Differences in the betaC-S lyase activities of viridans group streptococci

Roles of sulfur-containing compounds in fermented beverages with 2-furfurylthiol as a case example

Aroma is a critical component of the flavor and quality of beverages. Among the volatile chemicals responsible for fragrance perception, sulfur compounds are unique odorants due to their extremely low odor threshold. Although trace amounts of sulfur compounds can enhance the flavor profile of beverages, they can lead to off-odors. Sulfur compounds can be formed via Maillard reaction and microbial metabolism, imparting coffee aroma and altering the flavor of beverages. In order to increase the understanding of sulfur compounds in the field of food flavor, 2-furfurylthiol (FFT) was chosen as a representative to discuss the current status of their generation, sensory impact, enrichment, analytical methods, formation mechanisms, aroma deterioration, and aroma regulation. FFT is comprehensively reviewed, and the main beverages of interest are typically baijiu, beer, wine, and coffee. Challenges and recommendations for FFT are also discussed, including analytical methods and mechanisms of formation, interactions between FFT and other compounds, and the development of specific materials to extend the duration of aroma after release.

Virulence factors of Streptococcus anginosus - a molecular perspective

Streptococcus anginosus together with S. constellatus and S. intermedius constitute the Streptococcus anginosus group (SAG), until recently considered to be benign commensals of the human mucosa isolated predominantly from oral cavity, but also from upper respiratory, intestinal, and urogenital tracts. For years the virulence potential of SAG was underestimated, mainly due to complications in correct species identification and their assignment to the physiological microbiota. Still, SAG representatives have been associated with purulent infections at oral and non-oral sites resulting in abscesses formation and empyema. Also, life threatening blood infections caused by SAG have been reported. However, the understanding of SAG as potential pathogen is only fragmentary, albeit certain aspects of SAG infection seem sufficiently well described to deserve a systematic overview. In this review we summarize the current state of knowledge of the S. anginosus pathogenicity factors and their mechanisms of action.

Conversion of a Thiol Precursor into Aroma Compound 4-mercapto-4-methyl-2-pentanone Using Microbial Cell Extracts

4-Mercapto-4-methyl-2-pentanone (4MMP), a high-impact aroma compound with the box tree and black currant flavors was first identified in wines and could be released by microbial cysteine-S-conjugate β-lyases from its precursors. In this study, various yeasts and bacteria encoding β-lyases were selected to examine their β-lyase activities. A thiol precursor of 4MMP, cysteine-conjugate of 4MMP (cys-4MMP), was synthesized with a purity of >95% in a relatively environmentally friendly approach, and its chemical structure was confirmed by nuclear magnetic resonance spectroscopy. The β-lyase activities of the crude cell extract from the bacteria and yeast strains for different substrates were examined using a colorimetric method. Shewanella putrefaciens cell extract exhibited the highest β-lyase activity for all tested substrates. Additionally, the optimum pH and temperature for their β-lyase activities were determined. To monitor the conversion efficiency of precursor cys-4MMP to 4MMP, liquid chromatography-mass spectrometry was used. Our data indicate that selected bacteria and yeasts could convert cys-4MMP into 4MMP, and S. putrefaciens exhibited the best conversion yield. This study demonstrated the potential use of microbial cell extracts to produce sulfur-containing aroma compounds such as 4MMP.

Probiotics as an Adjunct Therapy for the Treatment of Halitosis, Dental Caries and Periodontitis

Probiotics and prebiotics are popular among consumers worldwide as natural approaches to prevent gastrointestinal diseases. The effects of their consumption on the gastrointestinal system have been extensively investigated. Recently, the efficacy of probiotics and prebiotics has been evaluated against naturally developing microbiome imbalance in the human body, such as in the oral cavity, skin, female urogenital tract, and respiratory tract. This review examines the scientific data related to the effects of probiotics on the treatment of diseases occurring in the oral cavity. Probiotics can effectively prevent and treat some infectious diseases in the oral cavity, such as halitosis and periodontitis, and can reduce the development of dental caries and the concentration of harmful bacteria, according to clinical studies. The results of this meta-analysis also suggest the use of probiotics to treat halitosis and periodontitis. However, the evidence may be inconclusive due in part to the use of a wide range of probiotics, non-standardized study design, small population size, poor quality reports, and inconsistent data. Therefore, future studies should homogenize terms and definitions for primary and secondary outcomes, increase the number of volunteers/patients in in vitro tests and clinical studies, and include an evaluation of the combined use of pre- and probiotics.

