Oral malodorous compound causes apoptosis and genomic DNA damage in human gingival fibroblasts

Using 8-Hydroxy-2'-Deoxiguanosine (8-OHdG) as a Reliable Biomarker for Assessing Periodontal Disease Associated with Diabetes

In recent years, research has shown that oxidative stress plays a significant role in chronic inflammatory conditions. The alteration of the oxidant/antioxidant balance leads to the appearance of free radicals, important molecules involved in both diabetes mellitus and periodontal disease. Diabetes is considered to be one of the major risk factors of periodontal disease and the inflammation characterizing this condition is associated with oxidative stress, implicitly resulting in oxidative damage to DNA. 8-Hydroxydeoxyguanosine (8-OHdG) is the most common stable product of oxidative DNA damage caused by reactive oxygen species, and its levels have been reported to increase in body fluids and tissues during inflammatory conditions. 8-OHdG emerges as a pivotal biomarker for assessing oxidative DNA damage, demonstrating its relevance across diverse health conditions, including neurodegenerative disorders, cancers, inflammatory conditions, and periodontal disease. Continued research in this field is crucial for developing more precise treatments and understanding the detailed link between oxidative stress and the progression of periodontitis. The use of the 8-OHdG biomarker in assessing and managing chronic periodontitis is an area of increased interest in dental research, with the potential to provide crucial information for diagnosis and treatment.

Mechanisms and Potential Clinical Implications of Oral Microbiome in Oral Squamous Cell Carcinoma

Microorganisms in the oral cavity are abundant in the human body. At present, more than 700 species of oral microorganisms have been identified. Recently, a lot of literature has indicated that the oral microbiota plays an important role in the occurrence, development, and prognosis of oral squamous cell carcinoma (OSCC) through various mechanisms. And researchers are now trying to utilize oral microbiota in cancer diagnosis and treatment. However, few articles systematically summarize the effects of oral microbes in the diagnosis, treatment, and disease outcomes of oral cancer. Herein, we made a summary of the microbial changes at cancerous sites and placed more emphasis on the mechanisms by which the oral microbiome promotes cancerization. Moreover, we aimed to find out the clinical value of the oral microbiome in OSCC.

Nanozyme based colorimetric detection of biogenic gaseous H2S using Ag@Au core/shell nanoplates with peroxidase-like activity

A highly sensitive and facile colorimetric assay is introduced for detecting biogenic gaseous H2S using peroxidase (POD)-like catalytic activity of silver core/gold shell nanoplates (Ag@Au NPls). H2S can react with Ag@Au NPls to form Ag2S or Au2S on their surface, which can reduce POD-like activity of Ag@Au NPls and consequently decrease the absorbance at 650 nm due to oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2). For in situ and multiple detection of H2S, we utilized a microplate cover with 24 polydimethylsiloxane inner wells where Ag@Au NPls reacted with H2S gas followed by treatment with TMB/H2O2. As a result, the change in absorbance at 650 nm showed a linear relationship with the H2S concentration in the range 0.33 to 2.96 μM (0.36 absorbance/μM H2S in PBS, R2 = 0.994) with a limit of detection of 263 nM and a relative standard deviation of 4.4%. Finally, this assay could detect H2S released from Eikenella corrodens, used as a model bacterium, in a short time (20 min) or at a low number of bacteria (1 × 104 colony forming units/mL). Therefore, this assay is expected to be applied for the study of H2S signaling in bacterial physiology, as well as measure H2S production released from other oral bacteria that cause halitosis and oral diseases, leading to the subsequent diagnosis.

Synergistically activated dual-locked fluorescent probes to monitor H2S-induced DNA damage

Naphthalimide-based fluorescent probes (NAN0-N3 and NAN6-N3) were developed with dual locked fluorescence. Here, ≥1.9 × 10^-2 mM of H₂S and ≥2.2 × 10^-2 μg mL^-1 of DNA could unlock a highly sensitive off-on fluorescence response through synergistic changes of the molecular structure and conformation. As such, the probes could monitor DNA damage induced by the overexpression of H₂S, and were able to evaluate the degree of apoptosis of living cells mediated by H₂S-induced mtDNA or nDNA damage.

Diversity and distribution of sulfur metabolic genes in the human gut microbiome and their association with colorectal cancer

BACKGROUND

Recent evidence implicates microbial sulfidogenesis as a potential trigger of colorectal cancer (CRC), highlighting the need for comprehensive knowledge of sulfur metabolism within the human gut. Microbial sulfidogenesis produces genotoxic hydrogen sulfide (H₂S) in the human colon using inorganic (sulfate) and organic (taurine/cysteine/methionine) substrates; however, the majority of studies have focused on sulfate reduction using dissimilatory sulfite reductases (Dsr).

RESULTS

Here, we show that genes for microbial sulfur metabolism are more abundant and diverse than previously observed and are statistically associated with CRC. Using ~ 17,000 bacterial genomes from publicly available stool metagenomes, we studied the diversity of sulfur metabolic genes in 667 participants across different health statuses: healthy, adenoma, and carcinoma. Sulfidogenic genes were harbored by 142 bacterial genera and both organic and inorganic sulfidogenic genes were associated with carcinoma. Significantly, the anaerobic sulfite reductase (asr) genes were twice as abundant as dsr, demonstrating that Asr is likely a more important contributor to sulfate reduction in the human gut than Dsr. We identified twelve potential pathways for reductive taurine metabolism and discovered novel genera harboring these pathways. Finally, the prevalence of metabolic genes for organic sulfur indicates that these understudied substrates may be the most abundant source of microbially derived H₂S.

CONCLUSIONS

Our findings significantly expand knowledge of microbial sulfur metabolism in the human gut. We show that genes for microbial sulfur metabolism in the human gut are more prevalent than previously known, irrespective of health status (i.e., in both healthy and diseased states). Our results significantly increase the diversity of pathways and bacteria that are associated with microbial sulfur metabolism in the human gut. Overall, our results have implications for understanding the role of the human gut microbiome and its potential contributions to the pathogenesis of CRC. Video abstract.

The Effect of Lemon Essential Oil on Halitosis

OBJECTIVES

To evaluate the effect of lemon essential oil (LEO) on salivary bacteria and volatile sulfur compound (VSC) production of patients with halitosis.

