Part:BBa_K2578811
Protein coding sequence for Homo sapiens metallothionein 1 (MT1A)
This is the basic part of the Homo sapien metallothionein 1 synthesizing gene (MT1A). The genomic sequence of the MT1A gene is referenced from NCBI (Gene ID 4489)[1].
Metallothioneins are small cysteine-rich proteins made of 61-68 amino acids which can be found in a broad range of organisms, including both eukaryotes and prokaryotes. The metallothioneins are expressed as intracellular protein. [2]
Metallothioneins are mainly responsible for metalloregulation in cells of living organisms. The rich Cysteine domains in metallothioneins allow the non-covalent binding of trace metals such as cadmium(Cd2+), lead(Pb2+), copper(Cu1+), (Cu2+) and mercury(Hg2+), etc. [3][4]
MT mammalian family contains four members, MT1 - MT4. Each member shares similar properties but slightly different affinity in binding different metals. Among most studies, it was found that cadmium, lead and mercury, which are some most toxic metal ions displayed the highest binding affinity with MTs. [5] These results show that MTs are capable in the use of bioremediation of toxic heavy metals.
As what has been mentioned above, this part is the protein coding sequence of human MT1A protein. This isoform of MT1 in human has been well reported to bind with copper and their expressions will be regulated directly by copper concentration in the cells. [6][7]
MT1A is involved in human metalloregulation (Including copper, cadmium etc.). In our studies, the human MT1A gene is being expressed in e. coli to enhance the ability of removing copper of their surrounding medium.
The basic part is ordered and synthesized by IDT in the form of composite part BBa_K2578810. The ordered plasmid is transformed in e.coliTOP10 by heat shock. Transformed e.coli are used to perform a copper absorption test.
The plasmid is also cloned into pSB1C3 backbone for part submission.
Assay : Test for copper absorption ability on engineered E.coli
Abstract of assay A
In preparation of this assay, transformed E.coli with MT plasmids (Homo sapiens and Elsholtzia haichowensis MT1 gene) and plasmid vector without insert (as control setup), are inoculated as E.coli colonies and incubated for another 18 hours in SOB medium. We then transferred the transformed E.coli in SOB medium to copper(II) sulphate solution, with concentration 2 mg/L and 10 mg/L, in a ratio of 1:9. E.coli was removed by centrifugation after 0 hours, 2 hours and 4 hours and 2.5 ml of supernatant was extracted to test for the absorbance after adding 175 ul of copper test solution. Using the standard curve produced by calibrating absorbance of solution against copper concentration in assay 3, we can estimate the copper concentration after incubation. Copper adsorption ability of the engineered E.coli can be studied from the information obtained.
Graph 1: Standard Curve of absorbance at 440 nm against copper concentration in SOB medium
We first conducted the assay with the 10mg/L copper(II) sulphate solution to determine the range of copper ion absorption by bacteria. E.coli transformed with Homo sapiens MT1 gene, Elsholtzia haichowensis MT1 gene are transferred to 10mg/L copper(II) sulphate solution after different incubation interval. And we used bacteria transformed with empty vector and SOB solution as control setups.
We measured the absorbance of the solution and the copper concentration is determined by using the standard curve.
