Looking for improved strains of Azotobacter vineladii and favorable culture conditions yielding high-molecular-weight poly(3-hydoxybutyrate)

Abstract

Background

Poly(3-hydroxybutyrate) (P3HB) is a polymer that presents properties similar to those of conventional plastics. The objective of the present study was to evaluate the influence of oxygen transfer rate (OTR) on the production and molecular weight of P3HB synthesized by the OP-PhbP2⁻ and OP-PhbP3⁺ mutant strains of Azotobacter vinelandii, which have inactivated the gene that expresses the PhbP2 phasin and overexpresses the PhbP3 phasin genes, respectively.

Results

Under high OTR_max (6.0 ± 0.04 mmol O₂ L⁻¹ h⁻¹) mutant OP-PhbP3⁺ exhibited a higher growth rate (0.12 ± 0.01 h⁻¹) and P3HB production (6.77 ± 0.19 g L⁻¹) than that achieved in the cultures using the OP-PhbP2⁻ mutant and OP wild-type strains (5.0 ± 0.1 g L⁻¹ for both strains). Under that condition, the OP-PhbP3⁺ strain also exhibited a lower specific oxygen consumption rate. In contrast, under a low OTR_max (2.8 ± 0.06 mmol O₂ L⁻¹ h⁻¹), the OP-PhbP2⁻ strain had a better performance, reaching 4.5 ± 0.35 g L⁻¹ of P3HB, during the stationary phase (36–72 h). Both mutant strains produced a polymer with a high molecular weight (close to 8000 kDa), regardless of the OTR of the cultures, which remained constant throughout the fermentation. In contrast, the molecular weight produced by the OP strain was in the range 5500 to 6700 kDa under the two conditions evaluated.

Conclusion

Overall, our results revealed the biotechnological potential of using modified strains, which overexpress PhbP3 phasin or have inactivated the gene that expresses the PhbP2 phasin, for the production of P3HB, affording a higher molecular weight than that produced by the OP strain. © 2024 Society of Chemical Industry (SCI).