*4.3.1 Genetic manipulation*

Many studies have been conducted on gene manipulation of cyanobacteria on metabolic engineering and PHB synthesis, *Synechhocystis sp.* PCC 6803 is the most studied strain. Insertion of *C. nectar* PHA operon into *Synechococcus* PCC 7942 increased the PHA production from 3 to 25% (dcw) [84]. The *Synechhocytis sp.* PCC 6803 was transfected with the PHA synthase gene from *C. nectar* and showed increased activity but net PHB content did not increase [73]. Overexpression of phaAB with 4 mM acetate supplementation showed an increase in PHB of up to 35% (dcw) in *Synechocytis sp. PCC6803* [85]. Wang et at. reported volumetric productivity of 263 mg.L<sup>1</sup> .d<sup>1</sup> and a yield of 1.84 g.L<sup>1</sup> by overexpression of the acetoacetyl-CoA reductase gene in *Synechocystis* [86]. **Table 2** summarizes further studies conducted on genetic manipulation for increasing PHB production.