MATERIALS AND METHODS

Saliva of five patients with halitosis was collected, after adding different concentrations (0.563-9 mg/ml) of LEO, detecting the growth of salivary bacteria, the formation of biofilm, and VSC production, and compare the difference of different concentrations of LEO on bacterial growth and VSC production. 48 volunteers were randomly divided into 4 groups. After gargling with LEO, cetylpyridinium chloride (CPC), chlorhexidine (CHX), and hydrogen peroxide (H₂ O₂ ) separately measure changes of VSC production and pH values at 30, 45, 60, 90, and 120 min and then compare the differences at different time points within group.

RESULTS

Compared with the negative control group, under subinhibitory concentrations of LEO (0.563-2.25 mg/ml), the biofilm formation and VSC production of salivary bacteria in LEO group were significantly inhibited (p < 0.05). Compared with the baseline, the VSC production of subjects decreased after rinsing with the LEO in 60 min (p < 0.05). After gargling with LEO, the pH value rose significantly in 30 min and reverted to the baseline level at 120 min (p < 0.05).

CONCLUSIONS

Lemon essential oil can inhibit the growth of salivary bacteria and reduce VSC production of patients with halitosis.

Role of Hydrogen Sulfide in Oral Disease

Oral diseases are among the most common human diseases yet less studied. These diseases affect both the physical, mental, and social health of the patients resulting in poor quality of life. They affect all ages, although severe stages are mostly observed in older individuals. Poor oral hygiene, genetics, and environmental factors contribute enormously to the development and progression of these diseases. Although there are available treatment options for these diseases, the recurrence of the diseases hinders their efficiency. Oral volatile sulfur compounds (VSCs) are highly produced in oral cavity as a result of bacteria activities. Together with bacteria components such as lipopolysaccharides, VSCs participate in the progression of oral diseases by regulating cellular activities and interfering with the immune response. Hydrogen sulfide (H2S) is a gaseous neurotransmitter primarily produced endogenously and is involved in the regulation of cellular activities. The gas is also among the VSCs produced by oral bacteria. In numerous diseases, H2S have been reported to have dual effects depending on the cell, concentration, and donor used. In oral diseases, high production and subsequent utilization of this gas have been reported. Also, this high production is associated with the progression of oral diseases. In this review, we will discuss the production of H2S in oral cavity, its interaction with cellular activities, and most importantly its role in oral diseases.

A novel fluorescent probe for detecting hydrogen sulfide in osteoblasts during lipopolysaccharide-mediated inflammation under periodontitis

Periodontitis, one of the most common chronic inflammatory diseases, affects the quality of life. Osteogenesis plays an important role in the disease. There is a connection between hydrogen sulfide (H₂S) and periodontitis, but according to the study has been published, the precise role of H₂S in inflammation remains in doubt. The main reason for the lack of research is that H₂S is an endogenous gasotransmitter, difficult to discern through testing. So, we synthesized a novel fluorescence probe which can detect H₂S in vitro. By using the novel H₂S fluorescence probe, we found that H₂S changes in osteoblasts mainly by cystathionine-γ-lyase, and H₂S increases under LPS stimulation. H₂S could be a potential marker for diagnosis of inflammatory diseases of bone, and might help deepen studies of the changes of H₂S level and promote the progression on the researches about pathogenesis of periodontitis.

A cocoa (Theobroma cacao L.) extract impairs the growth, virulence properties, and inflammatory potential of Fusobacterium nucleatum and improves oral epithelial barrier function

Fusobacterium nucleatum is associated with many conditions and diseases, including periodontal diseases that affect tooth-supporting tissues. The aim of the present study was to investigate the effects of a cocoa extract (Theobroma cacao L.) on F. nucleatum with respect to growth, biofilm formation, adherence, and hydrogen sulfide (H₂S) production. The anti-inflammatory properties and the effect on epithelial barrier function of the cocoa extract were also assessed. The cocoa extract, whose major phenolic compound is epicatechin, dose-dependently inhibited the growth, biofilm formation, adherence properties (basement membrane matrix, oral epithelial cells), and H₂S production of F. nucleatum. It also decreased IL-6 and IL-8 production by F. nucleatum-stimulated oral epithelial cells and inhibited F. nucleatum-induced NF-κB activation in monocytes. Lastly, the cocoa extract enhanced the barrier function of an oral epithelial model by increasing the transepithelial electrical resistance. We provide evidence that the beneficial properties of an epicatechin-rich cocoa extract may be useful for preventing and/or treating periodontal diseases.

A Fold Type II PLP-Dependent Enzyme from Fusobacterium nucleatum Functions as a Serine Synthase and Cysteine Synthase

Serine synthase (SS) from Fusobacterium nucleatum is a fold type II pyridoxal 5'-phosphate (PLP)-dependent enzyme that catalyzes the β-replacement of l-cysteine with water to form l-serine and H₂S. Herein, we show that SS can also function as a cysteine synthase, catalyzing the β-replacement of l-serine with bisulfide to produce l-cysteine and H₂O. The forward (serine synthase) and reverse (cysteine synthase) reactions occur with comparable turnover numbers and catalytic efficiencies for the amino acid substrate. Reaction of SS with l-cysteine leads to transient formation of a quinonoid species, suggesting that deprotonation of the Cα and β-elimination of the thiolate group from l-cysteine occur via a stepwise mechanism. In contrast, the quinonoid species was not detected in the formation of the α-aminoacrylate intermediate following reaction of SS with l-serine. A key active site residue, D232, was shown to stabilize the more chemically reactive ketoenamine PLP tautomer and also function as an acid/base catalyst in the forward and reverse reactions. Fluorescence resonance energy transfer between PLP and W99, the enzyme's only tryptophan residue, supports ligand-induced closure of the active site, which shields the PLP cofactor from the solvent and increases the basicity of D232. These results provide new insight into amino acid metabolism in F. nucleatum and highlight the multiple catalytic roles of D232 in a new member of the fold type II family of PLP-dependent enzymes.

