Polyhydroxyalkanoate Copolymer Production by Recombinant Strain 1F2 from Fructose or Carbon Dioxide as Sole Carbon Source.

strain H16 is a chemoautotrophic bacterium that oxidizes hydrogen and accumulates poly[()-3-hydroxybutyrate] [P(3HB)], a prominent polyhydroxyalkanoate (PHA), within its cell. utilizes fructose or CO as its sole carbon source for this process. A PHA-negative mutant of strain H16, known as strain PHB4, cannot produce PHA. Strain 1F2, derived from strain PHB4, is a leucine analog-resistant mutant. Remarkably, the recombinant 1F2 strain exhibits the capacity to synthesize 3HB-based PHA copolymers containing 3-hydroxyvalerate (3HV) and 3-hydroxy-4-methyvalerate (3H4MV) comonomer units from fructose or CO This ability is conferred by the expression of a broad substrate-specific PHA synthase and tolerance to feedback inhibition of branched amino acids. However, the total amount of comonomer units incorporated into PHA was up to around 5 mol%. In this study, strain 1F2 underwent genetic engineering to augment the comonomer supply incorporated into PHA. This enhancement involved several modifications, including the additional expression of the broad substrate-specific 3-ketothiolase gene (), the heterologous expression of the 2-ketoacid decarboxylase gene (), and the phenylacetaldehyde dehydrogenase gene (). Furthermore, the genome of strain 1F2 was altered through the deletion of the 3-hydroxyacyl-CoA dehydrogenase gene (). The introduction of resulted in increased 3HV incorporation, reaching 13.9 mol% from fructose and 6.4 mol% from CO. Additionally, the deletion resulted in the production of PHA copolymers containing ()-3-hydroxy-2-methylpropionate (3H2MP). Interestingly, deletion increased the weight-average molecular weight of the PHA to over 3.0 × 10 on fructose. Thus, it demonstrates the positive effects of deletion on the copolymer composition and molecular weight of PHA.