Oxygen transfer rate affect polyhydroxybutyrate production and oxidative stress response in submerged cultures of Rhizobium phaseoli

Abstract Oxygen is a key factor during free-state growth of Rhizobium phaseoli or symbiosis with common bean roots. Five different initial oxygen transfer rates (OTRI) were fix by dissolved oxygen control and constants stirrer speed rates to determine the growth of R. phaseoli in a lab-scale bioreactor. The biomass did not presented differences in the maximum concentrations for OTRI of 1.0, 1.7 and 5.9 mmol l−1 h−1. However, a sublethal effect was observed for 11.9 and 20.2 mmol l−1 h−1, where lower biomass, kinetic and stoichiometric parameters were determined. Catalase activity as an oxidative stress indicator was approximately two-fold greater with 20.2 mmol l−1 h−1 than lower OTRI. Polyhydroxybutyrate (PHB) production did not present differences in the maximum concentration. Nevertheless, an increase in PHB accumulation, yield on biomass and specific productivity were determined at the higher OTRI, suggesting a defense mechanism against oxidative stress induce by the enhancement of the oxygen transfer rates.