Trace elements and electrolytes in human resting mixed saliva after exercise

Impact of calcium ions at physiological concentrations on the adsorption behavior of proteins on silica nanoparticles

The adsorption of proteins on nanoparticles (NPs) largely decides the fate and bioeffects of NPs in vivo. However, bio-fluids are too complicated to directly study in them to reveal related mechanisms, and current studies on model systems often ignore some important biological factors, such as metal ions. Herein, we evaluate the effect of Ca2+ at physiological concentrations on the protein adsorption on negatively-charged silica NP (SNP50). It is found that Ca2+, as well as Mg2+ and several transition metal ions, significantly enhances the adsorption of negatively-charged proteins on SNP50. Moreover, the Ca2+-induced enhancement of protein adsorption leads to the reduced uptake of SNP50 by HeLa cells. A double-chelating mechanism is proposed for the enhanced adsorption of negatively-charged proteins by multivalent metal ions that can form 6 (or more) coordinate bonds, where the metal ions are chelated by both the surface groups of NPs and the surface residues of the adsorbed proteins. This mechanism is consistent with all experimental evidences from metal ions-induced changes of physicochemical properties of NPs to protein adsorption isotherms, and is validated with several model proteins as well as complicated serum. The findings highlight the importance of investigating the influences of physiological factors on the interaction between proteins and NPs.

Small regulatory RNAs are mediators of the Streptococcus mutans SloR regulon

Dental caries is among the most prevalent chronic infectious diseases worldwide. Streptococcus mutans , the chief causative agent of caries, uses a 25 kDa manganese dependent SloR protein to coordinate the uptake of essential manganese with the transcription of its virulence attributes. Small non-coding RNAs (sRNAs) can either enhance or repress gene expression and reports in the literature ascribe an emerging role for sRNAs in the environmental stress response. Herein, we identify 18-50 nt sRNAs as mediators of the S. mutans SloR and manganese regulons. Specifically, the results of sRNA-seq revealed 56 sRNAs in S. mutans that were differentially transcribed in the SloR-proficient UA159 and SloR-deficient GMS584 strains, and 109 sRNAs that were differentially expressed in UA159 cells grown in the presence of low versus high manganese. We describe SmsR1532 and SmsR1785 as SloR- and/or manganese-responsive sRNAs that are processed from large transcripts, and that bind SloR directly in their promoter regions. The predicted targets of these sRNAs include regulators of metal ion transport, growth management via a toxin-antitoxin operon, and oxidative stress tolerance. These findings support a role for sRNAs in coordinating intracellular metal ion homeostasis with virulence gene control in an important oral cariogen.

IMPORTANCE

Small regulatory RNAs (sRNAs) are critical mediators of environmental signaling, particularly in bacterial cells under stress, but their role in Streptococcus mutans is poorly understood. S. mutans, the principal causative agent of dental caries, uses a 25 kDa manganese-dependent protein, called SloR, to coordinate the regulated uptake of essential metal ions with the transcription of its virulence genes. In the present study, we identified and characterize sRNAs that are both SloR- and manganese-responsive. Taken together, this research can elucidate the details of regulatory networks that engage sRNAs in an important oral pathogen, and that can enable the development of an effective anti-caries therapeutic.

Influence of Swimming Training Session on Selected Saliva Components in Youth Swimmers

Exercise may induce many changes in biochemical parameters of the saliva. Thanks to non-invasive access, saliva can be used as a diagnostic material in physical activity monitoring. The aim of the study was comparison of selected salivary components in swimmers before and after training session. 40 male subjects aged 12–15, out of whom 30 were competitive swimmers and 10 control were involved in the study. Salivary samples were collected from all subjects in the morning, and in the afternoon; from the swimmers, they were also collected before and after the workout. Salivary flow rate-V, pH, total protein-P, alpha-amylase-Amy, salivary peroxidase-SPO, cortisol-C, total antioxidant status-TAS, sialic acid (free-FSA, bound-GSA, total-TSA), calcium-Ca, magnesium-Mg were measured. The swimmers assessed the workout intensity of training session using the RPE Foster’s scale. The circadian rhythm pattern of some salivary components and differences after training were found. In swimmers after the morning exercise significant increase of P (0.83 ± 0.27 vs. 1.10 ± 0.58 g/L), Amy (64.91 ± 70.86 vs. 87.07 ± 92.46IU/L), Ca (3.83 ± 1.33 vs. 4.99 ± 2.24 mg/L), Mg (0.52 ± 0.32 vs. 0.73 ± 0.34 mg/L), TAS (0.64 ± 0.27 vs. 0.72 ± 0.26 mmol/L) and decrease V (0.47 ± 0.37 vs. 0.36 ± 0.22 mg/min), C (5.86 ± 5.00 vs. 3.54 ± 5.07 μg/ml) were found. After the afternoon training significant increase of pH (7.13 ± 0.33 vs. 7.27 ± 0.24), Amy (111.53 ± 120.13 vs. 130.91 ± 161.14IU/L), Ca (3.72 ± 1.34 vs. 4.61 ± 1.58 mg/L), Mg (0.48 ± 0.28 vs. 0.60 ± 0.39 mg/L), TSA (5.64 ± 3.78 vs. 6.10 ± 3.08 mg/L), GSA (3.00 ± 3.06 vs. 3.38 ± 2.26 mg/L), and decrease of V (0.63 ± 0.63 vs. 0.49 ± 0.39 ml/min) were noticed. Before training in the morning in the swimmers significantly higher of V (0.47 ± 0.37 vs. 0.26 ± 0.15 mg/min), TAS (0.64 ± 0.27 vs. 0.40 ± 0.16 mmol/L), and lower pH (7.01 ± 0.46 vs. 7.53 ± 0.33), P (0.83 ± 0.27 vs. 1.86 ± 1.28 g/L), Amy (64.91 ± 70.86 vs. 146.56 ± 114.45IU/L) compared to the control were found. In the afternoon in swimmers before training session significantly lower pH (7.13 ± 0.33 vs. 7.53 ± 0.49) and Amy (111.53 ± 120.13 vs. 170.98 ± 107.72IU/L) in comparison to the control were noticed. The RPE scores were negatively correlated with V (rho = −0.500, p = 0.05 and pH (rho = −0.382, p = 0.03) measured after the morning session and after the afternoon training with V (rho = −0.570, p = 0.01) and Ca (rho = −0.401, p = 0.08). The levels of salivary flow rate, alpha amylase, cortisol, calcium, magnesium were associated with swimming training session, and showed circadian variation without a significant effect on their responses to exercise.

