Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) has biodegradable properties and has similar properties to polypropylene and polyethylene, so it can be used as a substitute for plastics. PHBV can be used in various ways because it can control physical properties according to the content of 3-hydroxyvalerate (3HV). In this study, we aim to achieve PHBV biosynthesis by searching for biosynthetic strains of PHBV and using makeolilees (ML), which is a discarded resource.
The strains biosynthesised PHBV wes isolated from soil and named Bacillus sp. EMK-5020. ML enzymatic hydrolysate (MLEH) was used as a carbon source of PHBV biosynthesis by Bacillus sp. EMK-5020 because MLEH contains complex molecules, including 103 g/L glucose and 27 g/L total-N. The secondary carbon source was used to increase 3HV mol% in PHBV and 3HV content was increased when propionic acid was used as a secondary carbon source. In the flask test, MLEH was used as a carbon source and 1.0 g/L propionic acid was added to the culture. The results of incubation, 2.1 g/L dry cell weight (DCW) and 37% PHBV containing 48 mol% 3HV was biosynthesized. Under the same conditions, the batch fermentation resulted in biosynthesis of 6.4 g/L DCW and 50% PHBV containing 8.9 mol% 3HV at 48 h. The total amount of 3HV after 12 h was not changed, and it was considered that the propionic acid was depleted and the low 3HV mol% was biosynthesized. The biosynthesized PHBV showed that temperature decomposition (Td) was 273℃, which was 20℃ higher than standard PHBV, and melting temperature (Tm) 156℃ and melting enthalpy (ΔHm) 58 J/g. number average molecular weight (Mn) 60,691 Da and weight average molecular weight (Mw) 152,613 Da confirmed that the molecular weight was halved compared to standard PHBV, but there was no change in properties due to molecular weight. Therefore, the present study shows that Bacillus sp. EMK-5020 strain can biosynthesize PHBV using MLEH as a carbon source, which has the advantage of reducing PHBV production cost.