Synthesis of Medium‐Chain‐Length Polyhydroxyalkanoate Homopolymers, Random Copolymers, and Block Copolymers by an Engineered Strain of Pseudomonas entomophila

Medium‐chain‐length polyhydroxyalkanoates (mcl‐PHAs), widely used in medical area, are commonly synthesized by Pseudomonas spp. This study tries to use β‐oxidation pathways engineered P. entomophila to achieve single source of a series of mcl‐monomers for microbial production of PHA homopolymers. The effort is proven successful for the first time to obtain a wide range of mcl‐PHA homopolymers from engineered P. entomophila LAC23 grown on various fatty acids, respectively, ranging from poly(3‐hydroxyheptanoate) to poly(3‐hydroxytetradecanoate). Effects of a PHA monomer chain length on thermal and crystallization properties including the changes of Tm, Tg, and Td5% are investigated. Additionally, strain LAC23 is used to synthesize random copolymers of 3‐hydroxyoctanoate (3HO) and 3‐hydroxydodecanoate (3HDD) or 3‐hydroxytetradecanoates, their compositions could be controlled by adjusting the ratios of two related fatty acids. Meanwhile, block copolymer P(3HO)‐b‐P(3HDD) is synthesized by the same strain. It is found for the first time that even‐ and odd number mcl‐PHA homopolymers have different physical properties. When the gene of the PHA synthase in the engineered P. entomophila is replaced by phaC from Aeromonas hydrophila 4AK4, poly(3‐hydroxybutyrate‐co‐30 mol%‐3‐hydroxyhexanoate) is synthesized. Therefore, P. entomophila can be used to synthesize the whole range of PHA (C7–C14) homopolymers, random‐ and block copolymers.