Efficacy of antimicrobial photodynamic therapy with Rose Bengal and blue light against cariogenic bacteria

OBJECTIVE

We evaluated the effect of antimicrobial photodynamic therapy (a-PDT) with Rose Bengal and blue light LED on bacteria that initiate and promote dental caries.

DESIGN

Colony forming units of Streptococcus mutans, Streptococcus sobrinus, Streptococcus sanguinis, and Lactobacillus salivarius under planktonic and biofilm conditions were counted after a-PDT treatment using Rose Bengal and blue light LED. In addition, cariogenic bacteria from saliva and dental plaques from ten volunteers were used for evaluation of a-PDT treatment.

RESULTS

We found that a-PDT using Rose Bengal at > 10 μg/mL had antimicrobial effects on oral Gram-positive S. mutans, S. sobrinus, S. sanguinis, and L. salivarius under both planktonic and biofilm conditions. The effect was also observed for cariogenic bacteria that formed biofilms containing water-insoluble glucans, through which the bacteria are firmly attached to the tooth surface. Moreover, a-PDT led to a marked reduction in cariogenic bacteria in saliva and dental plaques.

CONCLUSION

a-PDT could be a useful approach for controlling dental caries in dental surgery.

Induction and inhibition of oral malodor

Volatile sulfur compounds (VSCs) such as hydrogen sulfide (H₂ S) and methyl mercaptan (CH₃ SH) are the main components of oral malodor, and are produced as the end products of the proteolytic processes of oral microorganisms. The main pathway of proteolysis is the metabolism of sulfur-containing amino acids by gram-negative anaerobic bacteria. Gram-positive bacteria may promote VSC production by gram-negative anaerobes by cleaving sugar chains from glycoproteins and thus providing proteins. A large variety of bacteria within the oral microbiota are thought to be involved in the complex phenomenon of halitosis. Oral microbiota associated with a lack of oral malodor, oral microbiota associated with severe and H₂ S-dominant oral malodor, and oral microbiota associated with severe and CH₃ SH-dominant oral malodor have been distinguished through molecular approaches using the 16S rRNA gene. Pathological halitosis may primarily be addressed through treatment of causative diseases. In all cases, plaque control is the basis of oral malodor control, and dentifrices, mouthwashes, and functional foods play a supplementary role in addition to brushing. Recently, the use of natural ingredients in products tends to be favored due to the increase in antibiotic-resistant strains and the side effects of some chemical ingredients. In addition, probiotics and vaccines are expected to offer new strategies for improving the oral conditions through mechanisms other than antibacterial agents.

Efficacy of chlorine dioxide mouthwash in reducing oral malodor: A 2-week randomized, double-blind, crossover study

The aim of this clinical trial was to assess the inhibitory effects of a mouthwash containing 0.1% ClO2 used for 2 weeks on oral malodor, periodontal and salivary parameters, tongue coating, and Gram-negative and Gram-positive bacteria in saliva. Thirty-nine subjects with oral malodor were randomly assigned into two groups. In the first stage, one group was instructed to rinse with the experimental mouthwash (containing 0.1% ClO2), whereas the other group was instructed to rinse with the control mouthwash (sodium chloride 0.9%) for 2 weeks. After 4 weeks of washing out, in the second stage, each group then used the other mouthwash for 2 weeks. Oral malodor, periodontal status, tongue coating, salivary pH and flow rate, and the amounts of the salivary bacteria Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum, Porphyromonas gingivalis, Solobacterium moorei, Streptococcus salivarius, Treponema denticola, and Tannerella forsythia were evaluated at baseline and after 2 weeks of mouthwash use. After 12 hr and after 2 weeks, organoleptic scores and the levels of H2S and CH3SH were significantly lower in the experimental group compared with those in the control group. After 2 weeks, the experimental mouthwash appeared significantly effective in reducing plaque index, tongue-coating score, and the amounts of F. nucleatum, S. moorei, T. denticola, and T. forsythia in the whole saliva, compared with those at baseline. Mouthwash containing 0.1% ClO2 is effective in reducing oral malodor, dental plaque, tongue-coating accumulation, and the amounts of F. nucleatum, S. moorei, T. denticola, and T. forsythia in saliva.