A secret of salivary secretions: Multimodal effect of saliva in sensory perception of food

Saliva plays multifunctional roles in oral cavity. Even though its importance for the maintenance of oral health has long been established, the role of saliva in food perception has attracted increasing attention in recent years. We encourage researchers to discover the peculiarity of this biological fluid and aim to combine the data concerning all aspects of the saliva influence on the sensory perception of food. This review presents saliva as a unique material, which modulates food perception due to constant presence of saliva in the mouth and thanks to its composition. Therefore, we highlight the salivary components that contribute to these effects. Moreover, this review is an attempt to structure the effects of saliva on perception of different food categories, where the mechanisms of salivary impact in perception of liquid, semi-solid, and solid foods are revealed. Finally, we emphasize that the large inter-individual variability in salivary composition and secretion appear to contribute to the fact that everyone experiences food in their own way. Therefore, the design of the sensory studies should consider the properties of volunteers' saliva and also carefully monitor the experimental conditions that affect salivary composition and flow rate.

Exploring metal availability in the natural niche of Streptococcus pneumoniae to discover potential vaccine antigens

Nasopharyngeal colonization by Streptococcus pneumoniae is a prerequisite for pneumococcal transmission and disease. Current vaccines protect only against disease and colonization caused by a limited number of serotypes, consequently allowing serotype replacement and transmission. Therefore, the development of a broadly protective vaccine against colonization, transmission and disease is desired but requires a better understanding of pneumococcal adaptation to its natural niche. Hence, we measured the levels of free and protein-bound transition metals in human nasal fluid, to determine the effect of metal concentrations on the growth and proteome of S. pneumoniae. Pneumococci cultured in medium containing metal levels comparable to nasal fluid showed a highly distinct proteomic profile compared to standard culture conditions, including the increased abundance of nine conserved, putative surface-exposed proteins. AliA, an oligopeptide binding protein, was identified as the strongest protective antigen, demonstrated by the significantly reduced bacterial load in a murine colonization and a lethal mouse pneumonia model, highlighting its potential as vaccine antigen.

Changes in salivary electrolyte concentrations in mid-distance trained sled dogs during 12 weeks of incremental conditioning

Regular exercise improves the health status of dogs; however, extreme exertion in the absence of adequate fluid and electrolyte replacement may negatively impact health and performance due to dehydration and cardiovascular stress. Unlike humans and horses, dogs thermoregulate predominantly through respiration and salivation, yet there is a dearth of literature defining exercise-induced changes to canine salivary electrolytes. The study objective was to investigate the effects of exercise on salivary electrolyte concentrations, and to determine if adaptations may occur in response to incremental conditioning in client-owned Siberian Huskies. Sixteen dogs were used, with an average age of 4.8 ± 2.5 years and body weight of 24.3 ± 4.3 kg. A 12-week exercise regimen was designed to increase in distance each week, but weather played a role in setting the daily distance. Saliva samples were collected at weeks 0 (pre-run, 5.7 km), 5 (pre-run, 5.7, 39.0 km), and 11 (pre-run, 5.7, 39.0 km). Samples were analyzed for sodium, chloride, potassium, calcium, magnesium, and phosphorous using photometric and indirect ion-selective electrode analysis. When compared across weeks, sodium, chloride, potassium, and calcium concentrations did not differ at any sampling time point; however, phosphorus and magnesium concentrations increased from baseline. Data were then pooled across weeks to evaluate changes due to distance and level of conditioning. Sodium, chloride, and magnesium concentrations increased progressively with distance ran, suggesting that these electrolytes are primarily being lost as exercising dogs salivate. Repletion of these minerals may assist in preventing exercise-induced electrolyte imbalance in physically active dogs.

Salivary lubricity (ex vivo) enhances upon moderate exercise: A pilot study

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Moderate intensity exercise leads to enhanced lubrication performance of saliva.

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Such enhanced lubrication performance was sustained after 60 min of rest.

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Protein content and α-amylase activity in saliva was elevated post-exercise.

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Protein content and α-amylase activity returned to baseline with an hour.

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Effects of exercise on salivary mucin (MUC5B) content was not observed.

Objective

This study sought to examine the effects of moderate intensity exercise on lubrication performance of saliva. We hypothesized that exercise would result in enhanced salivary lubricity by direct sympathetic stimulation of the salivary proteins.

Study design

In total, 11 healthy young pre-menopausal female participants (mean age: 24.4 ± 1.8 years, BMI: 22.1 ± 1.9 kg/m²) were included in a within-subjects repeated measures experimental design. Unstimulated whole saliva was collected at rest (S₀), immediately after 45 min of moderate intensity cycling at ∼70 % maximum heart rate (mean: 133.4 ± 0.8 bpm) or time-match quiet rest (S₁), and after a 60 min of recovery period (S₂). Ex vivo salivary lubricity were measured using soft tribology. Total protein content, mucin (MUC5B) concentration, and α-amylase activity were determined.

Results

Tribology results revealed that moderate intensity exercise resulted in enhanced lubricity of saliva with an order-of-magnitude lower friction coefficients in the boundary regime at S₁ and S_2, with frictional forces being significantly lower at S₁ (p < 0.001) and S₂ (p < 0.001) as compared to the Control procedure. Total protein and α-amylase secretion also increased in the Exercise procedure at S₁ (p < 0.05), but concentrations returned to baseline levels at S₂.

Conclusions

Moderate intensity exercise leads to an increase in α-amylase and total protein secretion resulting in enhanced lubrication performance of the saliva. However, the lubrication performance was not related to MUC5B content, suggesting the role of other proteinaceous species acting as lubricants. This proof-of-concept study serves as the first step to design exercise interventions in populations with dry mouth conditions.