Hydrogen sulfide exacerbated periodontal inflammation and induced autophagy in experimental periodontitis

Hydrogen sulfide (H₂S), the metabolite produced by gram-negative bacteria, is present in deep periodontal pockets of periodontitis patients at high concentrations. The harsh conditions in the diseased periodontium may stimulate a local autophagy response. However, how H₂S participates in pathogenesis and whether H₂S induces autophagy in periodontitis remain partially unknown. In this article, we determined the role of the slow-releasing H₂S donor GYY4137 in experimental periodontitis and its possible regulation in autophagy involved. We found that GYY4137 dose-dependently decreased cell viability and increased the level of proinflammatory cytokines in LPS-stimulated human periodontal ligament cells (HPDLCs). Topically applied GYY4137 also exacerbated periodontal inflammation and alveolar bone loss in ligature-induced rats. Moreover, GYY4137 activated autophagy by upregulating the expression levels of the autophagy-related proteins LC3 and Beclin-1 and downregulating P62 in LPS-treated HPDLCs and inflamed periodontal tissues. Blocking autophagy with 3-methyladenine resulted in further increased expression of proinflammatory cytokines in LPS- and GYY4137-induced HPDLCs. Our results indicate that GYY4137 exerted proinflammatory effects and promoted autophagy in periodontitis, and the induced autophagy may function as a cytoprotective mechanism to prevent excessive inflammation.

Effects of Labrador Tea, Peppermint, and Winter Savory Essential Oils on Fusobacterium nucleatum

Bad breath or halitosis is an oral condition caused by volatile sulfur compounds (VSC) produced by bacteria found in the dental and tongue biofilms. Fusobacterium nucleatum is a Gram-negative anaerobic bacterium that has been strongly associated with halitosis. In this study, essential oils (EO) from three plants, Labrador tea (Rhododendron groenlandicum [Oeder] Kron & Judd), peppermint (Mentha x piperita L.), and winter savory (Satureja montana L.), were investigated for their effects on growth, biofilm formation and killing, and VSC production by F. nucleatum. Moreover, their biocompatibility with oral keratinocytes was investigated. Using a broth microdilution assay, winter savory EO and to a lesser extent Labrador tea and peppermint EO showed antibacterial activity against F. nucleatum. A treatment of pre-formed biofilms of F. nucleatum with EO also significantly decreased bacterial viability as determined by a luminescence assay monitoring adenosine triphosphate production. The EO were found to permeabilize the bacterial cell membrane, suggesting that it represents the target of the tested EO. The three EO under investigation were able to dose-dependently reduce VSC production by F. nucleatum. Lastly, no significant loss of cell viability was observed when oral keratinocytes were treated with the EO at concentrations effective against F. nucleatum. This study supports the potential of Labrador tea, peppermint, and winter savory EO as promising agents to control halitosis and promote oral health.

Hydrogen sulfide and DNA repair

Recent evidence has revealed that exposing cells to exogenous H 2 S or inhibiting cellular H 2 S synthesis can modulate cell cycle checkpoints, DNA damage and repair, and the expression of proteins involved in the maintenance of genomic stability, all suggesting that H 2 S plays an important role in the DNA damage response (DDR). Here we review the role of H 2 S in the DRR and maintenance of genomic stability. Treatment of various cell types with pharmacologic H 2 S donors or cellular H 2 S synthesis inhibitors modulate the G 1 checkpoint, inhibition of DNA synthesis, and cause p21, and p53 induction. Moreover, in some cell models H 2 S exposure induces PARP-1 and g-H2AX foci formation, increases PCNA, CHK2, Ku70, Ku80, and DNA polymerase-d protein expression, and maintains mitochondrial genomic stability. Our group has also revealed that H 2 S bioavailability and the ATR kinase regulate each other with ATR inhibition lowering cellular H 2 S concentrations, whereas intracellular H 2 S concentrations regulate ATR kinase activity via ATR serine 435 phosphorylation. In summary, these findings have many implications for the DDR, for cancer chemotherapy, and fundamental biochemical metabolic pathways involving H 2 S.

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Inhibition of the ATR kinase lowers intracellular H₂S concentrations.

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Inhibition of H₂S synthesis activates the ATR kinase and increases its kinase activity.

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Inhibition of H₂S synthesis combined with low-level oxidative stress increases genomic instability.

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These findings may have applications the cancer chemotherapeutics.

Effect of Sublethal Blue Light on Herbal Extract Activity Against Volatile Sulfide Compound Production by Fusobacterium nucleatum

Previously, we have shown that sublethal exposure of blue light caused increased cell membrane permeability in Fusobacterium nucleatum. The aim of the present study was to test the effect of this exposure on the activity of Lavender, Sage, Echinacea and Mastic gum extracts against volatile sulfide compound (VSC) production by Fusobacterium nucleatum. Bacterial suspensions were pre-exposed to blue light (400-500 nm) bellow minimal inhibitory dosage (sub-MID). Exposed and nonexposed samples were inoculated into test tubes containing growth medium, filtered saliva with or without herbal extracts. Following incubation, test tubes were tested for malodor production (odor judge scores), VSC levels (OralChroma), salivary protein degradation (SDS-PAGE) and bacterial cell membrane damage (fluorescence microscopy). Results showed that sub-MID blue light exposure significantly increased the ability of Lavender and Echinacea to reduce VSC production by Fusobacterium nucleatum by more than 30%. These results suggest that sublethal blue light exposure may be useful to increase the efficacy of antimalodor agents.

Multiple enzymes can make hydrogen sulfide from cysteine in Treponema denticola

Treponema denticola is a spirochete that is involved in causing periodontal diseases. This bacterium can produce H2S from thiol compounds found in the gingival crevicular fluid. Determining how H2S is made by oral bacteria is important since this molecule is present at high levels in periodontally-diseased pockets and the biological effects of H2S can explain some of the pathologies seen in periodontitis. Thus, it is of interest to identify the enzyme, or enzymes, involved in the synthesis of H2S by T. denticola. We, and others, have previously identified and characterized a T. denticola cystalysin, called HlyA, which hydrolyzes cysteine into H2S (and pyruvate and ammonia). However, there have been no studies to show that HlyA is, or is not, the only pathway that T. denticola can use to make H2S. To address this question, allelic replacement mutagenesis was used to make a deletion mutant (ΔhlyA) in the gene encoding HlyA. The mutant produces the same amount of H2S from cysteine as do wild type spirochetes, indicating that T. denticola has at least one other enzyme that can generate H2S from cysteine. To identify candidates for this other enzyme, a BLASTp search of T. denticola strain 33520 was done. There was one gene that encoded an HlyA homolog so we named it HlyB. Recombinant His-tagged HlyB was expressed in E. coli and partially purified. This enzyme was able to make H2S from cysteine in vitro. To test the role of HlyB in vivo, an HlyB deletion mutant (ΔhlyB) was constructed in T. denticola. This mutant still made normal levels of H2S from cysteine, but a strain mutated in both hly genes (ΔhlyA ΔhlyB) synthesizes significantly less H2S from cysteine. We conclude that the HlyA and HlyB enzymes perform redundant functions in vivo and are the major contributors to H2S production in T. denticola. However, at least one other enzyme can still convert cysteine to H2S in the ΔhlyA ΔhlyB mutant. An in silico analysis that identifies candidate genes for this other enzyme is presented.

