organisms are provided which express enzymes such as glycerol dehydratase , diol dehydratase , acyl - coa transferase , acyl - coa synthetase β - ketothiolase , acetoacetyl - coa reductase , pha synthase , glycerol - 3 - phosphate dehydrogenase and glycerol - 3 - phosphatase , which are useful for the production of phas . in some cases one or more of these genes are native to the host organism and the remainder are provided from transgenes . these organisms produce poly homopolymers or co - polymers incorporating 3 - hydroxypropionate or 3 - hydroxyvalerate monomers wherein the 3 - hydroxypropionate and 3 - hydroxyvalerate units are derived from the enzyme catalysed conversion of diols . suitable diols that can be used include 1 , 2 - propanediol , 1 , 3 propanediol and glycerol . biochemical pathways for obtaining the glycerol from normal cellular metabolites are also described . the pha polymers are readily recovered and industrially useful as polymers or as starting materials for a range of chemical intermediates including 1 , 3 - propanediol , 3 - hydroxypropionaldehyde , acrylics , malonic acid , esters and amines .