Transcriptional Profile during Deoxycholate-Induced Sporulation in a Clostridium perfringens Isolate Causing Foodborne Illness

Potent Bile Acid Microbial Metabolites Modulate Clostridium perfringens Virulence

Clostridium perfringens is a versatile pathogen, inducing diseases in the skin, intestine (such as chicken necrotic enteritis (NE)), and other organs. The classical sign of NE is the foul smell gas in the ballooned small intestine. We hypothesized that deoxycholic acid (DCA) reduced NE by inhibiting C. perfringens virulence signaling pathways. To evaluate the hypothesis, C. perfringens strains CP1 and wild-type (WT) HN13 and its mutants were cultured with different bile acids, including DCA and isoallolithocholic acid (isoalloLCA). Growth, hydrogen sulfide (H2S) production, and virulence gene expression were measured. Notably, isoalloLCA was more potent in reducing growth, H2S production, and virulence gene expression in CP1 and WT HN13 compared to DCA, while other bile acids were less potent compared to DCA. Interestingly, there was a slightly different impact between DCA and isoalloLCA on the growth, H2S production, and virulence gene expression in the three HN13 mutants, suggesting possibly different signaling pathways modulated by the two bile acids. In conclusion, DCA and isoalloLCA reduced C. perfringens virulence by transcriptionally modulating the pathogen signaling pathways. The findings could be used to design new strategies to prevent and treat C. perfringens-induced diseases.

Epigallocatechin gallate and Lactobacillus plantarum culture supernatants exert bactericidal activity and reduce biofilm formation in Clostridium perfringens

Clostridium perfringens forms biofilms and spores that are a source of food contamination. In this study, the antibacterial activities of Lactobacillus plantarum culture supernatants (LP-S), LP-S fractions, and the plant-derived compound epigallocatechin gallate (EG) were evaluated. Specifically, their effects on the viability and biofilm-forming ability of C. perfringens were assessed. Moreover, the expression of quorum sensing-regulated genes associated with the pathogenesis of this microorganism and that of genes involved in biofilm formation was also investigated. The results showed that both EG and the LP-S exerted bactericidal activity against all C. perfringens strains tested. The minimal bactericidal concentration (MBC) of EG was 75 µg/mL for all strains but ranged from 61 to 121 µg of total protein per mL for LP-S. EG exerted only minor effects on biofilm formation, whereas LP-S, particularly its 10 and 30 K fractions, significantly reduced the biofilm-forming ability of all the strains. The antibiofilm activity of LP-S was lost following preincubation with proteases, suggesting that it was mediated by a proteinaceous molecule. The treatment of C. perfringens with either EG or LP-S did not change the transcript levels of two CpAL (C. perfringens quorum-sensing Agr-like system)-related genes, agrB and agrD, which are known to be involved in the regulation of biofilms, suggesting that LP-S exerted its biofilm inhibitory activity downstream of CpAL signaling. In summary, we demonstrated the bactericidal activity of EG and LP-S against C. perfringens and antibiofilm activity of LP-S at a subinhibitory dose. Our results suggested that these compounds can be further explored for food safety applications to control agents such as C. perfringens.

CD25890, a conserved protein that modulates sporulation initiation in Clostridioides difficile

Bacteria that reside in the gastrointestinal tract of healthy humans are essential for our health, sustenance and well-being. About 50-60% of those bacteria have the ability to produce resilient spores that are important for the life cycle in the gut and for host-to-host transmission. A genomic signature for sporulation in the human intestine was recently described, which spans both commensals and pathogens such as Clostridioides difficile and contains several genes of unknown function. We report on the characterization of a signature gene, CD25890, which, as we show is involved in the control of sporulation initiation in C. difficile under certain nutritional conditions. Spo0A is the main regulatory protein controlling entry into sporulation and we show that an in-frame deletion of CD25890 results in increased expression of spo0A per cell and increased sporulation. The effect of CD25890 on spo0A is likely indirect and mediated through repression of the sinRR´ operon. Deletion of the CD25890 gene, however, does not alter the expression of the genes coding for the cytotoxins or the genes involved in biofilm formation. Our results suggest that CD25890 acts to modulate sporulation in response to the nutrients present in the environment.