Glutathione catabolism by Treponema denticola impacts its pathogenic potential

Treponema denticola is a spirochete that is etiologic for periodontal diseases. This bacterium is one of two periodontal pathogens that have been shown to have a complete three step enzymatic pathway (GTSP) that catabolizes glutathione to H2S. This pathway may contribute to the tissue pathology seen in periodontitis since diseased periodontal pockets have lower glutathione levels than healthy sites with a concomitant increase in H2S concentration. In order to be able to demonstrate that glutathione catabolism by the GTSP is critical for the pathogenic potential of T. denticola, allelic replacement mutagenesis was used to make a deletion mutant (Δggt) in the gene encoding the first enzyme in the GTSP. The mutant cannot produce H2S from glutathione since it lacks gamma-glutamyltransferase (GGT) activity. The hemolytic and hemoxidation activities of wild type T. denticola plus glutathione are reduced to background levels with the Δggt mutant and the mutant has lost the ability to grow aerobically when incubated with glutathione. The Δggt bacteria with glutathione cause less cell death in human gingival fibroblasts (hGFs) in vitro than do wild type T. denticola and the levels of hGF death correlate with the amounts of H2S produced. Importantly, the mutant spirochetes plus glutathione make significantly smaller lesions than wild type bacteria plus glutathione in a mouse back lesion model that assesses soft tissue destruction, a major symptom of periodontal diseases. Our results are the first to prove that T. denticola thiol-compound catabolism by its gamma-glutamyltransferase can play a significant role in the in the types of host tissue damage seen in periodontitis.

Structural insights into the catalytic mechanism of cysteine (hydroxyl) lyase from the hydrogen sulfide-producing oral pathogen, Fusobacterium nucleatum

Hydrogen sulfide (H2S) plays important roles in the pathogenesis of periodontitis. Oral pathogens typically produce H2S from l-cysteine in addition to pyruvate and . However, fn1055 from Fusobacterium nucleatum subsp. nucleatum ATCC 25586 encodes a pyridoxal 5′-phosphate (PLP)-dependent enzyme that catalyzes the production of H2S and l-serine from l-cysteine and H2O, an unusual cysteine (hydroxyl) lyase reaction (β-replacement reaction). To reveal the reaction mechanism, the crystal structure of substrate-free Fn1055 was determined. Based on this structure, a model of the l-cysteine-PLP Schiff base suggested that the thiol group forms hydrogen bonds with Asp232 and Ser74, and the substrate α-carboxylate interacts with Thr73 and Gln147. Asp232 is a unique residue to Fn1055 and its substitution to asparagine (D232N) resulted in almost complete loss of β-replacement activity. The D232N structure obtained in the presence of l-cysteine contained the α-aminoacrylate-PLP Schiff base in the active site, indicating that Asp232 is essential for the addition of water to the α-aminoacrylate to produce the l-serine-PLP Schiff base. Rapid-scan stopped-flow kinetic analyses showed an accumulation of the α-aminoacrylate intermediate during the reaction cycle, suggesting that water addition mediated by Asp232 is the rate-limiting step. In contrast, mutants containing substitutions of other active-site residues (Ser74, Thr73, and Gln147) exhibited reduced β-replacement activity by more than 100-fold. Finally, based on the structural and biochemical analyses, we propose a mechanism of the cysteine (hydroxyl) lyase reaction by Fn1055. The present study leads to elucidation of the H2S-producing mechanism in F. nucleatum.

Systemic effects of H2S inhalation at human equivalent dose of pathologic halitosis on rats

OBJECTIVES

Halitosis is composed by hundreds of toxic gases. It is still not clear whether halitosis gases self-inhaled by halitosis patients cause side effects. The aim of the study was to investigate the effect of H₂S inhalation at a low concentration (human equivalent dose of pathologic halitosis) on rats.

MATERIALS AND METHODS

The threshold level of pathologic halitosis perceived by humans at 250 ppb of H₂S was converted to rat equivalent concentration (4.15 ppm). In the experimental group, 8 rats were exposed to H₂S via continuous inhalation but not the control rats. After 50 days, blood parameters were measured and tissue samples were obtained from the brain, kidney and liver and examined histopathologically to determine any systemic effect.

RESULTS

While aspartate transaminase, creatine kinase-MB and lactate dehydrogenase levels were found to be significantly elevated, carbondioxide and alkaline phosphatase were decreased in experimental rats. Other blood parameters were not changed significantly. Experimental rats lost weight and became anxious. Histopathological examination showed mononuclear inflammatory cell invasion in the portal areas, nuclear glycogen vacuoles in the parenchymal area, single-cell necrosis in a few foci, clear expansion in the central hepatic vein and sinusoids, hyperplasia in Kupffer cells and potential fibrous tissue expansion in the portal areas in the experimental rats. However, no considerable histologic damage was observed in the brain and kidney specimens.

CONCLUSIONS

It can be concluded that H₂S inhalation equivalent to pathologic halitosis producing level in humans may lead to systemic effects, particularly heart or liver damage in rats.

The proteins of Fusobacterium spp. involved in hydrogen sulfide production from L-cysteine

BACKGROUND

Hydrogen sulfide (H₂S) is a toxic foul-smelling gas produced by subgingival biofilms in patients with periodontal disease and is suggested to be part of the pathogenesis of the disease. We studied the H₂S-producing protein expression of bacterial strains associated with periodontal disease. Further, we examined the effect of a cysteine-rich growth environment on the synthesis of intracellular enzymes in F. nucleatum polymorphum ATCC 10953. The proteins were subjected to one-dimensional (1DE) and two-dimensional (2DE) gel electrophoresis An in-gel activity assay was used to detect the H₂S-producing enzymes; Sulfide from H₂S, produced by the enzymes in the gel, reacted with bismuth forming bismuth sulfide, illustrated as brown bands (1D) or spots (2D) in the gel. The discovered proteins were identified with liquid chromatography - tandem mass spectrometry (LC-MS/MS).

