolutionary forces of genetic drift, mutation, selection, recombination, and gene flow. Here, we investigate how seed banks affect the processes underpinning evolution by reviewing existing theory, implementing novel simulations, and determining how and when dormancy can influence evolution as a population genetic process. We extend our analysis to examine how seed banks can alter macroevolutionary processes, including rates of speciation and extinction. Through the lens of population genetic theory, we can understand the extent that seed banks influence the evolutionary dynamics of microorganisms as well as other taxa.

Effect of cultivation pH on the surface hydrophobicity of Bacillus subtilis spores

Bacillus subtilis spores are often used as biological indicators (BI) to monitor decontamination processes with gaseous hydrogen peroxide. Results in practical inactivation validation tests, however, vary considerably with no available explanation so far. This study reports on the effect of cultivation pH on spore surface hydrophobicity. Surface hydrophobicity is suspected to have an impact on the decontamination of technical surfaces such as packaging material when gaseous, condensing hydrogen peroxide is applied. It is the aim of this study to examine the impact of different cultivation pH levels on surface hydrophobicity and resistance of B. subtilis spores. Submersed cultivation of B. subtilis in bioreactors at controlled conditions with different static pH levels led to contact angles ranged between 50° and 80°, which was analyzed with water on a homogeneous layer of spores on a filter sheet. Resistance of spores was also affected by the cultivation pH. The results show that the culturing conditions during BI production should be controlled to obtain BI with specified characteristics in inactivation validation tests.

Incorporating germination-induction into decontamination strategies for bacterial spores

Bacterial spores resist environmental extremes and protect key spore macromolecules until more supportive conditions arise. Spores germinate upon sensing specific molecules, such as nutrients. Germination is regulated by specialized mechanisms or structural features of the spore that limit contact with germinants and enzymes that regulate germination. Importantly, germination renders spores more susceptible to inactivating processes such as heat, desiccation, and ultraviolet radiation, to which they are normally refractory. Thus, germination can be intentionally induced through a process called germination-induction and subsequent treatment of these germinated spores with common disinfectants or gentle heat will inactivate them. However, while the principle of germination-induction has been shown effective in the laboratory, this strategy has not yet been fully implemented in real-word scenarios. Here, we briefly review the mechanisms of bacterial spore germination and discuss the evolution of germination-induction as a decontamination strategy. Finally, we examine progress towards implementing germination-induction in three contexts: biodefense, hospital settings and food manufacture.

SIGNIFICANCE AND IMPACT

This article reviews implementation of germination-induction as part of a decontamination strategy for the cleanup of bacterial spores. To our knowledge this is the first time that germination-induction studies have been reviewed in this context. This article will provide a resource which summarizes the mechanisms of germination in Clostridia and Bacillus species, challenges and successes in germination-induction, and potential areas where this strategy may be implemented.

Effects of High Pressure on Bacillus licheniformis Spore Germination and Inactivation

Bacillus and Clostridium species form spores, which pose a challenge to the food industry due to their ubiquitous nature and extreme resistance. Pressurization at <300 MPa triggers spore germination by activating germination receptors (GRs), while pressurization at >300 MPa likely triggers germination by opening dipicolinic acid (DPA) channels present in the inner membrane of the spores. In this work, we expose spores of Bacillus licheniformis, a species associated with food spoilage and occasionally with food poisoning, to high pressure (HP) for holding times of up to 2 h. By using mutant spores lacking one or several GRs, we dissect the roles of the GerA, Ynd, and GerK GRs in moderately HP (mHP; 150 MPa)-induced spore germination. We show that Ynd alone is sufficient for efficient mHP-induced spore germination. GerK also triggers germination with mHP, although at a reduced germination rate compared to that of Ynd. GerA stimulates mHP-induced germination but only in the presence of either the intact GerK or Ynd GR. These results suggests that the effectiveness of the individual GRs in mHP-induced germination differs from their effectiveness in nutrient-induced germination, where GerA plays an essential role. In contrast to Bacillus subtilis spores, treatment with very HP (vHP) of 550 MPa at 37°C did not promote effective germination of B. licheniformis spores. However, treatment with vHP in combination with elevated temperatures (60°C) gave a synergistic effect on spore germination and inactivation. Together, these results provide novel insights into how HP affects B. licheniformis spore germination and inactivation and the role of individual GRs in this process.IMPORTANCE Bacterial spores are inherently resistant to food-processing regimes, such as high-temperature short-time pasteurization, and may therefore compromise food durability and safety. The induction of spore germination facilitates subsequent inactivation by gentler processing conditions that maintain the sensory and nutritional qualities of the food. High-pressure (HP) processing is a nonthermal food-processing technology used to eliminate microbes from food. The application of this technology for spore eradication in the food industry requires a better understanding of how HP affects the spores of different bacterial species. The present study provides novel insights into how HP affects Bacillus licheniformis spores, a species associated with food spoilage and occasionally food poisoning. We describe the roles of different germination receptors in HP-induced germination and the effects of two different pressure levels on the germination and inactivation of spores. This study will potentially contribute to the effort to implement HP technology for spore inactivation in the food industry.