Manganese Uptake, Mediated by SloABC and MntH, Is Essential for the Fitness of Streptococcus mutans

Early epidemiological studies implicated manganese (Mn) as a possible caries-promoting agent, while laboratory studies have indicated that manganese stimulates the expression of virulence-related factors in the dental pathogen Streptococcus mutans To better understand the importance of manganese homeostasis to S. mutans pathophysiology, we first used RNA sequencing to obtain the global transcriptional profile of S. mutans UA159 grown under Mn-restricted conditions. Among the most highly expressed genes were those of the entire sloABC operon, encoding a dual iron/manganese transporter, and an uncharacterized gene, here mntH, that codes for a protein bearing strong similarity to Nramp-type transporters. While inactivation of sloC, which encodes the lipoprotein receptor of the SloABC system, or of mntH alone had no major consequence for the overall fitness of S. mutans, simultaneous inactivation of sloC and mntH (ΔsloC ΔmntH) impaired growth and survival under Mn-restricted conditions, including in human saliva or in the presence of calprotectin. Further, disruption of Mn transport resulted in diminished stress tolerance and reduced biofilm formation in the presence of sucrose. These phenotypes were markedly improved when cells were provided with excess Mn. Metal quantifications revealed that the single mutant strains contained intracellular levels of Mn similar to those seen with the parent strain, whereas Mn was nearly undetectable in the ΔsloC ΔmntH strain. Collectively, these results reveal that SloABC and MntH work independently and cooperatively to promote cell growth under Mn-restricted conditions and that maintenance of Mn homeostasis is essential for the expression of major virulence attributes in S. mutansIMPORTANCE As transition biometals such as manganese (Mn) are essential for all forms of life, the ability to scavenge biometals in the metal-restricted host environment is an important trait of successful cariogenic pathobionts. Here, we showed that the caries pathogen Streptococcus mutans utilizes two Mn transport systems, namely, SloABC and MntH, to acquire Mn from the environment and that the ability to maintain the cellular levels of Mn is important for the manifestation of characteristics that associate S. mutans with dental caries. Our results indicate that the development of strategies to deprive S. mutans of Mn hold promise in the combat against this important bacterial pathogen.

Candida albicans Interactions with Mucosal Surfaces during Health and Disease

Flexible adaptation to the host environment is a critical trait that underpins the success of numerous microbes. The polymorphic fungus Candida albicans has evolved to persist in the numerous challenging niches of the human body. The interaction of C. albicans with a mucosal surface is an essential prerequisite for fungal colonisation and epitomises the complex interface between microbe and host. C. albicans exhibits numerous adaptations to a healthy host that permit commensal colonisation of mucosal surfaces without provoking an overt immune response that may lead to clearance. Conversely, fungal adaptation to impaired immune fitness at mucosal surfaces enables pathogenic infiltration into underlying tissues, often with devastating consequences. This review will summarise our current understanding of the complex interactions that occur between C. albicans and the mucosal surfaces of the human body.

Antimony exposure and speciation in human biomarkers near an active mining area in Hunan, China

Antimony (Sb) exposure threatens human health. To identify human biomarkers for Sb exposure, we analyzed 480 environmental samples from an active Sb mining area in Hunan, China. Elevated Sb concentrations exceeding the reference level were detected in drinking water (70% of n = 83 total samples), foods (80%, n = 188), urine (95%, n = 63), saliva (44%, n = 48), hair (80%, n = 51) and nails (83%, n = 47). Drinking water contributed 85%-100% of the average daily dose (ADD) of Sb, and the total ADD (11.7 μg/kg bodyweight/day) was up to thirty times higher than the oral reference dose (0.4 μg/kg bodyweight/day) as recommended by USEPA. A positive correlation was found between ADD and Sb content in hair (p = 0.02), but not in urine (p = 0.051), saliva (p = 0.52) or nails (p = 0.85), suggesting that hair is the best non-invasive biomarker. Micro X-ray fluorescence analysis indicated that Sb is distributed in discrete spots in hair and nails, and Sb distribution is correlated with other metals. Methylated Sb species were predominant in urine (46%-100%) and saliva (74%-100%) in collected samples, implying that the human metabolic system adopts methylation as an effective pathway to detoxify and excrete Sb.

Unstimulated saliva: Background noise in taste molecules

Saliva is a highly complex bodily fluid composed of many proteins, peptides, small organic molecules, and ions. Saliva is produced and secreted by the major and minor salivary glands to protect the mouth and to participate in digestion. Generally, a distinction is made between unstimulated saliva that is a result of autonomic stimulation and stimulated saliva that is produced during chewing and taste stimulation. The link between saliva and sensory perception can thus be regarded in two ways: the role of unstimulated saliva as a background taste and the mechanistic role of stimulated saliva during eating. Indeed, unstimulated saliva (and its components) is continuously bathing our oral cavity and as such stimulates our taste receptors, thus playing a role in taste sensitivity. However, the role of unstimulated salivary components in mediating taste has been studied only in very few substances. To explore this question, this review attempts to compare data from the literature on unstimulated salivary composition with those on taste sensitivity. The main conclusion centres around the concept that the gustatory self-adaptation phenomenon may be relevant for only a few salivary compounds. Further studies at the level of the salivary Von Ebner glands and salivary pellicle are necessary before arriving at definitive conclusions on this subject. PRACTICAL APPLICATION: Unstimulated saliva contains taste substances that can influence sensory perception through taste adaptation. However, large inter-individual variability exists in unstimulated salivary composition both qualitatively and quantitatively. These differences may explain the variability in taste perception and thus the food choices and behaviors of an individual. Thus, in the context of providing personalized food and nutrition to the consumer, variability of unstimulated saliva should be considered for specific formulation of food products.

Salivary metals, age, and gender correlate with cultivable oral Candida carriage levels

Background: Little is known about the normal range of metal levels in unstimulated saliva, nor whether these might impact Candida carriage in healthy individuals. Both are important in determining which populations are at risk for candidiasis, as the availability of metal ions can influence the growth and pathogenesis of Candida albicans.

Objective: We quantified salivary metals of healthy individuals to determine the correlation with C. albicans oral colonization.

Design: Unstimulated whole saliva was collected from healthy adults and plated to determine fungal carriage, and metal content was measured using ICP-mass spectrometry (ICP-MS).

Results: Zinc was most abundant, followed by iron, copper, manganese, and nickel. Cultivable oral Candida carriage was found in 48% of people. Total protein levels did not differ in salivas from donors with or without carriage. However, innate fungicidal activity was increased in donors with carriage; correlations between levels of several metals were stronger in salivas with fungal carriage, indicating a shift in the oral environment. Concentrations of copper and manganese, as well as age and gender, were significantly predictive of carriage levels in a multiple regression model.

Conclusions: Salivary copper and manganese content along with age and gender could be used as a predictive metric for individuals that are more susceptible to Candida overgrowth.

