Production and enhancement of poly-β-hydroxybutyrate in cyanobacteria

Abstract

The accumulation and factors affecting Poly 3-hydroxybutyric acid (PHB) production in cyanobacteria have not been clearly documented. In the present study, three PHB producers belonging to cyanobacteria were identified as Oscillatoria salina, Anabaena cylindrica and Nostoc linckia, based on their morphological features and microscopic observations. Their growth and PHB production after 7, 14 and 21 days in BG11 medium were determined. The highest dry weight for the isolates was observed at stationary phase (14 days) and PHB accumulation (%, w/w of dry cells) increased with increasing dry weight up to 14 days, then a decline was observed after 21 days. At the stationary phase, cells of O. salina, A. cylindrica and N. linckia accumulated PHB up to 13.62, 11.88 and 10.03% (w/w of dry cells), respectively. The pH values between 8 and 9 were preferred for PHB accumulation. O. salina, A. cylindrica and N. linckia accumulated the highest PHB 17.31, 15.22 and 14.95%, respectively at pH 8. Nitrogen and phosphorus starvation were found stimulatory for PHB accumulation and he highest PHB production was recorded for O. salina, 20.41 and 26.32%, respectively after 14 days of incubation. Electron microscopic analyses of O. salina cells showed the bioplastic accumulation in granule-like structures which was extracted and studied using IRFT analysis. In conclusion, cyanobacteria are capable of synthesizing high poly--hydroxybutyrate (PHB) under stress.