Enhanced polyhydroxyalkanoate biosynthesis by Cupriavidus sp. CY-1 utilizing CO2 under controlled non-explosive conditions

The production of polyhydroxyalkanoate (PHA) using CO₂ through hydrogen-oxidizing bacteria under safe, non-explosive conditions is making impressive strides. The present study aimed to evaluate and demonstrate the growth and productivity of PHA by Cupriavidus sp. CY-1 under different non-explosive conditions, thereby providing critical data for practical applications. The experimental results highlighted the efficiency of the CY-1 strain in PHA biosynthesis, achieving a production rate of 11.87 g L^-1, which corresponds to a 90.6% yield when fermenting a gaseous substrate composed of H₂ (70%), O₂ (20%), and CO₂ (10%). The study also examined PHA production under different non-explosive conditions, including H₂ concentrations of 3.8% (v/v) and O₂ at 6.5% (v/v). Furthermore, the impact of CO (30% and higher) was assessed, revealing a detrimental effect on growth and PHA production. Notably, the addition of Tween 80 significantly enhanced PHA productivity. The effective utilization of CO₂ has confirmed poly[(R)-3-hydroxybutyrate] (PHB) as a valuable derived form of PHA. By implementing a two-step treatment with valeric acid, we successfully produced P(3HB-co-3HV) (PHBV) at a concentration of 1.47 g L^-1. This achievement highlights the potential to enhance PHA production through innovative strategies. Furthermore, the examination of phaC gene expression levels has facilitated accurate predictions of PHA productivity. The use of CO₂ from trichloroethylene (TCE) biodegradation faced concentration-related challenges; however, the higher CO₂ levels achieved from phenol biodegradation, at 1200 mg L^-1, indicate substantial potential for efficient PHA production.