The Cyanobacterial Route to Produce Poly-ß-hydroxybutyrate

Abstract

The amount of plastics produced in the world and released in the environment has dramatically increased putting societies and the environment to hard test. The biodegradable plastics are a potential solutions to reduce the environmental impact and the fossil resource exploitation.
Polyhydroxyalkanoates (PHAs) are widely adopted as building blocks for biodegradable plastic production and they may be produced by microorganisms. The poly-ß-hydroxybutyrate (PHB) is the most widespread and thoroughly characterized PHA found in bacteria. In particular, cyanobacteria are potential host systems for the PHB production, as they may synthesize this polymer from CO₂.
This contribution reports a joint research between the University of Napoli and the University of Amsterdam on the feasibility of PHB production by Synechocystis PCC6803. Both BG₁₁ (balanced conditions) and BG₀ (nitrogen-starved conditions) media were investigated to find the best growth conditions and optimal PHB production. Batch autotrophic cultures were carried out in inclined bubble column photobioreactors under 12h/12h light/dark cycles.
Cultures were characterized in terms of biomass, PHB content, pH and nitrate consumption. After cell-rupture with sonication the PHB concentration was assessed by means of GC, adopting a modified propanolysis method. The maximum PHB concentration was 4 mg/L and the maximum PHB productivity was 0.19 mg/(L day). The PHB content of the cells is definitively higher in nitrogen-starved medium (1 %) than in balanced medium (0.25 %).