Binding of small, acid-soluble spore proteins to DNA plays a significant role in the resistance of Bacillus subtilis spores to hydrogen peroxide

Role of the Nfo and ExoA apurinic/apyrimidinic endonucleases in repair of DNA damage during outgrowth of Bacillus subtilis spores

Germination and outgrowth are critical steps for returning Bacillus subtilis spores to life. However, oxidative stress due to full hydration of the spore core during germination and activation of metabolism in spore outgrowth may generate oxidative DNA damage that in many species is processed by apurinic/apyrimidinic (AP) endonucleases. B. subtilis spores possess two AP endonucleases, Nfo and ExoA; the outgrowth of spores lacking both of these enzymes was slowed, and the spores had an elevated mutation frequency, suggesting that these enzymes repair DNA lesions induced by oxidative stress during spore germination and outgrowth. Addition of H2O2 also slowed the outgrowth of nfo exoA spores and increased the mutation frequency, and nfo and exoA mutations slowed the outgrowth of spores deficient in either RecA, nucleotide excision repair (NER), or the DNA-protective alpha/beta-type small acid-soluble spore proteins (SASP). These results suggest that alpha/beta-type SASP protect DNA of germinating spores against damage that can be repaired by Nfo and ExoA, which is generated either spontaneously or promoted by addition of H2O2. The contribution of RecA and Nfo/ExoA was similar to but greater than that of NER in repair of DNA damage generated during spore germination and outgrowth. However, nfo and exoA mutations increased the spontaneous mutation frequencies of outgrown spores lacking uvrA or recA to about the same extent, suggesting that DNA lesions generated during spore germination and outgrowth are processed by Nfo/ExoA in combination with NER and/or RecA. These results suggest that Nfo/ExoA, RecA, the NER system, and alpha/beta-type SASP all contribute to the repair of and/or protection against oxidative damage of DNA in germinating and outgrowing spores.

Effect of small, acid-soluble proteins on spore resistance and germination under a combination of pressure and heat treatment

To find the range of pressure required for effective high-pressure inactivation of bacterial spores and to investigate the role of alpha/beta-type small, acid-soluble proteins (SASP) in spores under pressure treatment, mild heat was combined with pressure (room temperature to 65 degrees C and 100 to 500 MPa) and applied to wild-type and SASP-alpha-/beta- Bacillus subtilis spores. On the one hand, more than 4 log units of wild-type spores were reduced after pressurization at 100 to 500 MPa and 65 degrees C. On the other hand, the number of surviving mutant spores decreased by 2 log units at 100 MPa and by more than 5 log units at 500 MPa. At 500 MPa and 65 degrees C, both wild-type and mutant spore survivor counts were reduced by 5 log units. Interestingly, pressures of 100, 200, and 300 MPa at 65 degrees C inactivated wild-type SASP-alpha+/beta+ spores more than mutant SASP-alpha-/beta- spores, and this was attributed to less pressure-induced germination in SASP-alpha-/beta- spores than in wild-type SASP-alpha+/beta+ spores. However, there was no difference in the pressure resistance between SASP-alpha+/beta+ and SASP-alpha-/beta- spores at 100 MPa and ambient temperature (approximately 22 degrees C) for 30 min. A combination of high pressure and high temperature is very effective for inducing spore germination, and then inactivation of the germinated spore occurs because of the heat treatment. This study showed that alpha/beta-type SASP play a role in spore inactivation by increasing spore germination under 100 to 300 MPa at high temperature.

Mechanisms of killing of spores of Bacillus subtilis by dimethyldioxirane

AIMS

To determine the mechanisms of Bacillus subtilis spore resistance to and killing by a novel sporicide, dimethyldioxirane (DMDO) that was generated in situ from acetone and potassium peroxymonosulfate at neutral pH.

METHODS AND RESULTS

Spores of B. subtilis were effectively killed by DMDO. Rates of killing by DMDO of spores lacking most DNA protective alpha/beta-type small, acid-soluble spore proteins (alpha- beta- spores) or the major DNA repair protein, RecA, were very similar to that of wild-type spore killing. Survivors of wild-type and alpha- beta- spores treated with DMDO also exhibited no increase in mutations. Spores lacking much coat protein due either to mutation or chemical decoating were much more sensitive to DMDO than were wild-type spores, but were more resistant than growing cells. Wild-type spores killed with this reagent retained their large pool of dipicolinic acid (DPA), and the survivors of spores treated with DMDO were sensitized to wet heat. The DMDO-killed spores germinated with nutrients, albeit more slowly than untreated spores, but germinated faster than untreated spores with dodecylamine. The killed spores were also germinated by very high pressures and by lysozyme treatment in hypertonic medium, but many of these spores lysed shortly after their germination, and none of these treatments were able to revive the DMDO-killed spores.

CONCLUSIONS

DMDO is an effective reagent for killing B. subtilis spores. The spore coat is a major factor in spore resistance to DMDO, which does not kill spores by DNA damage or by inactivating some component needed for spore germination. Rather, this reagent appears to kill spores by damaging the spore's inner membrane in some fashion.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work demonstrates that DMDO is an effective decontaminant for spores of Bacillus species that can work under mild conditions, and the killed spores cannot be revived. Evidence has also been obtained on the mechanisms of spore resistance to and killing by this reagent.

A preliminary assessment ofBacillus anthracisspore inactivation using an electrochemically activated solution (ECASOL™)

AIM

To evaluate the efficacy of electrochemically activated solution (ECASOL) in decontaminating Bacillus anthracis Ames and Vollum 1B spores, with and without changing the source water hardness and final ECASOL pH.

METHODS AND RESULTS

Five different ECASOL formulations were generated, in which the source water hardness and final ECASOL pH were varied, resulting in cases where significant changes in free available chlorine (FAC) and oxidative-reduction potential (ORP) were observed. B. anthracis Ames and Vollum 1B spores were suspended in the various ECASOL formulations for 30 min, and decontamination efficacy was determined; calcium hypochlorite [5% high-test hypochlorite (HTH)] was used as a positive control. The five different ECASOL formulations yielded mean FAC levels ranging from 305 to 464 ppm, and mean ORP levels ranging from +826 to +1000 mV. Exposure to all the ECASOL formulations and 5% HTH resulted in >or=7.0 log reductions in both B. anthracis Ames and Vollum 1B spores.

CONCLUSIONS

The present testing demonstrated that ECASOL with a minimum of c. 300-ppm FAC levels and +800-mV ORP inactivated the B. anthracis spores in suspension, similar to 5% HTH.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results provide information for decontaminating B. anthracis Ames and Vollum 1B spores in suspension using ECASOL.

Killing of spores of Bacillus subtilis by tert-butyl hydroperoxide plus a TAML�activator

AIMS

To determine the effectiveness of tert-butyl hydroperoxide (tBHP) plus the cationic surfactant cetyltrimethyl ammonium bromide (CTAB) and a tetra-amido macrocyclic ligand (TAML) activator in killing spores of Bacillus subtilis and the mechanisms of spore resistance to and killing by this reagent.

