Molecular mass of Poly-3-hydroxybutyrate (P3HB) produced by Azotobacter vinelandii is influenced by the polymer content in the inoculum

Poly-3-hydroxybutyrate (P3HB) is a biopolymer produced by Azotobacter vinelandii. The physicochemical properties and applications of P3HB are strongly influenced by its weight-average molecular mass (Mw), and in A. vinelandii, it could be influenced by the culture conditions. The aim of this study was to evaluate the effect of the P3HB content of the inoculum on the Mw of the polymer produced by A. vinelandii OP in bioreactor cultures. A. vinelandii cells containing 20, 50 and 70% of P3HB were used as inoculum. The P3HB content in the inoculum affected the volumetric P3HB productivity (q_P3HB) and the Mw of P3HB. Those cultures inoculated with cells containing 20% of P3HB, achieved the highest q_P3HB (0.17 ± 0.018 g_P3HB L⁻¹ h⁻¹); whereas a P3HB content of 70% was reflected as a low q_P3HB (0.021 ± 0.002 g_P3HB L⁻¹ h⁻¹). On the other hand, using an inoculum with 70% of polymer content, the Mw of the biopolymer remained stable at values close to 3200 kDa; whereas, when an inoculum with 20% of P3HB was used, the Mw decreased drastically during early stages of cultivation. These results show that manipulating the P3HB content of the inoculum is possible to produce biopolymers with a suitable Mw.