the present biotechnological approach for the production of polyhydroxyalkanotes uses microbial systems . the high production costs makes them substantially more expensive than synthetic plastics . engineering a novel pathway in eucaryotic cell systems is a beneficial alternative to the production of phas in bacteria . this pathway will initially produce free fatty acids from the fatty acid synthetic pathway through the action of thioesterase , that will then add a coa moiety to the free fatty acid through the action of an acyl - coa synthetase , that will produce 3 - ketoacyl - coas from the acyl - coa through the action of a thiolase , that will produce r -- oh - acyl - coas from the 3 - keto acid coas through the action of a dehydrogenase isoform from yeasts . these r -- 3 - oh - acyl - coas will finally be used as substrate for the pha synthase reaction .