METHODS AND RESULTS

Killing of spores of B. subtilis by tBHP was greatly stimulated by the optimum ratio of concentrations of a TAML activator (1.7 micromol l(-1)) to tBHP (4.4%, vol/vol) plus a low level (270 mg l(-1)) of CTAB. Rates of killing of spores lacking most DNA protective alpha/beta-type small, acid-soluble spore proteins (alpha(-)beta(-) spores) or the major DNA repair protein, RecA, by tBHP plus CTAB and a TAML activator were essentially identical to that of wild-type spore killing. Survivors of wild-type and alpha(-)beta(-) spores treated with tBHP plus CTAB and a TAML activator also exhibited no increase in mutations. Spores lacking much coat protein either because of mutation or chemical decoating were much more sensitive to this reagent than were wild-type spores, but were more resistant than growing cells. Wild-type spores killed with this reagent retained their large pool of dipicolinic acid (DPA), and the survivors of spores treated with this reagent were sensitized to wet heat. The tBHP plus CTAB and TAML activator-killed spores germinated with nutrients, albeit more slowly than untreated spores, but germinated faster than untreated spores with dodecylamine. The killed spores were also germinated by application of 150 and 500 megaPascals of pressure for 15 min and by lysozyme treatment in hypertonic medium, but these spores lysed shortly after their germination.

CONCLUSIONS

The combination of tBHP plus CTAB and a TAML activator is effective in killing B. subtilis spores. The spore coat is a major factor in spore resistance to this reagent system, which does not kill spores by DNA damage or by inactivating some component needed for spore germination. Rather, this reagent system appears to kill spores by damaging the spore's inner membrane in some fashion.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work demonstrates that tBHP plus CTAB and a TAML activator is an effective and mild decontaminant for spores of Bacillus species. Evidence has also been obtained on the mechanisms of spore resistance to and killing by this reagent system.

Role of dipicolinic acid in resistance and stability of spores of Bacillus subtilis with or without DNA-protective alpha/beta-type small acid-soluble proteins

Dipicolinic acid (DPA) comprises approximately 10% of the dry weight of spores of Bacillus species. Although DPA has long been implicated in spore resistance to wet heat and spore stability, definitive evidence on the role of this abundant molecule in spore properties has generally been lacking. Bacillus subtilis strain FB122 (sleB spoVF) produced very stable spores that lacked DPA, and sporulation of this strain with DPA yielded spores with nearly normal DPA levels. DPA-replete and DPA-less FB122 spores had similar levels of the DNA protective alpha/beta-type small acid-soluble spore proteins (SASP), but the DPA-less spores lacked SASP-gamma. The DPA-less FB122 spores exhibited similar UV resistance to the DPA-replete spores but had lower resistance to wet heat, dry heat, hydrogen peroxide, and desiccation. Neither wet heat nor hydrogen peroxide killed the DPA-less spores by DNA damage, but desiccation did. The inability to synthesize both DPA and most alpha/beta-type SASP in strain PS3664 (sspA sspB sleB spoVF) resulted in spores that lost viability during sporulation, at least in part due to DNA damage. DPA-less PS3664 spores were more sensitive to wet heat than either DPA-less FB122 spores or DPA-replete PS3664 spores, and the latter also retained viability during sporulation. These and previous results indicate that, in addition to alpha/beta-type SASP, DPA also is extremely important in spore resistance and stability and, further, that DPA has some specific role(s) in protecting spore DNA from damage. Specific roles for DPA in protecting spore DNA against damage may well have been a major driving force for the spore's accumulation of the high levels of this small molecule.

Investigating the role of small, acid-soluble spore proteins (SASPs) in the resistance of Clostridium perfringens spores to heat

Background

Clostridium perfringens type A food poisoning is caused by enterotoxigenic C. perfringens type A isolates that typically possess high spore heat-resistance. The molecular basis for C. perfringens spore heat-resistance remains unknown. In the current study, we investigated the role of small, acid-soluble spore proteins (SASPs) in heat-resistance of spores produced by C. perfringens food poisoning isolates.

Results

Our current study demonstrated the presence of all three SASP-encoding genes (ssp1, 2 and 3) in five surveyed C. perfringens clinical food poisoning isolates. β-Glucuronidase assay showed that these ssp genes are expressed specifically during sporulation. Consistent with these expression results, our study also demonstrated the production of SASPs by C. perfringens food poisoning isolates. When the heat sensitivities of spores produced by a ssp3 knock-out mutant of a C. perfringens food poisoning isolate was compared with that of spores of the wild-type strain, spores of the ssp3 mutant were found to exhibit a lower decimal reduction value (D value) at 100°C than exhibited by the spores of wild-type strain. This effect was restored by complementing the ssp3 mutant with a recombinant plasmid carrying wild-type ssp3, suggesting that the observed differences in D values between spores of wild-type versus ssp3 mutant was due to the specific inactivation of ssp3. Furthermore, our DNA protection assay demonstrated that C. perfringens SASPs can protect DNA from DNase I digestion.

Conclusion

The results from our current study provide evidences that SASPs produced by C. perfringens food poisoning isolates play a role in protecting their spores from heat-damage, which is highly significant and relevant from a food safety perspective. Further detailed studies on mechanism of action of SASPs from C. perfringens should help in understanding the mechanism of protection of C. perfringens spores from heat-damage.

YtkD and MutT protect vegetative cells but not spores of Bacillus subtilis from oxidative stress

ytkD and mutT of Bacillus subtilis encode potential 8-oxo-dGTPases that can prevent the mutagenic effects of 8-oxo-dGTP. Loss of YtkD but not of MutT increased the spontaneous mutation frequency of growing cells. However, cells lacking both YtkD and MutT had a higher spontaneous mutation frequency than cells lacking YtkD. Loss of either YtkD or MutT sensitized growing cells to hydrogen peroxide (H2O2) and t-butylhydroperoxide (t-BHP), and the lack of both proteins sensitized growing cells to these agents even more. In contrast, B. subtilis spores lacking YtkD and MutT were not sensitized to H2O2, t-BHP, or heat. These results suggest (i) that YtkD and MutT play an antimutator role and protect growing cells of B. subtilis against oxidizing agents, and (ii) that neither YtkD nor MutT protects spores against potential DNA damage induced by oxidative stress or heat.

The Forespore Line of Gene Expression in Bacillus subtilis

Endospore formation by Bacillus subtilis involves three differentiating cell types, the predivisional cell, the mother cell, and the forespore. Here we report the program of gene expression in the forespore, which is governed by the RNA polymerase sigma factors sigma(F) and sigma(G) and the DNA-binding proteins RsfA and SpoVT. The sigma(F) factor turns on about 48 genes, including the gene for RsfA, which represses a gene in the sigma(F) regulon, and the gene for sigma(G). The sigma(G) factor newly activates 81 genes, including the gene for SpoVT, which turns on (in nine cases) or stimulates (in 11 cases) the expression of 20 genes that had been turned on by sigma(G) and represses the expression of 27 others. The forespore line of gene expression consists of many genes that contribute to morphogenesis and to the resistance and germination properties of the spore but few that have metabolic functions. Comparative genomics reveals a core of genes in the sigma(F) and sigma(G) regulons that are widely conserved among endospore-forming species but are absent from closely related, but non-spore-forming Listeria spp. Two such partially conserved genes (ykoU and ykoV), which are members of the sigma(G) regulon, are shown to confer dry-heat resistance to dormant spores. The ykoV gene product, a homolog of the non-homologous end-joining protein Ku, is shown to associate with the nucleoid during germination. Extending earlier work on gene expression in the predivisional cell and the mother cell, we present an integrated overview of the entire program of sporulation gene expression.

