Biosynthesis and Properties of Medium-Chain-Length Polyhydroxyalkanoates with Enriched Content of the Dominant Monomer

When grown in a nonanoic acid-limited chemostat at a dilution rate of 0.25 h(-1), Pseudomonas putida KT2440 produced poly(3-hydroxynonanoate-co-3-hydroxyheptanoate) containing 68 mol % 3-hydroxynonanoate (C9) and 32 mol % 3-hydroxyheptanoate (C7). Under the same conditions, but in the presence of acrylic acid, a fatty acid beta-oxidation inhibitor, the C9 monomer content increased to 88 mol %. Cofeeding glucose (3.9 g L-1) and nonanoic acid (2.9 +/- 0.1 g L-1) in continuous culture with 0.2 g L-1 of acrylic acid in the feed, further increased the C9 content to 95 mol %. A yield of PHA from nonanoic acid of 0.93 mol mol(-1) was attained. PHA with a 3-hydroxyoctanoate (C8) content of 98 mol % was produced with the same cofeeding methodology from octanoic acid. As the dominant monomer content increased, the melting point of the poly(3-hydroxynonanoate) copolymers increased from 46 to 63 degrees C and that of the poly(3-hydroxyoctanoate) copolymers from 54 to 62 degrees C. All copolymer compositions resulted in elongation to break values of about 1300%, but tensile strength at break and Young's modulus both increased with increasing amounts of the dominant monomer.