Synechocystis sp. PCC 6803 strains overexpressing pha genes were constructed and characterized for poly-
3-hydroxybutyrate (PHB) production. These pha overexpressing strains showed slightly reduced growth
rates. Under N-deprived condition, the strains overexpressing (OE) phaAB, phaEC and phaABEC showed
significantly higher PHB contents than the wild type. The maximum PHB content, a 2.6-fold increase producing
26% PHB (dcw), was observed in OE phaAB cells grown for 9 days in N-deprived medium. Under
this condition, these OE phaAB cells increased PHB production to 35% PHB (dcw) upon addition of 0.4%
(w/v) acetate. Higher PHB granules in OE phaAB cells were clearly visualized by both Nile red staining
and TEM imaging. All OE strains under N-deficient condition had increased glgX transcript levels.
Overall results demonstrate an enhanced PHB production in Synechocystis cells overexpressing pha genes,
particularly phaA and phaB, when grown in N-deprived medium containing 0.4% (w/v) acetate.