Decontamination assessment of Bacillus anthracis, Bacillus subtilis, and Geobacillus stearothermophilus spores on indoor surfaces using a hydrogen peroxide gas generator

AIMS

To evaluate the decontamination of Bacillus anthracis, Bacillus subtilis, and Geobacillus stearothermophilus spores on indoor surface materials using hydrogen peroxide gas.

METHODS AND RESULTS

Bacillus anthracis, B. subtilis, and G. stearothermophilus spores were dried on seven types of indoor surfaces and exposed to > or =1000 ppm hydrogen peroxide gas for 20 min. Hydrogen peroxide exposure significantly decreased viable B. anthracis, B. subtilis, and G. stearothermophilus spores on all test materials except G. stearothermophilus on industrial carpet. Significant differences were observed when comparing the reduction in viable spores of B. anthracis with both surrogates. The effectiveness of gaseous hydrogen peroxide on the growth of biological indicators and spore strips was evaluated in parallel as a qualitative assessment of decontamination. At 1 and 7 days postexposure, decontaminated biological indicators and spore strips exhibited no growth, while the nondecontaminated samples displayed growth.

CONCLUSIONS

Significant differences in decontamination efficacy of hydrogen peroxide gas on porous and nonporous surfaces were observed when comparing the mean log reduction in B. anthracis spores with B. subtilis and G. stearothermophilus spores.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results provide comparative information for the decontamination of B. anthracis spores with surrogates on indoor surfaces using hydrogen peroxide gas.

Role of the Nfo (YqfS) and ExoA apurinic/apyrimidinic endonucleases in protecting Bacillus subtilis spores from DNA damage

The Bacillus subtilis enzymes ExoA and Nfo (originally termed YqfS) are endonucleases that can repair apurinic/apyrimidinic (AP) sites and strand breaks in DNA. We have analyzed how the lack of ExoA and Nfo affects the resistance of growing cells and dormant spores of B. subtilis to a variety of treatments, some of which generate AP sites and DNA strand breaks. The lack of ExoA and Nfo sensitized spores (termed alpha-beta-) lacking the majority of their DNA-protective alpha/beta-type small, acid-soluble spore proteins (SASP) to wet heat. However, the lack of these enzymes had no effect on the wet-heat resistance of spores that retained alpha/beta-type SASP. The lack of either ExoA or Nfo sensitized wild-type spores to dry heat, but loss of both proteins was necessary to sensitize alpha-beta- spores to dry heat. The lack of ExoA and Nfo also sensitized alpha-beta-, but not wild-type, spores to desiccation. In contrast, loss of ExoA and Nfo did not sensitize growing cells or wild-type or alpha-beta- spores to hydrogen peroxide or t-butylhydroperoxide. Loss of ExoA and Nfo also did not increase the spontaneous mutation frequency of growing cells. exoA expression took place not only in growing cells, but also in the forespore compartment of the sporulating cell. These results, together with those from previous work, suggest that ExoA and Nfo are additional factors that protect B. subtilis spores from DNA damage accumulated during spore dormancy.

Site-directed mutagenesis and structural studies suggest that the germination protease, GPR, in spores of Bacillus species is an atypical aspartic acid protease

Germination protease (GPR) initiates the degradation of small, acid-soluble spore proteins (SASP) during germination of spores of Bacillus and Clostridium species. The GPR amino acid sequence is not homologous to members of the major protease families, and previous work has not identified residues involved in GPR catalysis. The current work has focused on identifying catalytically essential amino acids by mutagenesis of Bacillus megaterium gpr. A residue was selected for alteration if it (i) was conserved among spore-forming bacteria, (ii) was a potential nucleophile, and (iii) had not been ruled out as inessential for catalysis. GPR variants were overexpressed in Escherichia coli, and the active form (P41) was assayed for activity against SASP and the zymogen form (P46) was assayed for the ability to autoprocess to P41. Variants inactive against SASP and unable to autoprocess were analyzed by circular dichroism spectroscopy and multi-angle laser light scattering to determine whether the variant's inactivity was due to loss of secondary or quaternary structure, respectively. Variation of D127 and D193, but no other residues, resulted in inactive P46 and P41, while variants of each form were well structured and tetrameric, suggesting that D127 and D193 are essential for activity and autoprocessing. Mapping these two aspartate residues and a highly conserved lysine onto the B. megaterium P46 crystal structure revealed a striking similarity to the catalytic residues and propeptide lysine of aspartic acid proteases. These data indicate that GPR is an atypical aspartic acid protease.

Recurrent isolation of hydrogen peroxide-resistant spores of Bacillus pumilus from a spacecraft assembly facility

While the microbial diversity of a spacecraft assembly facility at the Jet Propulsion Laboratory (Pasadena, CA) was being monitored, H2O2-resistant bacterial strains were repeatedly isolated from various surface locations. H2O2 is a possible sterilant for spacecraft hardware because it is a low-temperature process and compatible with various modern-day spacecraft materials, electronics, and components. Both conventional biochemical testing and molecular analyses identified these strains as Bacillus pumilus. This Bacillus species was found in both unclassified (entrance floors, anteroom, and air-lock) and classified (floors, cabinet tops, and air) locations. Both vegetative cells and spores of several B. pumilus isolates were exposed to 5% liquid H2O2 for 60 min. Spores of each strain exhibited higher resistance than their respective vegetative cells to liquid H2O2. Results indicate that the H2O2 resistance observed in both vegetative cells and spores is strain-specific, as certain B. pumilus strains were two to three times more resistant than a standard Bacillus subtilis dosimetry strain. An example of this trend was observed when the type strain of B. pumilus, ATCC 7061, proved sensitive, whereas several environmental strains exhibited varying degrees of resistance, to H2O2. Repeated isolation of H2O2-resistant strains of B. pumilus in a clean-room is a concern because their persistence might potentially compromise life-detection missions, which have very strict cleanliness and sterility requirements for spacecraft hardware.

Rapid characterization of Bacillus spores targeting species-unique peptides produced with an atmospheric pressure matrix-assisted laser desorption/ionization source

New and improved strategies are eagerly sought for the rapid identification of microorganisms, particularly in mixtures. Mass spectrometry remains a powerful tool for this purpose. Small acid-soluble proteins (SASPs), which are relatively abundant in Bacillus spores, represent potential biomarkers for species characterization. Despite sharing extensive sequence homology, these proteins differ sufficiently in sequence for discrimination between species. This work focuses on the differences in sequence between SASPs from various Bacillus species. Compilation of SASP sequences from protein database searches, followed by in silico trypsin digestion and analysis of the resulting fragments, identified several species-specific peptides that could be targeted for analysis using mass spectrometry. This strategy was tested and found to be successful in the characterization of Bacillus spores both from individual species and in mixtures. Analysis was performed using an ion trap mass spectrometer with an atmospheric pressure MALDI source. This instrumentation offers the advantage of increased speed of analysis and accurate precursor ion selection for tandem mass spectrometric analysis compared with vacuum matrix-assisted laser desorption/ionization and time-of-flight instruments. The identification and targeting of species-specific peptides using this type of instrumentation offers a rapid, efficient strategy for the identification of Bacillus spores and can potentially be applied to different microorganisms.

Analysis of factors that influence the sensitivity of spores of Bacillus subtilis to DNA damaging chemicals

AIMS

To elucidate factors influencing the sensitivity of Bacillus subtilis spores to DNA damaging chemicals.

