Glycolysis

Aim

Glycolysis is native to all living cells, and uses glucose to produce pyruvate as the first step to producing energy in the form of ATP. Pyruvate is later converted to acetyl-CoA in the first step of the citric acid cycle. In Ralstonia eutropha, excess acetyl-coA is converted into poly(3-hydroxybuturate) (PHB) and stored as a carbon energy source (Hiroe et al., 2012). R. eutropha accomplishes this feat with the use of three genes:

• phaA, which codes for 3-ketothiolase and converts acetyl-CoA to acetoacetyl-CoA;
• phaB, which codes for acetoacetyl-CoA reductase, which converts acetoacetyl-CoA to (R)-3-hydroxybutyryl-CoA, and;
• phaC, which codes for pha synthase and converts (R)-3-hydroxybutyryl-CoA, to PHB.

Operon rearrangement

In R. eutropha, the aforementioned genes exist in the order phaCAB. However, literature has shown that the rearrangement of the operon to phaCBA results in higher production of PHB (Hiroe et al., 2012). Therefore, we decided to change the order of our operon.

Hiroe et al. showed that the content of PHB is dependent on the expression of phaB. This rearrangement from phaCAB to phaCBA will lead to higher expression of phaB compared to that of the native operon, resulting in more PHB produced. However, the molecular weight of PHB was not affected by the different expression of phaB, indicating the chemical structure of the polymer remained consistent.

Media/Culture composition

The phaCBA operon can utilize acetic acid present in fermented synthetic feces supernatant (which is referred to as "syn poo" supernatant). In order to test our gene construct, the operon was inserted into pET29(b)+. Competent E. coli (BL21) was then transformed with the plasmid. The overnights of successfully transformed cells was then used for our experiments. The different media composition used were glucose only and fermented syn poo supernatant. The glucose only condition will show the ability of our construct to use glucose as a feedstock (positive control) and the syn poo supernatant will be used to test whether our construct can synthesize PHB from synthetic feces.

Results

The results of the experiments for our phaCBA construct is given on results page and our parts registry.

References

Hiroe A, Tsuge K, Nomura CT, Itaya M, Tsuge T. 2012. Rearrangement of gene order in the phaCAB operon leads to effective production of ultrahigh-molecular-weight poly[(R)-3-hydroxybutyrate] in genetically engineered Escherichia coli. Appl. Environ. Microbiol. 78:3177–3184. 10.1128/AEM.07715-11.