Occurrence of Bacillus amyloliquefaciens as a systemic endophyte of vanilla orchids

We report the occurrence of Bacillus amyloliquefaciens in vanilla orchids (Vanilla phaeantha) and cultivated hybrid vanilla (V. planifolia × V. pompona) as a systemic bacterial endophyte. We determined with light microscopy and isolations that tissues of V. phaeantha and the cultivated hybrid were infected by a bacterial endophyte and that shoot meristems and stomatal areas of stems and leaves were densely colonized. We identified the endophyte as B. amyloliquefaciens using DNA sequence data. Since additional endophyte-free plants and seed of this orchid were not available, additional studies were performed on surrogate hosts Amaranthus caudatus, Ipomoea tricolor, and I. purpurea. Plants of A. caudatus inoculated with B. amyloliquefaciens demonstrated intracellular colonization of guard cells and other epidermal cells, confirming the pattern observed in the orchids. Isolations and histological studies suggest that the bacterium may penetrate deeply into developing plant tissues in shoot meristems, forming endospores in maturing tissues. B. amyloliquefaciens produced fungal inhibitors in culture. In controlled experiments using morning glory seedlings we showed that the bacterium promoted seedling growth and reduced seedling necrosis due to pathogens. We detected the gene for phosphopantetheinyl transferase (sfp), an enzyme in the pathway for production of antifungal lipopeptides, and purified the lipopeptide "surfactin" from cultures of the bacterium. We hypothesize that B. amyloliquefaciens is a robust endophyte and defensive mutualist of vanilla orchids. Whether the symbiosis between this bacterium and its hosts can be managed to protect vanilla crops from diseases is a question that should be evaluated in future research.

The combined effect of pasteurization intensity, water activity, pH and incubation temperature on the survival and outgrowth of spores of Bacillus cereus and Bacillus pumilus in artificial media and food products

The objective of the study was to evaluate the combined effects of pasteurization intensity (no heat treatment and 10 min at 70, 80 and 90 °C), water activity (aw) (0.960-0.990), pH (5.5-7.0) and storage temperature (7 and 10 °C) on the survival and outgrowth of psychrotolerant spores of Bacillus cereus FF119b and Bacillus pumilus FF128a. The experiments were performed in both artificial media and a validation was performed on real food products (cream, béchamel sauce and mixed vegetable soup). It was determined that in general, heat treatments of 10 min at 70 °C or 80 °C activated the spores of both B. cereus FF119b and B. pumilus FF128a, resulting in faster outgrowth compared to native (non-heat treated) spores. A pasteurization treatment of 10 min at 90 °C generally resulted in the longest lag periods before outgrowth of both isolates. Some of the spores were inactivated by this heat treatment, with more inactivation being observed the lower the pH value of the heating medium. Despite this, it was also observed that under some conditions the remaining (surviving) spores were actually activated as their outgrowth took place after a shorter period of time compared to native non-heated spores. While the response of B. cereus FF119b to the pasteurization intensity in cream and béchamel sauce was similar to the trends observed in the artificial media at 10 °C, in difference, outgrowth was only observed at 7 °C in both products when the spores had been heated for 10 min at 80 °C. Moreover, no inactivation was observed in cream or béchamel sauce when the spores were heated for 10 min at 90 °C in these two products. This was attributed to the protective effect of fat in the cream and the ingredients in the béchamel sauce. The study provides some insight into the potential microbial (stability and safety) consequences of the current trend towards milder heat treatments which is being pursued in the food industry.

