Team:Tokyo Tech/Projects/Urea-cooler/data
From 2011.igem.org
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<!-- left menu list --> | <!-- left menu list --> | ||
- | <div style="min-height: | + | <div style="min-height: 4850px; float: left;"> |
<div id="LeftMenu" style="top:70px;"> | <div id="LeftMenu" style="top:70px;"> | ||
<!--list of page menu: DO NOT WRITE LINKS NOT WRITTEN IN THIS PAGE --> | <!--list of page menu: DO NOT WRITE LINKS NOT WRITTEN IN THIS PAGE --> | ||
<ul> | <ul> | ||
<li> | <li> | ||
- | <a href="#1.">1. Characterization of rocF and Arg box</a> | + | <a href="#1.">1. Characterization of <i>rocF</i> and Arg box</a> |
<ul> | <ul> | ||
<li><a href="#1.1">1.1 Materials</a></li> | <li><a href="#1.1">1.1 Materials</a></li> | ||
- | <li><a href="#1.2">1.2 Methods</a></li> | + | <li> |
+ | <a href="#1.2">1.2 Methods</a> | ||
+ | <ul> | ||
+ | <li><a href="#1.2.1">1.2.1 Preparation of samples for urea concentration assay</a></li> | ||
+ | <li><a href="#1.2.2">1.2.2 Urea concentration assay</a></li> | ||
+ | </ul> | ||
+ | </li> | ||
<li><a href="#1.3">1.3 Results</a></li> | <li><a href="#1.3">1.3 Results</a></li> | ||
</ul> | </ul> | ||
</li> | </li> | ||
<li> | <li> | ||
- | <a href="#2.">2. Characterization of Ptrc-RBS-rocF-Argbox</a> | + | <a href="#2.">2. Characterization of Ptrc-RBS-<i>rocF</i>-Argbox</a> |
<ul> | <ul> | ||
<li><a href="#2.1">2.1 Materials</a></li> | <li><a href="#2.1">2.1 Materials</a></li> | ||
- | <li><a href="#2.2">2.2 Methods</a></li> | + | <li> |
+ | <a href="#2.2">2.2 Methods</a> | ||
+ | <ul> | ||
+ | <li><a href="#2.2.1">2.2.1 Preparation of samples for urea concentration assay</a></li> | ||
+ | <li><a href="#2.2.2">2.2.2 Urea concentration assay</a></li> | ||
+ | </ul> | ||
+ | </li> | ||
<li><a href="#2.3">2.3 Results</a></li> | <li><a href="#2.3">2.3 Results</a></li> | ||
</ul> | </ul> | ||
Line 331: | Line 369: | ||
<p> | <p> | ||
Expression plasmids used in this study are shown in Table 1. <br /> | Expression plasmids used in this study are shown in Table 1. <br /> | ||
+ | <div align="center"> | ||
<table border="1"> | <table border="1"> | ||
<caption> | <caption> | ||
Line 336: | Line 375: | ||
</caption> | </caption> | ||
<tr> | <tr> | ||
- | < | + | <th>Designation</th> |
- | < | + | <th>pSB3K3</th> |
- | < | + | <th>pSB1C3</th> |
</tr> | </tr> | ||
<tr> | <tr> | ||
Line 351: | Line 390: | ||
</tr> | </tr> | ||
<tr> | <tr> | ||
- | <td><i>rocF</i>+Arg box</td> | + | <td><i>rocF</i> + Arg box</td> |
<td>Ptrc-<i>rocF</i></td> | <td>Ptrc-<i>rocF</i></td> | ||
<td>Arg box</td> | <td>Arg box</td> | ||
</tr> | </tr> | ||
</table> | </table> | ||
- | Strain MG1655 was transformed with either mock, rocF or <i>rocF</i> + Arg. As shown in Table 1, <i>rocF</i> gene was introduced on pSB3K3 and Arg boxes were introduced on pSB1C3. | + | </div> |
+ | Strain MG1655 was transformed with either mock, <i>rocF</i> or <i>rocF</i> + Arg box. As shown in Table 1, <i>rocF</i> gene was introduced on pSB3K3 and Arg boxes were introduced on pSB1C3. | ||
</p> | </p> | ||
<h3 id="1.2">1.2 Methods</h3> | <h3 id="1.2">1.2 Methods</h3> | ||
- | <h4>1.2.1 Preparation of samples for urea concentration assay</h4> | + | <h4 id="1.2.1">1.2.1 Preparation of samples for urea concentration assay</h4> |
<p> | <p> | ||
<ol> | <ol> | ||
- | <li>A single colony of cells transformed with engineered plasmids (mock,<i>rocF</i> or <i>rocF</i>+Arg box) was inoculated into 3 mL of LB with appropriate antibiotics and grown to saturation at | + | <li> |
