Heterologous expression of phaC2 gene and poly-3-hydroxyalkanoate production by recombinant Cupriavidus necator strains using canola oil as carbon source

Many heterologous transformation studies have been carried out using the Cupriavidus necator PHB-4 strain to investigate the expression characteristics of various polyhydroxyalkanoate (PHA) synthase enzymes. In this study, we generated a recombinant C. necator PHB-4 strain by transforming a plasmid (pMRC03) harbouring the synthetic phaC2 gene of Pseudomonas putida CA-3. Under conditions favourable for expression of the phaC2 (P. put) CA-3 gene, canola oil was used as carbon source for the synthesis of PHAs. The expressed synthase polymerised monomers of 3-hydroxybutyrate (3-HB), 3-hydroxyvalerate (3-HV) and 3-hydroxyhexanoate (3-HHx) in the recombinant C. necator PHB-4 (pMRC03) strain. We then co-expressed the phaC2(P. put) (CA-3) gene with the native phaC1(C. ne) gene in wild type Cupriavidus necator H16 (C. necator H16 (pMRC03)). This co-expression produced a PHA blend of 3-HB, 3-HV, 3-HHx and 3-hydroxyoctanoate (3-HO) monomers in the presence of canola oil. Gas chromatography analysis revealed the presence of 94 mol% 3-HB, 1 mol% 3-HV, 4 mol% 3-HHx and 1 mol% 3-HO in a tetra-polymer. Thus, we confirmed that a synthetic phaC2 gene encoding the synthase enzyme is functionally active with substrates ranging from short to medium chain length PHAs.