Generation of 2-Furfurylthiol by Carbon-Sulfur Lyase from the Baijiu Yeast Saccharomyces cerevisiae G20

2-Furfurylthiol is the representative aroma compound of Chinese sesame-flavored baijiu. Previous studies demonstrated that baijiu yeasts could generate 2-furfurylthiol using furfural and l-cysteine as precursors and that the Saccharomyces cerevisiae genes STR3 and CYS3 are closely related to 2-furfurylthiol biosynthesis. To confirm the mechanism of the STR3- and CYS3-gene products on 2-furfurylthiol biosynthesis, their encoded proteins were purified, and we confirmed their activities as carbon-sulfur lyases. Str3p and Cys3p were able to cleave the cysteine-furfural conjugate to release 2-furfurylthiol. Moreover, the characterization of the enzymatic properties of the purified proteins shows good thermal stabilities and wide pH tolerances, which enable their strong potential for various applications. These data provide direct evidence that yeast Str3p and Cys3p release 2-furfurylthiol in vitro, which can be applied to improve baijiu flavor.

Characterization of C-S lyase from Lactobacillus delbrueckii subsp. bulgaricus ATCC BAA-365 and its potential role in food flavour applications

Volatile thiols have substantial impact on the aroma of many beverages and foods. Thus, the control of their formation, which has been linked to C-S lyase enzymatic activities, is of great significance in industrial applications involving food flavours. Herein, we have carried out a spectroscopic and functional characterization of a putative pyridoxal 5'-phosphate (PLP)-dependent C-S lyase from the lactic acid bacterium Lactobacillus delbrueckii subsp. bulgaricus ATCC BAA-365 (LDB C-S lyase). Recombinant LDB C-S lyase exists as a tetramer in solution and shows spectral properties of enzymes containing PLP as cofactor. The enzyme has a broad substrate specificity toward sulphur-containing amino acids with aminoethyl-L-cysteine and L-cystine being the most effective substrates over L-cysteine and L-cystathionine. Notably, the protein also reveals cysteine-S-conjugate β-lyase activity in vitro, and is able to cleave a cysteinylated substrate precursor into the corresponding flavour-contributing thiol, with a catalytic efficiency higher than L-cystathionine. Contrary to similar enzymes of other lactic acid bacteria however, LDB C-S lyase is not capable of α,γ-elimination activity towards L-methionine to produce methanethiol, which is a significant compound in flavour development. Based on our results, future developments can be expected regarding the flavour-forming potential of Lactobacillus C-S lyase and its use in enhancing food flavours.

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.

Effects of pH and lactate on hydrogen sulfide production by oral Veillonella spp

Indigenous oral bacteria in the tongue coating such as Veillonella have been identified as the main producers of hydrogen sulfide (H2S), one of the major components of oral malodor. However, there is little information on the physiological properties of H2S production by oral Veillonella such as metabolic activity and oral environmental factors which may affect H2S production. Thus, in the present study, the H2S-producing activity of growing cells, resting cells, and cell extracts of oral Veillonella species and the effects of oral environmental factors, including pH and lactate, were investigated. Type strains of Veillonella atypica, Veillonella dispar, and Veillonella parvula were used. These Veillonella species produced H2S during growth in the presence of l-cysteine. Resting cells of these bacteria produced H2S from l-cysteine, and the cell extracts showed enzymatic activity to convert l-cysteine to H2S. H2S production by resting cells was higher at pH 6 to 7 and lower at pH 5. The presence of lactate markedly increased H2S production by resting cells (4.5- to 23.7-fold), while lactate had no effect on enzymatic activity in cell extracts. In addition to H2S, ammonia was produced in cell extracts of all the strains, indicating that H2S was produced by the catalysis of cystathionine γ-lyase (EC 4.4.1.1). Serine was also produced in cell extracts of V. atypica and V. parvula, suggesting the involvement of cystathionine β-synthase lyase (EC 4.2.1.22) in these strains. This study indicates that Veillonella produce H2S from l-cysteine and that their H2S production can be regulated by oral environmental factors, namely, pH and lactate.

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 %).

