Known attempts using engineered bacteria to produce P(3HB-co-4HB) with carbon sources that are structurally unrelated to 4-hydroxybutyrate resulted in relatively low 4HB monomer content of 1.5 to 5 mol %. The current invention provides recombinant hosts for producing P(3HB-co-4HB) wherein the plasmid including succinate semialdehyde dehydrogenase gene (sucD gene) and 4-hydroxybutyrate dehydrogenase gene (4hbD gene) further includes pyruvate decarboxylase promoter (Ppdc). It was found that the 4HB monomer content in P(3HB-co-4HB) is significantly enhanced to be over 20 mol %, in the range of 8.8 to 23 mol %.