- | <li>The saturated culture was diluted 50-fold, grown till the log phase (OD<sub>600</sub> = 0.5).</li> | + | A single colony of cells transformed with engineered plasmids (mock, <i>rocF</i> or <i>rocF</i> + Arg box) was inoculated into 3 mL of LB with appropriate antibiotics and grown to saturation at 37°C. |
- | <li>The culture was induced with 1 mM IPTG at | + | </li> |
- | <li>1.5 mL of culture was centrifuged at 9,000 rpm for 1 minute and the supernatant fluid was used as a sample for urea concentration assay. </li> | + | <li> |
+ | The saturated culture was diluted 50-fold, grown till the log phase (OD<sub>600</sub> = 0.5). | ||
+ | </li> | ||
+ | <li> | ||
+ | The culture was induced with 1 mM IPTG at 37°C for 1 hour. | ||
+ | </li> | ||
+ | <li> | ||
+ | 1.5 mL of culture was centrifuged at 9,000 rpm for 1 minute and the supernatant fluid was used as a sample for urea concentration assay. | ||
+ | </li> | ||
</ol> | </ol> | ||
</p> | </p> | ||
- | <h4>1.2.2 Urea concentration assay</h4> | + | <h4 id="1.2.2">1.2.2 Urea concentration assay</h4> |
- | <p>Urea concentrations of the samples were determined colorimetrically with <a href="http://www.clonagen.com/clonagen/ab52e63f-4e38-4465-b325-5fd126415f1a/quantichrom_urea_assay_kit_product.aspx">DIUR-500 -QuantiChrom™ Urea Assay Kit obtained from BioAssay Systems</a>.<br /> | + | <p> |
- | Detailed methods are as follows. | + | Urea concentrations of the samples were determined colorimetrically with <a href="http://www.clonagen.com/clonagen/ab52e63f-4e38-4465-b325-5fd126415f1a/quantichrom_urea_assay_kit_product.aspx">DIUR-500 -QuantiChrom™ Urea Assay Kit obtained from BioAssay Systems</a>.<br /> |
+ | Detailed methods are as follows. | ||
<ol> | <ol> | ||
- | |||
- | |||
- | |||
<li> | <li> | ||
- | Optical density at 450 nm was read and urea concentration (mg/dL) of the sample was calculated as<br /> | + | 10 µL of the supernatant fluid from each sample, 10 µL blank(LB),and 10 µL standard (10 mg/dL urea LB) were transferred to wells of clear bottom 96-well plates. |
- | <img src="https://static.igem.org/mediawiki/2011/5/55/Kit_equation.png" alt="equation" />.<br /> | + | </li> |
+ | <li> | ||
+ | 200 µL working reagent for coloring reaction from DIUR-500 -QuantiChrom™ Urea Assay Kit was added and the wells were taped lightly to mix. | ||
+ | </li> | ||
+ | <li> | ||
+ | The mixture was incubated for 20 munites at room temperature. | ||
+ | </li> | ||
+ | <li> | ||
+ | Optical density at 450 nm was read and urea concentration (mg/dL) of the sample was calculated as<br align="center" /> | ||
+ | <div> | ||
+ | <img src="https://static.igem.org/mediawiki/2011/5/55/Kit_equation.png" alt="equation" />. | ||
+ | </div><br /> | ||
ODSAMPLE, ODBLANK and ODSTANDARD are OD<sub>450</sub> values of sample, standard and blank, respectively. | ODSAMPLE, ODBLANK and ODSTANDARD are OD<sub>450</sub> values of sample, standard and blank, respectively. | ||
</li> | </li> | ||
Line 388: | Line 445: | ||
</p> | </p> | ||
- | <h5> | + | <h5>Linear plot of OD<sub>450</sub> vs. urea concentration</h5> |
- | <p>To | + | <p> |
- | + | To test linearlity between OD<sub>450</sub> vs. urea concentration, 0, 0.5, 1.0, 2.5, 7.5, 10 mg/dL urea LB were assayed in triplicate with this urea assay kit in the same way as our bacterial samples. Plot of OD<sub>450</sub> values vs. urea concentrations we tested showed very good linearlity as shown in Fig. 1.<br /> | |
- | + | <div align="center"> | |
