Production of Biohydrogen and/or Poly-β-hydroxybutyrate by Rhodopseudomonas sp. Using Various Carbon Sources as Substrate.

The polyhydroxyalkanoates (PHA) are family of biopolyesters synthesized by numerous bacteria which are attracting a great attention due to their thermoplastic properties. Polyhydroxybutyrate (PHB) is the most common type of PHA which presents thermoplastic and biodegradable properties. It is synthesized under stressful conditions by heterotrophic bacteria and many photosynthetic microorganisms such as purple non-sulfur bacteria and cyanobacteria. Biological hydrogen (H2) production is being evaluated for use as a fuel since it is a promising substitute for carbonaceous fuels owing to its high conversion efficiency and high specific content. In the present work, the purple non-sulfur photosynthetic bacterium Rhodopseudomonas sp. for the simultaneous H2 photo-evolution and poly-β-hydroxybutyrate (PHB) production has been investigated. Three different types of carbon sources were tested in the presence of glutamate as a nitrogen source in a batch cultivation system, under continuous irradiance. The results indicated the fact that the type of carbon source in the culture broth affects in various ways the metabolic activity of the bacterial biomass, as evidenced by the production of PHB and/or H2 and biomass. The best carbon source for PHB accumulation and H2 production by Rhodopseudomonas sp. turned out to be the acetate, having the highest H2 production (2286 mL/L) and PHB accumulation (68.99 mg/L, 18.28% of cell dry weight).