Effect of acid stress on the physiology of biofilm cells of Streptococcus mutans
Bibliographic record
Abstract
Streptococcus mutans is a component of the dental plaque biofilm and an important aetiological agent in dental caries. Although this organism growing in the suspended (planktonic) state has been well characterized, relatively little is known about its physiology in biofilms, particularly in the acidic environments associated with caries development. The authors determined the effect of biofilm age (1-5 days) and cell density on selected metabolic properties under conditions of glucose limitation in a biofilm-chemostat at pH 7.5 and compared these baseline values with those of 3 day biofilms subjected to acid stress. Biofilm cell biomass more than doubled over the 5 day experimental period under baseline conditions, with the glycolytic rate, glucose uptake, glucose-PTS (phosphotransferase system) activity and protein synthesis maximum at 1-2 days. DNA and RNA synthesis increased for the first 3 days before decreasing in the 5 day biofilms, while H(+)/ATPase activity was higher in 5 day biofilms than 1 day biofilms, with overall activity 5-13-fold higher per cell unit than in the associated planktonic cells. Glucose pulsing (50 mM final concentration) for three consecutive days without pH control for 5 h (pH 4.39+/-0.02) resulted in a progressive decrease in planktonic cell numbers; however, the rate of acid formation and glucose utilization in the chemostat by these cells increased per cell unit. Assays for carbohydrate metabolism in the latter cells showed increased activity, as did an assay for H(+)/ATPase (8-fold); however, DNA, RNA and protein synthesis were repressed (0.3-0.7-fold). Although the 3 day biofilm viable cell counts declined by 51 % on glucose pulsing, all the physiological parameters measured by cell unit increased in activity, with notable increases in RNA and protein synthesis (4.6-7.6-fold). The results indicate that the maintenance of intracellular pH homeostasis is the basis of the enhanced physiological status and acid tolerance of biofilm cells.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".