+ | <img src="https://static.igem.org/mediawiki/2011/8/81/Linear_plot.png" alt="Standard curve for coloring reaction in urea assay" width="400px" /><br /> | ||
+ | Fig. 1 Linear plot of OD<sub>450</sub> vs. urea concentration | ||
+ | </div> | ||
</p> | </p> | ||
<h3 id="1.3">1.3 Results</h3> | <h3 id="1.3">1.3 Results</h3> | ||
- | <p>Each sample was assayed in duplicate urea concentration detected in each sample is shown in Table 2. | + | <p>Each sample was assayed in duplicate urea concentration detected in each sample is shown in Table 2. Fig. 2 shows the average of these 2 values.<br /> |
</p> | </p> | ||
+ | <div align="center"> | ||
<table border="2"> | <table border="2"> | ||
<caption>Table 2. Urea concentrations detected in duplicated</caption> | <caption>Table 2. Urea concentrations detected in duplicated</caption> | ||
<tr> | <tr> | ||
- | < | + | <th>Colony No.</th> |
- | < | + | <th>mock</th> |
- | < | + | <th><i>rocF</i></th> |
- | < | + | <th><i>rocF</i> + Arg box</th> |
</tr> | </tr> | ||
<tr> | <tr> | ||
Line 425: | Line 486: | ||
</tr> | </tr> | ||
<tr> | <tr> | ||
- | <td> | + | <td>S.D.</td> |
<td>0.80</td> | <td>0.80</td> | ||
<td>0.44</td> | <td>0.44</td> | ||
Line 431: | Line 492: | ||
</tr> | </tr> | ||
</table> | </table> | ||
+ | </div> | ||
<center> | <center> | ||
- | <img src="https://static.igem.org/mediawiki/2011/ | + | <img src="https://static.igem.org/mediawiki/2011/c/cb/Arg_box_on_1C3.png" width="400px" align="center" /> |
<div class="graph_title"> | <div class="graph_title"> | ||
- | + | Fig. 2 The average of concentration values detected in duplicate | |
</div> | </div> | ||
</center><br /> | </center><br /> | ||
Line 441: | Line 503: | ||
<h2 id="2.">2. Characterization of Ptrc-RBS-<i>rocF</i>-Argbox</h2> | <h2 id="2.">2. Characterization of Ptrc-RBS-<i>rocF</i>-Argbox</h2> | ||
<h3 id="2.1">2.1 Materials</h3> | <h3 id="2.1">2.1 Materials</h3> | ||
- | <p>Expression plasmids used in this study are listed in | + | <p>Expression plasmids used in this study are listed in Table 1.</p> |
+ | <div align="center"> | ||
<table border="3"> | <table border="3"> | ||
<caption>Table 3. Expression plasmids used in this study</caption> | <caption>Table 3. Expression plasmids used in this study</caption> | ||
<tr> | <tr> | ||
- | < | + | <th>Designation</th> |
- | < | + | <th>Parent vector</th> |
- | < | + | <th>Introduced sequence(s)</th> |
</tr> | </tr> | ||
<tr> | <tr> | ||
<td>Mock (3K3)</td> | <td>Mock (3K3)</td> | ||
- | <td> | + | <td>pSB3K3</td> |
<td>PlacIQ</td> | <td>PlacIQ</td> | ||
</tr> | </tr> | ||
Line 461: | Line 524: | ||
</tr> | </tr> | ||
<tr> | <tr> | ||
- | <td><i>rocF</i> | + | <td><i>rocF</i> - Arg box (3K3)</td> |
<td>pSB3K3</td> | <td>pSB3K3</td> | ||
<td>Ptrc-<i>rocF</i>-Arg box</td> | <td>Ptrc-<i>rocF</i>-Arg box</td> | ||
Line 468: | Line 531: | ||
<td>Mock (6A1)</td> | <td>Mock (6A1)</td> | ||
<td>pSB6A1</td> | <td>pSB6A1</td> | ||
- | <td>gfp (promoter-less)</td> | + | <td><i>gfp</i> (promoter-less)</td> |
</tr> | </tr> | ||
<tr> | <tr> | ||
Line 476: | Line 539: | ||
</tr> | </tr> | ||
<tr> | <tr> | ||
- | <td><i>rocF</i> | + | <td><i>rocF</i> - Arg box (6A1)</td> |
<td>pSB6A1</td> | <td>pSB6A1</td> | ||
<td>Ptrc-<i>rocF</i>-Arg box</td> | <td>Ptrc-<i>rocF</i>-Arg box</td> | ||
</tr> | </tr> | ||
</table> | </table> | ||
+ | </div> | ||
<p> | <p> | ||
- | In one experiment, MG1655 (argR +) and JE6852 (argR -) were respectively transformed with either mock(3K3), <i>rocF</i>(3K3) or <i>rocF</i>-Arg box(3K3). | + | In one experiment, MG1655 (<i>argR</i> +) and JE6852 (<i>argR</i> -) were respectively transformed with either mock(3K3), <i>rocF</i> (3K3) or <i>rocF</i> - Arg box(3K3). |