Characterization of airborne bacteria at an underground subway station

The reliable detection of airborne biological threat agents depends on several factors, including the performance criteria of the detector and its operational environment. One step in improving the detector's performance is to increase our knowledge of the biological aerosol background in potential operational environments. Subway stations are enclosed public environments, which may be regarded as potential targets for incidents involving biological threat agents. In this study, the airborne bacterial community at a subway station in Norway was characterized (concentration level, diversity, and virulence- and survival-associated properties). In addition, a SASS 3100 high-volume air sampler and a matrix-assisted laser desorption ionization-time of flight mass spectrometry-based isolate screening procedure was used for these studies. The daytime level of airborne bacteria at the station was higher than the nighttime and outdoor levels, and the relative bacterial spore number was higher in outdoor air than at the station. The bacterial content, particle concentration, and size distribution were stable within each environment throughout the study (May to September 2010). The majority of the airborne bacteria belonged to the genera Bacillus, Micrococcus, and Staphylococcus, but a total of 37 different genera were identified in the air. These results suggest that anthropogenic sources are major contributors to airborne bacteria at subway stations and that such airborne communities could harbor virulence- and survival-associated properties of potential relevance for biological detection and surveillance, as well as for public health. Our findings also contribute to the development of realistic testing and evaluation schemes for biological detection/surveillance systems by providing information that can be used to mimic real-life operational airborne environments in controlled aerosol test chambers.

Conditions Affecting Germination of Clostridium botulinum 62A Spores in a Chemically Defined Medium

Spores of Clostridium botulinum type 62A were germinated in a chemically defined medium (8 mm l-cysteine, 11.9 mm sodium bicarbonate, 4.4 mm sodium thioglycolate; buffered with 100 mm TES, pH 7.0). The rate and extent of germination were increased when an aqueous spore suspension was heated sublethally (80 C, 60 min) before addition to the germination medium. Neither sublethal nor lethal doses of gamma radiation had any marked effect on subsequent germination. Maximum germination (>90% in 2 hr) in the defined medium occurred in the pH range of 6.5 to 7.5, at 30 to 37 C, with an l-cysteine level of 8 mm. Increasing l-cysteine to 32 mm increased the rate (over that with 8 mm l-cysteine) but not the extent of germination. The rate and extent of germination increased with NaHCO(3) addition to 8.3 mm, but increasing levels to 11.9 mm had no further effect. For maximum germination, 2.2 mm sodium thioglycolate was required and higher levels (to 8.8 mm) had no further enhancing or inhibitory effect. Under optimal conditions for germination, 97% of the spores had become heat sensitive; 98% had become sensitive to radiation; 88 and 91% had become phase dark and stainable, respectively, and the spore suspension had lost 46% of its initial optical density by 2 hr. Loss of heat resistance preceded loss of radiation resistance, acquisition of stainability, and phase darkening by about 12 min.

Modification of GerQ reveals a functional relationship between Tgl and YabG in the coat of Bacillus subtilis spores

Here we describe the functional relationship between YabG and transglutaminase (Tgl), enzymes that modify the spore coat proteins of Bacillus subtilis. In wild-type spores at 37 degrees C, Tgl mediates the crosslinking of GerQ into higher molecular mass forms; however, some GerQ multimers are found in tgl mutant spores, indicating that Tgl is not essential. Immunoblotting showed that spores isolated from a yabG mutant after sporulation at 37 degrees C contain only very low levels of GerQ multimers. Heat treatment for 20 min at 60 degrees C, which maximally activates the enzymatic activity of Tgl, caused crosslinking of GerQ in isolated yabG spores but not in tgl/yabG double-mutant spores. In addition, the germination frequency of the tgl/yabG spores in the presence of l-alanine with or without heat activation at 60 degrees C was lower than that of wild-type spores. These findings suggest that Tgl cooperates with YabG to mediate the temperature-dependent modification of the coat proteins, a process associated with spore germination in B. subtilis.