Foodborne pathogens in the omics era

Outbreaks and deaths related to Foodborne Diseases (FBD) occur constantly in the world, as a result of the consumption of contaminated foodstuffs with pathogens such as Listeria monocytogenes, Escherichia coli, Staphylococcus aureus, Salmonella spp, Clostridium spp. and Campylobacter spp. The purpose of this review is to discuss the main omic techniques applied in foodborne pathogen and to demonstrate their functionalities through the food chain and to guarantee the food safety. The main techniques presented are genomic, transcriptomic, secretomic, proteomic, and metabolomic, which together, in the field of food and nutrition, are known as "Foodomics." This review had highlighted the potential of omics to integrate variables that contribute to food safety and to enable us to understand their application on foodborne diseases. The appropriate use of these techniques had driven the definition of critical parameters to achieve successful results in the improvement of consumers health, costs and to obtain safe and high-quality products.

Berberine alters gut microbial function through modulation of bile acids

BACKGROUND

Berberine (BBR) is a plant-based nutraceutical that has been used for millennia to treat diarrheal infections and in contemporary medicine to improve patient lipid profiles. Reduction in lipids, particularly cholesterol, is achieved partly through up-regulation of bile acid synthesis and excretion into the gastrointestinal tract (GI). The efficacy of BBR is also thought to be dependent on structural and functional alterations of the gut microbiome. However, knowledge of the effects of BBR on gut microbiome communities is currently lacking. Distinguishing indirect effects of BBR on bacteria through altered bile acid profiles is particularly important in understanding how dietary nutraceuticals alter the microbiome.

RESULTS

Germfree mice were colonized with a defined minimal gut bacterial consortium capable of functional bile acid metabolism (Bacteroides vulgatus, Bacteroides uniformis, Parabacteroides distasonis, Bilophila wadsworthia, Clostridium hylemonae, Clostridium hiranonis, Blautia producta; B4PC2). Multi-omics (bile acid metabolomics, 16S rDNA sequencing, cecal metatranscriptomics) were performed in order to provide a simple in vivo model from which to identify network-based correlations between bile acids and bacterial transcripts in the presence and absence of dietary BBR. Significant alterations in network topology and connectivity in function were observed, despite similarity in gut microbial alpha diversity (P = 0.30) and beta-diversity (P = 0.123) between control and BBR treatment. BBR increased cecal bile acid concentrations, (P < 0.05), most notably deoxycholic acid (DCA) (P < 0.001). Overall, analysis of transcriptomes and correlation networks indicates both bacterial species-specific responses to BBR, as well as functional commonalities among species, such as up-regulation of Na+/H+ antiporter, cell wall synthesis/repair, carbohydrate metabolism and amino acid metabolism. Bile acid concentrations in the GI tract increased significantly during BBR treatment and developed extensive correlation networks with expressed genes in the B4PC2 community.

CONCLUSIONS

This work has important implications for interpreting the effects of BBR on structure and function of the complex gut microbiome, which may lead to targeted pharmaceutical interventions aimed to achieve the positive physiological effects previously observed with BBR supplementation.

The Great ESKAPE: Exploring the Crossroads of Bile and Antibiotic Resistance in Bacterial Pathogens

Throughout the course of infection, many pathogens encounter bactericidal conditions that threaten the viability of the bacteria and impede the establishment of infection. Bile is one of the most innately bactericidal compounds present in humans, functioning to reduce the bacterial burden in the gastrointestinal tract while also aiding in digestion. It is becoming increasingly apparent that pathogens successfully resist the bactericidal conditions of bile, including bacteria that do not normally cause gastrointestinal infections. This review highlights the ability of Enterococcus, Staphylococcus, Klebsiella, Acinetobacter, Pseudomonas, Enterobacter (ESKAPE), and other enteric pathogens to resist bile and how these interactions can impact the sensitivity of bacteria to various antimicrobial agents. Given that pathogen exposure to bile is an essential component to gastrointestinal transit that cannot be avoided, understanding how bile resistance mechanisms align with antimicrobial resistance is vital to our ability to develop new, successful therapeutics in an age of widespread and increasing antimicrobial resistance.

