Acid tolerance and the involvement of secondary metabolism in Streptococcus mutans
Bibliographic record
Abstract
Dental caries is the dissolution of tooth enamel caused by the acidic end-products produced from bacterial metabolism of dietary carbohydrates. Streptococcus mutans, a ubiquitous constituent of human dental plaque, is an etiological agent of dental caries. Two of S. mutans' cariogenic attributes are acidogenicity and aciduricity. Acidogenicity is the ability to produce acids from carbohydrate catabolism. Furthermore, S. mutans has developed a complex response network allowing it the ability to survive in this acidic environment, termed aciduricity. Studies have shown regulation at the genomic and proteomic levels is paramount in aciduricity for S. mutans (29, 91, 92, 153, 168, 170). Among the pathways showing up-regulation to acid were the citrate metabolism pathway (29), the glyoxalase pathway (91, 170), and the pyruvate dehydrogenase pathway (168). The goal of this work was to investigate the mode of acid tolerance for three secondary metabolic pathways; citrate transport and metabolism, the glyoxalase pathway (focused on LGL) and pyruvate dehydrogenase (focused on PdhA) in S. mutans. S. mutans is capable of citrate transport, via the CitM transporter. Transport is most efficient when coupled with Fe 3+. The end-product of citrate metabolism is aspartate. The citrate metabolic pathway includes citrate lyase as citrate accumulates in a citrate lyase knockout mutant. Citrate was found to be toxic to S. mutans, however, pre-exposure to citrate resulted in increased acid tolerance. LGL is involved in the detoxification of methylglyoxal, illustrated by the absence of enzyme activity in an lgl mutant (LGLKO), hypersensitivity of LGLKO to methylglyoxal, and increased transcription of lgl in the presence of exogenous methylglyoxal. Transcriptional analysis revealed pdhA responded to conditions favouring heterofermentation; decreased expression in response to excess glucose, and increased expression during stationary growth phase compared with mid-logarithmic phase growth. The isogenic mutants, LGLKO and PDHAKO, were acid-sensitive. Both mutants had reduced growth capacity at pH 5.0, decreased survival at pH 3.2, and decreased survival in an acidic bio-fermenter compared with wild-type. Both genes were up-regulated during growth at pH 5.0 compared with growth at pH 7.5 and during the process of acid adaptation. This work highlighted the importance of these three secondary metabolic pathways in the aciduricity of S. mutans.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 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 source (direct Gemma or distilled Codex), 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".