Production of polyhydroxyalkanoates and carotenoids through cultivation of different bacterial strains using brown algae hydrolysate as a carbon source

Abstract

Abstract Laminaria japonica biomass was investigated as an untapped carbon source for polyhydroxyalkanoates (PHA) accumulation via batch and fed-batch cultivation of three different bacterial strains including Cupriavidus necator NCIMB 11599, Paracoccus sp. LL1, and Bacillus megaterium ALA2. Algal biomass (10% (w/v)) was treated with different sulfuric and hydrochloric acid concentrations (0.1, 0.15, 0.2, and 0.3 N). Increasing acid concentration led to a significant increase in reducing sugar production, giving rise to a maximum production of 6.1 and 5.9 g/L for H2SO4 and HCl pretreatment, respectively. Shake flask culture revealed that C. necator, Paracoccus sp. LL1, and B. megaterium ALA2 were able to produce PHA up to 19–32% of their dry cell weight (DCW) under 2% of reducing sugar supplementation. Overall, C. necator showed the highest level of PHA accumulation (1.58 g/L, 32% of DCW). By batch and fed-batch culture, PHA content was enhanced to 44 and 49%, respectively. Along with PHA, Paracoccus sp. LL1 was able to produce 0.9 mg/L of carotenoids after 96 h of cultivation in flask culture. Carotenoid production was enhanced by batch and fed-batch culture to 1.45 and 2.3 mg/L, respectively. Based on Fourier transform infrared spectroscopy, gas chromatography, and 1H nuclear magnetic resonance spectroscopy, the produced PHA polymers were identified as poly(3-hydroxybutyrate) or poly(3-hydroxybutyrate-co-3-hydroxyvalerate).