Rate-limiting steps of glucose and sorbitol metabolism in Streptococcus mutans cells exposed to air

Metabolomic Studies of Oral Biofilm, Oral Cancer, and Beyond

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

The redox-sensing regulator Rex modulates central carbon metabolism, stress tolerance response and biofilm formation by Streptococcus mutans

The Rex repressor has been implicated in regulation of central carbon and energy metabolism in gram-positive bacteria. We have previously shown that Streptococcus mutans, the primary causative agent of dental caries, alters its transcriptome upon Rex-deficiency and renders S. mutans to have increased susceptibility to oxidative stress, aberrations in glucan production, and poor biofilm formation. In this study, we showed that rex in S. mutans is co-transcribed as an operon with downstream guaA, encoding a putative glutamine amidotransferase. Electrophoretic mobility shift assays showed that recombinant Rex bound promoters of target genes avidly and specifically, including those down-regulated in response to Rex-deficiency, and that the ability of recombinant Rex to bind to selected promoters was modulated by NADH and NAD(+). Results suggest that Rex in S. mutans can function as an activator in response to intracellular NADH/NAD(+) level, although the exact binding site for activator Rex remains unclear. Consistent with a role in oxidative stress tolerance, hydrogen peroxide challenge assays showed that the Rex-deficient mutant, TW239, and the Rex/GuaA double mutant, JB314, were more susceptible to hydrogen peroxide killing than the wildtype, UA159. Relative to UA159, JB314 displayed major defects in biofilm formation, with a decrease of more than 50-fold in biomass after 48-hours. Collectively, these results further suggest that Rex in S. mutans regulates fermentation pathways, oxidative stress tolerance, and biofilm formation in response to intracellular NADH/NAD(+) level. Current effort is being directed to further investigation of the role of GuaA in S. mutans cellular physiology.

Streptococci-human papilloma virus interaction with ethanol exposure leads to keratinocyte damage

PURPOSE

Ethanol, human papilloma virus (HPV), and poor oral hygiene are risk factors that have been attributed to oral carcinogenesis. Streptococci sp and HPV infections are common in the head and neck, often associated with sexual activity. Although HPV is linked to head and neck squamous cell carcinoma, it is unclear whether there is a similar role for Streptococci sp. This cell study examines whether Streptococci sp and HPV-16 with exposure to ethyl alcohol (ETOH) can act as cofactors in the malignant transformation of oral keratinocytes.

MATERIALS AND METHODS

ETOH (0.1%-20% vol/vol) was used to investigate Streptococci sp attachment with immortalized E6-expressing HPV/HOK-16B cells, human oral buccal keratinocytes, and foreskin keratinocytes. Streptococci sp (Streptococci mutans [LT11]) and various strains of acetaldehyde (AA) producer and nonproducer Streptococcus salivarius (110-1, 109-2, 101-7, and 107-1) and a lactic acid producer bacterium, Lactobacillus rhamnosus (24-1 and 25-2), were examined for interactions with keratinocytes by use of a green dye (percent of cells with colonies after 24 hours). Carcinogens, AA, malondialdehyde, DNA damage, and proliferation (5'-bromo-2-deoxyuridine) among keratinocytes were also quantified.

RESULTS

AA and malondialdehyde production from permissible Streptococci sp significantly increased with attachment to keratinocytes, whereas L rhamnosus did not significantly attach to keratinocytes. This attachment was associated with enhanced levels of AA adduct formation, proliferation (5'-bromo-2-deoxyuridine incorporation), and enhanced migration through integrin-coated basement membrane by HPV oral keratinocytes, which are characteristics of a malignant phenotype.

CONCLUSIONS

These cell studies suggest that oral Streptococci sp and HPV (HPV-16) cooperate to transform oral keratinocytes after low-level ETOH (1%) exposure. These results appear to suggest a significant clinical interaction, but further validation is warranted.

Metabolomics of supragingival plaque and oral bacteria

Dental caries is initiated by demineralization of the tooth surface through acid production by sugar metabolism of supragingival plaque microflora. To elucidate the sugar metabolic system, we used CE-MS to perform metabolomics of the central carbon metabolism, the EMP pathway, the pentose-phosphate pathway, and the TCA cycle in supra- gingival plaque and representative oral bacteria, Streptococcus and Actinomyces. Supragingival plaque contained all the targeted metabolites in the central carbon metabolism, except erythrose 4-phosphate in the pentose-phosphate pathway. After glucose rinse, glucose 6-phosphate, fructose 6-phosphate, fructose 1,6-bisphosphate, dihydroxyacetone phosphate, and pyruvate in the EMP pathway and 6-phosphogluconate, ribulose 5-phosphate, and sedoheptulose 7-phosphate in the pentose-phosphate pathway, and acetyl CoA were increased. Meanwhile, 3-phosphoglycerate and phosphoenolpyruvate in the EMP pathway and succinate, fumarate, and malate in the TCA cycle were decreased. These pathways and changes in metabolites observed in supragingival plaque were similar to the integration of metabolite profiles in Streptococcus and Actinomyces.

