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

- Photoperiods might offer energy savings in H2 production by photofermentation.
- IZT culture kept H2 production under both continuous lighting and photoperiods.
- H2 production by R. capsulatus declined under photoperiods.
- R. capsulatus tripled and IZT doubled PHB accumulation under photoperiods.

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 H2) of 1300 ± 43 mL H2 L−1 under continuous illumination and light-dark cycles of 30 or 60 min. In contrast, R. capsulatus reduced its Paccum H2 by 20% under 30:30 min light-dark cycles, but tripled its poly-β-hydroxybutyrate (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.

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