Revision as of 12:25, 20 September 2015

MerR activator under constitutive promoter and induceble merT promoter with 5 UTR -sfGFP

Mercury sensor activator under the control of the constitutive promoter (<a href="https://parts.igem.org/Part:BBa_K608002" target="_blank">BBa_K608002</a>) with mercury induceble promoter and 5´untranslated region which increses the output of the sfGFP which is used for detection.

Usage and Biology

For our sensor, we use parts ( BBa_K346002 and BBa_K346001) of the mercury sensor constructed by iGEM team Peking 2010. These Parts consist of the Mer operon from Shigella flexneri R100 plasmid Tn21, a mercury dependent operon. The expression of the Mer operon is regulated by the activator MerR. The MeR transcription however is regulated by itself. Mercury can bind to the C-terminal located cysteines and generates a conformal change to activate the expression (N.L. Brown et al.2003). Our mercury Sensor contains MerR, which is under control of a constitutive promoter and specific promoter MerT. sfGFP protein is used as measuring output signal and it´s transcription is controlled by the 5` untranslated region, which enhances the following reporter protein sfGFP .

Sequence and Features

Mercury

The main sources of mercury exposure are generated through humans. For example mercury contamination can be caused by medical waste (damaged measurement instruments), Fluorescent-lamps, Chloralkali plants and thermal power plants. In the environment, mercury is one of the most toxic elements . Acute effects of a mercury intoxication can range from diseases of the liver, kidney, gastrointestinal tract, to neuromuscular and neurological problems. A chronic intoxication of mercury results in kidney changes, changes in the central nervous system and other effects like cancer. The World Health Organization recommends a limit of 6 µg/L in drinking water.

in vivo

One of the already existing sensors we used for our system is the mercury sensor consisting of MerR the activator and the mercury specific promoter pmerT. The promoter is regulated by the MerR, which binds Hg²⁺-ions. Similar to the former sensors we added a sfGFP for detection via fluorescence.

For our mercury sensor we used parts of the mercury sensor constructed by iGEM team Peking 2010. These parts consist of the mercury dependent mer operon from Shigella flexneri R100 plasmid Tn21. The expression of the genes in the mer operon depends on the regulation by MerR its activator and promoter PmerT. For our sensor we used the codon optimized activator (BBa_K1758340), under control of a constitutive promoter,(BBa_K346001). Additionally to this activator we designed and constructed the specific promoter PmerT(BBa_K346002)(figure 2). For our sensor we added a 5’-UTR downstreamd of this promoter, which increased the fluorscence of the used reporter protein sfGFP.

BBa_K1758343), which consists of the activator under the control of a constitutive promoter BBa_K1758340)and the operator and promoter sequence of the mercury inducible promoter. An untranslated region in front of the sfGFP, which is used for detection, enhances its expression ( BBa_K1758342).">

We tested our mercury sensor with sfGFP as reporter gene, to test the functionality of the system. Moreover we tested different concentrations. The kinetic of our sensors response to different mercury concentrations is shown in figure 3. A strong increase in fluorescence levels is notecible after induction with mercury after 120 min. For better visualization the kinetics of figure 3 are represented as bars in figure 4. A fluorescence level difference for 120 min and 190 min is represented.

In vivo data show a highly significant, well working sensor, which even reacts to concentrations below the threshold of the water guidelines by the WHO (Figure 3 and 4).

The mercury detection was measured during the cultivation of E. coli KRX at 37 °C (Figure 3 and 4). The strain contained the plasmid with the activator merR under the control of a constitutive promoter and the specific promoter with an operator binding site, which reacts to the activator with bound Hg ²⁺-ions. The specific promoter is located upstream of the sfGFP CDS. Therefore, the mercury in the medium is detected via formation of sfGFP. In vivothis sensor devise shows a fast answer to occurrence of his heavy metal contrary to the other sensor systems In vivo.

Therefore we tested our sensor in vitro to check if an already functioning highly optimized sensor provides required data for guideline detections.