Steady-State Measurements of Lactic Acid Production in a Wild-Type and a Putative D-Lactic Acid Dehydrogenase-Negative Mutant of Zymomonas mobilis
Bibliographic record
Abstract
This work represents a continuation of our investigation into environmental conditions that promote lactic acid synthesis by Zymomonas mobilis. The characteristic near theoretical yield of ethanol from glucose by Z. mobilis can be compromised by the synthesis of D - and L-lactic acid. The production of lactic acid is exacerbated by the following conditions: pH 6.0, yeast extract, and reduced growth rate. At a specific growth rate of 0.048/h, the average yield of DL-lactate from glucose in a yeast extract-based medium at pH 6.0 was 0.15 g/g. This represents a reduction in ethanol yield of about 10% relative to the yield at a growth rate of 0.15/h. Very little lactic acid was produced at pH 5.0 or using a defined salts medium (without yeast extract) Under permissive and comparable culture conditions, a tetracycline-resistant, D-ldh negative mutant produced about 50% less lactic acid than its parent strain Zm ATCC 39676. D-lactic acid was detected in the cell-free spent fermentation medium of the mutant, but this could be owing to the presence of a racemase enzyme. Under the steady-state growth conditions provided by the chemostat, the specific rate of glucose consumption was altered at a constant growth rate of 0.075/h. Shifting from glucose-limited to nitrogen-limited growth, or increasing the temperature, caused an increase in the specific rate of glucose catabolism. There was good correlation between an increase in glycolytic flux and a decrease in lactic acid yield from glucose. This study points to a mechanistic link between the glycolytic flux and the control of end-product glucose metabolism. Implications of reduced glycolytic flux in pentose-fermenting recombinant Z. mobilis strains, relative to increased byproduct synthesis, is discussed.
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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) | 0.000 | 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) | 0.000 | 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".