Two-dimensional difference gel electrophoresis analysis of Streptococcus uberis in response to mutagenesis-inducing ciprofloxacin challenge

In Streptococcus uberis, the fluoroquinolone antibiotic ciprofloxacin induces a mutagenic response that is distinct from the SOS paradigm. Two-dimensional differential gel electrophoresis was employed to investigate the effect of ciprofloxacin exposure on the proteome of S. uberis. Twenty-four protein spots exhibiting differential expression (p < 0.05) were identified as enzymes with potential role in oxidative stress, NADH generation and nucleotide biosynthesis. We suggest that these metabolic changes provide S. uberis means to stimulate mutagenesis and adaptation.

Effects of oxygen on biofilm formation and the AtlA autolysin of Streptococcus mutans

The Streptococcus mutans atlA gene encodes an autolysin required for biofilm maturation and biogenesis of a normal cell surface. We found that the capacity to form biofilms by S. mutans, one of the principal causative agents of dental caries, was dramatically impaired by growth of the organism in an aerated environment and that cells exposed to oxygen displayed marked changes in surface protein profiles. Inactivation of the atlA gene alleviated repression of biofilm formation in the presence of oxygen. Also, the formation of long chains, a characteristic of AtlA-deficient strains, was less evident in cells grown with aeration. The SMu0629 gene is immediately upstream of atlA and encodes a product that contains a C-X-X-C motif, a characteristic of thiol-disulfide oxidoreductases. Inactivation of SMu0629 significantly reduced the levels of AtlA protein and led to resistance to autolysis. The SMu0629 mutant also displayed an enhanced capacity to form biofilms in the presence of oxygen compared to that of the parental strain. The expression of SMu0629 was shown to be under the control of the VicRK two-component system, which influences oxidative stress tolerance in S. mutans. Disruption of vicK also led to inhibition of processing of AtlA, and the mutant was hyperresistant to autolysis. When grown under aerobic conditions, the vicK mutant also showed significantly increased biofilm formation compared to strain UA159. This study illustrates the central role of AtlA and VicK in orchestrating growth on surfaces and envelope biogenesis in response to redox conditions.

Xylitol Inhibition of Acid Production and Growth of Mutans Streptococci in the Presence of Various Dietary Sugars under Strictly Anaerobic Conditions

The aim of this study was to investigate the inhibitory effect of xylitol on the growth of and acid production by mutans streptococci in the presence of various dietary sugars, and the relationship between the inhibition and the accumulation of xylitol 5-phosphate (X5P) under strictly anaerobic conditions like those in the deep layers of dental plaque. Xylitol retarded the growth of mutans streptococci in the presence of glucose (G), galactose (Gal), maltose (M), lactose (L) or sucrose (S) as an energy source, though the inhibition of growth on fructose (Fr) was small. Xylitol inhibited acid production by washed cells of Streptococci mutans from G, Gal, M, L or S (12-83% inhibition). S. mutans accumulated X5P intracellularly through activity of the phosphoenolpyruvate-xylitol phosphotransferase system (PEP-xylitol PTS) when they fermented these sugars in the presence of xylitol. However, in the presence of Fr, no inhibition of acid production was observed. In addition, the amounts of X5P during the fermentation of Fr were smaller than those of other sugars in spite of the presence of PEP-xylitol PTS activity. These results suggest that along with the intracellular accumulation of X5P, xylitol decreases the growth and acid production of mutans streptococci in the presence of various dietary sugars except Fr.

The time-course of acid excretion, levels of fluorescence dependent on cellular nicotinamide adenine nucleotide and glycolytic intermediates of Streptococcus mutans cells exposed and not exposed to air in the presence of glucose and sorbitol

The aim of this study was to examine glucose and sorbitol metabolism in Streptococcus mutans cells exposed and not exposed to air at the coexistence of these compounds by measuring acid excretion, levels of fluorescence dependent on cellular NADH and glycolytic intermediates. An aliquot of bacterial cells grown under strictly anaerobic conditions (anaerobic cells) was exposed temporarily to air (aerobic cells). When glucose was added to the anaerobic cells metabolizing sorbitol, the acid excretion was increased. The level of NADH decreased initially and then increased to the higher plateau level than that during glucose metabolism. The aerobic cells neither metabolized sorbitol nor contained glycolytic intermediates. However, 2 min after glucose was added in the presence of sorbitol, the acid excretion was started slowly and the intermediates appeared. The level of NADH was decreased at first and then increased. These results suggested that the anaerobic S. mutans cells metabolized glucose and sorbitol simultaneously, and that in the presence of sorbitol the aerobic cells could start to metabolize glucose 2 min after glucose was added, as the intermediates (phosphoenopyruvate potential) for the glucose transport were accumulated.