Difference between revisions of "Part:BBa K2260001"

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phaC1-J4 with polyhistidine tags

Overview

In order to utilize short and medium chain length volatile fatty acids (VFAs) our part consists of phaC1 (Pseudomonas aeruginosa) and phaJ4 (Pseudomonas putida). Transcription of phaJ4 leads to expression of enoyl-coA hydratase and pha synthase from phaC1. These enzymes are involved in the pathway that leads to conversion of volatile fatty acids (VFAs) such as acetic acid, propionic acid, butyric acid, etc. to poly[(R)-3-hydroxybutyrate] (PHB). The gene construct also includes histidine tags upstream of each gene and contains two ribosome binding sites (RBS).

This part was inserted into pET29(b)+ downstream a T7 promoter and lacZ. Thus, expression of phaC1J4 gene was induced using Isopropyl β-D-1-thiogalactopyranoside (IPTG). E. coli (BL21) was transformed with the plasmid containing the gene construct. The bacteria was used in our experiments to test the ability of the part to synthesize PHB in different conditions. The three different conditions used were pure VFAs only, fermented synthetic feces supernatant (which is referred as "syn poo" supernatant on this page), and glucose only.

PHB from fermented "syn poo" supernatant

In order to test the construct in the different conditions, overnights (O/Ns) of our construct and negative control (E. coli transformed with pET29(b)+ containing no insert) was were used. The O/Ns were grown for ~24 hours and the OD₆₀₀ was adjusted to be in the range 0.4-0.7. The table below shows the OD₆₀₀ readings taken before inoculation.

Three replicates were carried out for each of the conditions. Our construct and negative control O/Ns were added to the media containing carbon sources. The composition of the media in each of the twelve 125 mL Erlenmeyer flasks is given below:

The cells were allowed to grow in the media for ~24 hours and centrifuged. Cells were then resuspended in (1x) PBS for extraction and the OD₆₀₀ was recorded before proceeding to other steps for extraction. The table below shows the recorded OD₆₀₀.

After extraction of PHB from cells using sodium hypochlorite extraction method the final weights of tube containing the product was weighed and recorded as follows:

HPLC of PHB

Karr et. al showed that digestion of PHB in sulphuric acid leads to the production of crotonic acid (1983). The protocol used for PHB digestion is given here. About 0.025 g of PHB was digested for 15 mins and 30 mins. For each of the durations low and high dilution factors were used. Figure 2, 3, 4 and 5 show the HPLC results.

Discussion of HPLC results

The HPLC results had a crotonic acid peak for all samples. This confirmed that the obtained product was PHB. Although we were successful at detecting PHB using HPLC, the obtained amount of crotonic acid may be lower than the actual amount produced as the method of quantification of PHB using HPLC requires further development. In particular, an optimal digestion time needs to be selected so that all of the PHB in the sample digests to crotonic acid without further degradation of crotonic acid. The PHB extraction method can also be optimized to minimize the amount of PHB lost during extraction.

References

Karr DB, Waters JK, Emerich DW. Analysis of Poly-β-Hydroxybutyrate in Rhizobium japonicum Bacteroids by Ion-Exclusion High-Pressure Liquid Chromatography and UV Detection . Applied and Environmental Microbiology. 1983;46(6):1339-1344.