Autotrophic production of polyhydroxyalkanoates using acidogenic-derived H₂ and CO₂ from fruit waste

The environmental concerns regarding fossil plastics call for alternative biopolymers such as polyhydroxyalkanoates (PHAs) whose manufacturing costs are however still too elevated. Autotrophic microbes like Cupriavidus necator, able to convert CO₂ and H₂ into PHAs, offer an additional strategy. Typically, the preferred source for CO₂ and H₂ are expensive pure gases or syngas, which has toxic compounds for most PHAs-accumulating strains. In this work, for the first time, H₂ and CO₂ originating from an acidogenic reactor were converted autotrophically into poly(3-hydroxybutyrate) P(3HB). During the first stage, a mixed microbial community continuously catabolized melon waste into H₂ (26.7 %) and CO₂ (49.2 %) that were then used in a second bioreactor by C. necator DSM 545 to accumulate 1.7 g/L P(3HB). Additionally, the VFAs (13 gCOD/L) produced during acidogenesis were processed into 2.7 g/L of P(3HB-co-3HV). This is the first proof-of-concept of using acidogenic-derived H₂ and CO₂ from fruit waste to produce PHAs.