- | In another experiment, MG1655 (argR +) and JD24293 (argR -) were respectively transformed with either mock(6A1), <i>rocF</i>(6A1) or <i>rocF</i>-Arg box(6A1). | + | In another experiment, MG1655 (<i>argR</i> +) and JD24293 (<i>argR</i> -) were respectively transformed with either mock(6A1), <i>rocF</i> (6A1) or <i>rocF</i> - Arg box(6A1). Both JE6852 and JD24293 were obtained from National Institute of Genetics. |
</p> | </p> | ||
<h3 id="2.2">2.2 Methods</h3> | <h3 id="2.2">2.2 Methods</h3> | ||
- | <h4>2.2.1 Preparation of samples for urea concentration assay</h4> | + | <h4 id="2.2.1">2.2.1 Preparation of samples for urea concentration assay</h4> |
<p> | <p> | ||
<ol> | <ol> | ||
- | <li>A single colony of cells transformed with engineered plasmids (mock,<i>rocF</i> or <i>rocF</i> | + | <li> |
- | <li>The saturated culture was diluted 50-fold, grown till the log phase (OD<sub>600</sub> = 0.5).</li> | + | A single colony of cells transformed with engineered plasmids (mock, <i>rocF</i> or <i>rocF</i> - Arg box) was inoculated into 3 mL of LB with appropriate antibiotics and grown to saturation at 37°C. |
- | <li>The culture was induced with 1 mM IPTG at | + | </li> |
- | <li>1.5 mL of culture was centrifuged at 9,000 rpm for 1 minute and the supernatant fluid was used as a sample for urea concentration assay. </li> | + | <li> |
+ | The saturated culture was diluted 50-fold, grown till the log phase (OD<sub>600</sub> = 0.5). | ||
+ | </li> | ||
+ | <li> | ||
+ | The culture was induced with 1 mM IPTG at 37°C for 1 hour. | ||
+ | </li> | ||
+ | <li> | ||
+ | 1.5 mL of culture was centrifuged at 9,000 rpm for 1 minute and the supernatant fluid was used as a sample for urea concentration assay. | ||
+ | </li> | ||
</ol> | </ol> | ||
</p> | </p> | ||
- | <h4>2.2.2 Urea concentration assay</h4> | + | <h4 id="2.2.2">2.2.2 Urea concentration assay</h4> |
- | <p>Urea concentrations of the samples were determined colorimetrically with <a href="http://www.clonagen.com/clonagen/ab52e63f-4e38-4465-b325-5fd126415f1a/quantichrom_urea_assay_kit_product.aspx">DIUR-500 -QuantiChrom™ Urea Assay Kit obtained from BioAssay Systems</a>.<br /> | + | <p> |
+ | Urea concentrations of the samples were determined colorimetrically with <a href="http://www.clonagen.com/clonagen/ab52e63f-4e38-4465-b325-5fd126415f1a/quantichrom_urea_assay_kit_product.aspx">DIUR-500 -QuantiChrom™ Urea Assay Kit obtained from BioAssay Systems</a>.<br /> | ||
Detailed methods are as follows. | Detailed methods are as follows. | ||
<ol> | <ol> | ||
- | <li>10 µL of the supernatant fluid from each sample, 10 µL blank(LB),and 10 µL standard (10 mg/dL urea LB) were transferred to wells of clear bottom 96-well plates. </li> | + | <li> |
- | <li>200 µL working reagent for coloring reaction from DIUR-500 -QuantiChrom™ Urea Assay Kit was added and the wells were taped lightly to mix.</li> | + | 10 µL of the supernatant fluid from each sample, 10 µL blank(LB),and 10 µL standard (10 mg/dL urea LB) were transferred to wells of clear bottom 96-well plates. |
- | <li>The mixture was incubated for 20 munites at room temperature.</li> | + | </li> |
+ | <li> | ||
+ | 200 µL working reagent for coloring reaction from DIUR-500 -QuantiChrom™ Urea Assay Kit was added and the wells were taped lightly to mix. | ||
+ | </li> | ||
+ | <li> | ||
