Poly-3-hydroxybutyrate production by Azotobacter vinelandii strains in batch cultures at different oxygen transfer rates

BACKGROUND: Poly-3-hydroxybutyrate (PHB) is a polyester that can be accumulated by Azotobacter vinelandii. This polymer is a biodegradable thermoplastic material used for producing plastics for packaging, biobased films, and biocompatible implants. RESULTS: PHB produced by wild-type A. vinelandii and a mutant OP strain were evaluated at different agitation rates. The oxygen transfer rate (OTR) evolution was characterized in cultures grown at 300, 400, 500 and 600 rpm, showing for the first time the OTR evolution in cultures of mutant OP. Under the conditions evaluated, the cultures were limited by oxygen. In the cultures grown with the OP strain, lower OTR and specific oxygen uptake rate were obtained, indicating a lower necessity for oxygen for growth in this mutant. A higher amount of PHB can be produced by decreasing the OTR. A maximum PHB of 79% on dry weight was observed in the cultures with the wild-type strain, whereas the highest PHB productivity (0.18 g L^-1 h^-1) was obtained in cultures of A. vinelandii OP conducted at 600 rpm. CONCLUSION: The amount of PHB produced during the period of oxygen limitation can be controlled by the OTR, opening the possibility to evaluate this parameter as a criterion for scaling-up PHB production by A. vinelandii.