METHODS AND RESULTS

Wild-type spores of B. subtilis made at lower temperatures were more sensitive to the DNA damaging chemicals formaldehyde and nitrous acid than were spores made at higher temperatures, but this was not the case with the DNA alkylating agents ethylmethanesulphonate and methylmethanesulphonate. Spores lacking most DNA protective alpha/beta-type small, acid-soluble proteins (termed alpha-beta- spores) made at lower temperatures were also more sensitive to killing through DNA damage by hydrogen peroxide than were alpha-beta- spores made at higher temperatures. The spore coat, whose composition varies significantly with sporulation temperature, played only a minor role in spore resistance to these DNA damaging agents. Spores made at lower temperatures exhibited higher permeability to the methylamine and germinated more rapidly with the surfactant dodecylamine than did spores made at higher temperatures. Treatment of spores with the oxidizing agent cumene hydroperoxide sensitized the surviving spores to all these DNA damaging agents. The fatty acid composition of the inner membrane of spores made at different temperatures differed significantly, but levels of unsaturated fatty acids in the inner membrane did not influence spore resistance to DNA damaging agents or the sensitization to such agents by prior treatment with cumene hydroperoxide.

CONCLUSIONS

The higher rates of methylamine permeation across the inner membrane of spores made at lower temperatures and the greater sensitivity of wild-type spores made at lower temperatures to formaldehyde and nitrous acid and of alpha-beta- spores made at lower temperatures to hydrogen peroxide, all agents that must pass through the spore's inner membrane to damage DNA in the spore core, suggest that the permeability of the inner membrane is a significant factor influencing spore sensitivity to these agents. The sensitization of spores to DNA damaging chemicals by pretreatment with an oxidizing agent, a treatment that increases the permeability of the spore's inner membrane, and the more rapid dodecylamine germination of spores made at lower temperatures are consistent with this suggestion.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results in this communication provide new insight into the factors that influence the resistance of spores of Bacillus species to chemicals that kill spores by damaging spore DNA.

Treatment with oxidizing agents damages the inner membrane of spores of Bacillus subtilis and sensitizes spores to subsequent stress

AIMS

To determine if treatment of Bacillus subtilis spores with a variety of oxidizing agents causes damage to the spore's inner membrane.

METHODS AND RESULTS

Spores of B. subtilis were killed 80-99% with wet heat or a variety of oxidizing agents, including betadine, chlorine dioxide, cumene hydroperoxide, hydrogen peroxide, Oxone, ozone, sodium hypochlorite and t-butylhydroperoxide, and the agents neutralized and/or removed. Survivors of spores pretreated with oxidizing agents exhibited increased sensitivity to killing by a normally minimal lethal heat treatment, while spores pretreated with wet heat did not. In addition, spores treated with wet heat or the oxidizing agents, except sodium hypochlorite, were more sensitive to high NaCl in plating media than were untreated spores. The core region of spores treated with at least two oxidizing agents was also penetrated much more readily by methylamine than was the core of untreated spores, and spores treated with oxidizing agents but not wet heat germinated faster with dodecylamine than did untreated spores. Spores of strains with very different levels of unsaturated fatty acids in their inner membrane exhibited essentially identical resistance to oxidizing agents.

CONCLUSIONS

Treatment of spores with oxidizing agents has been suggested to cause damage to the spore's inner membrane, a membrane whose integrity is essential for spore viability. The sensitization of spores to killing by heat and to high salt after pretreatment with oxidizing agents is consistent with and supports this suggestion. Presumably mild pretreatment with oxidizing agents causes some damage to the spore's inner membrane. While this damage may not be lethal under normal conditions, the damaged inner membrane may be less able to maintain its integrity, when dormant spores are exposed to high temperature or when germinated spores are faced with osmotic stress. Triggering of spore germination by dodecylamine likely involves action by this agent on the spore's inner membrane allowing release of the spore core's depot of dipicolinic acid. Presumably dodecylamine more readily alters the permeability of a damaged inner membrane and thus more readily triggers germination of spores pretreated with oxidizing agents. Damage to the inner spore membrane by oxidizing agents is also consistent with the more rapid penetration of methylamine into the core of treated spores, as the inner membrane is likely the crucial permeability barrier to methylamine entry into the spore core. As spores of strains with very different levels of unsaturated fatty acids in their inner membrane exhibited essentially identical resistance to oxidizing agents, it is not through oxidation of unsaturated fatty acids that oxidizing agents kill and/or damage spores. Perhaps these agents work by causing oxidative damage to key proteins in the spore's inner membrane.

SIGNIFICANCE AND IMPACT OF THE STUDY

The more rapid heat killing and germination with dodecylamine, the greater permeability of the spore core and the osmotic stress sensitivity in outgrowth of spores pretreated with oxidizing agents is consistent with such agents causing damage to the spore's inner membrane, even if this damage is not lethal under normal conditions. It may be possible to take advantage of this phenomenon to devise improved, less costly regimens for spore inactivation.

Killing of Bacillus subtilis spores by a modified Fenton reagent containing CuCl2 and ascorbic acid

Bacillus subtilis spores were killed by CuCl(2)-ascorbic acid, chloride ions were essential for killing of spores, and spores with defective coats were killed more rapidly. CuCl(2)-ascorbic acid did not damage spore DNA, and spores killed by this reagent initiated germination. However, spores killed by CuCl(2)-ascorbic acid may have damage to their inner membrane.

Mechanisms of Bacillus subtilis spore resistance to and killing by aqueous ozone

AIMS

To determine the mechanisms of Bacillus subtilis spore killing by and resistance to aqueous ozone.

METHODS AND RESULTS

Killing of B. subtilis spores by aqueous ozone was not due to damage to the spore's DNA, as wild-type spores were not mutagenized by ozone and wild-type and recA spores exhibited very similar ozone sensitivity. Spores (termed alpha-beta-) lacking the two major DNA protective alpha/beta-type small, acid-soluble spore proteins exhibited decreased ozone resistance but were also not mutagenized by ozone, and alpha-beta- and alpha-beta-recA spores exhibited identical ozone sensitivity. Killing of spores by ozone was greatly increased if spores were chemically decoated or carried a mutation in a gene encoding a protein essential for assembly of the spore coat. Ozone killing did not cause release of the spore core's large depot of dipicolinic acid (DPA), but these killed spores released all of their DPA after a subsequent normally sublethal heat treatment and also released DPA much more readily when germinated in dodecylamine than did untreated spores. However, ozone-killed spores did not germinate with either nutrients or Ca(2+)-DPA and could not be recovered by lysozyme treatment.

CONCLUSIONS

Ozone does not kill spores by DNA damage, and the major factor in spore resistance to this agent appears to be the spore coat. Spore killing by ozone seems to render the spores defective in germination, perhaps because of damage to the spore's inner membrane.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results provide information on the mechanisms of spore killing by and resistance to ozone.

Mechanisms of killing of Bacillus subtilis spores by Decon and OxoneTM, two general decontaminants for biological agents

AIMS

To determine the mechanisms of Bacillus subtilis spore killing by and resistance to the general biological decontamination agents, Decon and Oxone.

METHODS AND RESULTS

Spores of B. subtilis treated with Decon or Oxone did not accumulate DNA damage and were not mutagenized. Spore killing by these agents was increased if spores were decoated. Spores prepared at higher temperatures were more resistant to these agents, consistent with a major role for spore coats in this resistance. Neither Decon nor Oxone released the spore core's depot of dipicolinic acid (DPA), but Decon- and Oxone-treated spores more readily released DPA upon a subsequent normally sublethal heat treatment. Decon- and Oxone-killed spores initiated germination with dodecylamine more rapidly than untreated spores, but could not complete germination triggered by nutrients or Ca(2+)-DPA and did not degrade their peptidoglycan cortex. However, lysozyme treatment did not recover these spores.

