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Production of poly(3-hydroxybutyrate) by Rhodococcus qingshengii N9T-4 using the oligotrophic gene expression system
Akihiro Otsuka1, Izumi Orita2, Hiroya Yurimoto3
1Department of Engineering, Graduate School of Integrated Science and Technology, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu, 432-8561, Japan.
Scientific Reports
|July 22, 2025
Summary
This study engineered Rhodococcus qingshengii N9T-4 to produce polyhydroxybutyrate (PHB), a bioplastic, under oligotrophic conditions. This demonstrates a low-cost, low-carbon method for bioplastic production.
Area of Science:
- Microbiology
- Biotechnology
- Metabolic Engineering
Background:
- Rhodococcus qingshengii N9T-4 is a super oligotroph, capable of growth on minimal media.
- Oligotrophic conditions offer potential for low-cost bioprocessing.
- Polyhydroxyalkanoates (PHAs) are biodegradable polyesters with significant industrial applications.
Purpose of the Study:
- To engineer Rhodococcus qingshengii N9T-4 for poly(3-hydroxybutyrate) (PHB) production.
- To investigate PHB biosynthesis under oligotrophic conditions.
- To identify optimal conditions for PHB production in this strain.
Main Methods:
- Expression of the Cupriavidus necator H16 phaC1AB1 operon in R. qingshengii N9T-4 under the aldA promoter.
- Nile Red staining to detect PHA accumulation.
- Fatty-acid methyl ester analysis to confirm PHA composition.
- Transmission electron microscopy to visualize PHA granules.
- Evaluation of different carbon and nitrogen sources for PHA production.
Main Results:
- Successful expression of PHA biosynthesis genes and significant PHB accumulation (20.8 ± 1.4 wt% of dry cell weight) in R. qingshengii N9T-4.
- Identification of ethanol as the most effective carbon source for PHB production.
- Confirmation of PHB as the sole PHA type produced.
- Visualization of PHA granules within the engineered cells.
- Demonstration that ethanol addition did not inhibit oligotrophic gene expression or metabolism.
Conclusions:
- Rhodococcus qingshengii N9T-4 can be engineered for oligotrophic production of poly(3-hydroxybutyrate).
- This approach offers a sustainable and cost-effective route for bioplastic manufacturing.
- Further optimization using ethanol as a carbon source is feasible without compromising oligotrophic metabolism.
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