Slow food for lactobacilli: characterization of 1,2-propanediol metabolism in <i>Levilactobacillus parabrevis</i> FUA3697 in sourdough
Bibliographic record
Abstract
ABSTRACT Some lactobacilli convert lactate to acetate and 1,2-propanediol in the stationary phase of growth, but the key enzyme of the pathway, lactaldehyde dehydrogenase, has not been characterized in any of the Lactobacillales . It was, therefore, the aim of this study to characterize lactate to 1,2-propanediol conversion in Levilactobacillus parabrevis FUA3697. The strain converted lactate to 1,2-propanediol during 14 days of incubation. The concentration of 1,2-propanediol was higher in media with maltose, glucose, and fructose as carbon sources when compared to arabinose; the addition of lactate increased the 1,2-propanediol formation. The 1,2-propanediol formation was higher in sourdough than in laboratory media and higher in sorghum sourdoughs than in wheat sourdoughs. The construction of a mutant strain Lv. parabrevis FUA3697Δ aldA confirmed that AldA is responsible for the conversion, as the mutant strain did not produce 1,2-propanediol. Competition experiments demonstrated that the disruption of aldA slightly decreased the competitiveness in wheat sourdoughs but not in sorghum sourdoughs. After incubation of the strains over 28 days at 4°C, the wild-type strain resumed growth and acidification faster than the aldA -deficient isogenic mutant. In summary, lactate conversion to acetate and 1,2-propanediol maintains slow metabolic activity over weeks or even months, thus increasing the ecological fitness. IMPORTANCE The genes coding for lactate conversion to 1,2-propanediol are relatively broadly distributed in heterofermentative lactobacilli and also present in few homofermentative lactobacilli. To date, the conversion has been verified experimentally only in Lentilactobacillus buchneri , few other lentilactobacilli and, more recently, Levilactobacillus lettrarii . 1,2-Propanediol is a substrate for further conversion to propionic acid. The metabolic pathway contributes to spoilage of pickles and cider but is considered a beneficial metabolic trait in silage and sourdough fermentations. Our results document that lactobacilli using this pathway can be employed for improved activity and competitiveness of starter cultures that are distributed under refrigerated conditions.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 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 | 0.000 |
| 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".