+ | The mixture was incubated for 20 munites at room temperature. | ||
+ | </li> | ||
<li> | <li> | ||
Optical density at 450 nm was read and urea concentration (mg/dL) of the sample was calculated as<br /> | Optical density at 450 nm was read and urea concentration (mg/dL) of the sample was calculated as<br /> | ||
Line 516: | Line 595: | ||
</p> | </p> | ||
- | <h5> | + | <h5>Linear plot of OD<sub>450</sub> vs. urea concentration</h5> |
- | <p>To | + | <p> |
- | + | To test linearlity between OD<sub>450</sub> vs. urea concentration, 0, 0.5, 1.0, 2.5, 7.5, 10 mg/dL urea LB were assayed in triplicate with this urea assay kit in the same way as our bacterial samples. Plot of OD<sub>450</sub> values vs. urea concentrations we tested showed very good linearlity as shown in Fig. 1.<br /> | |
- | + | <div align="center"> | |
- | + | <img src="https://static.igem.org/mediawiki/2011/8/81/Linear_plot.png" alt="Standard curve for coloring reaction in urea assay" width="400px" /><br /> | |
+ | Fig. 3 Linear plot of OD<sub>450</sub> vs. urea concentration | ||
+ | </div> | ||
+ | </p> | ||
<h3 id="2.3">2.3 Results</h3> | <h3 id="2.3">2.3 Results</h3> | ||
<center> | <center> | ||
- | <img src="https://static.igem.org/mediawiki/2011/ | + | <img src="https://static.igem.org/mediawiki/2011/b/bc/RocF_and_Arg_box_on_3K3.png" width="400px" align="center" /> |
<div class="graph_title"> | <div class="graph_title"> | ||
- | + | Fig. 4 Urea concentration detected in bacterial samples on pSB3K3 | |
</div> | </div> | ||
</center> | </center> | ||
<center> | <center> | ||
- | <img src="https://static.igem.org/mediawiki/2011/ | + | <img src="https://static.igem.org/mediawiki/2011/0/01/RocF_and_Arg_box_on_6A1_%283%29.png" width="400px" align="center" /> |
<div class="graph_title"> | <div class="graph_title"> | ||
- | + | Fig. 5 Urea concentration detected in bacterial samples on pSB6A1 | |
</div> | </div> | ||
</center><br /> | </center><br /> | ||
<p> | <p> | ||
- | In MG1655(argR +), addition of Trc promoter-<i>rocF</i> led to | + | Similar results were obtained in both the experiment with samples on pSB3K3 and the experiment with samples on pSB6A1. In MG1655(<i>argR</i> +), addition of Trc promoter-<i>rocF</i> led to production of more urea compared to mock as expected. These results show that insertion of <i>rocF</i> resulted in arginase production, therefore completing the urea cycle in <i>E. coli</i>. In the same strain, however, addition of Arg box sequence led to little change in urea production. The reason why the effect of Arg boxes was not apparent is probably that both pSB3K3 and pSB6A1 are low-copy-number plasmids. Low-copy-number plasmids are not capable of introducing enough number of Arg boxes to effectively deactivate the arginine repressor. Both of the plasmids containing <i>rocF</i> gene in the strains with a loss-of-function mutation in <i>argR</i>(a gene which codes arginine repressor) produce urea more efficiently than those in MG1655(<i>argR</i> +). |
</p> | </p> | ||
<p> | <p> | ||
- | These results are in line with the fact that | + | These results are in line with the fact that for strains with a loss-of-function mutation in <i>argR</i> gene, deactivation of arginine repressor by Arg boxes is not needed and addition of the Arg box does not result in increase of urea production. |
</p> | </p> | ||
Latest revision as of 03:51, 29 October 2011
Assay Method and Results
1. Characterization of rocF and Arg box
1.1 Materials
Expression plasmids used in this study are shown in Table 1.