RESULTS

Cysteine synthase and proteins involved in the production of the coenzyme pyridoxal 5'phosphate (that catalyzes the production of H₂S) were frequently found among the discovered enzymes. Interestingly, a higher expression of H₂S-producing enzymes was detected from bacteria incubated without cysteine prior to the experiment.

CONCLUSIONS

Numerous enzymes, identified as cysteine synthase, were involved in the production of H₂S from cysteine and the expression varied among Fusobacterium spp. and strains. No enzymes were detected with the in-gel activity assay among the other periodontitis-associated bacteria tested. The expression of the H₂S-producing enzymes was dependent on environmental conditions such as cysteine concentration and pH but less dependent on the presence of serum and hemin.

In vitro effects of Melaleuca alternifolia essential oil on growth and production of volatile sulphur compounds by oral bacteria

Objective

Halitosis can be caused by microorganisms that produce volatile sulphur compounds (VSCs), which colonize the surface of the tongue and subgingival sites. Studies have reported that the use of natural products can reduce the bacterial load and, consequently, the development of halitosis. The aim of this study was to evaluate the antimicrobial activity of the essential oil of Melaleuca alternifolia on the growth and volatile sulphur compound (VSC) production of oral bacteria compared with chlorhexidine.

Material and Methods

The effects of these substances were evaluated by the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) in planktonic cultures of Porphyromonas gingivalis and Porphyromonas endodontalis. In addition, gas chromatography analyses were performed to measure the concentration of VSCs from bacterial cultures and to characterize M. alternifolia oil components.

Results

The MIC and MBC values were as follows: M. alternifolia - P. gingivalis (MIC and MBC=0.007%), P. endodontalis (MIC and MBC=0.007%=0.5%); chlorhexidine - P. gingivalis and P. endodontalis (MIC and MBC=1.5 mg/mL). M. alternifolia significantly reduced the growth and production of hydrogen sulfide (H2S) by P. gingivalis (p<0.05, ANOVA-Dunnet) and the H2S and methyl mercaptan (CH3SH) levels of P. endodontalis (p<0.05, ANOVA-Dunnet). Chlorhexidine reduced the growth of both microorganisms without altering the production of VSC in P. endodontalis. For P. gingivalis, the production of H2S and CH3SH decreased (p<0.05, ANOVA-Dunnet).

Conclusion

M. alternifolia can reduce bacterial growth and VSCs production and could be used as an alternative to chlorhexidine.

Hydrogen sulfide enhances pancreatic β-cell differentiation from human tooth under normal and glucotoxic conditions

Aim: Glucotoxicity obstructs pancreatic differentiation from adult stem cells. The aim was to develop a novel protocol for differentiation of dental pulp stem cells (DPSCs) into pancreatic β cells and determine the effect of H2S on glucotoxicity. Materials & methods: DPSCs were differentiated with media containing 5.5 or 25.0 mM glucose, exposed to 1 ng/ml H2S. Glucotoxicity, expression of β-cell markers, INS, PDX1 and GLUT2, and PI3K/AKT pathway were assessed. Results: H2S exposure increased insulin and C-peptide, and protected DPSC-derived pancreatic β-like cells from glucotoxicity and upregulated INS, PDX1 and GLUT2, and genes of PI3K/AKT pathway. Conclusion: H2S improved effects of glucotoxicity on β-like cells via PI3K/AKT pathway. The protocol for pancreatic β-cell differentiation might have applications in regenerative medicine rather than swine pancreas transplantation.

Production of endogenous hydrogen sulfide in human gingival tissue

OBJECTIVE

Endogenous hydrogen sulfide (H₂S) has recently been shown to play an important role in inflammation, but the role of endogenous H₂S in the human gingival tissue is unknown. The aim of this study was to investigate whether gingiva had enzymes for H₂S synthesis, and whether the effect of these enzymes for H₂S production changed with periodontal inflammation.

DESIGN

Gingival tissues were collected from patients undergoing periodontal operation including gingivitis, moderate chronic periodontitis, severe chronic periodontitis and normal controls. RT-PCR and western blotting were performed to measure mRNA and protein levels of cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) for H₂S production. Immunohistochemistry was carried out to detect the location of the enzymes. H₂S levels and synthesis in gingival tissue were evaluated with modified methylene blue method.

RESULTS

The mRNA and protein of CBS and CSE were both expressed in human gingiva and raised significantly in moderate and severe periodontitis compared of that in healthy control. CBS, but not CSE, increased in gingivitis (p<0.05). However, there was no significant difference of H₂S level and synthesis among these groups (p>0.05).

CONCLUSIONS

Both CBS and CSE were expressed in human gingival tissue. The mRNA and protein levels of CBS and CSE were up-regulated in periodontitis.

Programmed cell death in periodontitis: recent advances and future perspectives

Periodontitis is a highly prevalent infectious disease, characterized by destruction of the periodontium, and is the main cause of tooth loss. Periodontitis is initiated by periodontal pathogens, while other risk factors including smoking, stress, and systemic diseases aggravate its progression. Periodontitis affects many people worldwide, but the molecular mechanisms by which pathogens and risk factors destroy the periodontium are unclear. Programmed cell death (PCD), different from necrosis, is an active cell death mediated by a cascade of gene expression events and can be mainly classified into apoptosis, autophagy, necroptosis, and pyroptosis. Although PCD is involved in many inflammatory diseases, its correlation with periodontitis is unclear. After reviewing the relevant published articles, we found that apoptosis has indeed been reported to play a role in periodontitis. However, the role of autophagy in periodontitis needs further verification. Additionally, implication of necroptosis or pyroptosis in periodontitis remains unknown. Therefore, we recommend future studies, which will unravel the pivotal role of PCD in periodontitis, allowing us to prevent, diagnose, and treat the disease, as well as predict its outcomes.

Structural changes in periodontium of rats exposed to a low concentration of hydrogen sulfide for 50 days

The aim of the present study was to investigate the effect of H2S inhalation at a low concentration (at human equivalent dose of pathologic halitosis) on rat periodontium over a long term (50 days). The threshold level of pathologic halitosis perceived by humans at 250 ppb of H2S was converted to rat equivalent concentration (4.15 ppm). Rats in the experimental (H2S) group (n = 8) were exposed to H2S continuously but not the control rats (n = 8). After 50 days, periodontal tissue samples were taken from the mandibular first molar region and examined histopathologically to determine inflammatory cell infiltration (ICI), osteoblastic activities, number of osteoclasts, and resorption lacunae.

