0501 Comparative genomics of Lactobacillus brevis uncovers its common capability for efficiently synthesizing neuroactive γ-aminobutyric acid
Bibliographic record
Abstract
γ-Aminobutyric acid (GABA) is the chief inhibitory neurotransmitter in mammalian central nervous system and has shown anti-hypertensive and anti-depressant activities to the host after oral administration. However, its content in natural animal and plant products is too low to deliver benefits to human. Thus, GABA synthesized by food-grade bacteria such as Lactobacillus and Bifidobacterium is an important source and its producers could be used for manufacturing GABA-rich fermented dairy foods. Many GABA-producing Lactobacillus and Bifidobacterium strains have been isolated and characterized in the last decade and have shown strain-specific capability in the synthesis of GABA. Among these GABA producers, Lactobacillus brevis seems to be the most common cell factory for synthesizing GABA. In this study, comparative genomic approach was used to identify which LAB species have the common ability to produce high amount of GABA and to identify the essential genetic elements for GABA production. It was found that gene encoding glutamic acid decarboxylase (GAD) and an intact gad operon were present in all the sequenced strains of L. brevis at the species level, but not all the strains of other Lactobacillus and Bifidobacterium species possess an intact gad operon including a regulator gadR, a gadA- or gadB-encoding GAD, and an antiporter gadC. This suggests the common capability of L. brevis to synthesize GABA. Moreover, enzyme assay for two GADs from L. brevis indicated that both enzymes are functional with high activities. Carbohydrate utilization by model strain Lb. brevis NPS-QW-145 generated different lactic acid production, which showed strong positive correlation with its GABA yields suggesting that intracellular lactic acid production triggers its GABA biosynthesis, which was also evidenced by the intracellular pH level of the cells. Moreover, among all of acid resistance (AR) pathways in Lb. brevis, GAD pathway contributed to late acid resistance whereas tyrosine decarboxylation (TDC) and arginine deimination (ADI) pathways were activated during lag and log phases, which were confirmed by transcriptional profiles and concentrations of the end metabolites of each AR. The present study highlights the common capability of Lb. brevis for highly efficient biosynthesis of GABA.
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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 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".