Difference between revisions of "Team:HKUST-Rice/Potassium Sensor/dummy1"

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<div class="project_image" style="padding-top:0">
 
<div class="project_image" style="padding-top:0">
 
<img style="width:80%" src="https://static.igem.org/mediawiki/2015/d/d8/HKUST_Rice15_potassium_figure_int.png" alt="image caption">
 
<img style="width:80%" src="https://static.igem.org/mediawiki/2015/d/d8/HKUST_Rice15_potassium_figure_int.png" alt="image caption">
<p style="font-size:110%; padding-left:6%;"><strong>Figure 2. Construction and Testing of <i>P<sub>kdpF</sub></i>.</strong> A) Positions of base substitutions to standardize <i>P<sub>kdpF</sub></i> into RFC10 format. B) Single time point transfer curve for <i>P<sub>kdpF</sub></i> variants along a gradient of [K<sup>+</sup>] C) Relative GFP synthesis rate calculated from 3 measurement time points. Error bar present SEM from 3 biological replicates.</p></div>
+
<p style="font-size:110%; padding-left:6%;"><strong>Figure 2. Construction and Testing of <i>P<sub>kdpF</sub></i>.</strong> A) Positions of base substitutions to standardize <i>P<sub>kdpF</sub></i> into RFC10 format. B) Single time point transfer curve for <i>P<sub>kdpF</sub></i> variants along a gradient of [K<sup>+</sup>] C) Relative GFP synthesis rate calculated from 3 measurement time points. Error bar present SEM from 3 biological replicates.</p></div>
</div>
+
<p>To construct a potassium-sensing device, we cloned the promoter upstream of <i>kdpFABC</i> operon, <i>P<sub>kdpF</sub></i></a>, and fused it with a translation unit for GFP reporter <a href="http://parts.igem.org/Part:BBa_E0240"target="_blank">BBa_E0240</a> in BioBrick RFC10 standard. The promoter activity can then be reported by the GFP level under different K<sup>+</sup> concentrations.</p>
 
 
<p>To construct a potassium-sensing device, we cloned the promoter upstream of <i>kdpFABC</i> operon, <i>P<sub>kdpF</sub></i></a>, and fused it with a translation unit for GFP reporter <a href="http://parts.igem.org/Part:BBa_E0240"target="_blank">BBa_E0240</a> in BioBrick RFC10 standard. The promoter activity can then be reported by the GFP level under different K<sup>+</sup> concentrations.</p>
+
<p>However,<i>P<sub>kdpF</sub></i> contains an illegal <i>EcoR</i>I site that prohibits standard assembly. We tackled this by constructing and testing 3 mutated versions with A (<a href ="http://parts.igem.org/wiki/index.php?title=Part:BBa_K1682002"target="_blank">BBa_K1682002</a>) , C (<a href ="http://parts.igem.org/wiki/index.php?title=Part:BBa_K1682003"target="_blank">BBa_K1682003</a>), or G (<a href ="http://parts.igem.org/wiki/index.php?title=Part:BBa_K1682004"target="_blank">BBa_K1682004</a>) substituting the orignal T.</p>
+
<p>However,<i>P<sub>kdpF</sub></i> contains an illegal <i>EcoR</i>I site that prohibits standard assembly. We tackled this by constructing and testing 3 mutated versions with A (<a href ="http://parts.igem.org/wiki/index.php?title=Part:BBa_K1682002"target="_blank">BBa_K1682002</a>) , C (<a href ="http://parts.igem.org/wiki/index.php?title=Part:BBa_K1682003"target="_blank">BBa_K1682003</a>), or G (<a href ="http://parts.igem.org/wiki/index.php?title=Part:BBa_K1682004"target="_blank">BBa_K1682004</a>) substituting the orignal T.</p>
+
<p>Our results showed that all 3 variants are functional and sense [K<sup>+</sup>] from 0 to 0.1 mM. The C and G mutants had higher maximum promoter activities than the WT or A mutant. <i>P<sub>kdpF</sub></i>[-15,T>G] performed well in both strength and reliablity and was therefore used in subsequent experiments.</p>
 +
<hr class="para">
 +
</div>
 