Sulcular epithelium layer destruction was observed in the H2S group. Frequency of ICI was significantly higher in the H2S group compared to the control group ( P <0.05). The number of osteoclasts were found significantly higher in the H2S group (34.28 ± 3.28) compared to the control group (8.85 ± 1.85) ( P <0.05) and the number of resorption lacunae were also higher in the cementum tissue (6.1 ± 2.4) and alveolar bone (3.8 ± 1.5) versus their corresponding control groups (1.6 ± 0.5 and 1.4 ± 0.5, respectively) ( P <0.05). There were no statistically significant differences between the two groups with regard to osteoblastic activity. H2S inhalation induces inflammatory changes in the periodontium as well as resorption of the alveolar bone and cementum tissue in rats. These histopathologic changes in periodontal tissues support the idea that long-term H2S inhalation may have a destructive effect on periodontal tissues.

Metabolomic Studies of Oral Biofilm, Oral Cancer, and Beyond

Oral diseases are known to be closely associated with oral biofilm metabolism, while cancer tissue is reported to possess specific metabolism such as the ‘Warburg effect’. Metabolomics might be a useful method for clarifying the whole metabolic systems that operate in oral biofilm and oral cancer, however, technical limitations have hampered such research. Fortunately, metabolomics techniques have developed rapidly in the past decade, which has helped to solve these difficulties. In vivo metabolomic analyses of the oral biofilm have produced various findings. Some of these findings agreed with the in vitro results obtained in conventional metabolic studies using representative oral bacteria, while others differed markedly from them. Metabolomic analyses of oral cancer tissue not only revealed differences between metabolomic profiles of cancer and normal tissue, but have also suggested a specific metabolic system operates in oral cancer tissue. Saliva contains a variety of metabolites, some of which might be associated with oral or systemic disease; therefore, metabolomics analysis of saliva could be useful for identifying disease-specific biomarkers. Metabolomic analyses of the oral biofilm, oral cancer, and saliva could contribute to the development of accurate diagnostic, techniques, safe and effective treatments, and preventive strategies for oral and systemic diseases.

Enamel surface changes caused by hydrogen sulfide

BACKGROUND

Volatile sulfur compounds (VSCs) produced inside the mouth are a well-known cause of halitosis. Recent studies have suggested that VSCs modify the pathology of periodontitis by encouraging the migration of bacterial toxins associated with increased permeability of gingival epithelia, and enhancing the production of matrix metalloproteinases in gingival connective tissue. Nonetheless, the effects on the enamel of direct exposure to VSCs within the oral cavity remain unclear. In the present study, we observed the effects of VSCs in the form of hydrogen sulfide (H2S) on enamel surfaces and determined their effects on restorations.

MATERIALS AND METHODS

Extracted human tooth and bovine tooth samples were divided into the H2S experimental side and the control side. We observed the effects of H2S on enamel surfaces using electron microscopy and conducted a shear test.

RESULTS

We found that exposure to H2S obscured the enamel surface's crystal structure. The surface also exhibited coarseness and reticular changes. Shear testing did not reveal any differences in bond strength.

CONCLUSIONS

Our findings suggested that H2S occurring inside the mouth causes changes to the crystal structure of the enamel surface that can lead to tooth wear, but that it does not diminish the effects of dental bonding in adhesive restorations.

The Negative Effects of Volatile Sulphur Compounds

Oral malodor has been studied extensively in humans but not necessarily to the same degree in our veterinary patients where malodor constitutes a significant problem. Breath malodor may originate from the mouth, or from an extra oral source, originating from other organ systems such as gastrointestinal, respiratory, or even systemic disease. Oral malodor is a result of microbial metabolism of exogenous and endogenous proteinaceous substrates leading to the production of compounds such as indole, skatole, tyramine, cadaverine, puterescine, mercaptans, and sulphides. Volatile sulphur compounds have been shown to be the main cause of oral malodor. Although most clients perceive oral malodor to be primarily a cosmetic problem, there is an increasing volume of evidence in human dental literature demonstrating that volatile sulphur compounds produced by bacteria, even at low concentrations, are toxic to tissues and play a role in the pathogenesis of periodontitis. This article reviews the current available literature in human dentistry looking at these negative effects. No veterinary studies have been conducted looking at the negative effects of volatile sulphur compounds specifically, but as this article highlights, we should be aware of the potential negative effects of volatile sulphur compounds and consider this an area of future research.

Detection of volatile malodorous compounds in breath: current analytical techniques and implications in human disease

For the last few decades intense scientific research has been placed on the relationship between trace substances found in exhaled breath such as volatile organic compounds (VOC) and a wide range of local or systemic diseases. Although currently there is no general consensus, results imply that VOC have a different profile depending on the organ or disease that generates them. The association between a specific pathology and exhaled breath odor is particularly evident in patients with medical conditions such as liver, renal or oral diseases. In other cases the unpleasant odors can be associated with the whole body and have a genetic underlying cause. The present review describes the current advances in identifying and quantifying VOC used as biomarkers for a number of systemic diseases. A special focus will be placed on volatiles that characterize unpleasant breath 'fingerprints' such as fetor hepaticus; uremic fetor; fetor ex ore or trimethylaminuria.

Hydrogen sulphide increases hepatic differentiation of human tooth pulp stem cells compared with human bone marrow stem cells

AIM

To determine the differences in stem cell properties, in hepatic differentiation and in the effects of hydrogen sulphide (H2 S) on hepatic differentiation between human bone marrow stem cells (hBMC) and stem cells from human exfoliated primary tooth pulp (SHED).

METHODOLOGY

CD117(+) cells were magnetically separated and subjected to hepatic differentiation. CD117(+) cell lineages were characterized for transcription factors indicative of stem cells by qRT-PCR. For the last 9 days of the differentiation, the test cells were exposed to 0.1 ng mL(-1) H2 S. Immunocytochemistry and flow cytometry of albumin, alpha-fetoprotein and carbamoyl phosphate synthetase were carried out after differentiation. Urea concentration and glycogen synthesis were also determined.