The 'in vivo lifestyle' of bile acid 7α-dehydroxylating bacteria: comparative genomics, metatranscriptomic, and bile acid metabolomics analysis of a defined microbial community in gnotobiotic mice

The formation of secondary bile acids by gut microbes is a current topic of considerable biomedical interest. However, a detailed understanding of the biology of anaerobic bacteria in the genus Clostridium that are capable of generating secondary bile acids is lacking. We therefore sought to determine the transcriptional responses of two prominent secondary bile acid producing bacteria, Clostridium hylemonae and Clostridium hiranonis to bile salts (in vitro) and the cecal environment of gnotobiotic mice. The genomes of C. hylemonae DSM 15053 and C. hiranonis DSM 13275 were closed, and found to encode 3,647 genes (3,584 protein-coding) and 2,363 predicted genes (of which 2,239 are protein-coding), respectively, and 1,035 orthologs were shared between C. hylemonae and C. hiranonis. RNA-Seq analysis was performed in growth medium alone, and in the presence of cholic acid (CA) and deoxycholic acid (DCA). Growth with CA resulted in differential expression (>0.58 log₂FC; FDR < 0.05) of 197 genes in C. hiranonis and 118 genes in C. hylemonae. The bile acid-inducible operons (bai) from each organism were highly upregulated in the presence of CA but not DCA. We then colonized germ-free mice with human gut bacterial isolates capable of metabolizing taurine-conjugated bile acids. This consortium included bile salt hydrolase-expressing Bacteroides uniformis ATCC 8492, Bacteroides vulgatus ATCC 8482, Parabacteroides distasonis DSM 20701, as well as taurine-respiring Bilophila wadsworthia DSM 11045, and deoxycholic/lithocholic acid generating Clostridium hylemonae DSM 15053 and Clostridium hiranonis DSM 13275. Butyrate and iso-bile acid-forming Blautia producta ATCC 27340 was also included. The Bacteroidetes made up 84.71% of 16S rDNA cecal reads, B. wadsworthia, constituted 14.7%, and the clostridia made up <.75% of 16S rDNA cecal reads. Bile acid metabolomics of the cecum, serum, and liver indicate that the synthetic community were capable of functional bile salt deconjugation, oxidation/isomerization, and 7α-dehydroxylation of bile acids. Cecal metatranscriptome analysis revealed expression of genes involved in metabolism of taurine-conjugated bile acids. The in vivo transcriptomes of C. hylemonae and C. hiranonis suggest fermentation of simple sugars and utilization of amino acids glycine and proline as electron acceptors. Genes predicted to be involved in trimethylamine (TMA) formation were also expressed.

Impact of deoxycholate on Clostridioides difficile growth, toxin production, and sporulation

Purpose

Bile acids play an important role in Clostridioides difficile life cycle. Deoxycholate (DCA), one of the most abundant secondary bile acids, is known to inhibit vegetative growth and toxin production. However, limited data are available on the role of DCA on C. difficile sporulation. Here, we investigated the phenotypic and genotypic impact of DCA on the growth, toxin production, and sporulation of C. difficile.

Methodology

Four genetically divergent C. difficile strains were cultured in nutrient-rich broth with and without DCA at various concentrations, and growth activity was evaluated for each strain. Cytotoxicity assays using culture supernatants from cells grown in nutrient-rich broth with and without 0.01% DCA were conducted. Sporulation efficiency was determined using sporulation media with and without 0.01% DCA. Transcript levels of tcdB and spo0A were analyzed using quantitative reverse-transcription polymerase chain reaction.

Results

We found that DCA led to growth reduction in a dose-depended manner and regulated toxin production by repressing tcdB expression during vegetative growth. To our knowledge, we have also provided the first evidence that DCA reduces C. difficile sporulation efficiency through the downregulation of spo0A expression during the sporulation stage.

Conclusions

DCA modulates C. difficile sporulation, vegetative growth, and toxin production.