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.

KINETICS OF SPORE GERMINATION

McCormick, Neil G. (University of Virginia, Charlottesville). Kinetics of spore germination. J. Bacteriol. 89:1180-1185. 1965.-An empirically derived equation was developed which accurately describes the time-course of the decrease in optical density during spore germination. A method is described for calculating the final value, the inflection point, and the maximal velocity from knowledge of three experimental values and the initial value at time-zero. A number of germination curves were analyzed by application of the equation, and the effects of various environmental conditions on the parameters of the equation (k, c, and alpha) are noted. The constant c was found to be dependent upon the temperature and perhaps upon the degree of heat activation and the l-alanine concentration. The constants k and alpha appear to be more basic functions of the initial state of the spore suspension. Variation of the concentration of spores changes only the initial optical density, but does not change any of the three constants.

[Ethylene oxide sterilization. II. Influence of test devices on the performance of biological monitors and its evaluation]

In view of the importance of the assurance of the sterility of medical devices, with a large incidence of tubular forms, a study of biological monitors was undertaken, using paper as a carrier, the dimension of the test specimens being the variable considered. After the sterilization process in an industrial cycle, followed by the recovery of the surviving spores through inoculation of the carriers into thioglycolate broth, soybean-casein broth and this last with the addition of bromothymol blue. No differences were found between the growth promoting capacity of these 3 media. The effectiveness of sterilization was dependent on the dimension of the test specimens. The periodic determination of residual gas content on the test specimens, as well as the monitoring of the industrial environment demonstrate the need and importance of the legislation in force.

Heat killing of bacterial spores analyzed by differential scanning calorimetry

Thermograms of the exosporium-lacking dormant spores of Bacillus megaterium ATCC 33729, obtained by differential scanning calorimetry, showed three major irreversible endothermic transitions with peaks at 56, 100, and 114 degrees C and a major irreversible exothermic transition with a peak at 119 degrees C. The 114 degrees C transition was identified with coat proteins, and the 56 degrees C transition was identified with heat inactivation. Thermograms of the germinated spores and vegetative cells were much alike, including an endothermic transition attributable to DNA. The ascending part of the main endothermic 100 degrees C transition in the dormant-spore thermograms corresponded to a first-order reaction and was correlated with spore death; i.e., greater than 99.9% of the spores were killed when the transition peak was reached. The maximum death rate of the dormant spores during calorimetry, calculated from separately measured D and z values, occurred at temperatures above the 73 degrees C onset of thermal denaturation and was equivalent to the maximum inactivation rate calculated for the critical target. Most of the spore killing occurred before the release of most of the dipicolinic acid and other intraprotoplast materials. The exothermic 119 degrees C transition was a consequence of the endothermic 100 degrees C transition and probably represented the aggregation of intraprotoplast spore components. Taken together with prior evidence, the results suggest that a crucial protein is the rate-limiting primary target in the heat killing of dormant bacterial spores.

Effects of heat-, CaCl2- and ethanol-treatments on activation of Bacillus spores

The effects of heat, CaCl2, and ethanol on activation of Bacillus spores were determined by monitoring the absorbance decrease during germination in inosine. Bacillus cereus T, B. subtilis A and B. megaterium QM B1551 spores were activated by heat- and CaCl2-treatments. Ethanol activated B. megaterium and B. subtilis spores yet did not activate B. cereus spores. CaCl2- and ethanol-activations were less effective than heat-activation as judged by optimal germination rates and germination extents. The presence of CaCl2 during heat-treatment inhibited heat-activation of all three Bacillus spores without affecting viability or dipicolinic acid content of the spores. The electrophoretic patterns of coat plus outer membrane proteins extracted from Bacillus spores treated with CaCl2 and heat in the presence of CaCl2 were similar to each other and were distinctively different from the patterns of proteins from unactivated spores or the spores treated with heat and/or ethanol.

