Photoautotrophic poly(3-hydroxybutyrate) production by a wild-type Synechococcus elongatus isolated from an extreme environment

[Display omitted] •A wild-type of S. elongatus UAM–C/S03 was identified using a polyphasic approach.•S. elongatus UAM–C/S03 grew between pH 7–12 and accumulated 9% PHB in DWC.•PHB accumulation yielded the maximum under N-starvation, with 29% or 58 mg L−1 d−1.•Stress conditions promoted carbohydrate accumulation up to 51% with EPS release.•The CO2 fixation rate ranged high for this species, at 674 mg L−1 d−1. The photoautotrophic poly(3-hydroxybutyrate) (PHB) production by cyanobacteria is an attractive option as it only requires CO2 and light. In this work, a new wild-type strain producing PHB, Synechococcus elongatus UAM–C/S03, was identified using a polyphasic approach. The strain was cultured in a photobioreactor operated under N-sufficiency conditions at different pH values (7 to 11) and fed with CO2 on demand. We also evaluated the production of PHB under N-starving conditions. Highest biomass productivity, 324 mg L−1 d−1, and CO2 capture, 674 mg L−1 d−1, were obtained at pH 7 and under N-sufficiency conditions. The strain accumulated 29.42% of PHB in dry cell weight (DCW) under N-starvation conditions without pH control, and highest PHB productivity was 58.10 mg L−1 d−1. The highest carbohydrate content registered at pH 8, 50.84% in DCW, along with a release of carbon-based organic compounds, suggested the presence of exopolysaccharides in the culture medium.