RESULTS

Genes expressed in SHED were also expressed in BMC. No difference in expression level of hepatic markers was shown by immunofluorescence. SHED showed more positive cells than hBMC (P < 0.01). H2 S increased the number of positive cells in both cultures (P < 0.01). Urea concentration and glycogen synthesis increased significantly after H2 S exposure (P < 0.001 and P < 0.05, respectively). Real-time PCR data were analysed by RT(2) profiler RT-PCR Array Data Analysis version 3.5 (Qiagen), and ELISA data were analysed by Bonferroni's multiple comparison using Windows spss version 16 (SPSS Inc, Chicago, IL, USA). Bonferroni's multiple comparison test was also carried out after angle transformation for the percentage data of flow cytometer using Windows spss(®) version 16 (SPSS Inc). Statistical significance was accepted at P < 0.05.

CONCLUSIONS

Stem cells from human exfoliated primary tooth pulp and BMC have similar properties. The level of hepatic differentiation in SHED compared with BMC was the same or higher. H2 S increased the level of hepatic differentiation.

Hydrogen sulfide in cell survival: a double-edged sword

Hydrogen sulfide (H(2)S) has been found to play an important role as a signal molecule in regulating cell survival. It appears paradoxical that, on one side, H(2)S acts as a physiological intercellular messenger to stimulate cell growth, and on the other side, it may display cytotoxic activity. This article summarizes the current body of evidence demonstrating the cytoprotective versus cytotoxic effects of H(2)S in mammalian cells and describes the janus-faced properties of this important gasotransmitter. This article will also provide a brief description of the current signaling mechanisms that have been demonstrated to be responsible for these different actions. The pharmacologic regulation of H(2)S production and the potential clinical significance of H(2)S are highlighted.

Microbial volatile compounds in health and disease conditions

Microbial cultures and/or microbial associated diseases often have a characteristic smell. Volatile organic compounds (VOCs) are produced by all microorganisms as part of their normal metabolism. The types and classes of VOC produced is wide, including fatty acids and their derivatives (e.g. hydrocarbons, aliphatic alcohols and ketones), aromatic compounds, nitrogen containing compounds, and volatile sulfur compounds. A diversity of ecological niches exist in the human body which can support a polymicrobial community, with the exact VOC profile of a given anatomical site being dependent on that produced by both the host component and the microbial species present. The detection of VOCs is of interest to various disciplines, hence numerous analytical approaches have been developed to accurately characterize and measure VOCs in the laboratory, often from patient derived samples. Using these technological advancements it is evident that VOCs are indicative of both health and disease states. Many of these techniques are still largely confined to the research laboratory, but it is envisaged that in future bedside 'VOC profiling' will enable rapid characterization of microbial associated disease, providing vital information to healthcare practitioners.

Association between volatile sulfur compounds and periodontal disease progression in elderly non-smokers

BACKGROUND

Periodontal pathogenic microorganisms produce volatile sulfur compounds (VSCs), such as hydrogen sulfide, methyl mercaptan, and dimethyl sulfide. VSCs are toxic to periodontal tissue. Therefore, there is a relationship between periodontitis and the VSC level of mouth air. However, the association between VSC and periodontal disease progression has not been investigated in a longitudinal study. The purpose of this study is to evaluate the association between VSCs in mouth air and periodontal disease progression among elderly dentulous non-smokers.

METHODS

Two hundred forty-one dentulous non-smokers (103 males and 138 females; all 70 years old) had their VSC levels examined with a portable sulfide monitor, and their periodontal status was assessed. Periodontal examinations were performed at baseline and once a year for 3 years to investigate the clinical attachment levels of all teeth. Participants were classified by membership in tertile groups (lowest, middle, and highest) according to the value of baseline VSC measurements.

RESULTS

In negative binomial regression analysis, the number of teeth with periodontal disease progression for participants in the highest tertile of VSC measurement was greater (incidence rate ratio of 1.33, P = 0.011) than for the reference group (lowest tertile of VSC measurement) after simultaneously adjusting for sex, number of remaining teeth, and maximum clinical attachment level.

CONCLUSIONS

VSC measurements were significantly associated with periodontal disease progression in a non-smoking dentulous elderly population. This suggests that VSC measurements are useful for the diagnosis of periodontal disease progression.

Identification of an L-methionine γ-lyase involved in the production of hydrogen sulfide from L-cysteine in Fusobacterium nucleatum subsp. nucleatum ATCC 25586

Fusobacterium nucleatum produces an abundance of hydrogen sulfide (H(2)S) in the oral cavity that is mediated by several enzymes. The identification and characterization of three distinct enzymes (Fn0625, Fn1055 and Fn1220) in F. nucleatum that catalyse the production of H(2)S from l-cysteine have been reported. In the current study, a novel enzyme involved in the production of H(2)S in F. nucleatum ATCC 25586, whose molecular mass had been estimated to be approximately 130 kDa, was identified by two-dimensional electrophoresis combined with MALDI-TOF MS. The enzyme, Fn1419, has previously been characterized as an l-methionine γ-lyase. SDS-PAGE and gel-filtration chromatography indicated that Fn1419 has a molecular mass of 43 kDa and forms tetramers in solution. Unlike other enzymes associated with H(2)S production in F. nucleatum, the quaternary structure of Fn1419 was not completely disrupted by exposure to SDS. The purified recombinant enzyme exhibited a K(m) of 0.32±0.02 mM and a k(cat) of 0.69±0.01 s(-1). Based on current and published data, the enzymic activity for H(2)S production from l-cysteine in F. nucleatum is ranked as follows: Fn1220>Fn1055>Fn1419>Fn0625. Based on kinetic values and relative mRNA levels of the respective genes, as determined by real-time quantitative PCR, the amount of H(2)S produced by Fn1419 was estimated to be 1.9 % of the total H(2)S produced from l-cysteine in F. nucleatum ATCC 25586. In comparison, Fn1220 appeared to contribute significantly to H(2)S production (87.6 %).

Identification and enzymic analysis of a novel protein associated with production of hydrogen sulfide and l-serine from l-cysteine in Fusobacterium nucleatum subsp. nucleatum ATCC 25586

A third enzyme that produces hydrogen sulfide from l-cysteine was identified in Fusobacterium nucleatum subsp. nucleatum. The fn1055 gene was cloned from a cosmid library constructed with genomic DNA of F. nucleatum ATCC 25586. Despite the database annotation that the product of fn1055 is a cysteine synthase, reverse-phase HPLC revealed that no l-cysteine was produced in vitro by the purified Fn1055 protein; however, the enzyme did produce l-serine. In addition, a cysteine auxotroph, Escherichia coli NK3, transformed with a plasmid containing the fn1055 gene did not grow without cysteine, which further suggests that Fn1055 does not function as a cysteine synthase. The Michaelis–Menten kinetics (K m = 0.09±0.001 mM and k cat = 5.43±0.64 s−1) of the purified enzyme showed that the capacity of Fn1055 to produce hydrogen sulfide was between that of two other enzymes, Fn0625 and Fn1220. Incubation of Fn1055 with l-cysteine resulted in the production of hydrogen sulfide, but not of pyruvate, ammonia or lanthionine, which are all byproducts produced in addition to hydrogen sulfide when Fn0625 or Fn1220 is incubated with l-cysteine. Instead, Fn1055 produced l-serine in its reaction with l-cysteine. Fn1055 produces hydrogen sulfide from l-cysteine by a mechanism that is different from that of Fn0625 or Fn1220.

