Polyhydroxyalkanoate (PHA) biosynthesis from directly valorized ragi husk and sesame oil cake by Bacillus megaterium strain Ti3: Statistical optimization and characterization.

Polyhydroxyalkanoates (PHAs) signify the most promising biological substitute to petrochemical plastics. Renewable and inexpensive agro-industrial by-products can be used as potent fermentation feedstocks for sustainable PHA biosynthesis. This study aimed at using a wild type B. megaterium strain Ti3 innate hydrolytic enzyme/s for eco-friendly valorization of 16 lignocellulosic agrowastes to PHA without pretreatments. Initial hydrolytic screening PHA concentration of (0.04-0.17 g/L), highlighted the strain's metabolic versatility. Pareto ranking of Taguchi orthogonal array (TOA) established ragi husk (RH), sesame oil cake (SOC) and KH2PO4 as the most influential factors (p < 0.05). The optimized and validated Response surface methodology (RSM) model (R2, 0.979; desirability, 1) resulted in 3.8 and 3.6 fold increased PHA production, 4.3 and 3.25 fold increased PHA productivity. A positive correlation (r2, 0.5-0.97) was observed amid the producer innate hydrolytic enzymes (lipase, amylase and cellulase) and PHA production. The PHA was characterized by 1H and 13C NMR, GPC, TGA. The polymer was identified as a scl-mcl copolyester with 92% 3HB (3-hydroxybutyrate) and 8% 3HHp (3-hydroxyheptanoate) monomers by NMR. This the first report on B. megaterium self-enzyme reliant non-food agrowastes bioconversion to PHA with 3HHp (3-hydroxyheptanoate) monomers excluding precursor addition, commercial enzymes, pure carbon and nitrogen sources.