Photosynthetic mixed culture polyhydroxyalkanoate (PHA) production from individual and mixed volatile fatty acids (VFAs): Substrate preferences and co-substrate uptake

•Substrate composition influenced the PHA production of a photosynthetic mixed culture.•Acetate and butyrate led to PHB formation and propionate to a HB:HV co-polymer.•Acetate can act as a co-substrate increasing butyrate and propionate uptake rates.•Substrate preference for butyrate in relation to acetate and propionate was observed.•Results prospect the utilization of fermented wastes as substrate for PHA production. This work studied the effect of the substrate feeding composition on the polyhydroxyalkanoate (PHA) accumulation capacity of an acetate enriched photosynthetic mixed culture (PMC). From the six tested organic acids – malate, citrate, lactate, acetate, propionate and butyrate – only the three volatile fatty acids (VFAs) enabled PHA production, with acetate and butyrate leading to polyhydroxybutyrate (PHB) formation and propionate leading to a HB:HV copolymer with a 51% fraction of hydroxyvalerate (HV). Also, results showed an acceleration of butyrate and propionate consumption when fed in the presence of acetate, suggesting that the latter can act as a co-substrate for butyrate and propionate uptake. Furthermore, results suggest that some PMC bacterial groups present a substrate preference for butyrate in relation to acetate and propionate. These findings indicate the possibility of feeding the PMC with cheap VFA rich fermented wastes, leading to a more cost-effective and environmentally sustainable PHA production system.