Results
Table 1: Change of absorbance in 0, 2, 4 hours with engineered bacteria
| Sample | Absorbance | copper concentration, mg/L | ||||
|---|---|---|---|---|---|---|
| 0 h | 2 h | 4 h | 0 h | 2 h | 4 h | |
| Elsholtzia haichowensis MT1 gene | 1.14 | 0.95 | 0.95 | 10.2 | 8.1 | 8.1 |
| 1.11 | 1.02 | 0.96 | 9.8 | 8.9 | 8.2 | |
| Homo sapiens MT1 gene | 1.14 | 1.02 | 1.01 | 10.2 | 8.9 | 8.8 |
| 1.14 | 0.99 | 0.85 | 10.2 | 8.6 | 7.1 | |
| Empty Vector | 1.14 | 0.98 | 0.94 | 10.2 | 8.5 | 8 |
| 1.14 | 0.94 | 0.78 | 10.2 | 8 | 6.3 | |
| SOB medium | 1.18 | 1.18 | 1.18 | 10.6 | 10.6 | 10.6 |
| 1.18 | 1.18 | 1.18 | 10.6 | 10.6 | 10.6 | |
Table 2: Copper absorption by engineered bacteria in 0, 2, 4 hours (10 mg/L)
| Sample | Inital Concentration of copper, mg/L | Change of concentration, mg/L | % change of concentration | ||
|---|---|---|---|---|---|
| after 2 hour | after 4 hour | after 2 hour | after 4 hour | ||
| Elsholtzia haichowensis MT1 gene | 10.2 | -2 | -2 | -19.90% | -19.90% |
| 9.8 | -1 | -1.6 | -9.70% | -16.20% | |
| Homo sapiens MT1 gene | 10.2 | -1.3 | -1.4 | -12.60% | -13.60% |
| 10.2 | -1.6 | -3.1 | -15.70% | -30.40% | |
| Empty Vector | 10.2 | -1.7 | -2.1 | -16.80% | -21.00% |
| 10.2 | -2.1 | -3.8 | -21.00% | -37.70% | |
| SOB medium | 10.6 | 0 | 0 | 0.00% | 0.00% |
| 10.6 | 0 | 0 | 0.00% | 0.00% | |
Table 3: Average copper absorption by engineered bacteria in 0, 2, 4 hours
| Sample | average initial concentration,mg/L | average chage of concentration, mg/L | average % change of concentration | ||
|---|---|---|---|---|---|
| after 2 hour | after 4 hour | after 2 hour | after 4 hour | ||
| Elsholtzia haichowensis MT1 gene | 10 | -1.5 | -1.8 | -15% | -18% |
| Homo sapiens MT1 gene | 10.2 | -1.45 | -2.25 | -14% | -22% |
| Empty Vector | 10.2 | -1.9 | -2.95 | -19% | -29% |
| SOB medium | 10.6 | 0 | 0 | 0% | 0% |
Graph 2: Effect of engineered bacteria on copper concentration
Graph 3: Average decrease in copper concentration after incubation with engineered bacteria
*Error Bar is standard deviation of estimated copper concentration
Graph 4: Percentage decrease in copper concentration after incubation with engineered bacteria
From the result, that is a significant decrease in copper concentration of the solution with E.coli with empty vector while comparing it to the SOB solution. While there is no change in the concentration for SOB medium, there is a decrease of 19% of copper concentration for E.coli after 2 hours of incubation and a decrease of 29% after 4 hours of incubation. Showing that E.coli itself are able to absorb copper ions.
Also, we could see that the copper concentration of the solution with Homo sapiens MT1 decrease 0.96 mg/L(14%) after 2 hours and 1.63 mg/L(22%) after 4 hours. Comparing with the control setup, we found the decreases of copper concentration in two setups are similar. Thus, we interpreted that the copper absorbed by E.coli transformed with Homo sapiens MT1 is similar to that absorbed by untransformed E.coli, meaning the present of Homo sapiens MT1 gene does not have significant effect in absorbing copper.
The copper concentration of the solution with Elsholtzia haichowensis EhMT1 decreased 1.49 mg/L(15%) within 2 hours and 3.02 mg/L(18%) within 4 hours. The concentration change of it and the control setup are similar so it is also interpreted that the copper absorbed by E.coli transformed with Elsholtzia haichowensis MT1 is similar to that absorbed by untransformed E.coli, meaning the present of Elsholtzia haichowensis MT1 gene does not have significant effect in absorbing copper.
To conclude, E.coli itself can absorb copper ions, E.coli with empty vector and transformed bacteria with the Elsholtzia haichowensis MT1 gene or Homo sapiens MT1 gene show similar copper ion absorbing ability.