Engineering Saccharomyces cerevisiae to release 3-Mercaptohexan-1-ol during fermentation through overexpression of an S. cerevisiae Gene, STR3, for improvement of wine aroma

Sulfur-containing aroma compounds are key contributors to the flavor of a diverse range of foods and beverages. The tropical fruit characters of Vitis vinifera L. cv. Sauvignon blanc wines are attributed to the presence of the aromatic thiols 3-mercaptohexan-1-ol (3MH), 3-mercaptohexan-1-ol-acetate, and 4-mercapto-4-methylpentan-2-one (4MMP). These volatile thiols are found in small amounts in grape juice and are formed from nonvolatile cysteinylated precursors during fermentation. In this study, we overexpressed a Saccharomyces cerevisiae gene, STR3, which led to an increase in 3MH release during fermentation of a V. vinifera L. cv. Sauvignon blanc juice. Characterization of the enzymatic properties of Str3p confirmed it to be a pyridoxal-5'-phosphate-dependent cystathionine β-lyase, and we demonstrated that this enzyme was able to cleave the cysteinylated precursors of 3MH and 4MMP to release the free thiols. These data provide direct evidence for a yeast enzyme able to release aromatic thiols in vitro that can be applied in the development of self-cloned yeast to enhance wine flavor.

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.

Crystallization and preliminary X-ray analysis of betaC-S lyases from two oral Streptococci

Hydrogen sulfide, which causes oral malodour, is generally produced from L-cysteine by the action of betaC-S lyase from oral bacteria. The betaC-S lyases from two oral bacteria, Streptococcus anginosus and S. gordonii, have been cloned, overproduced, purified and crystallized. X-ray diffraction data were collected from the two types of crystals using synchrotron radiation. The crystal of S. anginosus betaC-S lyase belonged to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 67.0, b = 111.1, c = 216.4 A, and the crystal of S. gordonii betaC-S lyase belonged to the same space group, with unit-cell parameters a = 58.0, b = 73.9. c = 187.6 A. The structures of the betaC-S lyases were solved by molecular-replacement techniques.

Identification and molecular analysis of βC–S lyase producing hydrogen sulfide in Streptococcus intermedius

Hydrogen sulfide (H2S) is a toxic gas that induces the modification and release of haemoglobin in erythrocytes; however, it also functions in methionine biosynthesis in bacteria.βC–S lyase, encoded by thelcdgene, is responsible for bacterial H2S production through the cleavage ofl-cysteine. In this study, 26 of 29 crude extracts from reference and clinical strains ofStreptococcus intermediusproduced H2S froml-cysteine. The capacities in those strains were not higher than those in strains of the other anginosus group of streptococci,Streptococcus anginosusandStreptococcus constellatus, but were much greater than those in strains ofStreptococcus gordonii, which is known to have an extremely low capacity for H2S production. Incubation of the remaining three extracts withl-cysteine did not result in H2S production. Sequence analysis revealed that thelcdgenes from these three strains (S. intermediusstrains ATCC 27335, IMU151 and IMU202) contained mutations or small deletions. H2S production in crude extracts prepared fromS. intermediusATCC 27335 was restored by repairing thelcdgene sequence in genomic DNA. The kinetic properties of the purified recombinant protein encoded by the repairedlcdgene were comparable to those of native proteins produced by H2S-producing strains, whereas the truncated protein produced byS. intermediusATCC 27335 had no enzymic activity withl-cysteine orl-cystathionine. However, real-time PCR analysis indicated that thelcdgene in strains ATCC 27335, IMU151 and IMU202 is transcribed and regulated in a manner similar to that in the H2S-producing strain.

Bioremediation of cadmium by growing Rhodobacter sphaeroides: kinetic characteristic and mechanism studies

The removal kinetic characteristic and mechanism of cadmium by growing Rhodobacter sphaeroides were investigated. The removal data were fitted to the second-order equation, with a correlation coefficient, R2=0.9790-0.9916. Furthermore, it was found that the removal mechanism of cadmium was predominantly governed by bioprecipitation as cadmium sulfide with biosorption contributing to a minor extent. Also, the results revealed that the activities of cysteine desulfhydrase in strains grown in the presence of 10 and 20 mg/l of cadmium were higher than in the control, while the activities in the presence of 30 and 40 mg/l of cadmium were lower than in the control. Content analysis of subcellular fractionation showed that cadmium was mostly removed and transformed by precipitation on the cell wall.

