Accumulation of polyhydroxybutyrate in Synechocystis sp. isolated from wastewaters: Effect of salinity, light, and P content in the biomass

Cyanobacteria are of particular interest as they can produce Polyhydroxybutyrate (PHB), which is a promising alternative to oil-based plastics, using only inorganic carbon and solar light. However, new strategies should be found to further increase their PHB content. In this study, the effect of salinity, light intensity, and internal phosphorus content in the inoculated biomass, on the production of PHB with the cyanobacteria Synechocystis sp. were investigated. Results indicated that a sudden increase in salinity (together with nutrients starvation) stimulated the accumulation of PHB. In a first experiment where the cells were adapted to an electrical conductivity of 12 mS cm−1, a maximum content of PHB of a 7.5%VSS was achieved by adding NaCl and NaHCO3- (electrical conductivity of 28 mS cm−1). While in a second experiment, where cells were not adapted, similar PHB content (7.2%VSS) was achieved by adding only NaCl and C-HCO3-, providing only 11.4 mS cm−1. Furthermore, it was observed a reduced molecular weight of the polymer (38 kDa with respect to around 100 kDa), when really high salinities were used. Eventually, it was observed an increased production of glycogen (maximum of a 32%VSS) when high illumination (500 µmol m−2 s−1) was applied. Similar PHB content was obtained independently of the illumination. However, the PHB productivity (15.7 mgPHB L−1 d−1) was increased with light intensity. These results contribute to decipher the effect of important parameters in the PHB production and bring research a step forward towards the optimization of PHB production with Synechocystis sp.