Poly(3-hydroxybutyrate) accumulation by Azotobacter vinelandii under different oxygen transfer strategies

Abstract

Azotobacter vinelandii OP is a bacterium that produces poly(3-hydroxybutyrate) (PHB). PHB production in a stirred bioreactor, at different oxygen transfer strategies, was evaluated. By applying different oxygen contents in the inlet gas, the oxygen transfer rate (OTR) was changed under a constant agitation rate. Batch cultures were performed without dissolved oxygen tension (DOT) control (using 9% and 21% oxygen in the inlet gas) and under DOT control (4%) using gas blending. The cultures that developed without DOT control were limited by oxygen. As result of varying the oxygen content in the inlet gas, a lower OTR (4.6 mmol L −1  h −1 ) and specific oxygen uptake rate (11.6 mmol g −1  h −1 ) were obtained using 9% oxygen in the inlet gas. The use of 9% oxygen in the inlet gas was the most suitable for improving the intracellular PHB content (56 ± 6 w w −1 ). For the first time, PHB accumulation in A. vinelandii OP cultures, developed with different OTRs, was compared under homogeneous mixing conditions, demonstrating that bacterial respiration affects PHB synthesis. These results can be used to design new oxygen transfer strategies to produce PHB under productive conditions.