Level of minerals and trace elements in the urine of the participants of mountain ultra-marathon race

The aim of the present study was to explore impact of endurance exercise on urinary level of minerals and trace elements as well as on some oxidative stress and biochemical parameters. Urine samples were collected from participants (n=21) of mountain ultra-marathon race (53km; Medvednica, Zagreb, Croatia), before (baseline value), immediately after, 12h and 24h after the race. In urine samples level of minerals (Ca, P, K and Na) and trace elements (Se, Zn, Mn, Cu, Fe and Co) were assessed using the bench top Total reflection X-ray Fluorescence (TXRF) spectrometer. Oxidative stress was determined as level of malondialdehyde (MDA). Immediately after the race level of minerals, trace elements, MDA, creatinine, ketones, erythrocytes and specific gravity increased compared to their baseline value. In 24h follow-up trace elements involved in antioxidant defence, MDA and biochemical parameters returned to their baseline values, Cu and Co remained increased as after the race, Fe and K tended to return to baseline values while Ca, P and Na continued to increase. Mountain ultra-marathon resulted in alteration of physiologically important minerals and trace elements that for some minerals and trace elements persist, indicating their involvement in recovery processes. However, due to their loss in urine, level of minerals and trace elements in athletes participating in endurance exercise should be monitored.

PcpA Promotes Higher Levels of Infection and Modulates Recruitment of Myeloid-Derived Suppressor Cells during Pneumococcal Pneumonia

We used two different infection models to investigate the kinetics of the PcpA-dependent pneumococcal disease in mice. In a bacteremic pneumonia model, we observed a PcpA-dependent increase in bacterial burden in the lungs, blood, liver, bronchoalveolar lavage, and spleens of mice at 24 h postinfection. This PcpA-dependent effect on bacterial burden appeared earlier (within 12 h) in the focal pneumonia model, which lacks bacteremia or sepsis. Histological changes show that the ability of pneumococci to make PcpA was associated with unresolved inflammation in both models of infection. Using our bacteremic pneumonia model we further investigated the effects of PcpA on recruitment of innate immune regulatory cells. The presence of PcpA was associated with increased IL-6 levels, suppressed production of TRAIL, and reduced infiltration of polymorphonuclear cells. The ability of pneumococci to make PcpA negatively modulated both the infiltration and apoptosis of macrophages and the recruitment of myeloid-derived suppressor-like cells. The latter have been shown to facilitate the clearance and control of bacterial pneumonia. Taken together, the ability to make PcpA was strongly associated with increased bacterial burden, inflammation, and negative regulation of innate immune cell recruitment to the lung tissue during bacteremic pneumonia.

ClpL is a chaperone without auxiliary factors

Caseinolytic protease L (ClpL) is a member of the heat shock protein (Hsp) 100 family, which is found mostly in Gram-positive bacteria. Here, ClpL, a major HSP in Streptococcus pneumoniae (pneumococcus), was biochemically characterized in vitro. Recombinant ClpL shows nucleotide hydrolase, refolding, holdase and disaggregation activity using either Mg(2+) or Mn(2+) and does not require the DnaK system for chaperone activity. ClpL exhibits two features distinct from other HSP100 family proteins: (a) Mn(2+) enhances hydrolase activity, as well as chaperone activity; and (b) NTPase activity. ClpL forms a hexamer in the presence of ADP, ATP and ATP-γ-S. Mutational analysis using double-mutant proteins mutated at the two Walker A motifs (K127A/T128A and K458A/T459A) revealed that both nucleotide-binding domains are involved in chaperone activity, ATP hydrolase activity and hexamerization. Overall, pneumococcal ClpL is a unique Mn(2+) -dependent Hsp100 family member that has chaperone activity without other co-chaperones.

The roles of AMY1 copies and protein expression in human salivary α-amylase activity

Salivary α-amylase (sAA) activity has been extensively investigated in nutrition and psychology. But few studies were performed to assess the role played by sAA gene (AMY1) copies and protein expression in basal and stimulus-induced sAA activity. The sAA activity, amount and AMY1 copy number were determined from 184 saliva samples pre- and post-citric acid stimulation. Our findings showed that citric acid could induce significant increase in sAA activity, total sAA amount, and glycosylated sAA amount, among which the glycosylated sAA amount had the largest response. The correlation analysis showed that AMY1 copy number, total sAA amount and AMY1 copy number×total sAA amount had significantly positive and successively increasing correlations with sAA activity in unstimulated and stimulated saliva, respectively, and furthermore, we observed higher correlations in unstimulated saliva when compared with the corresponding correlations in stimulated saliva. We also observed significant correlations between glycosylated sAA amount and sAA activity in unstimulated and stimulated saliva, respectively. Interestingly, the correlations were higher in stimulated saliva than in unstimulated saliva, and the correlations between glycosylated sAA amount and sAA activity were higher than that of between total sAA amount and sAA activity in stimulated saliva. Moreover, total sAA amount ratio and glycosylated sAA amount ratio showed significantly positive correlation with sAA activity ratio. AMY1 copy number had no correlation with sAA activity ratio. These findings suggested that AMY1 copy number and sAA amount played crucial roles in sAA activity; however, the roles were attenuated after stimulation due to fortified release of glycosylated sAA.

The effect of social stress on salivary trace elements

Social stress can alter the saliva in favor of metabolism of trace elements. This study aimed to assess the effect of social stress on salivary copper (Cu), zinc (Zn), manganese (Mn), and iron (Fe) contents in dental students before and after a comprehensive English test. Twelve students with an average age of 27 years were selected from three dental schools. The students were carries-free, and salivary samples were collected 1 week before the test day and right before the comprehensive English test. Unstimulated saliva was collected from the participants. The pH of the saliva samples was measured using a portable pH meter, and the salivary trace element contents were determined using an atomic absorption spectrophotometer. After checking data to be normally distributed, Student's paired t test was used for statistical analysis. Salivary pH significantly increased right before the English test. Salivary Cu concentration decreased in students after the test (P > 0.05). The level of Zn, Mn, and Fe increased, while only Mn change was statistically significant (P < 0.001). Under the limitations of this study, induction of social stress led to a significant increase in Mn concentration in the saliva. The salivary Cu, Zn, and Fe contents, however, did not exhibit significant changes. Changes in salivary inorganic trace element content, as a result of physiological stress, might influence health of teeth, enamel, and oral mucosal tissues.

Enterococcus faecalis zinc-responsive proteins mediate bacterial defence against zinc overload, lysozyme and oxidative stress

Two Enterococcus faecalis genes encoding the P-type ATPase EF1400 and the putative SapB protein EF0759 were previously shown to be strongly upregulated in the presence of high concentrations of zinc. In the present work, we showed that a Zn(2+)-responsive DNA-binding motif (zim) is present in the promoter regions of these genes. Both proteins were further studied with respect to their involvement in zinc homeostasis and invasion of the host. EF0759 contributed to intramacrophage survival by an as-yet unknown mechanism(s). EF1400, here renamed ZntAEf, is an ATPase with specificity for zinc and plays a role in dealing with several host defences, i.e. zinc overload, oxidative stress and lysozyme; it provides E. faecalis cells with the ability to survive inside macrophages. As these three host defence mechanisms are important at several sites in the host, i.e. inside macrophages and in saliva, this work suggested that ZntAEf constitutes a crucial E. faecalis defence mechanism that is likely to contribute to the ability of this bacterium to endure life inside its host.

