Effect of levulinic acid on production of polyhydroxyalkanoates from food waste by Haloferax mediterranei

Abstract

Polyhydroxyalkanoates (PHA), especially poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is considered as the most suitable candidate to replace petrochemical plastics. However, the high production cost and the composition of the monomers in the copolymer are the major constraints in production. The 3-hydroxyvalerate (3HV) rich copolymers are ideal for various applications due to their lower melting points, improved elasticity, and ductility. Haloferax mediterranei is a suitable microorganism for the production of biopolymer PHBV from biowaste. Nevertheless, the potential of H. mediterranei cultivated on food waste as sustainable substrate and levulinic acid as an inducer has not been explored for PHBV production. This study aims at the valorization of food waste as low-cost substrate and evaluation of effect of levulinic acid in the production and composition of PHBV using H. mediterranei. Shake-flask fermentations using different concentrations of salt, glucose and levulinic acid were first performed to optimize the cultivation conditions. The highest growth of the halophile was observed at salt concentration of 15% and glucose of concentration 10 g/L. Under optimized growth conditions, H. mediterranei was cultivated for PHBV production in fed-batch bioreactor with pulse fed levulinic acid. The maximum biomass of 3.19 ± 0.66 g/L was achieved after 140 h of cultivation with 3 g/L of levulinic acid. A decrease in H. mediterranei growth was noticed with the increase in levulinic acid concentration in the range of 3-10 g/L. The overall yield of PHBV at 3, 5, 7 and 10 g/L of levulinic acid were 18.23%, 56.70%, 31.54%, 21.29%, respectively. The optimum concentration of 5 g/L of levulinic acid was found to produce the maximum yield of 56.70% PHBV with 18.55 mol% 3HV content. A correlation between levulinic acid concentrations and PHBV production established in this study can serve as an important reference for future large-scale production.

Keywords: Fed-batch fermentation; Food waste; Haloferax mediterranei; Levulinic acid; Poly(3-hydroxybutyrate-co-3-hydroxyvalerate); Polyhydroxyalkanoates.