CONCLUSIONS

Decon and Oxone do not kill B. subtilis spores by DNA damage, and a major factor in spore resistance to these agents is the spore coat. Spore killing by both agents renders spores defective in germination, possibly because of damage to the inner membrane of spore.

SIGNIFICANCE AND IMPACT OF STUDY

These results provide information on the mechanisms of the killing of bacterial spores by Decon and Oxone.

Mechanisms of killing of Bacillus subtilis spores by hypochlorite and chlorine dioxide

AIMS

To determine the mechanisms of Bacillus subtilis spore killing by hypochlorite and chlorine dioxide, and its resistance against them.

METHODS AND RESULTS

Spores of B. subtilis treated with hypochlorite or chlorine dioxide did not accumulate damage to their DNA, as spores with or without the two major DNA protective alpha/beta-type small, acid soluble spore proteins exhibited similar sensitivity to these chemicals; these agents also did not cause spore mutagenesis and their efficacy in spore killing was not increased by the absence of a major DNA repair pathway. Spore killing by these two chemicals was greatly increased if spores were first chemically decoated or if spores carried a mutation in a gene encoding a protein essential for assembly of many spore coat proteins. Spores prepared at a higher temperature were also much more resistant to these agents. Neither hypochlorite nor chlorine dioxide treatment caused release of the spore core's large depot of dipicolinic acid (DPA), but hypochlorite- and chlorine dioxide-treated spores much more readily released DPA upon a subsequent normally sub-lethal heat treatment than did untreated spores. Hypochlorite-killed spores could not initiate the germination process with either nutrients or a 1 : 1 chelate of Ca2+-DPA, and these spores could not be recovered by lysozyme treatment. Chlorine dioxide-treated spores also did not germinate with Ca2+-DPA and could not be recovered by lysozyme treatment, but did germinate with nutrients. However, while germinated chlorine dioxide-killed spores released DPA and degraded their peptidoglycan cortex, they did not initiate metabolism and many of these germinated spores were dead as determined by a viability stain that discriminates live cells from dead ones on the basis of their permeability properties.

CONCLUSIONS

Hypochlorite and chlorine dioxide do not kill B. subtilis spores by DNA damage, and a major factor in spore resistance to these agents appears to be the spore coat. Spore killing by hypochlorite appears to render spores defective in germination, possibly because of severe damage to the spore's inner membrane. While chlorine dioxide-killed spores can undergo the initial steps in spore germination, these germinated spores can go no further in this process probably because of some type of membrane damage.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results provide information on the mechanisms of the killing of bacterial spores by hypochlorite and chlorine dioxide.

Disinfection of water containing natural organic matter by using ozone-initiated radical reactions

Ozone is widely used to disinfect drinking water and wastewater due to its strong biocidal oxidizing properties. Recently, it was reported that hydroxyl radicals ((.)OH), resulting from ozone decomposition, play a significant role in microbial inactivation when Bacillus subtilis endospores were used as the test microorganisms in pH controlled distilled water. However, it is not yet known how natural organic matter (NOM), which is ubiquitous in sources of drinking water, affects this process of disinfection by ozone-initiated radical reactions. Two types of water matrix were considered for this study. One is water containing humic acid, which is commercially available. The other is water from the Han River. This study reported that hydroxyl radicals, initiated by the ozone chain reaction, were significantly effective at B. subtilis endospore inactivation in water containing NOM, as well as in pH-controlled distilled water. The type of NOM and the pH have a considerable effect on the percentage of disinfection by hydroxyl radicals, which ranged from 20 to 50%. In addition, the theoretical T value of hydroxyl radicals for 2-log B. subtilis removal was estimated to be about 2.4 x 10(4) times smaller than that of ozone, assuming that there is no synergistic activity between ozone and hydroxyl radicals.

The effect of acid shock on sporulating Bacillus subtilis cells

AIMS

To study the effect of acid shock in sporulation on the production of acid-shock proteins, and on the heat resistance and germination characteristics of the spores formed subsequently.

METHODS AND RESULTS

Bacillus subtilis wild-type (SASP-alpha+beta+) and mutant (SASP-alpha-beta-) cells in 2 x SG medium at 30 degrees C were acid-shocked with HCl (pH 4, 4.3, 5 and 6 against a control pH of 6.2) for 30 min, 1 h into sporulation. The D85-value of B. subtilis wild-type (but not mutant) spores formed from sporulating cells acid-shocked at pH 5 increased from 46.5 min to 78.8 min, and there was also an increase in the resistance of wild-type acid-shocked spores at both 90 degrees C and 95 degrees C. ALA- or AGFK-initiated germination of pH 5-shocked spores was the same as that of non-acid-shocked spores. Two-dimensional gel electrophoresis showed only one novel acid-shock protein, identified as a vegetative catalase 1 (KatA), which appeared 30 min after acid shock but was lost later in sporulation.

CONCLUSIONS

Acid shock at pH 5 increased the heat resistance of spores subsequently formed in B. subtilis wild type. The catalase, KatA, was induced by acid shock early in sporulation, but since it was degraded later in sporulation, it appears to act to increase heat resistance by altering spore structure.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first proteomic study of acid shock in sporulating B. subtilis cells. The increasing spore heat resistance produced by acid shock may have significance for the heat resistance of spores formed in the food industry.

Luminometric and differential scanning calorimetry (DSC) studies on heat- and radiation inactivation of Bacillus subtilis luxAB spores

A bioluminescent derivative of Bacillus subtilis containing a plasmid encoding a luxAB fusion under control of a vegetative promoter and gives bioluminescence upon addition of an exogenous long-chain aldehyde has been used as test organism. Its spore populations have been produced and their heat- and radiation survival curves established. Heat-sensitization effect of pre-irradiation of spores was proven not only by colony counting but also with differential scanning calorimetry. Under a linearly programmed temperature increase, the heat destruction of spores surviving 2.5 kGy gamma irradiation resulted in at a few centigrade lower temperature than that of untreated spores. Heat denaturation endotherms in the DSC-thermogram of irradiated spores were shifted to lower temperatures as well. Comparative turbidimetric, luminometric and phase-contrast microscopic studies of untreated, heat-treated and irradiated spore populations showed that the kinetics of germination and the light emission during germination of radiation-inactivated spores were the same as those of untreated spores, revealing that the pre-formed luciferase enzyme packaged into the spores during sporulation remained intact after an irradiation dose causing 90% decrease in number of colony forming spores. Therefore, in contrast to heat-treated spores, the initial bioluminescence reading upon germination of irradiated spores does not reflect the viable count of their population.

Studies on the mechanism of killing of Bacillus subtilis spores by hydrogen peroxide

AIMS

To determine the mechanism of killing of Bacillus subtilis spores by hydrogen peroxide.

METHODS AND RESULTS

Killing of spores of B. subtilis with hydrogen peroxide caused no release of dipicolinic acid (DPA) and hydrogen peroxide-killed spores were not appreciably sensitized for DPA release upon a subsequent heat treatment. Hydrogen peroxide-killed spores appeared to initiate germination normally, released DPA and hydrolysed significant amounts of their cortex. However, the germinated killed spores did not swell, did not accumulate ATP or reduced flavin mononucleotide and the cores of these germinated spores were not accessible to nucleic acid stains.

