Response surface optimization of poly (3-hydroxyalkanoic acid) production using oleic acid as an alternative carbon source by Pseudomonas aeruginosa

• Optimization of PHA production using statistical design.
• Oleic acid used as an economically viable option, to reduce production costs of PHA.
• PHA production depended on the concentration of nitrogen source at linear, quadratic and interactive levels.
• An increase in 1.6 times of PHA production achieved.

This study aims at optimizing medium-chain-length Polyhydroxyalkanoate (MCL-PHA) production from Pseudomonas aeruginosa 13003 culture using the statistical design techniques of 2-level factorial design and RSM. Two-level factorial design with eight variables viz. oleic acid, (NH4)2PO4, incubation time, trace metal solution, MgCl2, K2HPO4, KH2PO4 and inoculum was performed to screen for nutrients that were significantly affecting MCL-PHA production. After the values for the less-influential variables were fixed, oleic acid, (NH4)2PO4, K2HPO4 and KH2PO4 having high t-values were selected to study their optimal relationship for maximal PHA production using 24 Central Composite Design. The optimal composition of the medium was found to be at 7.5 g L−1 oleic acid, 0.4 g L−1 (NH4)2PO4, 3.0 g L−1 K2HPO4 and 1.5 g L−1 KH2PO4 which gave 60% of CDW as MCL-PHA. This optimization resulted in a 1.6 times increase in the PHA content (60% mass fraction in contrast to 36%). On analysis carbon to nitrogen ratio of 19 was found to be optimum for PHA production. This is the first report on the use of CCD to improve MCL-PHA production from P. aeruginosa.