Heterologous Expression of <i>Vitreoscilla</i> Hemoglobin in <i>Pseudomonas putida</i> KT2440 for the Production of <i>mcl</i> -PHA in Carbon-Limited Fermentations
Bibliographic record
Abstract
The heterologous expression of Vitreoscilla hemoglobin (VHb) is known to enhance short-chain-length (scl) and short-chain-length-medium-chain-length (scl-mcl) polyhydroxyalkanoate (PHA) production in Escherichia coli, Aeromonas hydrophila and Pseudomonas putida, but has not been evaluated for the production of medium-chain-length (mcl) PHA in pseudomonads. Three recombinant strains of P. putida KT2440 were constructed, harboring pBBR1MCS-2 expression plasmids containing 0, 1 and 2 copies of the vgb gene. The vgb gene was placed under the control of the lac promoter, which conferred constitutive expression of vgb, since no lac repressor was produced. Mcl-PHA production was assessed in nonanoic acid-limited, fed-batch fermentations with exponential feeding. Although the VHb levels in the engineered strains were comparable to those observed in vgb-bearing pseudomonads, the recombinant strains had lower biomass production, PHA accumulation, volumetric productivity and product yield when compared to the wild-type strain. The performance of the plasmid-harboring strains decreased with increasing vgb copy numbers, presumably due to an increased metabolic burden arising from plasmid expression. All the fermentations ended at similar times due to insufficient oxygen supply and subsequent uncontrollable foaming, demonstrating that VHb production did not alleviate oxygen limitation. These results indicate that the effectiveness of VHb engineering must be assessed on a case-by-case basis.
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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) | 0.000 | 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 | 0.001 |
| 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 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".