Molecular mass of poly-3-hydroxybutyrate (P3HB) produced by Azotobacter vinelandii is determined by the ratio of synthesis and degradation under fixed dissolved oxygen tension

• Molecular mass of P3HB is not influenced by dissolved oxygen tension between 1 to 15%.
• Culture stage strongly influences the P3HB molecular mass.
• High molecular mass of P3HB correlated with a high activity of P3HB synthase.
• Mean molecular mass of P3HB (5500 kDa) is the highest reported in A. vinelandii.

Poly-3-hydroxybutyrate (P3HB) is an intracellular polyester produced by numerous bacteria, including Azotobacter vinelandii. Thermo-mechanical properties and biomedical applications of P3HB depend on its molecular mass (MM), which in turn is controlled by the balance between synthesis and degradation of the polymer during its biosynthesis. The aim of this study was to determine the activity levels of enzymes involved in the synthesis and degradation of P3HB and their effect on the molecular mass of the polymer produced by A. vinelandii strain OP under the conditions of dissolved oxygen tension of 1 and 15%. The results show that the MM of P3HB changed between the exponential and stationary growth phases, under both oxygen conditions. During the exponential growth phase, the mean molecular mass (MMM) of P3HB was high (4800 kDa), coincident with a high activity P3HB synthase and with a low activity of P3HB depolymerase. In contrast, during the stationary phase, the P3HB MM decreased to 3600 kDa, because of the increased activity of the P3HB depolymerase.

Schematic representation about the effect of activity of enzymes of P3HB cycle on the molecular mass of the polymer accumulated by A. vinelandii OP.Figure optionsDownload as PowerPoint slide