Designed by: Erika Schneider Group: iGEM18_Bielefeld-CeBiTec (2018-09-02)
Sequence and Features
- 10COMPATIBLE WITH RFC
- 12COMPATIBLE WITH RFC
- 21Illegal XhoI site found at 279
- 23COMPATIBLE WITH RFC
- 25COMPATIBLE WITH RFC
- 1000Illegal BsaI.rc site found at 265
The basic part BBa_K2638002, copD, is an inner membrane importer for copper ions. It is part of our accumulation system in E. coli. In its native organism Pseudomonas brassicacearum 3RE2-7 it is expressed next to copC, which supports effective uptake.
We expressed the gene in two different expression systems, one with a T7 promoter and RBS (BBa_K2638004) and the other with a pBAD/araC and RBS system (BBa_K2638006). All results also in comparison with the other importers we characterized can be found on our accumulation results page.
Using the growth curve data from E. coliDH5α carrying BBa_K2638006 we also compared relative growth of a strain at 2 mM or 3 mM Cu(II) against the growth at 0 mM Cu(II) for not induced and induced cultures (figure 3). The data shows that supplementary copper even benefits growth at low concentrations. At small copper concentrations non-induced cells grow even faster then without added CuSO4 (9.9 % with 2 mM Cu(II) and 21.2 % with 3 mM Cu(II)). Upon induction with arabinose this changes and growth is inhibited by 21.5% ± 3.3% at 2 mM Cu(II) and 42 % ± 5.4 % with 3 mM Cu(II). This is a strong indicator for successful copper uptake.
Membrane Permeability Assays
1-N-phenylnaphthylamine membrane-permeabilization (NPN) assays are a fast method to measure the permeability of outer cell membranes. The NPN assays were all performed under the same conditions. The cells were either induced with 0.1 % rhamnose and 0.1 mM IPTG or with 1 % arabinose. Afterwards, fluorescence was measured in the range from 380 – 550 nm after exitation with light with the wavelength of 355 nm. The fluorescence values for every measurement were normalized to the fluorescence value at 382 nm.
In both strains which expressed the copD composite parts BBa_2638004 (T7 promoter, RBS and copD) and BBa_K2638006 (pBAD/araC promoter, RBS and copD) a higher increase in the percental fluorescence increase was shown compared to the pSB1C3 control strain (yellow curve figure 3). The strain expressing copD under control of the pBAD/araC promoter with RBS (BBa_K2638006, blue curve in figure 3) showed a maximum of 94.16 ± 10.89 % in the fluorescence emission at 408 nm. This is an increase of 59.03 % to the empty control vector pSB1C3. The copD strain with the T7 promoter (BBa_2638004, red curve in figure 3) showed a maximum regarding the fluorescence of 68.10 ± 2.84 % at 408 nm. This is an increase of 32.99 % in comparison to the empty vector control. The difference increased fluorescence at 408 nm of both copD expressing strains compared to the empty vector control show a substantial increased of the membrane permeability of E. coli. This also indicates substantial uptake.
Specifity of Cu(II) uptake is shown with an ONPG-assay (orhto-Nitrophenyl-β-galactoside assay). The ONPG assay shows no unspecific uptake for copD and the other analyzed constructs (figure 4).
For a complete discussion look up the results page
In general our data shows that our copper uptake Biobricks work as expected. The import of copper can be shown by increasing toxic effects on cells, as the growth curves indicate an obvious growth inhibition for OprC and CopD. The CopD encoding Biobricks BBa_K2638002, BBa_K2638004 and BBa_K2638006 show the most impressive results both in the toxicity test and the NPN assay. This result was expected, as the import of Cu(II) occurs actively across the inner cell membrane into the cytoplasm (Lawton et al., 2016), where toxic effects have the strongest impact.
Further interesting experiments would be the combination of OprC (BBa_K2638200), CopC (BBa_K2638001) with CopD (BBa_2638002) in one biobrick. The combination of an importer into the periplasm and into the cytoplasm could improve the effectivity of uptake dramatically. To further support CopD, CopC could deliver Cu(II) to the transporter through the periplasm. The already performed growth experiments could be performed and measurements of intracellular copper may be conducted.