Sporulation and Germination in Clostridial Pathogens

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

Phosphorothioation of foreign DNA influences the transformation efficiency in Clostridium perfringens NCTC8239

Major advances in Clostridium perfringens genetics have been achieved through the development of electroporation-induced transformation; however, highly transformable strains are still limited. SM101 is the only useful strain for genetic manipulation via transformation in C. perfringens causing foodborne illness (FBI). We focused on the FBI strain NCTC8239, which is transformed at a low frequency, because it has a gene cassette that is predicted to encode enzymes involved in DNA phosphorothioation (PT). The oxidant-dependent degradation of NCTC8239 genomic DNA suggested that the genome is PT-modified. When foreign DNA was PT-modified using a plasmid expressing Salmonella enterica PT modification enzymes, the transformation efficiency of NCTC8239 was significantly higher than that using an unmodified plasmid. We then attempted to establish a highly transformable derivative of NCTC8239, and focused on DptFGH, which are predicted to be PT restriction enzymes. A dptG-null mutant exhibited significantly higher transformation efficiency with unmodified foreign DNA than did the wild-type strain. Furthermore, the mutant was transformed with the unmodified plasmid as efficiently as with a PT-modified plasmid, implying that DptG is involved in PT-dependent restriction. Thus, the present results revealed that PT modifications of foreign DNA influence the transformation frequency of NCTC8239 and suggest that PT is a factor contributing to transformation efficiency in NCTC8239.

Clostridium scindens ATCC 35704: Integration of Nutritional Requirements, the Complete Genome Sequence, and Global Transcriptional Responses to Bile Acids

In the human gut, Clostridium scindens ATCC 35704 is a predominant bacterium and one of the major bile acid 7α-dehydroxylating anaerobes. While this organism is well-studied relative to bile acid metabolism, little is known about the basic nutrition and physiology of C. scindens ATCC 35704. To determine the amino acid and vitamin requirements of C. scindens, the leave-one-out (one amino acid group or vitamin) technique was used to eliminate the nonessential amino acids and vitamins. With this approach, the amino acid tryptophan and three vitamins (riboflavin, pantothenate, and pyridoxal) were found to be required for the growth of C. scindens In the newly developed defined medium, C. scindens fermented glucose mainly to ethanol, acetate, formate, and H_2. The genome of C. scindens ATCC 35704 was completed through PacBio sequencing. Pathway analysis of the genome sequence coupled with transcriptome sequencing (RNA-Seq) under defined culture conditions revealed consistency with the growth requirements and end products of glucose metabolism. Induction with bile acids revealed complex and differential responses to cholic acid and deoxycholic acid, including the expression of potentially novel bile acid-inducible genes involved in cholic acid metabolism. Responses to toxic deoxycholic acid included expression of genes predicted to be involved in DNA repair, oxidative stress, cell wall maintenance/metabolism, chaperone synthesis, and downregulation of one-third of the genome. These analyses provide valuable insight into the overall biology of C. scindens which may be important in treatment of disease associated with increased colonic secondary bile acids.IMPORTANCE C. scindens is one of a few identified gut bacterial species capable of converting host cholic acid into disease-associated secondary bile acids such as deoxycholic acid. The current work represents an important advance in understanding the nutritional requirements and response to bile acids of the medically important human gut bacterium, C. scindens ATCC 35704. A defined medium has been developed which will further the understanding of bile acid metabolism in the context of growth substrates, cofactors, and other metabolites in the vertebrate gut. Analysis of the complete genome supports the nutritional requirements reported here. Genome-wide transcriptomic analysis of gene expression in the presence of cholic acid and deoxycholic acid provides a unique insight into the complex response of C. scindens ATCC 35704 to primary and secondary bile acids. Also revealed are genes with the potential to function in bile acid transport and metabolism.

Enterotoxic Clostridia: Clostridium perfringens Enteric Diseases

In humans and livestock, Clostridium perfringens is an important cause of intestinal infections that manifest as enteritis, enterocolitis, or enterotoxemia. This virulence is largely related to the toxin-producing ability of C. perfringens. This article primarily focuses on the C. perfringens type F strains that cause a very common type of human food poisoning and many cases of nonfoodborne human gastrointestinal diseases. The enteric virulence of type F strains is dependent on their ability to produce C. perfringens enterotoxin (CPE). CPE has a unique amino acid sequence but belongs structurally to the aerolysin pore-forming toxin family. The action of CPE begins with binding of the toxin to claudin receptors, followed by oligomerization of the bound toxin into a prepore on the host membrane surface. Each CPE molecule in the prepore then extends a beta-hairpin to form, collectively, a beta-barrel membrane pore that kills cells by increasing calcium influx. The cpe gene is typically encoded on the chromosome of type F food poisoning strains but is encoded by conjugative plasmids in nonfoodborne human gastrointestinal disease type F strains. During disease, CPE is produced when C. perfringens sporulates in the intestines. Beyond type F strains, C. perfringens type C strains producing beta-toxin and type A strains producing a toxin named CPILE or BEC have been associated with human intestinal infections. C. perfringens is also an important cause of enteritis, enterocolitis, and enterotoxemia in livestock and poultry due to intestinal growth and toxin production.