CONCLUSIONS

These data indicate that treatment with hydrogen peroxide results in spores in which the core cannot swell properly during spore germination.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results provide further information on the mechanism of killing of spores of Bacillus species by hydrogen peroxide.

Analysis of the properties of spores of Bacillus subtilis prepared at different temperatures

AIMS

To determine the effect of sporulation temperature on Bacillus subtilis spore resistance and spore composition.

METHODS AND RESULTS

Bacillus subtilis spores prepared at temperatures from 22 to 48 degrees C had identical amounts of dipicolinic acid and small, acid-soluble proteins but the core water content was lower in spores prepared at higher temperatures. As expected from this latter finding, spores prepared at higher temperatures were more resistant to wet heat than were spores prepared at lower temperatures. Spores prepared at higher temperatures were also more resistant to hydrogen peroxide, Betadine, formaldehyde, glutaraldehyde and a superoxidized water, Sterilox. However, spores prepared at high and low temperatures exhibited nearly identical resistance to u.v. radiation and dry heat. The cortex peptidoglycan in spores prepared at different temperatures showed very little difference in structure with only a small, albeit significant, increase in the percentage of muramic acid with a crosslink in spores prepared at higher temperatures. In contrast, there were readily detectable differences in the levels of coat proteins in spores prepared at different temperatures and the levels of at least one coat protein, CotA, fell significantly as the sporulation temperature increased. However, this latter change was not due to a reduction in cotA gene expression at higher temperatures.

CONCLUSIONS

The temperature of sporulation affects a number of spore properties, including resistance to many different stress factors, and also results in significant alterations in the spore coat and cortex composition.

SIGNIFICANCE AND IMPACT OF THE STUDY

The precise conditions for the formation of B. subtilis spores have a large effect on many spore properties.

Base-change mutations induced by various treatments of Bacillus subtilis spores with and without DNA protective small, acid-soluble spore proteins

Previous work has shown that spores of wild-type Bacillus subtilis are more resistant to killing by dry and wet heat, low vacuum lyophilization and hydrogen peroxide than are spores lacking the majority of their DNA protective alpha/beta-type small, acid-soluble spore proteins (SASP) (termed alpha(-)beta(-) spores). These four treatments kill alpha(-)beta(-) spores in large part by DNA damage with accompanying mutagenesis, but only dry heat kills wild-type spores by DNA damage and mutagenesis. DNA sequence analysis of nalidixic acid-resistant (nal(r)) mutants generated by these treatments has now shown that the nal(r) mutations are base changes in the gyrA gene that encodes one subunit of DNA gyrase. Analysis of the DNA sequence of the gyrA gene in a large number of nal(r) mutants also indicates that: (1) base changes induced by hydrogen peroxide and wet heat in alpha(-)beta(-) spores are similar to those in spontaneous nal(r) mutants with only a few notable differences; (2) base changes induced by dry heat in wild-type spores and low vacuum lyophilization of alpha(-)beta(-) spores are similar, and include a high level of a tandem base change seen previously only in spores treated with very high vacuum and (3) base changes induced by lyophilization and dry heat are very different from those in spontaneous mutants in wild-type and alpha(-)beta(-) spores, which exhibit only one significant difference. While the initial DNA damage generated in spores by dry heat, lyophilization or high vacuum is almost certainly different than that generated by hydrogen peroxide or wet heat, the precise nature of the DNA damage remains to be determined.

Differential efficacy of a chlorine dioxide-containing sanitizer against single species and binary biofilms of a dairy-associated Bacillus cereus and a Pseudomonas fluorescens isolate

AIMS

Daily exposure to 100 p.p.m. chlorine dioxide of single species and binary biofilms of dairy-associated Bacillus cereus DL5 and Pseudomonas fluorescens M2, attached to stainless steel surfaces in a laboratory flow system, was studied.

METHODS AND RESULTS

Surfaces were sampled daily before and after sanitizer treatment and cells and spores dislodged and enumerated by standard methods. Duplicate surfaces were prepared for confocal scanning laser microscopy (CSLM) and scanning electron microscopy. Higher counts of Ps. fluorescens M2 were obtained in single species biofilms, microcolonies stained green (viable) in CSLM images and were closely packed on attachment surfaces. By contrast, higher counts of B. cereus DL5 were obtained in binary biofilms, microcolonies stained green in CSLM images, but were more spread out. Lower spore counts were obtained for B. cereus DL5 in binary biofilms. The survival of Ps. fluorescens M2 cells after exposure to chlorine dioxide was apparently enhanced by the presence of B. cereus DL5 in binary biofilms. By contrast, B. cereus DL5 showed increased susceptibility to sanitizer treatment in the presence of Ps. fluorescens M2.

CONCLUSIONS

Co-cultured bacteria in biofilms influence each other with respect to attachment capabilities and sanitizer resistance/susceptibility.

SIGNIFICANCE AND IMPACT OF THE STUDY

Binary biofilms endemic in food-processing industries can survive sanitation regimes and may represent reservoirs of product contamination leading to subsequent spoilage and/or food safety risks.

Sporicidal action of ozone and hydrogen peroxide: a comparative study

Elimination of contaminating spores on packaging materials and food-contact surfaces remains a challenge to the food industry. Hydrogen peroxide and chlorine are the most commonly used sanitizers to eliminate these contaminants, and ozone was recommended recently as an alternative. Hence, we compared the sporicidal action of ozone and hydrogen peroxide against selected foodborne spores of Bacillus spp. Under identical treatment conditions, 11 microg/ml aqueous ozone decreased spore counts by 1.3 to 6.1 log10 cfu/ml depending upon the bacterial species tested. Hydrogen peroxide (10%, w/w), produced only 0.32 to 1.6 log10 cfu/ml reductions in spore counts. Thus, hydrogen peroxide, at approximately 10,000-fold higher concentration, was less effective than ozone against Bacillus spores. Resistance of spores to ozone was highest for Bacillus stearothermophilus and lowest for B. cereus. Therefore, spores of B. stearothermophilus are suitable for testing the efficacy of sanitization by ozone. Electron microscopic study of ozone-treated B. subtilis spores suggests the outer spore coat layers as a probable site of action of ozone.

An alpha/beta-type, small, acid-soluble spore protein which has very high affinity for DNA prevents outgrowth of Bacillus subtilis spores

A derivative of SspC, a minor alpha/beta-type, small, acid-soluble spore protein (SASP) from Bacillus subtilis, was generated that has a very high affinity for DNA. This protein (SspC(Delta11-D13K)) was able to confer UV resistance on spores lacking alpha/beta-type SASP, and spores with SspC(Delta11-D13K) triggered germination normally. However, SspC(Delta11-D13K) blocked outgrowth of > or = 90% of germinated spores, and SspC(Delta11-D13K) persisted in these germinated spores, whereas wild-type SspC was almost completely degraded. The outgrowth phenotype of spores with SspC(Delta11-D13K) is proposed to be due to the high stability of the SspC(Delta11-D13K)-DNA complex, which prevents rapid degradation of this alpha/beta-type SASP early in germination. The persistence of this protein on spore DNA then interferes with transcription during spore outgrowth.