Activation of Clostridium perfringens spores under conditions that disrupt hydrophobic interactions of biological macromolecules

The effect of hydrophobic interactions on the activation of C. perfringens NCTC 8679 spores was examined by heating spores under conditions that modify the hydrophobic properties of biological macromolecules. After the activation treatment and a washing procedure, germination was determined by measuring the decrease in optical density of spores suspended in an enriched germination medium. Activation was inhibited for spores that were treated under conditions that strengthen hydrophobic interactions, i.e., a decrease in pH or the presence of structure-stabilizing neutral salts. Activation was enhanced by treatment under conditions that disrupt hydrophobic interactions, i.e., an increase in pH or the presence of urea, dibucaine, or denaturing neutral salts. A deactivation treatment with the antichaotropic salt (NH4)2SO4 reversed activation by the chaotropic salt CaCl2 and to a lesser extent reversed activation by sublethal heat (75 degrees C) or urea. Most treatments that enhanced activation increased spore injury at higher temperatures, which resulted in decreased germination. However, (NH4)2SO4 and a decrease in pH from 5.6 to 3.8, which inhibited activation, also favored injury. The results suggest that activation involves a conformational change of a spore protein(s) through weakening of hydrophobic molecular forces and that activation and injury occur at different spore sites.

Factors influencing the resistance of biological monitors to ethylene oxide

The resistance of bacterial spore monitors is markedly influenced by the environmental conditions existing during development of spores and, subsequently, in the preparation and evaluation of the monitor. Sporulation medium, suspending medium, pasteurization and storage conditions influence resistance of spores of Bacillus subtilis var. niger to ethylene oxide, but incubation temperature and age of sporulating culture appear to be unimportant. The conditions under which the spore suspension is dried on the supporting medium of the monitor exerts a major influence on resistance. Spores exposed to ethylene oxide are abnormally susceptible to damage by shaking with Ballotini, a method frequently used to recover spores from monitors. Nutritional conditions, pH and temperature of incubation influence the ability of survivors to form colonies on solidified media.

The effect of quaternary ammonium compounds and amine oxides on spores of Bacillus cereus

The effect of 1-dodecylpiperidine 1-oxide and N,N'-bis(dodecyldimethyl)-1,2-ethane diammonium dibromide on the spores of Bacillus cereus. particularly their binding to intact spores and spores with reduced cystine bonds, was investigated. The Langmuir type of binding is involved in both cases. Both compounds decreased the thermoresistance of spores. DPNO decreased the fraction of non-germinating spores, the effect of the drug increasing with increasing concentration. This phenomenon was associated with a faster release of dipicolinic acid to the medium. Only microgermination proceeded in the presence of BDED and dipicolinic acid was released only in substantially lower amounts. Both compounds also influenced respiration.

An investigation of membrane fluidity changes during sporulation and germination of Bacillus megaterium K.M. measured by electron spin and nuclear magnetic resonance spectroscopy

Changes in membrane and macromolecular fluidity which may accompany the differentiation processes of sporulation and germination in Bacillus megaterium K.M. are examined by electron spin and nuclear magnetic resonance spectroscopy. No change in membrane lipid fluidity is observed in isolated forespores up to stage VI. Between stage VI and release of mature spores, the ESR spectrum of doxylstearic acid spin labels becomes polycrystalline. This change in spectral fluidity is completely reversed during germination and is paralleled by the rapid release of Ca2+ from the spore. NMR studies also show that the mature spore has reduced macromolecular mobility and an increased nonexchangeable water pool compared with vegetative cells.

Release of dipicolinic acid and calcium and activation of Bacillus stearothermophilus spores as a function of time, temperature and pH

The kinetics of release of dipicolinic acid and calcium from Bacillus stearothermophilus spores and the rate of increase of colony count have been shown to be determined by conditions of time, temperature and pH. The apparent activation energies for release of dipicolinic acid, calcium and colony count increase were similar. The results support the hypothesis that breaking of dormancy involves a rupture of dipicolinic acid bonds and that the nature of these bonds rather than the dipicolinic acid content determines dormancy and resistance.