On the example of the strain Synechocystis PCC 680325 the pathway can be drawn as given in Figure 1. Four enzymes are necessary to synthesize polymeric PHB from Acetyl-CoA. This general synthesis pathway does not differ much between hetero- and photo-autotrophic prokaryotes. However, in cyanobacteria, the four genes are located on two different positions in the genome (see Fig. 4) and are regulated by two different operons. Wang et al. identified phaEC to be the bottleneck in PHB synthesis and replaced the native genes with the more efficient thioesterase II (TesB) deriving from E. coli.