Amino Acid Catabolic Pathways of Lactic Acid Bacteria

Lactic acid bacteria (LAB) constitute a diverse group of Gram positive obligately fermentative microorganisms which include both beneficial and pathogenic strains. LAB generally have complex nutritional requirements and therefore they are usually associated with nutrient-rich environments such as animal bodies, plants and foodstuffs. Amino acids represent an important resource for LAB and their utilization serves a number of physiological roles such as intracellular pH control, generation of metabolic energy or redox power, and resistance to stress. As a consequence, the regulation of amino acid catabolism involves a wide set of both general and specific regulators and shows significant differences among LAB. Moreover, due to their fermentative metabolism, LAB amino acid catabolic pathways in some cases differ significantly from those described in best studied prokaryotic model organisms such as Escherichia coli or Bacillus subtilis. Thus, LAB amino acid catabolism constitutes an interesting case for the study of metabolic pathways. Furthermore, LAB are involved in the production of a great variety of fermented products so that the products of amino acid catabolism are also relevant for the safety and the quality of fermented products.

A preliminary study of the effect of probiotic Streptococcus salivarius K12 on oral malodour parameters

AIMS

To determine whether dosing with bacteriocin-producing Streptococcus salivarius following an antimicrobial mouthwash effects a change in oral malodour parameters and in the composition of the oral microbiota of subjects with halitosis.

MATERIALS AND RESULTS

Twenty-three subjects with halitosis undertook a 3-day regimen of chlorhexidine (CHX) mouth rinsing, followed at intervals by the use of lozenges containing either S. salivarius K12 or placebo. Assessment of the subjects' volatile sulphur compound (VSC) levels 1 week after treatment initiation showed that 85% of the K12-treated group and 30% of the placebo group had substantial (>100 ppb) reductions. The bacterial composition of the saliva was monitored by culture and PCR-denaturing gradient gel electrophoresis (PCR-DGGE). Changes in the PCR-DGGE profiles occurred in most subjects following K12 treatment. In vitro testing showed that S. salivarius K12 suppressed the growth of black-pigmented bacteria in saliva samples and also in various reference strains of bacteria implicated in halitosis.

CONCLUSIONS

Administration of bacteriocin-producing S. salivarius after an oral antimicrobial mouthwash reduces oral VSC levels.

SIGNIFICANCE AND IMPACT OF THE STUDY

The outcome of this preliminary study indicates that the replacement of bacteria implicated in halitosis by colonization with competitive bacteria such as S. salivarius K12 may provide an effective strategy to reduce the severity of halitosis.

Homogeneous enzymatic assay for L-cysteine with betaC-S lyase

We have developed a new enzymatic assay for determining L-cysteine concentration. The method involves the use of betaC-S lyase from Streptococcus anginosus, which catalyzes the alpha,beta-elimination of L-cysteine to hydrogen sulfide, pyruvate, and ammonia. The production of pyruvate is measured by D-lactate dehydrogenase and NADH. The decrease in NADH was proportional to the L-cysteine concentration up to 1.0 mM. When serum samples were used, within-day and day-to-day coefficient variations were below 4%. This method is simple, and can easily and reliably be used for accurate determination of L-cysteine concentration in serum or other samples.

Sulfur amino acid metabolism and its control in Lactococcus lactis IL1403

Cysteine and methionine availability influences many processes in the cell. In bacteria, transcription of the specific genes involved in the synthesis of these two amino acids is usually regulated by different mechanisms or regulators. Pathways for the synthesis of cysteine and methionine and their interconversion were experimentally determined for Lactococcus lactis, a lactic acid bacterium commonly found in food. A new gene, yhcE, was shown to be involved in methionine recycling to cysteine. Surprisingly, 18 genes, representing almost all genes of these pathways, are under the control of a LysR-type activator, FhuR, also named CmbR. DNA microarray experiments showed that FhuR targets are restricted to this set of 18 genes clustered in seven transcriptional units, while cysteine starvation modifies the transcription level of several other genes potentially involved in oxidoreduction processes. Purified FhuR binds a 13-bp box centered 46 to 53 bp upstream of the transcriptional starts from the seven regulated promoters, while a second box with the same consensus is present upstream of the first binding box, separated by 8 to 10 bp. O-Acetyl serine increases FhuR binding affinity to its binding boxes. The overall view of sulfur amino acid metabolism and its regulation in L. lactis indicates that CysE could be a master enzyme controlling the activity of FhuR by providing its effector, while other controls at the enzymatic level appear to be necessary to compensate the absence of differential regulation of the genes involved in the interconversion of methionine and cysteine and other biosynthesis genes.