Abstract of assay B
According to the World Health Organization’s guidelines for drinking water quality[1], 2 mg/L is the guideline value for copper concentration. We found the copper concentration would decrease around 2 mg/L after incubating the bacteria in 10 mg/L copper solution for 4 hours. We would like to know whether the concentration would decrease to 0 mg/L if the bacteria is incubated in 2 mg/L copper solution, or would the solution reach an equilibrium. Upon the question, we conducted the test of incubating transformed E.coli in 2 mg/L copper solution to investigate it.
Results
Table 4: Change of absorbance in 0, 2, 4 hour with engineered bacteria
| Sample | Absorbance | copper concentration, mg/L | ||||
|---|---|---|---|---|---|---|
| 0 h | 2 h | 4 h | 0 h | 2 h | 4 h | |
| Elsholtzia haichowensis MT1 gene | 0.37 | 0.37 | 0.35 | 2.0 | 2.0 | 1.7 |
| Homo sapiens MT1 gene | 0.44 | 0.34 | 0.28 | 2.7 | 1.6 | 1.0 |
| Empty Vector | 0.37 | 0.34 | 0.34 | 2.0 | 1.6 | 1.6 |
| Empty Vector | 0.42 | 0.34 | 0.29 | 2.0 | 1.6 | 1.1 |
Table 5: Copper absorption by engineered bacteria in 0, 2, 4 hours(2 mg/L)
| Sample | Initial concentration,mg/L | Change of concentration, mg/L | % change of concentration | ||
|---|---|---|---|---|---|
| after 2 hour | after 4 hour | after 2 hour | after 4 hour | ||
| Elsholtzia haichowensis MT1 gene | 2.0 | 0.0 | -0.2 | -0.0% | -10.9% |
| Homo sapiens MT1 gene | 2.7 | -1.1 | -1.7 | -39.4% | -63.0% |
| Empty Vector | 2.0 | -0.3 | -0.3 | -16.3% | -16.3% |
| Empty Vector | 2.5 | -0.9 | -1.4 | -34.2% | -55.6% |
Graph 5: Effect of engineered bacteria on copper concentration (2 mg/L)
We conducted this assay with two cultures of transformed E.coli with empty vector. While there is a decrease of 0.3mg/L (16.3%) in the medium with an initial copper concentration of 2.0mg/L, there is also a decrease of 1.4mg/L(55.6%) in the one with an initial concentration of 2.5mg/L.
For the transformed bacteria with Elsholtzia haichowensis MT1 gene, there is a decrease of 0.2 mg/L (10.9%) after 4 hours of incubation in 2mg/L copper solution.
For transformed E.coli with Homo sapiens MT1 gene, there is a decrease of 1.1mg/L (39.4%) after 2 hours of incubation and 1.7mg/L(63.0%) after 4 hours of incubation in 2mg/L copper solution.
Table 6: Comparing copper absorption by engineered bacteria with different initial copper concentration
| Sample | Initial concentration,mg/L | Change of concentration, mg/L | % change of concentration | ||
|---|---|---|---|---|---|
| after 2 hour | after 4 hour | after 2 hour | after 4 hour | ||
| Elsholtzia haichowensis MT1 gene | 9.8 | -1.0 | -1.6 | -9.7% | -16.2% |
| 2.0 | -0.0 | -0.2 | -0.0% | -10.9% | |
| Homo sapiens MT1 gene | 10.2 | -1.6 | -3.1 | -15.7% | -30.4% |
| 2.7 | -1.1 | -1.7 | -39.4% | -63.0% | |
| Empty Vector(Set A) | 10.2 | -1.7 | -2.1 | -16.8% | -21.0% |
| 2.0 | -0.3 | -0.3 | -16.3% | -16.3% | |
| Empty Vector(set B) | 10.2 | -2.1 | -3.8 | -21.0% | -37.7% |
| 2.5 | -0.9 | -1.4 | -34.2% | -55.6% | |
Graph 6: Decrease in copper concentration with different initial copper concentration for EhMT1 transformant
For transformed bacteria with Elsholtzia haichowensis MT1 gene. It shows similar percentage decrease of copper concentration when they are tested in different initial copper concentration. While there is a decrease of 1.60mg/L (16.2%) when the E.coli are incubated in 10mg/L copper solution for 4 hours, there is also a decrease of 0.23 mg/L (10.9%) for solution with E.coli incubated in 2mg/L copper solution for the same amount of time. It shows that the net absorption of transformed bacteria with Elsholtzia haichowensis MT1 gene stops when it reaches an equilibrium.
