Production of polyhydroxybutyrate (PHB) of high and ultra-high molecular weight by Azotobacter vinelandii in batch and fed-batch cultures

BACKGROUNDPolyhydroxybutyrate (PHB) is a biopolymer with thermo-mechanical properties like those of plastics produced by the petrochemical industry. These properties are improved in PHBs of high or ultra-high weight average molecular weight. Azotobacter vinelandiiOPNA is a potential producer of large quantities of PHB, having ultra-high molecular weight by fed-batch production strategies. RESULTSIn batch and fed-batch cultures at different carbon-nitrogen molar ratios (10, 14 and 18), the OPNA strain produced PHB of high and ultra-high weight average molecular weight, with values between 2.3 and 6.6 MDa. In this strain, the weight average molecular weight was highly dependent on the initial carbon-nitrogen ratio, reaching the highest value (6.6 MDa) in batch cultures conducted with a carbon-nitrogen ratio of 18 and the lowest (2.3) with a carbon-nitrogen ratio of 10. On the other hand, using a two feeding-pulses fed-batch strategy, the highest global PHB volumetric productivity (0.56 g L-1 h(-1)) and polymer concentration (27.6 g L-1) were obtained. CONCLUSIONThe OPNA strain accumulated up to 80% of PHB of ultra-high molecular weight as a function of the initial carbon-nitrogen molar ratio. Using a simple fed-batch strategy of two feeding-pulses was possible to produce up to 27 g L-1 of PHB. (c) 2016 Society of Chemical Industry