Designation | pSB3K3 | pSB1C3 |
---|---|---|
mock | PlacIQ | Alcohol-dehydrogenase(promoter-less) |
rocF | Ptrc-rocF | Alcohol-dehydrogenase(promoter-less) |
rocF + Arg box | Ptrc-rocF | Arg box |
1.2 Methods
1.2.1 Preparation of samples for urea concentration assay
- A single colony of cells transformed with engineered plasmids (mock, rocF or rocF + Arg box) was inoculated into 3 mL of LB with appropriate antibiotics and grown to saturation at 37°C.
- The saturated culture was diluted 50-fold, grown till the log phase (OD600 = 0.5).
- The culture was induced with 1 mM IPTG at 37°C for 1 hour.
- 1.5 mL of culture was centrifuged at 9,000 rpm for 1 minute and the supernatant fluid was used as a sample for urea concentration assay.
1.2.2 Urea concentration assay
Urea concentrations of the samples were determined colorimetrically with DIUR-500 -QuantiChrom™ Urea Assay Kit obtained from BioAssay Systems.
Detailed methods are as follows.
- 10 µL of the supernatant fluid from each sample, 10 µL blank(LB),and 10 µL standard (10 mg/dL urea LB) were transferred to wells of clear bottom 96-well plates.
- 200 µL working reagent for coloring reaction from DIUR-500 -QuantiChrom™ Urea Assay Kit was added and the wells were taped lightly to mix.
- The mixture was incubated for 20 munites at room temperature.
-
Optical density at 450 nm was read and urea concentration (mg/dL) of the sample was calculated as
.
ODSAMPLE, ODBLANK and ODSTANDARD are OD450 values of sample, standard and blank, respectively.
Linear plot of OD450 vs. urea concentration
To test linearlity between OD450 vs. urea concentration, 0, 0.5, 1.0, 2.5, 7.5, 10 mg/dL urea LB were assayed in triplicate with this urea assay kit in the same way as our bacterial samples. Plot of OD450 values vs. urea concentrations we tested showed very good linearlity as shown in Fig. 1.
![Standard curve for coloring reaction in urea assay](https://static.igem.org/mediawiki/2011/8/81/Linear_plot.png)
Fig. 1 Linear plot of OD450 vs. urea concentration
1.3 Results
Each sample was assayed in duplicate urea concentration detected in each sample is shown in Table 2. Fig. 2 shows the average of these 2 values.
Colony No. | mock | rocF | rocF + Arg box |
---|---|---|---|
#1 | 1.9 | 4.9 | 7.3 |
#2 | 0.75 | 4.3 | 7.2 |
Average | 1.3 | 4.6 | 7.2 |
S.D. | 0.80 | 0.44 | 0.080 |
![](https://static.igem.org/mediawiki/2011/c/cb/Arg_box_on_1C3.png)
2. Characterization of Ptrc-RBS-rocF-Argbox
2.1 Materials
Expression plasmids used in this study are listed in Table 1.
