A recombinant strain of Salmonella enterica serovar Typhimurium (mutant in propionate-activation activity) was metabolically engineered to control the composition of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a polyhydroxyalkanoate copolymer with commercially desirable properties. A gene (prpE) encoding propionyl-CoA synthetase was placed under the control of the IPTG-inducible taclacUV5 promoter (P-taclacUV5) while the polyhydroxyalkanoate synthesis operon (phaBCA) from Acinetobacter sp. RA3849 was coexpressed under the control of the arabinose-inducible araBAD promoter (P-BAD), S. enterica, harboring both constructs, was grown in medium containing a fixed substrate concentration and the composition of the copolymer was varied between 2 mol% and 25 mol% 3-hydroxyvalerate by controlling the IPTG level in the medium. This "dial-a-composition" system should find application in cases where the substrate concentration of feedstream for PHBV bioplastic production is not adjustable.