Genome-wide identification of genes essential for the survival of Streptococcus pneumoniae in human saliva

Since Streptococcus pneumoniae transmits through droplet spread, this respiratory tract pathogen may be able to survive in saliva. Here, we show that saliva supports survival of clinically relevant S. pneumoniae strains for more than 24 h in a capsule-independent manner. Moreover, saliva induced growth of S. pneumoniae in growth-permissive conditions, suggesting that S. pneumoniae is well adapted for uptake of nutrients from this bodily fluid. By using Tn-seq, a method for genome-wide negative selection screening, we identified 147 genes potentially required for growth and survival of S. pneumoniae in saliva, among which genes predicted to be involved in cell envelope biosynthesis, cell transport, amino acid metabolism, and stress response predominated. The Tn-seq findings were validated by testing a panel of directed gene deletion mutants for their ability to survive in saliva under two testing conditions: at room temperature without CO₂, representing transmission, and at 37°C with CO₂, representing in-host carriage. These validation experiments confirmed that the plsX gene and the amiACDEF and aroDEBC operons, involved in respectively fatty acid metabolism, oligopeptide transport, and biosynthesis of aromatic amino acids play an important role in the growth and survival of S. pneumoniae in saliva at 37°C. In conclusion, this study shows that S. pneumoniae is well-adapted for growth and survival in human saliva and provides a genome-wide list of genes potentially involved in adaptation. This notion supports earlier evidence that S. pneumoniae can use human saliva as a vector for transmission.

A role for the DtxR family of metalloregulators in gram-positive pathogenesis

Given the central role of transition metal ions in a variety of biochemical processes, the colonization, survival, and proliferation of a bacterium within a host hinges upon its ability to overcome the metal ion deprivation that characterizes nutritional immunity. Metalloregulatory, or 'metal-sensing' proteins have evolved in bacteria to mediate metal ion homeostasis by activating or repressing the expression of genes encoding metal ion transport systems upon binding their cognate metal ion. Yet increasing evidence in the literature supports an additional role for these metalloregulatory proteins in pathogenesis. Herein, we survey studies on the DtxR family of metalloregulators, namely DtxR (Cornyebacterium diphtheriae), SloR (Streptococcus mutans), MtsR (Streptococcus pyogenes), and MntR (Staphylococcus aureus) to describe how metalloregulation enables adaptive virulence gene expression within the mammalian host. This research has important implications for drug design, as the generation of hyper-repressive metalloregulatory proteins may represent a mechanism by which to attenuate bacterial pathogenicity. The fact that metalloregulators are unique to prokaryotes makes these proteins especially attractive therapeutic targets.

Acute effects of moderate and strenuous running on trace element distribution in the brain, liver, and spleen of trained rats

OBJECTIVE

Trace elements such as manganese (Mn), cobalt (Co) and chromium (Cr) play key roles in metabolic reactions and are important in many physiological enzymatic processes. In this study, we aimed to investigate the acute effects of moderate and strenuous running (treadmill) exercise on the levels of Mn, Co and Cr in the brain, liver, and spleen of trained rats.

STUDY DESIGN

Animal experiment.

MATERIAL AND METHODS

Twenty-one Wistar-Albino adult male rats were used in the study. Rats were grouped as control group (no mandated exercise; n=8), moderate exercise group (30 min exercise duration; n=7), and strenuous exercise group (60 min exercise duration; n=6). The levels of Mn, Co, and Cr in the frontal lobe, temporal lobe, brain stem, liver, and spleen were determined by atomic absorption spectrophotometer.

RESULTS

Cr levels in liver of rats increased in parallel to the time course of running supporting the exercise training effect on the action of insulin. Compared to the control group, the level of Co significantly decreased in the brain stem of rats in the moderate exercise group (p=0.009) and in the frontal lobe of rats in the strenuous exercise group (p=0.004). In the strenuous exercise group, an examination of the brain stem revealed that the level of Mn significantly decreased (p=0.001), and levels of Co and Cr were apparently depleted to the extent that these elements were no longer detectable.

CONCLUSION

A notable finding is that during or after single bout strenuous exercise, levels of Co decreased in the spleen and particularly decreased in the brain stem of regularly trained rats. From this study, it can be inferred that sportsmen should aware trace element disturbances among the body parts or depletion of some trace elements after single bout of chronic strenuous running exercise.

EfaR is a major regulator of Enterococcus faecalis manganese transporters and influences processes involved in host colonization and infection

Metal ions, in particular manganese, are important modulators of bacterial pathogenicity. However, little is known about the role of manganese-dependent proteins in the nosocomial pathogen Enterococcus faecalis, a major cause of bacterial endocarditis. The present study demonstrates that the DtxR/MntR family metalloregulator EfaR of E. faecalis controls the expression of several of its regulon members in a manganese-dependent way. We also show that efaR inactivation impairs the ability of E. faecalis to form biofilms, to survive inside macrophages, and to tolerate oxidative stress. Our results reveal that EfaR is an important modulator of E. faecalis virulence and link manganese homeostasis to enterococcal pathogenicity.

Science behind human saliva

Saliva is a complex fluid, which influences oral health through specific and nonspecific physical and chemical properties. The importance of saliva in our everyday activities and the medicinal properties it possesses are often taken for granted. However, when disruptions in the quality or quantity of saliva do occur in an individual, it is likely that he or she will experience detrimental effects on oral and systemic health. Often head and neck radiotherapy has serious and detrimental side effects on the oral cavity including the loss of salivary gland function and a persistent complaint of a dry mouth (xerostomia). Thus, saliva has a myriad of beneficial functions that are essential to our well-being. Although saliva has been extensively investigated as a medium, few laboratories have studied saliva in the context of its role in maintaining oral and general health.

Comparison of blood and saliva lactate level after maximum intensity exercise

Several studies have described high correlation of salivary and blood lactate level during exercise. Measuring the effectiveness and intensity of training, lactate concentration in blood, and lately in saliva are used.The aim of our study was to evaluate the correlation between the concentration and timing of salivary and blood lactate level in endurance athletes and non-athletes after a maximal treadmill test, and to identify physiological and biochemical factors affecting these lactate levels.Sixteen volunteers (8 athletes and 8 non-athletes) performed maximal intensity (Astrand) treadmill test. Anthropometric characteristics, body composition and physiological parameters (heart rate, RR-variability) were measured in both studied groups. Blood and whole saliva samples were collected before and 1, 4, 8, 12, 15, 20 min after the exercise test. Lactate level changes were monitored in the two groups and two lactate peaks were registered at different timeperiods in athletes. We found significant correlation between several measured parameters (salivary lactate - total body water, salivary lactate - RR-variability, maximal salivary lactate - maximal heart rate during exercise, salivary- and blood lactate -1 min after exercise test). Stronger correlation was noted between salivary lactate and blood lactate in athletes, than in controls.

