Sodium acetate stimulates PHB biosynthesis in synechocystis sp. PCC 6803

Synechocystis sp. pee 6803 cell growth and poly-β-hydroxybutyrate (PHB) biosynthesis were studied in the presence of sodium acetate (NaAc). For nitrogen-sufficient conditions, 15 mmol/L NaAc improved the PHB content up to 9.9% (w/w) while for nitrogen-starved conditions, the PHB content was up to 15.2% (w/w). NaAc at levels below 20 mmol/L promoted cell growth in the first six days, but the growth slowed on the seventh day when the NaAc concentration exceeded 15 mmol/L. The PHB content in the final biomass reached 11.0% of the dry cellular weight in the presence of 20 mmol/L NaAc. Two adjacent open reading frames (ORFs) in the genome of Synechocystis sp. pee 6803, slr1993 and slr1994, were assigned to phbA and phbB, respectively, while the phbC gene was found to be far from these genes. This may account for the low expression of PHB in cyanobacteria.