Equilibrium and kinetic binding interactions between DNA and a group of novel, nonspecific DNA-binding proteins from spores of Bacillus and Clostridium species

Binding of alpha/beta-type small acid-soluble spore proteins (SASP) is the major determinant of DNA resistance to damage caused by UV radiation, heat, and oxidizing agents in spores of Bacillus and Clostridium species. Analysis of several alpha/beta-type SASP showed that these proteins have essentially no secondary structure in the absence of DNA, but become significantly alpha-helical upon binding to double-stranded DNAs or oligonucleotides. Folding of alpha/beta-type SASP induced by a variety of DNAs and oligonucleotides was measured by CD spectroscopy, and this allowed determination of a DNA binding site size of 4 base pairs as well as equilibrium binding parameters of the alpha/beta-type SASP-DNA interaction. Analysis of the equilibrium binding data further allowed determination of both intrinsic binding constants (K) and cooperativity factors (omega), as the alpha/beta-type SASP-DNA interaction was significantly cooperative, with the degree of cooperativity depending on both the bound DNA and the salt concentration. Kinetic analysis of the interaction of one alpha/beta-type SASP, SspC(Tyr), with DNA indicated that each binding event involves the dimerization of SspC(Tyr) monomers at a DNA binding site. The implications of these findings for the structure of the alpha/beta-type SASP.DNA complex and the physiology of alpha/beta-type SASP degradation during spore germination are discussed.

Method to sensitize bacterial spores to subsequent killing by dry heat or ultraviolet irradiation

Hydrogen peroxide and ultraviolet irradiation are known to interact synergistically for killing of bacterial spores. Synergy could be demonstrated with spores of Bacillus megaterium ATCC19213 adsorbed to filter paper strips or glass coverslips treated first with the peroxide and then dried for as long as 48 h prior to UV irradiation. This delayed action was considered to be due to absorption of the peroxide by the spores in an active but not readily vaporized form, which could become sporicidal also if the spores were heated to 50 degrees C. B. megaterium spores mixed with 0.1% (32.6 mM) H(2)O(2) solution appeared to absorb as much as 15 micromol/mg dry weight or about 0.5 mg/mg, but only a third to half of the peroxide could be recovered by water washing. A part of the unrecovered peroxide was degraded in reactions resulting in measurable production of oxygen. Degradation was not reduced by heating the spores to 65 degrees C or by azide and so appeared to be non-enzymatic. Spores of the anaerobe Clostridium sporogenes were also sensitized to ultraviolet killing by H(2)O(2) treatment followed by drying. They appear to absorb less peroxide, only about 2 micromol/mg, but had lower capacities to degrade H(2)O(2) so that nearly all of the peroxide could be recovered by washing with water. The findings presented should be helpful in the design of new methods for synergistic killing of spores by H(2)O(2) and UV irradiation or dry heat, especially involving, for example, packaging materials.

Characterization of spores of Bacillus subtilis which lack dipicolinic acid

Spores of Bacillus subtilis with a mutation in spoVF cannot synthesize dipicolinic acid (DPA) and are too unstable to be purified and studied in detail. However, the spores of a strain lacking the three major germinant receptors (termed Deltager3), as well as spoVF, can be isolated, although they spontaneously germinate much more readily than Deltager3 spores. The Deltager3 spoVF spores lack DPA and have higher levels of core water than Deltager3 spores, although sporulation with DPA restores close to normal levels of DPA and core water to Deltager3 spoVF spores. The DPA-less spores have normal cortical and coat layers, as observed with an electron microscope, but their core region appears to be more hydrated than that of spores with DPA. The Deltager3 spoVF spores also contain minimal levels of the processed active form (termed P(41)) of the germination protease, GPR, a finding consistent with the known requirement for DPA and dehydration for GPR autoprocessing. However, any P(41) formed in Deltager3 spoVF spores may be at least transiently active on one of this protease's small acid-soluble spore protein (SASP) substrates, SASP-gamma. Analysis of the resistance of wild-type, Deltager3, and Deltager3 spoVF spores to various agents led to the following conclusions: (i) DPA and core water content play no role in spore resistance to dry heat, dessication, or glutaraldehyde; (ii) an elevated core water content is associated with decreased spore resistance to wet heat, hydrogen peroxide, formaldehyde, and the iodine-based disinfectant Betadine; (iii) the absence of DPA increases spore resistance to UV radiation; and (iv) wild-type spores are more resistant than Deltager3 spores to Betadine and glutaraldehyde. These results are discussed in view of current models of spore resistance and spore germination.

Mechanisms of killing of spores of Bacillus subtilis by iodine, glutaraldehyde and nitrous acid

Treatment of wild-type spores of Bacillus subtilis with glutaraldehyde or an iodine-based disinfectant (Betadine) did not cause detectable mutagenesis, and spores (termed alpha-beta-) lacking the major DNA-protective alpha/beta-type, small, acid-soluble proteins (SASP) exhibited similar sensitivity to these agents. A recA mutation did not sensitize wild-type or alpha-beta- spores to Betadine or glutaraldehyde, nor did spore treatment with these agents result in significant expression of a recA-lacZ fusion when the treated spores germinated. Spore glutaraldehyde sensitivity was increased dramatically by removal of much spore coat protein, but this treatment had no effect on Betadine sensitivity. In contrast, nitrous acid treatment of wild-type and alpha-beta- spores caused significant mutagenesis, with alpha-beta- spores being much more sensitive to this agent. A recA mutation further sensitized both wild-type and alpha-beta- spores to nitrous acid, and there was significant expression of a recA-lacZ fusion when nitrous acid-treated spores germinated. These results indicate that: (a) nitrous acid kills B. subtilis spores at least in part by DNA damage, and alpha/beta-type SASP protect against this DNA damage; (b) killing of spores by glutaraldehyde or Betadine is not due to DNA damage; and (c) the spore coat protects spores against killing by glutaraldehyde but not Betadine. Further analysis also demonstrated that spores treated with nitrous acid still germinated normally, while those treated with glutaraldehyde or Betadine did not.

Role of the spore coat layers in Bacillus subtilis spore resistance to hydrogen peroxide, artificial UV-C, UV-B, and solar UV radiation

Spores of Bacillus subtilis possess a thick protein coat that consists of an electron-dense outer coat layer and a lamellalike inner coat layer. The spore coat has been shown to confer resistance to lysozyme and other sporicidal substances. In this study, spore coat-defective mutants of B. subtilis (containing the gerE36 and/or cotE::cat mutation) were used to study the relative contributions of spore coat layers to spore resistance to hydrogen peroxide (H(2)O(2)) and various artificial and solar UV treatments. Spores of strains carrying mutations in gerE and/or cotE were very sensitive to lysozyme and to 5% H(2)O(2), as were chemically decoated spores of the wild-type parental strain. Spores of all coat-defective strains were as resistant to 254-nm UV-C radiation as wild-type spores were. Spores possessing the gerE36 mutation were significantly more sensitive to artificial UV-B and solar UV radiation than wild-type spores were. In contrast, spores of strains possessing the cotE::cat mutation were significantly more resistant to all of the UV treatments used than wild-type spores were. Spores of strains carrying both the gerE36 and cotE::cat mutations behaved like gerE36 mutant spores. Our results indicate that the spore coat, particularly the inner coat layer, plays a role in spore resistance to environmentally relevant UV wavelengths.

