Defatted Chlorella biomass as a renewable carbon source for polyhydroxyalkanoates and carotenoids co-production

Abstract

Defatted Chlorella biomass was investigated as an unconventional and promising carbon source for the co-production of polyhydroxyalkanoates and cartenoids via batch cultivation of Paracoccus sp. LL1. 10% (w/v) of algal biomass was subjected to acid hydrolysis using different concentrations (0.1, 0.2, 0.3, and 0.5 N) of either sulfuric or hydrochloric acid to yield fermentable sugars. Regardless of the acid type, reducing sugar content significantly increased with an increasing acid concentration, reaching a maximum yield of 52 and 46 g/L respectively for hydrochloric and sulfuric acid catalyzed hydrolysis at the highest acid concentrations (p < 0.05). Shake flask fermentation process showed the ability of Paracoccus sp. LL1 to convert fermentable sugars from 0.3 N hydrochloric acid catalyzed hydrolysis into polyhydroxyalkanoates and carotenoids with a maximum product concentration of 1.48 g/L (i.e., 37.4% of dry cell weight) and 6.08 mg/L, respectively. Moreover, 144 and 92% increases in polyhydroxyalkanoates and carotenoids production (i.e., 3.62 g/L polyhydroxyalkanoates and 11.7 mg/L carotenoids) was recorded upon upscaling the biotransformation of defatted Chlorella biomass hydrolysate in 5 L fermenter by Paracoccus sp. LL1. Notably, these results corresponded to 92 and 54% greater production of polyhydroxyalkanoates and carotenoids than those observed in fermenter operated under identical conditions with glucose as a carbon source. Subsequent analyses of gas chromatography, Fourier transform infrared spectroscopy, and 1H nuclear magnetic resonance spectroscopy further identified the accumulated polyhydroxyalkanoate as a copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate with a 3-hydroxyvalerate fraction of 6.22 mol%.