The bile salt glycocholate induces global changes in gene and protein expression and activates virulence in enterotoxigenic Escherichia coli

Pathogenic bacteria use specific host factors to modulate virulence and stress responses during infection. We found previously that the host factor bile and the bile component glyco-conjugated cholate (NaGCH, sodium glycocholate) upregulate the colonization factor CS5 in enterotoxigenic Escherichia coli (ETEC). To further understand the global regulatory effects of bile and NaGCH, we performed Illumina RNA-Seq and found that crude bile and NaGCH altered the expression of 61 genes in CS5 + CS6 ETEC isolates. The most striking finding was high induction of the CS5 operon (csfA-F), its putative transcription factor csvR, and the putative ETEC virulence factor cexE. iTRAQ-coupled LC-MS/MS proteomic analyses verified induction of the plasmid-borne virulence proteins CS5 and CexE and also showed that NaGCH affected the expression of bacterial membrane proteins. Furthermore, NaGCH induced bacteria to aggregate, increased their adherence to epithelial cells, and reduced their motility. Our results indicate that CS5 + CS6 ETEC use NaGCH present in the small intestine as a signal to initiate colonization of the epithelium.

An enhanced green fluorescence protein (EGFP)-based reporter assay for quantitative detection of sporulation in Clostridium perfringens SM101

Clostridium perfringens type F is a spore-forming anaerobe that causes bacterial food-borne illness in humans. The disease develops when ingested vegetative cells reach the intestinal tract and begin to form spores that produce the diarrheagenic C. perfringens enterotoxin (CPE). Given that CPE production is regulated by the master regulator of sporulation (transcription factor Spo0A), the identification of sporulation-inducing factors in the intestine is relevant to better understanding of the disease. To examine these factors, we established assays to quantify C. perfringens sporulation stage under microscopy by using two fluorescent reporters, namely, Evoglow-Bs2 and CpEGFP. When the reporter genes were placed under control of the cpe promoter, both protein products were expressed specifically during sporulation. However, the intensity of the anaerobic reporter Evoglow-Bs2 was weak and rapidly photobleached during microscopic observation. Alternatively, CpEGFP, a canonical green fluorescence protein with optimized codon usage for Clostridium species, was readily detectable in the mother-cell compartment of most bacteria at early stages of sporulation. Additionally, CpEGFP expression predicted final spore yield and was quantifiable in 96-well plates using fluorescence plate reader. These results indicate that CpEGFP can be used to analyze the sporulation of C. perfringens and has a potential application in the large-scale screening of sporulation-regulating biomolecules.

Effect of sublethal heat treatment on the later stage of germination-to-outgrowth of Clostridium perfringens spores

Sublethal heating of spores has long been known to stimulate or activate germination; however, the underlying mechanisms are not yet fully understood. In this study, the entire germination-to-outgrowth process of spores from Clostridium perfringens, an anaerobic sporeformer, was visualized at single-cell resolution. Quantitative analysis revealed that sublethal heating significantly reduces the time from completion of germination to the beginning of the first cell division, indicating that sublethal heating of C. perfringens spores not only sensitizes the responsiveness of germinant receptors but also directly or indirectly facilitates multiple steps during the bacterial regrowth process.

