Effect of light-dark cycles on hydrogen and poly-β-hydroxybutyrate production by a photoheterotrophic culture and Rhodobacter capsulatus using a dark fermentation effluent as substrate

A Rhodobacter capsulatus strain and a photoheterotrophic culture (IZT) were cultivated to produce hydrogen under different light-dark cycles. A dark fermentation effluent (DFE) was used as substrate. It was found that IZT culture had an average cumulative hydrogen production (Paccum H-2) of 1300 +/- 43 mL H-2 L-1 under continuous illumination and light-dark cycles of 30 or 60 min. In contrast, R. capsulatus reduced its Paccum H-2 by 20% under 30: 30 min light-dark cycles, but tripled its poly-bhydroxybutyrate (PHB) content (308 +/- 2 mgPHB gdw(-1)) compared to continuous illumination. The highest PHB content by IZT culture was 178 +/- 10 mgPHB gdw(-1) under 15: 15 min light-dark cycles. PCR-DGGE analysis revealed that the IZT culture was mainly composed of Rhodopseudomonas palustris identified with high nucleotide similarity (99%). The evaluated cultures might be used for hydrogen and PHB production. They might provide energy savings by using light-dark cycles and DFE valorization. (C) 2016 Elsevier Ltd. All rights reserved.