Impact of manganese, copper and zinc ions on the transcriptome of the nosocomial pathogen Enterococcus faecalis V583

Mechanisms that enable Enterococcus to cope with different environmental stresses and their contribution to the switch from commensalism to pathogenicity of this organism are still poorly understood. Maintenance of intracellular homeostasis of metal ions is crucial for survival of these bacteria. In particular Zn(2+), Mn(2+) and Cu(2+) are very important metal ions as they are co-factors of many enzymes, are involved in oxidative stress defense and have a role in the immune system of the host. Their concentrations inside the human body vary hugely, which makes it imperative for Enterococcus to fine-tune metal ion homeostasis in order to survive inside the host and colonize it. Little is known about metal regulation in Enterococcus faecalis. Here we present the first genome-wide description of gene expression of E. faecalis V583 growing in the presence of high concentrations of zinc, manganese or copper ions. The DNA microarray experiments revealed that mostly transporters are involved in the responses of E. faecalis to prolonged exposure to high metal concentrations although genes involved in cellular processes, in energy and amino acid metabolisms and genes related to the cell envelope also seem to play important roles.

Central role of manganese in regulation of stress responses, physiology, and metabolism in Streptococcus pneumoniae

The importance of Mn(2+) for pneumococcal physiology and virulence has been studied extensively. However, the specific cellular role(s) for which Mn(2+) is required are yet to be fully elucidated. Here, we analyzed the effect of Mn(2+) limitation on the transcriptome and proteome of Streptococcus pneumoniae D39. This was carried out by comparing a deletion mutant lacking the solute binding protein of the high-affinity Mn(2+) transporter, pneumococcal surface antigen A (PsaA), with its isogenic wild-type counterpart. We provide clear evidence for the Mn(2+)-dependent regulation of the expression of oxidative-stress-response enzymes SpxB and Mn(2+)-SodA and virulence-associated genes pcpA and prtA. We also demonstrate the upregulation of at least one oxidative- and nitrosative-stress-response gene cluster, comprising adhC, nmlR, and czcD, in response to Mn(2+) stress. A significant increase in 6-phosphogluconate dehydrogenase activity in the psaA mutant grown under Mn(2+)-replete conditions and upregulation of an oligopeptide ABC permease (AppDCBA) were also observed. Together, the results of transcriptomic and proteomic analyses provided evidence for Mn(2+) having a central role in activating or stimulating enzymes involved in central carbon and general metabolism. Our results also highlight the importance of high-affinity Mn(2+) transport by PsaA in pneumococcal competence, physiology, and metabolism and elucidate mechanisms underlying the response to Mn(2+) stress.

MtsR is a dual regulator that controls virulence genes and metabolic functions in addition to metal homeostasis in the group A streptococcus

MtsR is a metal-dependent regulator in the group A streptococcus (GAS) that directly represses the transcription of genes involved in haem and metal uptake. While MtsR has been implicated in GAS virulence, the DNA recognition and full regulatory scope exerted by the protein are unknown. In this study we identified the shr promoter (P(shr)) and mapped MtsR binding to a 69 bp segment in P(shr) that overlaps the core promoter elements. A global transcriptional analysis demonstrated that MtsR modulates the expression of 64 genes in GAS, 44 of which were upregulated and 20 were downregulated in the mtsR mutant. MtsR controls genes with diverse functions including metal homeostasis, nucleic acid and amino acid metabolism, and protein fate. Importantly, the MtsR regulon includes mga, emm49 and ska, which are central for GAS pathogenesis. MtsR binding to the promoter region of both negatively and positively regulated genes demonstrates that it functions as a dual regulator. MtsR footprints are large (47-130 bp) and vary between target promoters. A 16 bp motif that consists of an interrupted palindrome is implicated in the DNA recognition by the metalloregulator. In conclusion, we report here that MtsR is a global regulator in GAS that shapes the expression of vital virulence factors and genes involved in metabolic functions and metal transport, and we discuss the implications for the GAS disease process.

Manganese regulation of virulence factors and oxidative stress resistance in Neisseria gonorrhoeae

Neisseria gonorrhoeae has evolved a complex and novel network of oxidative stress responses, including defence mechanisms that are dependent on manganese (Mn). We performed systematic analyses at the transcriptomic and proteomic (1D SDS-PAGE and Isotope-Coded Affinity Tag [ICAT]) levels to investigate the global expression changes that take place in a high Mn environment, which results in a Mn-dependent oxidative stress resistance phenotype. These studies revealed that there were proteins regulated at the post-transcriptional level under conditions of increased Mn concentration, including proteins involved in virulence (e.g., pilin, a key adhesin), oxidative stress defence (e.g., superoxide dismutase), cellular metabolism, protein synthesis, RNA processing and cell division. Mn regulation of inorganic pyrophosphatase (Ppa) indicated the potential involvement of phosphate metabolism in the Mn-dependent oxidative stress defence. A detailed analysis of the role of Ppa and polyphosphate kinase (Ppk) in the gonococcal oxidative stress response revealed that ppk and ppa mutant strains showed increased resistance to oxidative stress. Investigation of these mutants grown with high Mn suggests that phosphate and pyrophosphate are involved in Mn-dependent oxidative stress resistance.

A plausible role of salivary copper in antimicrobial activity of histatin-5--metal binding and oxidative activity of its copper complex

Histatin-5 (Hn5) is an antimicrobial salivary peptide of 24 amino acids. Two specific metal-binding sites were revealed with electronic, NMR, and EPR spectroscopy. The complex Cu(2)(II)-Hn5 effectively oxidizes catechol, exhibiting enzyme-like kinetics (k(cat)=0.011 and 0.060 s(-1) and k(cat)/K(m)=19 and 50 M(-1)s(-1) without and with 12.8mM H(2)O(2), respectively). The significant oxidative activity may contribute to the biological activity of this antibiotic metallopeptide.