RelA/DTD-mediated regulation of spore formation and toxin production by Clostridium perfringens type A strain SM101

RelA is a global regulator for stationary phase development in the model bacterium Bacillus subtilis. The relA gene forms a bicistronic operon with the downstream dtd gene. In this study, we evaluated the significance of RelA and DTD proteins in spore formation and toxin production by an important gastrointestinal pathogen Clostridium perfringens. Our β-glucuronidase assay showed that in C. perfringens strain SM101, relA forms a bicistronic operon with its downstream dtd gene, and the relA promoter is expressed during both vegetative and sporulation conditions. By constructing double relA dtd and single dtd mutants in C. perfringens SM101, we found that: (1) RelA is required for maintaining the efficient growth capacity of SM101 cells during vegetative conditions; (2) both RelA and DTD are required for spore formation and enterotoxin (CPE) production by SM101; (3) RelA/DTD activate CodY, which is known to activate spore formation and CPE production in SM101 by activating a key sporulation-specific σ factor F; (4) as expected, RelA/DTD activate sporulation-specific σ factors (σ^E, σ^F, σ^G and σ^K) by positively regulating Spo0A production; and finally (5) RelA, but not DTD, negatively regulates phospholipase C (PLC) production by repressing plc gene expression. Collectively, our results demonstrate that RelA modulates cellular physiology such as growth, spore formation and toxin production by C. perfringens type A strain SM101, although DTD also plays a role in these pleiotropic functions in coordination with RelA during sporulation. These findings have implications for the understanding of the mechanisms involved in the infectious cycle of C. perfringens.

Effects of Bile Acids and Nisin on the Production of Enterotoxin by Clostridium perfringens in a Nutrient-Rich Medium

Clostridium perfringens is the second most common cause of bacterial foodborne illness in the United States, with nearly a million cases each year. C. perfringens enterotoxin (CPE), produced during sporulation, damages intestinal epithelial cells by pore formation, which results in watery diarrhea. The effects of low concentrations of nisin and bile acids on sporulation and toxin production were investigated in C. perfringens SM101, which carries an enterotoxin gene on the chromosome, in a nutrient-rich medium. Bile acids and nisin increased production of enterotoxin in cultures; bile acids had the highest effect. Both compounds stimulated the transcription of enterotoxin and sporulation-related genes and production of spores during the early growth phase. They also delayed spore outgrowth and nisin was more inhibitory. Bile acids and nisin enhanced enterotoxin production in some but not all other C. perfringens isolates tested. Low concentrations of bile acids and nisin may act as a stress signal for the initiation of sporulation and the early transcription of sporulation-related genes in some strains of C. perfringens, which may result in increased strain-specific production of enterotoxin in those strains. This is the first report showing that nisin and bile acids stimulated the transcription of enterotoxin and sporulation-related genes in a nutrient-rich bacterial culture medium.

Nitrate salts suppress sporulation and production of enterotoxin in Clostridium perfringens strain NCTC8239

Clostridium perfringens type A is a common source of food-borne illness in humans. Ingested vegetative cells sporulate in the small intestinal tract and in the process produce C. perfringens enterotoxin (CPE). Although sporulation plays a critical role in the pathogenesis of food-borne illness, the molecules triggering/inhibiting sporulation are still largely unknown. It has previously been reported by our group that sporulation is induced in C. perfringens strain NCTC8239 co-cultured with Caco-2 cells in Dulbecco's Modified Eagle Medium (DMEM). In contrast, an equivalent amount of spores was not observed when bacteria were co-cultured in Roswell Park Memorial Institute-1640 medium (RPMI). In the present study it was found that, when these two media are mixed, RPMI inhibits sporulation and CPE production induced in DMEM. When a component of RPMI was added to DMEM, it was found that calcium nitrate (Ca[NO₃ ]₂ ) significantly inhibits sporulation and CPE production. The number of spores increased when Ca(NO₃ )₂ -deficient RPMI was used. The other nitrate salts significantly suppressed sporulation, whereas the calcium salts used did not. qPCR revealed that nitrate salts increased expression of bacterial nitrate/nitrite reductase. Furthermore, it was found that nitrite and nitric oxide suppress sporulation. In the sporulation stages, Ca(NO₃ )₂ down-regulated the genes controlled by Spo0A, a master regulator of sporulation, but not spo0A itself. Collectively, these results indicate that nitrate salts suppress sporulation and CPE production by down-regulating Spo0A-regulated genes in C. perfringens strain NCTC8239. Nitrate reduction may be associated with inhibition of sporulation.