Effect of pH and salinity on photofermentative hydrogen and poly-hydroxybutyric acid production via Rhodobacter capsulatus YO3

Date

2025-05-10

Author

Hoşafcı, Ertan
Ateş, Candan
Volkan, Aşkın Efe
Koku, Harun
Bayramoğlu, Tuba Hande

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The production of poly-hydroxybutyrate (PHB) and H2 via Rhodobacter capsulatus YO3, an uptake hydrogenase deficient (hup−) mutant, was investigated in this study. The pH and salinity of the bioreactor medium were investigated as potential factors to enhance production of PHB and H2. Initial controlled pH and salinity ranges of 7.0–8.5 and 1500–4000 mgNa+/L, respectively, were studied. Initial set demonstrated that under a constant pH of 7.7, increasing the salinity of the medium enhanced maximum PHB production slightly. The highest PHB accumulation (57.5 ± 0.2 %) occurred at pH 8.5 under 1500 mgNa+/L, but was unstable and degraded rapidly. Further sets were run to uncouple the effect of pH and salinity. Higher initial pH and salinity levels hindered H2 productivity, with PHB production sustained only under moderate stress. The most significant drop in both H2 and PHB production occurred with high pH (>8.0) and Na+ (>3000 mg/L) levels applied together. The study suggests that relatively lower pH (7.0–7.5) and Na+ concentration (≈1500 mg/L) favor production of both products. Under moderate stress of either higher pH or salinity, cells accumulate and sustain PHB, but under combined stress of high pH and Na+, production shifts towards H2. Severe conditions inhibit both processes. For practical applications with saline wastewater, pH control is critical, as a pH of 7.0–7.5 can reduce salinity's adverse effects. Gradual increases in salinity may help cultures adapt, enhancing efficient substrate use for H2 or PHB production.

Subject Keywords

Hydrogen, pH, Poly-hydroxybutyric acid, Rhodobacter capsulatus, Salinity, Sodium

URI

https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=105000208193&origin=inward
https://hdl.handle.net/11511/114341

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Department of Environmental Engineering, Article