Formaldehyde kills spores of Bacillus subtilis by DNA damage and small, acid-soluble spore proteins of the alpha/beta-type protect spores against this DNA damage

Killing of wild-type spores of Bacillus subtilis with formaldehyde also caused significant mutagenesis; spores (termed alpha-beta-) lacking the two major alpha/beta-type small, acid-soluble spore proteins (SASP) were more sensitive to both formaldehyde killing and mutagenesis. A recA mutation sensitized both wild-type and alpha-beta- spores to formaldehyde treatment, which caused significant expression of a recA-lacZ fusion when the treated spores germinated. Formaldehyde also caused protein-DNA cross-linking in both wild-type and alpha-beta- spores. These results indicate that: (i) formaldehyde kills B. subtilis spores at least in part by DNA damage and (b) alpha/beta-type SASP protect against spore killing by formaldehyde, presumably by protecting spore DNA.

Structural studies of a novel germination protease from spores of Bacillus megaterium

The amino acid sequence-specific protease (termed GPR) in the bacterium Bacillus megaterium initiates the rapid degradation of small, acid-soluble spore proteins during the germination of spores of this organism. GPR is synthesized during spore formation as an inactive zymogen termed P46, which later autoprocesses to a smaller active form termed P41, which acts during spore germination. However, GPR exhibits no obvious mechanistic or amino acid sequence similarity to any of the known classes of proteases. To initiate the determination of the mechanisms of P46 to P41 conversion, P46 inactivity, and P41 catalysis, B. megaterium GPR has been overexpressed in Escherichia coli and purified to homogeneity by anion-exchange and size exclusion chromatography, and crystals of both P46 and P41 have been obtained by the vapor diffusion method. P46 crystals diffracted x rays to 3.5 A but the crystals of P41 diffracted x rays to only 6.5 A. A native x-ray diffraction data set of P46 has been collected; the unit cell parameters are a = b = 76.8, c = 313.1 A, alpha = beta = gamma = 90 degrees; the space group is tetragonal P41212 or P43212. The asymmetric unit contains two monomeric molecules with a crystal volume per unit protein mass of 2. 85 A3/Da and a solvent content of about 57%. An isomorphous heavy atom derivative data set has also been obtained for P46 crystals with potassium dicyanoaurate (I).

Antiseptics and disinfectants: activity, action, and resistance

Antiseptics and disinfectants are extensively used in hospitals and other health care settings for a variety of topical and hard-surface applications. A wide variety of active chemical agents (biocides) are found in these products, many of which have been used for hundreds of years, including alcohols, phenols, iodine, and chlorine. Most of these active agents demonstrate broad-spectrum antimicrobial activity; however, little is known about the mode of action of these agents in comparison to antibiotics. This review considers what is known about the mode of action and spectrum of activity of antiseptics and disinfectants. The widespread use of these products has prompted some speculation on the development of microbial resistance, in particular whether antibiotic resistance is induced by antiseptics or disinfectants. Known mechanisms of microbial resistance (both intrinsic and acquired) to biocides are reviewed, with emphasis on the clinical implications of these reports.

Structure and mechanism of action of the protease that degrades small, acid-soluble spore proteins during germination of spores of Bacillus species

The germination protease (GPR) of Bacillus megaterium initiates the degradation of small, acid-soluble proteins during spore germination. Trypsin treatment of the 46-kDa GPR zymogen (termed P46) removes an approximately 15-kDa C-terminal domain generating a 30-kDa species (P30) which is stable against further digestion. While P30 is not active, it does autoprocess to a smaller form by cleavage of the same bond cleaved in conversion of P46 to the active 41-kDa form of GPR (P41). Trypsin treatment of P41 cleaves the same bond in the C-terminal part of the protein as is cleaved in the P46-->P30 conversion. While the approximately 29-kDa species generated by trypsin treatment of P41 is active, it is rapidly degraded further by trypsin to small inactive fragments. These results, as well as a thermal melting temperature for P41 which is 13 degreesC lower than that for P46 and the unfolding of P41 at significantly lower concentrations of guanidine hydrochloride than for P46, are further evidence for a difference in tertiary structure between P46 and P41, with P46 presumably having a more compact stable structure. However, circular dichroism spectroscopy revealed no significant difference in the secondary structure content of P46 and P41. The removal of approximately 30% of P46 or P41 without significant loss in enzyme activity localized GPR's catalytic residues to the N-terminal two-thirds of the molecule. This finding, as well as comparison of the amino acid sequences of GPR from three different species, analysis of several site-directed GPR mutants, determination of the metal ion content of purified GPR, and lack of inhibition of P41 by a number of protease inhibitors, suggests that GPR is not a member of a previously described class of protease.

Heat killing of Bacillus subtilis spores in water is not due to oxidative damage

The heat resistance of wild-type spores of Bacillus subtilis or spores (termed alpha-beta-) lacking DNA protective alpha/beta-type small, acid-soluble spore proteins was not altered by anaerobiosis or high concentrations of the free radical scavenging agents ethanethiol and ethanedithiol. Heat-killed wild-type and alpha-beta- spores exhibited no increase in either protein carbonyl content or oxidized bases in DNA. These data strongly suggest that oxidative damage to spore macromolecules does not contribute significantly to spore killing by heat.

Comparative study of pressure-induced germination of Bacillus subtilis spores at low and high pressures

We have studied pressure-induced germination of Bacillus subtilis spores at moderate (100 MPa) and high (500 to 600 MPa) pressures. Although we found comparable germination efficiencies under both conditions by using heat sensitivity as a criterion for germination, the sensitivity of pressure-germinated spores to some other agents was found to depend on the pressure used. Spores germinated at 100 MPa were more sensitive to pressure (>200 MPa), UV light, and hydrogen peroxide than were those germinated at 600 MPa. Since small, acid-soluble proteins (SASPs) and dipicolinic acid (DPA) are known to be involved in spore resistance to UV light and hydrogen peroxide, we studied the fate of these compounds during pressure germination. DPA was released upon both low- and high-pressure germination, but SASP degradation, which normally accompanies nutrient-induced germination, occurred upon low-pressure germination but not upon high-pressure germination. These results adequately explain the UV and hydrogen peroxide resistance of spores germinated at 600 MPa. The resistance to pressure inactivation of 600-MPa-germinated spores could also, at least partly, be attributed to alpha/beta-type SASPs, since mutants deficient in alpha/beta-type SASPs were more sensitive to inactivation at 600 MPa. Further, germination at 100 MPa resulted in rapid ATP generation, as is the case in nutrient-induced germination, but no ATP was formed during germination at 600 MPa. These results suggest that spore germination can be initiated by low- and high-pressure treatments but is arrested at an early stage in the latter case. The implications for the use of high pressure as a preservation treatment are discussed.

Small, Acid-Soluble Spore Proteins of the alpha/beta Type Do Not Protect the DNA in Bacillus subtilis Spores against Base Alkylation

Ethyl methanesulfonate (EMS) killed wild-type Bacillus subtilis spores as rapidly as spores lacking small, acid-soluble proteins (SASP) of the alpha/beta type (alpha-beta- spores), and 20% of the survivors had obvious mutations. A recA mutation increased the EMS sensitivity of wild-type and alpha-beta- spores similarly but reduced their mutagenesis; EMS treatment of dormant spores also resulted in the induction of RecA synthesis during spore germination. EMS generated similar levels of alkylated bases in wild-type and alpha-beta- spore DNAs, in purified DNA, or in DNA saturated with alpha/beta-type SASP. Ethylene oxide (EtO) also generated similar levels of base alkylation in wild-type and alpha-beta- spore DNAs. These data indicate that EMS and EtO kill spores at least in part by DNA damage but that alpha/beta-type SASP, which protect DNA against many types of damage, do not protect spore DNA from base alkylation.