Strain-specific impact of PsaR of Streptococcus pneumoniae on global gene expression and virulence

Previous studies have indicated that PsaR of Streptococcus pneumoniae is a manganese-dependent regulator, negatively affecting the expression of at least seven genes. Here, we extended these observations by transcriptome and proteome analysis of psaR mutants in strains D39 and TIGR4. The microarray analysis identified three shared PsaR targets: the psa operon, pcpA and prtA. In addition, we found 31 genes to be regulated by PsaR in D39 only, most strikingly a cellobiose-specific phosphotransferase system (PTS) and a putative bacteriocin operon (sp0142-sp0146). In TIGR4, 14 PsaR gene targets were detected, with the rlrA pathogenicity islet being the most pronounced. Proteomics confirmed most of the shared gene targets. To examine the contribution of PsaR to pneumococcal virulence, we compared D39 and TIGR4 wild-type (wt) and psaR mutants in three murine infection models. During colonization, no clear effect was observed of the psaR mutation in either D39 or TIGR4. In the pneumonia model, small but significant differences were observed in the lungs of mice infected with either D39wt or DeltapsaR: D39DeltapsaR had an initial advantage in survival in the lungs. Conversely, TIGR4DeltapsaR-infected mice had significantly lower bacterial loads at 24 h only. Finally, during experimental bacteraemia, D39DeltapsaR-infected mice had significantly lower bacterial loads in the bloodstream than wt-infected mice for the first 24 h of infection. TIGR4DeltapsaR showed attenuation at 36 h only. In conclusion, our results show that PsaR of D39 and TIGR4 has a strain-specific role in global gene expression and in the development of bacteraemia in mice.

Role of the manganese efflux system mntE for signalling and pathogenesis in Streptococcus pneumoniae

The ability of bacteria to sense and respond to both environmental and intracellular metal concentrations plays an important role in pathogenesis. The acquisition of manganese is vital for the virulence of several bacterial species. Although manganese uptake systems have been well studied in bacteria, no manganese efflux system has yet been identified. In this study we have identified a cation diffusion facilitator (CDF) protein (Sp1552) of unknown substrate specificity that functions as a manganese export system in Streptococcus pneumoniae. We designated the gene for this manganese efflux system mntE and found that the mutant strain was highly sensitive to manganese stress. Although the mutant was more resistant to oxidative stress and produced more H(2)O(2) and pili, it had reduced virulence in a murine model of infection, indicating that manganese export plays a role in host pathogenesis. There was a distinct differential transcriptional response to extracellular and intracellular manganese accumulation. Our study indicates that manganese efflux is required for invasive disease and may provide a useful antimicrobial target to devise future therapeutics.

Mn and Cu concentrations in mixed saliva of elementary school children in relation to sex, age, and dental caries

To examine the standard Mn and Cu concentrations in mixed saliva from children and the relationship between these levels and dental caries, resting mixed saliva samples obtained from 527 children of an elementary school in Kitakyushu City were collected at 10:00-11:30 a.m. during December 2004. The Mn and Cu concentrations were determined using simultaneous multi-element atomic absorption spectrometry. The standard Mn and Cu levels were 22.0+/-15.2 and 3.8+/-4.1ng/mL, respectively, in the sound teeth group. Mn levels were significantly higher in boys (25.4+/-17.4ng/mL) than girls (19.1+/-12.3ng/mL) and also higher in upper (25.5+/-16.4ng/mL) than lower (19.0+/-13.5ng/mL) grades. The Cu level was unaffected by sex and age in the sound teeth group. The Cu level in children with caries experience (5.7+/-5.3ng/mL) was significantly higher than that of the sound teeth group. Moreover, the Cu levels in children with untreated caries were significantly higher than that of the sound teeth group, and increased with the number of untreated teeth. No significant difference was found in the Cu concentrations between the group in which all decayed teeth were treated and the sound teeth group. The Mn levels were similar with or without caries and treatment. These findings indicate that the Mn level in mixed saliva depended on sex and age, and suggest the possibility of Cu dissolving into mixed saliva by demineralization due to dental caries.

Streptococcus pneumoniae surface protein PcpA elicits protection against lung infection and fatal sepsis

Previous studies have suggested that pneumococcal choline binding protein A (PcpA) is important for the full virulence of Streptococcus pneumoniae, and its amino acid sequence suggests that it may play a role in cellular adherence. PcpA is under the control of a manganese-dependent regulator and is only expressed at low manganese concentrations, similar to those found in the blood and lungs. PcpA expression is repressed under high manganese concentrations, similar to those found in secretions. In this study, we have demonstrated that PcpA elicits statistically significant protection in murine models of pneumonia and sepsis. In the model of pneumonia with each of four challenge strains, statistically fewer S. pneumoniae cells were recovered from the lungs of mice immunized with PcpA and alum versus mice immunized with alum only. The immunizations reduced the median CFU by 4- to 400-fold (average of 28-fold). In the model of sepsis using strain TIGR4, PcpA expression resulted in shorter times to become moribund and subcutaneous immunization with PcpA increased survival times of mice infected with wild-type PcpA-expressing pneumococci.

Effects of manganese on Streptococcus mutans planktonic and biofilm growth

Streptococcus mutans, an agent of dental caries, was tested for growth in the presence or absence of manganese (Mn), since studies have linked Mn levels with cariogenic potential. Seven S. mutans serotype c strains were grown in chemically defined medium under different atmospheric conditions: 5% CO2, O2-enriched 5% CO2 (shaking) and anaerobic. There was significant strain variability with respect to Mn requirements under the various conditions tested. Both sucrose-dependent and sucrose-independent biofilm growth by strain UA159 were affected by the absence of Mn. S. mutans strains show highly variable responses to both high and low Mn concentrations.

Role of Porphyromonas gingivalis FeoB2 in metal uptake and oxidative stress protection

