The photoautotrophically grown cyanobacterium Oscillatoria okeni TISTR 8549 was found to produce bioplastic poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). This PHBV production occurred under nitrogen deprivation (-N) that yielded PHBV accumulation of 14 +/- 4% (w/w DW) in which 3hydroxyvalerate accounted for 5.5 mol%. The heterotrophically grown (-N condition with acetate supplementation) cells under light showed no increase of PHBV storage, but under dark condition these cells increased PHBV accumulation to 42 +/- 8% (w/w DW) with 6.5 mol% of 3-hydroxyvalerate. Compared to poly-3-hydroxybutyrate (PHB), the PHBV from O. okeni had a lower melting temperature by 5-7 degrees C, a higher % elongation at break by 4-7 times and a greater Young's elastic modulus by 2.3-2.5 times. (C) 2017 Elsevier Ltd. All rights reserved.