Difference between revisions of "Part:BBa K2739009"

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Hybrid promoter-PhaCAB-Bktb

This is a composite part that was created to allow us to test the functionality of BktB. PHA operon is known to produce bioplastic PHB. The coexpression of the BktB allow the production of copolymer, PHBV.

Usage and Biology

The BktB was isolated from R. eutropha H16 and being recognised as a phaA paralogous, which allows the formation of 3-ketovaleryl-CoA.

as the most important paralogous gene for PHBV production since it showed higher substrate specificity to the C5 monomer and used 3-ketovaleryl-CoA more efficiently (Mifune et al 2010).

and leads to PHBV production. In order to enhance the 3HV fraction in PHBV, paralog bktB was introduced into E. coli BL21 (DE3) with co-expression of phaCAB operon from Ralstonia eutropha. 

Figure 1. Schematic illustration of the pathways leading to the PHBV biosynthesis.

Results and Discussion

In order to investigate the effect of produced protein BktB on cell growth, cells that harboured pSB1C3-phaCAB, pSB1C3-phaCAB-bktB or pSB1C3-phaCB-bktB were cultivated with 3 % glucose and various concentrations of propionic acid. Cell growth over time for strains expressing three different constructs and negative control with 3 % glucose was showed in Figure 3.14, in which E. coli strain BL21 (DE3) harbouring pSB1C3-phaCAB-bktB, pSB1C3-phaCB-bktB and pSB1C3 reached maximum optical density after 30 hours of cultivation and their maximum optical densities were estimated to be approximately OD600 1.0. Cells that harboured pSB1C3-phaCAB reached stationary phase after 50 hours with highest final optical density of OD600 1.5.

Figure . Time course of cell growth for different construction plasmids. Glucose was added into culture medium as carbon resource with final concentration of 3 %. OD600 was taken after 16 hours, 24 hours, 32 hours, 48 hours and 56 hours. Standard deviation was showed as error bar.

E. coli strain BL21 (DE3) that harboured these two plasmids was spread on the Nile red agar plates with negative control (pSB1C3) respectively, and two plates were exposed to blue light. Compared with negative control, the strong Nile red fluorescence from strains that harboured either pSB1C3-phaCAB-bktB or pSB1C3-phaCB-bktB, indicating that PHA (PHB and PHBV) production was assessed after 24 hours.

Figure 2. Nile red agar plate detection of PHA production.

Paralogous gene bktB represented similar function with phaA gene in the pathway, which showed higher specificity to C5 monomers contributed to the PHBV productivity and 3HV fraction. Although gas chromatograph remained to be done to analyse PHBV composition, lower melting temperature still gave strong suggestion that replace phaA gene with bktB could significantly increase the PHBV content in PHA production and co-expression of two genes would show small increase of PHBV production. Combined with the culture condition optimisation, cells harbouring pSB1C3-phaCB-bktB showed great potential to improve production of PHBV with higher 3HV fraction.

Table 1. Melting Temperature Measurement

Future work

Gas chromatograph analysis remain to be done to give more specific information about the composition of extracted PHA products including the percentage of PHBV content and the fraction of 3HV in PHBV, which are essential for confirming the effect of bktB on PHBV production.

References

Yu, S.T., Lin, C.C. and Too, J.R., 2005. PHBV production by Ralstonia eutropha in a continuous stirred tank reactor. Process Biochemistry, 40(8), pp.2729-2734. Shojaosadati, S.A., Varedi Kolaei, S.M. and Babaeipour, V. 2008. Recent advances in high cell density cultivation for production of recombinant protein. Iranian Journal of Biotechnology, 6(2), pp.63-84. Mifune, J., Nakamura, S. and Fukui, T., 2010. Engineering of pha operon on Cupriavidus necator chromosome for efficient biosynthesis of poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) from vegetable oil. Polymer Degradation and Stability, 95(8), pp.1305-1312.

Sequence and Features