Porphyromonas gingivalis, a gram-negative anaerobic bacterium, is a recognized periodontopathogen. It exhibits a high degree of aerotolerance and is able to survive in host cells, indicating that efficient oxidative stress protection mechanisms must be present in this organism. Manganese homeostasis plays a major role in oxidative stress protection in a variety of organisms; however, the transport and role of this metal in P. gingivalis is not well understood. Analysis of the genome of P. gingivalis W83 revealed the presence of two genes encoding homologs of a ferrous iron transport protein, FeoB1 and FeoB2. FeoB2 has been implicated in manganese accumulation in P. gingivalis. We sought to determine the role of the FeoB2 protein in metal transport as well as its contribution to resistance to oxygen radicals. Quantitative reverse transcriptase PCR analyses demonstrated that expression of feoB2 is induced in the presence of oxygen. The role of FeoB2 was investigated using an isogenic mutant strain deficient in the putative transporter. We characterized the FeoB2-mediated metal transport using (55)Fe(2+) and (54)Mn(2+). The FeoB2-deficient mutant had dramatically reduced rates of manganese uptake (0.028 pmol/min/10(7) bacteria) compared with the parental strain (0.33 pmol/min/10(7) bacteria) (after 20 min of uptake using 50 nM of (54)Mn(2+)). The iron uptake rates, however, were higher in the mutant strain (0.75 pmol/min/10(7) bacteria) than in the wild type (0.39 pmol/min/10(7) bacteria). Interestingly, reduced survival rates were also noted for the mutant strain after exposure to H(2)O(2) and to atmospheric oxygen compared to the parental strain cultured under the same conditions. In addition, in vitro infection of host cells with the wild type, the FeoB2-deficient mutant, and the same-site revertant revealed that the mutant had a significantly decreased capability for intracellular survival in the host cells compared to the wild-type strain. Our results demonstrate that feoB2 encodes a major manganese transporter required for protection of the bacterium from oxidative stress generated by atmospheric oxygen and H(2)O(2). Furthermore, we show that FeoB2 and acquisition of manganese are required for intracellular survival of P. gingivalis in host cells.

Development of an analytical method using microchip capillary electrophoresis for the measurement of fluorescein-labeled salivary components in response to exercise stress

We have developed an analytical method using microchip capillary electrophoresis (microchip CE) for the high-speed separation of fluorescein-labeled salivary components in response to exercise stress. Optimal separation was obtained using a borate buffer at pH 9.5 containing 10 mM beta-cyclodextrin and 1.0% (w/v) methylcellulose. To minimize individual differences in human saliva, such as viscosity, conductivity, and contaminants, the concentration of methylcellulose in the analytical conditions played a key factor. The optimized separation conditions produced identical electropherograms successfully despite of the use of different microchips made from quartz glass or poly-methylmethacrylate (PMMA). In addition, a practical application of bicycle ergometer stress was performed. Some components in human saliva showed a marked decrease after exercise stress.

Mn2+-dependent regulation of multiple genes in Streptococcus pneumoniae through PsaR and the resultant impact on virulence

The concentration of Mn2+ is 1,000-fold higher in secretions than it is at internal sites of the body, making it a potential signal by which bacteria can sense a shift from a mucosal environment to a more invasive site. PsaR, a metal-dependent regulator in Streptococcus pneumoniae, was found to negatively affect the transcription of psaBCA, pcpA, rrgA, rrgB, rrgC, srtBCD, and rlrA in the presence of Mn2+. psaBCA encode an ABC-type transporter for Mn2+. pcpA, rrgA, rrgB, and rrgC encode several outer surface proteins. srtBCD encode a cluster of sortase enzymes, and rlrA encodes a transcriptional regulator. Steady-state RNA levels are high under low Mn2+ concentrations in the wild-type strain and are elevated under both high and low Mn2+ concentrations in a psaR mutant strain. RlrA is an activator of rrgA, rrgB, rrgC, and srtBCD (D. Hava and A. Camilli, Mol. Microbiol. 45:1389-1406, 2002), suggesting that PsaR may indirectly control these genes through rlrA, while PsaR-dependent repression of psaBCA, pcpA, and rlrA transcription is direct. The impact of Mn2+-dependent regulation on virulence was further examined in mouse models of pneumonia and nasopharyngeal carriage. The abilities of DeltapsaR, pcpA, and DeltapsaR DeltapcpA mutant strains to colonize the lung were reduced compared to those of the wild type, confirming that both PcpA-mediated gene regulation and PsaR-mediated gene regulation are required for full virulence in the establishment of pneumonia. Neither PcpA nor PsaR was found to be required for colonization of the nasopharynx in a carriage model. This is the first demonstration of Mn2+ acting as a signal for the expression of virulence factors within different host sites.

The sloABCR operon of Streptococcus mutans encodes an Mn and Fe transport system required for endocarditis virulence and its Mn-dependent repressor

Streptococcus mutans belongs to the viridans group of oral streptococci, which is the leading cause of endocarditis in humans. The LraI family of lipoproteins in viridans group streptococci and other bacteria have been shown to function as virulence factors, adhesins, or ABC-type metal transporters. We previously reported the identification of the S. mutans LraI operon, sloABCR, which encodes components of a putative metal uptake system composed of SloA, an ATP-binding protein, SloB, an integral membrane protein, and SloC, a solute-binding lipoprotein, as well as a metal-dependent regulator, SloR. We report here the functional analysis of this operon. By Western blotting, addition of Mn to the growth medium repressed SloC expression in a wild-type strain but not in a sloR mutant. Other metals tested had little effect. Cells were also tested for aerobic growth in media stripped of metals then reconstituted with Mg and either Mn or Fe. Fe at 10 micro M supported growth of the wild-type strain but not of a sloA or sloC mutant. Mn at 0.1 micro M supported growth of the wild-type strain and sloR mutant but not of sloA or sloC mutants. The combined results suggest that the SloABC proteins transport both metals, although the SloR protein represses this system only in response to Mn. These conclusions are supported by (55)Fe uptake studies with Mn as a competitor. Finally, a sloA mutant demonstrated loss of virulence in a rat model of endocarditis, suggesting that metal transport is required for endocarditis pathogenesis.

Genetic characterization of a Streptococcus mutans LraI family operon and role in virulence

Proteins belonging to the LraI (for "lipoprotein receptor antigen") family function as adhesins in several streptococci, as a virulence factor for endocarditis in at least one of these species, and potentially as metal transporters in many bacteria. We have identified and characterized the chromosomal locus containing the LraI family gene (designated sloC) from Streptococcus mutans, an agent of dental caries and endocarditis in humans. Northern blot analysis indicated that sloC is cotranscribed with three other genes. As with other LraI operons, the sloA and sloB genes apparently encode components of an ATP-binding cassette transport system. The product of the fourth gene, sloR, has homology to the metal-dependent regulator from Corynebacterium diphtheriae, DtxR. A potential binding site for SloR was identified upstream from the sloABCR operon and was conserved upstream from LraI operons in several other streptococci. Potential SloR homologs were identified in the unfinished genomic sequences from two of these, S. pneumoniae and S. pyogenes. Mutagenesis of sloC in S. mutans resulted in apparent loss of expression of the entire operon as assessed by Northern blot analysis. The sloC mutant was indistinguishable from its wild-type parent in a gnotobiotic rat model of caries but was significantly less virulent in a rat model of endocarditis. Virulence for endocarditis was restored by correction of the sloC mutation but not by provision of the sloC gene in trans, suggesting that virulence requires the expression of other genes in the sloC operon.