Polyhydroxybutyrate (PHB) Production Using an Arabinose-Inducible Expression System in Comparison With Cold Shock Inducible Expression System in Escherichia coli.

Cupriavidus necator strain A-04 has shown 16S rRNA gene identity to the well-known industrial strain C. necator H16. Nevertheless, the cell characteristics and polyhydroxyalkanoate (PHA) production ability of C. necator strain A-04 were different from those of C. necator H16. This study aimed to express PHA biosynthesis genes of C. necator strain A-04 in Escherichia coli via an arabinose-inducible expression system. In this study, the PHA biosynthesis operon of C. necator strain A-04, consisting of three genes encoding acetyl-CoA acetyltransferase (phaAA-04, 1182 bp, 40.6 kDa), acetoacetyl-CoA reductase (phaBA-04, 741 bp, 26.4 kDa) and PHB synthase Class I (phaCA-04, 1770 bp), was identified. Sequence analysis of the phaAA-04, phaBA-04, and phaCA-04 genes revealed that phaCA-04 was 99% similar to phaCH16 from C. necator H16. The difference in amino acid residue situated at position 122 of phaCA-04 was proline, whereas that of C. necator H16 was leucine. The intact phaCABA-04 operon was cloned into the arabinose-inducible araBAD promoter and transformed into E. coli strains Top 10, JM109 and XL-1 blue. The results showed that optimal conditions obtained from shaken flask experiments yielded 6.1 ± 1.1 g/L cell dry mass (CDM), a PHB content of 93.3 ± 0.9% (w/w) and a productivity of 0.24 g/(L⋅h), whereas the wild-type C. necator strain A-04 accumulated 78% (w/w) PHB with a productivity of 0.09 g/(L⋅h). Finally, for the scaled-up studies, fed-batch cultivations by pH-stat control in a 5-L fermenter of E. coli strains XL1-Blue harboring pBAD/Thio-TOPO-phaCABA-04 and pColdTF-phaCABA-04 in MR or LB medium, leading to a PHB production of 31.4 ± 0.9 g/L at 54 h with a PHB content of 83.0 ± 3.8% (w/w), a CDM of 37.8 ± 1.2 g/L, a Y P/S value of 0.39 g PHB/g glucose and a productivity of 0.6 g PHB/(L⋅h) using pColdTF-phaCABA-04 in MR medium. In addition, PHB production was 29.0 ± 1.1 g/L with 60.2 ± 2.3% PHB content in the CDM of 53.1 ± 1.0 g/L, a Y P/S value of 0.21 g PHB/g glucose and a productivity of 0.4 g PHB/(L⋅h) using pBAD/Thio-TOPO-phaCABA-04 in LB medium. Thus, a relatively high PHB concentration and productivity were achieved, which demonstrated the possibility of industrial production of PHB.