Biosynthesis of poly(3-hydroxypropionate-co-3-hydroxybutyrate) with fully controllable structures from glycerol.

As the most representative biodegradable thermoplastic, poly(3-hydroxybutyrate) (P3HB) has a limited range of applications because of its poor thermal and physical properties. To improve its properties, a novel biosynthetic system was designed to produce poly(3-hydroxypropionate-co-3-hydroxybutyrate) (P(3HP-co-3HB)) with fully controllable structures from inexpensive carbon source. In this system, two parallel synthetic pathways controlled by independent regulatory systems were used to produce the 3HP and 3HB monomers, respectively. Through tuning the expression level of appropriate genes, P(3HP-co-3HB) copolyesters were synthesized with a wide range of 3HP fraction from 11.5 mol% to 94.6 mol%. Differential scanning calorimetry analysis demonstrated that the thermal properties of P(3HP-co-3HB) copolymer were totally dependent on its composition. The bioreactor cultivation was also performed and accumulated 9.8 g/L P(48.2 mol% 3HP-co-3HB) using glycerol as sole carbon source, which represented the highest production so far.