Team:TU Delft/Project/conclusions

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Revision as of 22:20, 27 October 2010

Conclusions

We have shown that using the concept of BioBricks it is possible to design an organism that (1) reacts to its environment (sensing), (2) influences the solubility of hydrocarbons (solubility) , (3) exhibits a higher tolerance towards solvents and salts (survival) and (4) implements (parts) of novel pathways (alkane degradation). This chassis could be used for example the biological degradation of residual oil in oil sands tailing waters, or the treatment of waste water from the oil industry.

Alkane Degradation

According to our analysis, the enzymatic activities of our recombinant strain and the negative control are statistically different at confidence level of 0.95, which means that the part BBa_K398018 increases 2 times the alcohol dehydrogenase activity in the cell extract. We can conclude from our data that the parts BBa_K398005 and BBa_K398018 have biological activity; particularly when we used BBa_K398018 the enzyme activity of E. coli cell extracts became equivalent to 3% of the in vitro activity of the positive control: Pseudomonas putida a natural alkane-degrading bacterium.

Our results also suggest that the recombinant strains E. coli 029A and E. coli 030A functionally express our biobricks. From our data we conclude that the biobrick [http://partsregistry.org/Part:BBa_K398006 BBa_K398006] under the promoter-rbs combination BBa_J23100-BBa_J61117 increases the dodecanal dehydrogenase activity in E. coli cell extracts 2-fold; whereas the expression of the same protein using the part BBa_J13002 as promoter-rbs combo increases the same activity 3-fold. Moreover, the enzymatic activities measured for the constructs BBa_K398029 and BBa_K398030 were equivalent to 33.98% and 42.01% of the Pseudomonas putida aldehyde dehydrogenase activity, respectively.

Survival

Salt tolerance

Our biobrick has enabled us to increase the salt tolerance of E.coli by an average of 20%. But due to the range of effects caused by increased salt stress, complete tolerance using a single protein is impossible. As such we hope to have made a first step and that the future iGEM teams will be able to build upon this knowledge.

Solvent tolerance

Our biobrick has enabled us to increase the solvent tolerance of E.coli when n-hexane is present in the culture medium at high concentrations. According to our findings, the growth rate of E.coli is improved 60% at a n-hexane concentration of 10%(v/v).

Solubility

To overcome the mass‐transfer limitation between the water and oil fase, a gene encoding for AlnA, a protein with emulsifying properties was expressed. The increased solubility of about 20% was determined by a new method. We suggest that in future research the protein is tagged, so it can be isolated with higher purity.

Sensing

After the pre cultures are grown in glucose, it needs to switch to alkanes as a feedstock. Therefore we designed a biobrick switch that can sense the absence of glucose: pCaif.

This new promoter combined with B0032 has a GFP production rate of 3.975E07 GFP molecules/second/O.D. during the stationary phase. Moreover, we demonstrated that this promoter is more active during stationary phase (high cAMP levels). Finally, in the presence of a secondary carbon source the GFP production rate decreases due to the catabolism of the secondary C-source.

Anderson RBS Characterizations

In order to tune the protein expressions of the alkane degrading genes we've characterized 5 members of the Anderson RBS family using an improved protein production model taking dilution into account. The following relative efficiencies were found: