Phasins are proteins, which are located on the surface of Polyhydroxybutyrate (P3HB) granules and that carry out activities that affect the polymer metabolism. This study aimed to evaluate the effect of inactivating phasins PhbP2 or PhbP3 on the growth rate, production and molecular mass of P3HB in cultures under low or high oxygen transfer rates (OTR). The results reveal that under high OTRₘₐₓ conditions (between 8.1 and 8.9 mmol L⁻¹ h⁻¹ depending on the strain evaluated), the absence of phasins PhbP2 and PhbP3 resulted in a strong negative effect on the growth rate. In contrast, the rates of specific oxygen consumption increased in the case of cultures with strains where phasins were absent. This behavior was not observed under conditions at a low oxygen transfer rate (3.9 ± 0.71 mol L⁻¹ h⁻¹); where both growth and oxygen consumption were the same for the different strains evaluated. It was observed, at high OTRₘₐₓ that the absence of phasin PhbP3 harms the P3HB synthesis, finding a decrease of 30 % in the polymer production at the end of cultivation; however, the molecular weight of the polymer remained constant during the course of cultivation. In summary, it can be concluded that both growth and polymer synthesis were affected when phasin PhbP3 was absent from the P3HB granule, especially at high OTRₘₐₓ.
