Effect Of Different Propionic Acid Feeding Methods On The Production Of Poly(Hydroxybutyrate-Co-Hydroxyvalerate) From Waste Frying Oil In A Fed-Batch Culture Of Cupriavidus Necator
With increasing environmental concerns, interest in natural and biodegradable polymers such as polyhydroxyalkanoates (PHA) produced by microorganisms has increased in today's world. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)], an important member of the PHA family has better thermomechanical properties such as better ductility, better toughness and lower melting temperature compared to poly(3-hydroxybutyrate) [P(3HB)] due to the 3-hydroxyvalerate (3HV) monomer it contains. Thus, 3HV unit fraction of the P(3HB-co-3HV) affect several important properties of the copolymer. P(3HB-co-3HV) can be synthesized by Cupriavidus necator using a carbon source and a 3HV precursor such as propionic acid (PA). To produce P(3HB-co-3HV) in a cost-efficient manner, different PA feeding strategies were investigated in a fed-batch culture (5 L bioreactor) of Cupriavidus necator using waste frying oil as the main carbon source. While continuous feeding was inefficient in increasing the 3HV content, the results of pulse wise feeding were promising for high yield production of P(3HB-co-3HV). By a pulse wise PA (1:3 diluted in oil) feeding method with 0.4 g/L by every pulse starting at 24 h cultivation a P(3HB-co-3HV) yield of 102.8 g/L with a 10.2 wt% 3HV content were obtained. By employing another pulse wise feeding strategy (PA feeding between 24-36 h: 0.25 g/L with every pulse and 36-60 h: 0.2 g/L with every pulse), we could obtain a higher 3HV content (23.8 wt%), but the P(3HB-co-3HV) yield was decreased to 85.1 g/L. According to the desired properties of the copolymer, the 3HV monomer composition can be regulated by choosing one of the feeding strategies described.
Keywords - Polyhydroxyalkanoates, Poly(3-hydroxybutyrate-co-3-hydroxyvalerate), Propionic acid feeding, Cupriavidus necator,Waste frying oil.