Designation | Parent vector | Introduced sequence(s) |
---|---|---|
Mock (3K3) | pSB3K3 | PlacIQ |
rocF (3K3) | pSB3K3 | Ptrc-rocF |
rocF - Arg box (3K3) | pSB3K3 | Ptrc-rocF-Arg box |
Mock (6A1) | pSB6A1 | gfp (promoter-less) |
rocF (6A1) | pSB6A1 | Ptrc-rocF |
rocF - Arg box (6A1) | pSB6A1 | Ptrc-rocF-Arg box |
In one experiment, MG1655 (argR +) and JE6852 (argR -) were respectively transformed with either mock(3K3), rocF (3K3) or rocF - Arg box(3K3). In another experiment, MG1655 (argR +) and JD24293 (argR -) were respectively transformed with either mock(6A1), rocF (6A1) or rocF - Arg box(6A1). Both JE6852 and JD24293 were obtained from National Institute of Genetics.
2.2 Methods
2.2.1 Preparation of samples for urea concentration assay
- A single colony of cells transformed with engineered plasmids (mock, rocF or rocF - Arg box) was inoculated into 3 mL of LB with appropriate antibiotics and grown to saturation at 37°C.
- The saturated culture was diluted 50-fold, grown till the log phase (OD600 = 0.5).
- The culture was induced with 1 mM IPTG at 37°C for 1 hour.
- 1.5 mL of culture was centrifuged at 9,000 rpm for 1 minute and the supernatant fluid was used as a sample for urea concentration assay.
2.2.2 Urea concentration assay
Urea concentrations of the samples were determined colorimetrically with DIUR-500 -QuantiChrom™ Urea Assay Kit obtained from BioAssay Systems.
Detailed methods are as follows.
- 10 µL of the supernatant fluid from each sample, 10 µL blank(LB),and 10 µL standard (10 mg/dL urea LB) were transferred to wells of clear bottom 96-well plates.
- 200 µL working reagent for coloring reaction from DIUR-500 -QuantiChrom™ Urea Assay Kit was added and the wells were taped lightly to mix.
- The mixture was incubated for 20 munites at room temperature.
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Optical density at 450 nm was read and urea concentration (mg/dL) of the sample was calculated as
.
ODSAMPLE, ODBLANK and ODSTANDARD are OD450 values of sample, standard and blank, respectively.
Linear plot of OD450 vs. urea concentration
To test linearlity between OD450 vs. urea concentration, 0, 0.5, 1.0, 2.5, 7.5, 10 mg/dL urea LB were assayed in triplicate with this urea assay kit in the same way as our bacterial samples. Plot of OD450 values vs. urea concentrations we tested showed very good linearlity as shown in Fig. 1.
![Standard curve for coloring reaction in urea assay](https://static.igem.org/mediawiki/2011/8/81/Linear_plot.png)
Fig. 3 Linear plot of OD450 vs. urea concentration
2.3 Results
![](https://static.igem.org/mediawiki/2011/b/bc/RocF_and_Arg_box_on_3K3.png)
![](https://static.igem.org/mediawiki/2011/0/01/RocF_and_Arg_box_on_6A1_%283%29.png)
Similar results were obtained in both the experiment with samples on pSB3K3 and the experiment with samples on pSB6A1. In MG1655(argR +), addition of Trc promoter-rocF led to production of more urea compared to mock as expected. These results show that insertion of rocF resulted in arginase production, therefore completing the urea cycle in E. coli. In the same strain, however, addition of Arg box sequence led to little change in urea production. The reason why the effect of Arg boxes was not apparent is probably that both pSB3K3 and pSB6A1 are low-copy-number plasmids. Low-copy-number plasmids are not capable of introducing enough number of Arg boxes to effectively deactivate the arginine repressor. Both of the plasmids containing rocF gene in the strains with a loss-of-function mutation in argR(a gene which codes arginine repressor) produce urea more efficiently than those in MG1655(argR +).
These results are in line with the fact that for strains with a loss-of-function mutation in argR gene, deactivation of arginine repressor by Arg boxes is not needed and addition of the Arg box does not result in increase of urea production.