Polyhydroxybutyrate production in one-stage by purple phototrophic bacteria: Influence of alkaline pH, ethanol, and C/N ratios

Abstract

This work aimed to evaluate the effect of alkaline pH, nutrient limitation, nitrogen source, C/N ratio, and ethanol addition on polyhydroxybutyrate (PHB) production by a photoheterotrophic mixed culture enriched in Rhodopseudomonas palustris. The results demonstrated the natural alkalinization of the culture medium was enough to induce PHB accumulation in the mixed culture. The combination of alkaline pH, nitrogen, sulfur, or phosphate deficiency negatively affected polymer production. The incorporation of glutamate for biomass synthesis was better than that of ammonium, which had a positive effect on PHB production. Interestingly, ethanol addition improved the PHB accumulation by 25 %, but without consumption. PHB production improved at low C/N ratios, where 27 ± 0.9% of the carbon source was transformed into biopolymers. The evaluated factors allowed the biomass PHB content to increase by 60%, reaching PHB production of 219 ± 5 mg/L. The PHB production by the photoheterotrophic mixed culture is associated with growth, allowing the PHB production in one stage. That has significant advantages in technical-practical terms, such as reducing the time of the process, dispensing with the separation of biomass from the feast phase to the famine phase, and requiring a single reactor.