The rationale and potential for the reduction of oral malodour using Streptococcus salivarius probiotics

The primary treatment for oral malodour is the reduction of bacterial populations, especially those present on the tongue, by use of a variety of antimicrobial agents or mechanical devices. However, shortly after treatment the problematic bacteria quickly repopulate the tongue and the malodour returns. In our studies, we have used a broadly-active antimicrobial (chlorhexidine) to effect temporary depletion of the oral microbiota and then have attempted to repopulate the tongue surface with Streptococcus salivarius K12, a benign commensal probiotic. The objective of this is to prevent re-establishment of non-desirable bacterial populations and thus help limit the re-occurrence of oral malodour over a prolonged period. In this paper, we discuss why contemporary probiotics are inadequate for treatment of oral malodour and examine the rationale for selection of particular bacterial species for future use in the treatment of this condition. In our preliminary trials of the use of a chlorhexidine rinse followed by strain K12 lozenges, the majority (8/13) of subjects with confirmed halitosis maintained reduced breath levels of volatile sulphur compounds for at least 2 weeks. We conclude that probiotic bacterial strains originally sourced from the indigenous oral microbiotas of healthy humans may have potential application as adjuncts for the prevention and treatment of halitosis.

The PatB protein of Bacillus subtilis is a C-S-lyase

The PatB protein of Bacillus subtilis had both cystathionine beta-lyase and cysteine desulfhydrase activities in vitro. The apparent K(m) value of the PatB protein for cystathionine was threefold higher than that of the MetC protein, the previously characterized cystathionine beta-lyase of B. subtilis. In the presence of cystathionine as sole sulfur source, the patB gene present on a multicopy plasmid restored the growth of a metC mutant. In addition, the patB metC double mutant was unable to grow in the presence of sulfate or cystine while the patB or metC single mutants grew similarly to the wild-type strains in the presence of the same sulfur sources. In a metC mutant, the PatB protein can replace the MetC enzyme in the methionine biosynthetic pathway.

Antimicrobial effects of a new therapeutic liquid dentifrice formulation on oral bacteria including odorigenic species

The control of oral malodor is well-recognized in efforts to improve oral health. Antimicrobial formulations can mitigate oral malodor, however, procedures to assess effects on oral bacteria including those implicated in halitosis are unavailable. This investigation examined the antimicrobial effects of a new liquid triclosan/copolymer dentifrice (test) formulation that demonstrated significant inhibition of oral malodor in previous organoleptic clinical studies. Procedures compared antimicrobial effects of the test and control formulations on a range of oral micro-organisms including members implicated in halitosis, substantive antimicrobial effects of formulations with hydroxyapatite as a surrogate for human teeth and ex vivo effects on oral bacteria from human volunteers. With Actinomyces viscosus, as a model system, the test formulation demonstrated a dose-dependent effect. At these concentrations the test formulation provided significant antimicrobial effects on 13 strains of oral bacteria including those implicated in bad breath at selected posttreatment time points. Treatment of hydroxyapatite by the test dentifrice resulted in a significant and substantive antimicrobial effect vs. controls. Oral bacteria from subjects treated ex vivo with the test dentifrice resulted in significant reductions in cultivable oral bacteria and odorigenic bacteria producing hydrogen sulfide. In summary, microbiological methods adapted to study odorigenic bacteria demonstrate the significant antimicrobial effects of the test (triclosan/copolymer) dentifrice with laboratory and clinical strains of oral bacteria implicated in bad breath.

Homocysteine biosynthesis pathways of Streptococcus anginosus

A gene (cgs) encoding cystathionine gamma-synthase was cloned from Streptococcus anginosus, and its protein was purified and characterized. The cgs gene and the immediately downstream lcd gene were shown to be cotranscribed as an operon. High-performance liquid chromatography analyses showed that the S. anginosus Cgs not only has cystathionine gamma-synthase activity, but also expresses O-acetylhomoserine sulfhydrylase activity. These results suggest that S. anginosus has the capacity to utilize both the transsulfuration and direct sulfhydrylation pathways for homocysteine biosynthesis.