Oral malodorous compound causes oxidative stress and p53-mediated programmed cell death in keratinocyte stem cells

BACKGROUND

It is well known that hydrogen sulfide (H(2)S), the main substance causing physiologic halitosis, is also involved in the etiology of periodontitis. Gingival crevicular epithelium is the first barrier against periodontal pathogens and their products; keratinocyte stem cells play key roles in maintaining this barrier. An increased apoptotic process can affect keratinocyte stem cells, having a direct impact on oral epithelial tissue architecture. Our objective is to determine whether H(2)S induces apoptosis in human keratinocyte stem cells.

METHODS

Apoptosis levels; p53 activity; reactive oxygen species; mitochondrial membrane depolarization; cytochrome C release; and caspase-9, -8, and -3 were assessed using enzyme-linked immunosorbent assay and flow cytometry. Genomic DNA damage was examined using single-cell gel electrophoresis. Real-time polymerase chain reaction was used for Bax detection.

RESULTS

The percentage of apoptotic cells was significantly increased (20.5% +/- 1.6% versus 4.5% +/- 1.1% at 24 hours and 37.8% +/- 5.4% versus 4.8% +/- 0.9% at 48 hours; P <0.05, respectively; n = 5). Mitochondrial membrane potential was collapsed and reactive oxygen species levels were significantly increased compared to their control groups. At each time point the amount of released cytochrome C into the cytosol was significantly increased. Caspase-9 and -3 activities were significantly increased (P <0.05), whereas caspase-8 remained inactive. After both 24 and 48 hours, total and phosphorylated p53 levels were significantly increased.

CONCLUSION

We conclude that H(2)S can induce apoptosis in human keratinocyte stem cells, a key component of the epithelial barrier, following DNA damage and p53 activation.

The pleiotropic CymR regulator of Staphylococcus aureus plays an important role in virulence and stress response

We have characterized a novel pleiotropic role for CymR, the master regulator of cysteine metabolism. We show here that CymR plays an important role both in stress response and virulence of Staphylococcus aureus. Genes involved in detoxification processes, including oxidative stress response and metal ion homeostasis, were differentially expressed in a ΔcymR mutant. Deletion of cymR resulted in increased sensitivity to hydrogen peroxide-, disulfide-, tellurite- and copper-induced stresses. Estimation of metabolite pools suggests that this heightened sensitivity could be the result of profound metabolic changes in the ΔcymR mutant, with an increase in the intracellular cysteine pool and hydrogen sulfide formation. Since resistance to oxidative stress within the host organism is important for pathogen survival, we investigated the role of CymR during the infectious process. Our results indicate that the deletion of cymR promotes survival of S. aureus inside macrophages, whereas virulence of the ΔcymR mutant is highly impaired in mice. These data indicate that CymR plays a major role in virulence and adaptation of S. aureus for survival within the host.

Staphylococcus aureus is a very harmful human pathogen that is a major cause of nosocomial infections. Humans have developed sophisticated defense strategies against invading bacteria, including the innate immune response, with the generation of an oxidative burst inside phagocytic cells. Staphylococcal infections are extremely difficult to eradicate due to the remarkable capacity of these bacteria to adapt to different environmental conditions both inside and outside the host organism. Sulfur metabolism is essential for all living organisms and is tightly controlled by regulatory proteins. In this paper, we revealed an important role for CymR, a major regulator of sulfur metabolism, in adaptation of S. aureus to the host environment. Inactivation of the gene encoding this regulator in S. aureus leads to a mutant bacterium with increased vulnerability to stress conditions including oxidative stress encountered inside the host. More importantly, the deletion of the cymR gene strongly affected the interaction of S. aureus with its host, leading to impaired virulence in mice. Our results place CymR among the potential targets for attenuation of S. aureus infections.

Production of hydrogen sulfide by two enzymes associated with biosynthesis of homocysteine and lanthionine in Fusobacterium nucleatum subsp. nucleatum ATCC 25586

Fusobacterium nucleatum produces a large amount of the toxic metabolite hydrogen sulfide in the oral cavity. Here, we report the molecular basis of F. nucleatum H(2)S production, which is associated with two different enzymes: the previously reported Cdl (Fn1220) and the newly identified Lcd (Fn0625). SDS-PAGE analysis with activity staining revealed that crude enzyme extracts from F. nucleatum ATCC 25586 contained three major H(2)S-producing proteins. Two of the proteins with low molecular masses migrated similarly to purified Fn0625 and Fn1220. Their kinetic values suggested that Fn0625 had a lower enzymic capacity to produce H(2)S from L-cysteine (approximately 30%) than Fn1220. The Fn0625 protein degraded a variety of substrates containing betaC-S linkages to produce ammonia, pyruvate and sulfur-containing products. Unlike Fn0625, Fn1220 produced neither pyruvate nor ammonia from L-cysteine. Reversed-phase HPLC separation and mass spectrometry showed that incubation of L-cysteine with Fn1220 produced H(2)S and an uncommon amino acid, lanthionine, which is a natural constituent of the peptidoglycans of F. nucleatum ATCC 25586. In contrast, most of the sulfur-containing substrates tested, except L-cysteine, were not used by Fn1220. Real-time PCR analysis demonstrated that the fn1220 gene showed several-fold higher expression than fn0625 and housekeeping genes in exponential-phase cultures of F. nucleatum. Thus, we conclude that Fn0625 and Fn1220 produce H(2)S in distinct manners: Fn0625 carries out beta-elimination of L-cysteine to produce H(2)S, pyruvate and ammonia, whereas Fn1220 catalyses the beta-replacement of L-cysteine to produce H(2)S and lanthionine, the latter of which may be used for peptidoglycan formation in F. nucleatum.