Graph 7: Decrease in copper concentration with different initial copper concentration for MT1A transformant
For transformed bacteria with Homo Sapiens MT1 gene. The difference of the percentage decrease of copper concentration when they are tested in different initial copper concentration is large. While there is a decrease of 3.09mg/L (30.4%) when the E.coli are incubated in 10mg/L copper solution for 4 hours, there is also a decrease of 1.70 mg/L (63%) for solution with E.coli incubated in 2mg/L copper solution for the same amount of time.
However, when we look at the data, the initial absorbance it show is 0.44 that the concentration of copper in the solution is 2.7mg/L according to the standard curve which it supposed to be 2.0mg/L. It shows that this set of data is unreliable. We hoped to conduct the assay again to obtain a more accurate set of data but we failed to do so due to time limit.
Graph 8: Decrease in copper concentration with different initial copper concentration for empty vector transformant
For the transformed bacteria with empty vector (Set A) it shows similar percentage decrease of copper concentration when they are tested in different initial copper concentration. While there is a decrease of 1.70mg/L (16.8%) when the E.coli are incubated in 10mg/L copper solution for 2 hours, there is also a decrease of 0.32 mg/L (16.3%) for solution with E.coli incubated in 2 mg/L copper solution for the same amount of time. It shows that the net absorption of transformed bacteria with empty vector (Set A) stops when it reaches an equilibrium.
For Set B of E.coli transformed with empty vector, the difference of the percentage change between the two different initial copper concentration is large, while there is a decrease of 3.83mg/L (33.7%) when the E.coli are incubated in 10mg/L copper solution for 4 hours, there is also a decrease of 1.38mg/L (55.6%) for solution with E.coli incubated in 2mg/L copper solution for the same amount of time. However, we notice that this set of data has a similar problem with the one of Homo Sapiens MT1 gene that the initial copper concentration deduced from the standard curve is much larger than it supposed to be. The concentration deduced from the standard is 2.5mg/L which the theoretical concentration is 2.0mg/L. Therefore, the data set B is unreliable, but we failed to perform it again due to time limit.
To conclude, the copper concentration does not decrease from 2 mg/L to 0 mg/L after 4 hours as we expected. Instead, we found that the copper concentration decreased by a similar percentage as the solutions did in the 10 mg/L test. Therefore, we can conclude that the net copper ion absorption stops when it reaches equilibrium.
Graph 9: Decrease in copper concentration with different inital copper concentration
Conclusion
Here are the few points that we would like to draw after the assays
- Transforming plasmid with metallothioneins might not be able to enhance E.coli’s copper absorption ability.
- By comparing the percentage of change in copper concentration between solutions with different transformed E.coli incubated, we cannot observe a significant difference between E.coli cloned with empty vectors, cloned with Elsholtzia haichowensis MT1 gene or Homo sapiens MT1 gene.
- The reason behind might be the failure of expressing eukaryotic genes in prokaryotic cells such as E.coli.
- By comparing the results from the assays using 2mg/L and 10mg/L, we found that the percentage change of copper concentration is similar between empty vector E.coli and transgenic E.coli, and both of them can absorb around 20-30% of copper ions after 4 hours of incubation.
Prospect
In the future, we would like to improve our device by lowering the copper concentration more effectively, causing a greater percentage decrease. Also, we aim to use the findings to design a device to absorb copper ions in water.
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