 
<p>Our results showed that all 3 variants are functional and sense [K<sup>+</sup>] from 0 to 0.1 mM. The C and G mutants had higher maximum promoter activities than the WT or A mutant. <i>P<sub>kdpF</sub></i>[-15,T>G] performed well in both strength and reliablity and was therefore used in subsequent experiments.</p>
+
<div class="project_row">
 +
<p class="subTitle">Relative Promoter Unit Measurement of <i>P<sub>kdpF</sub></i>[-15,T>G]</p>
 +
<div class="project_image">
 +
<img id="Kgraph" src="https://static.igem.org/mediawiki/2015/9/90/HKUST-Rice15_%28log_10%29_RPU_of_kdpFp--15%2CT_G-_in_DH10B_-RPU-.png" alt="image caption">
 +
<p style="font-size:110%; padding-left:6%;"><strong>Figure 3. Relative promoter units (RPU) of <i>P<sub>kdpF</sub></i>[-15,T>G] under different [K<sup>+</sup>].</strong> Error bar present SEM from 3 independent experiments on different days.</p></div>
 +
<p>We decided to report the promoter activites of <i>P<sub>kdpF</sub></i>[-15,T>G] in Relative Promoter Units (RPU) because this will allow future users to compare its promoter strength with that from another promoter, and perhaps, further improve this part. The activities of P<sub>kdpF</sub></i>[-15,T>G] in different [K<sup>+</sup>] were measured and compared to that by BBa_I20260 following a modified protocol (see below) from Kelly et. al (2009), and was found to be ~0.5 RPU at 0mM K<sup>+</sup> and ~0.13 RPU 0.025 mM K<sup>+</sup>. From 0 - 0.4 mM K<sup>+</sup>, there is a 3.8 fold change in RPU.</p>
 
<hr class="para">
 
<hr class="para">
 
</div>
 
</div>
 
 
 
<div class="project_row">
 
<div class="project_row">
<p  class="subTitle">Relative Promoter Unit Measurement of <i>P<sub>kdpF</sub></i>[-15,T>G]</p>
+
<p  class="subTitle">Interference from other Endogenous Systems</p>
 
<div class="project_image">
 
<div class="project_image">
<img id="Kgraph" src="https://static.igem.org/mediawiki/2015/9/90/HKUST-Rice15_%28log_10%29_RPU_of_kdpFp--15%2CT_G-_in_DH10B_-RPU-.png" alt="image caption">
+
<img style="width:80%" src="https://static.igem.org/mediawiki/2015/4/40/HKUST_Rice15_Comparison_of_kdpFp_in_E_2.png" alt="image caption">
<p style="font-size:110%; padding-left:6%;"><strong>Figure 3. Relative promoter units (RPU) of <i>P<sub>kdpF</sub></i>[-15,T>G] under different [K<sup>+</sup>].</strong> Error bar present SEM from 3 independent experiments on different days.</p></div>
+
<p style="font-size:110%; padding-left:6%;"><strong>Figure 4. Comparison between the activities of <i>P<sub>kdpF</sub></i>[-15, T>G] in DH10B and TK2240 strain. </strong> Error bar present SEM from 3 biological replicates.</p>
<p>We decided to report the promoter activites of <i>P<sub>kdpF</sub></i>[-15,T>G] in Relative Promoter Units (RPU) because this will allow future users to compare its promoter strength with that from another promoter, and perhaps, further improve this part. The activities of P<sub>kdpF</sub></i>[-15,T>G] in different [K<sup>+</sup>] were measured and compared to that by BBa_I20260 following a modified protocol (see below) from Kelly et. al (2009), and was found to be ~0.5 RPU at 0mM K<sup>+</sup> and ~0.13 RPU 0.025 mM K<sup>+</sup>. From 0 - 0.4 mM K<sup>+</sup>, there is a 3.8 fold change in RPU.</p>
+
</div>
<hr class="para">
+
<div class="des">
</div>
+
<p>The low-affinity K<sup>+</sup> transport systems Trk and Kup native to <i>E. coli</i> are constitutively expressed (Epstein & Kim, 1971). Laermann et al. (2013) discovered that knocking out the two systems in the strain TK2240 <i>(kdp+ Δtrk Δkup)</i> will result in a increase in expression of the <i>kdpFABC</i> system. We repeated that comparsion using DH10B with our <i>P<sub>kdpF</sub></i>[-15,T>G] promoter but obtained different results - below 0.0125 mM K<sup>+</sup>, the activity of the promoter in DH10B was significantly greater than that in TK2240. Only when [K<sup>+</sup>] > 0.05mM would we be able to observe stronger promoter activities in TK2240. We are uncertain about what causes the discrepancies in the comparisons.</p>
+
</div>
<div class="project_row">
+
<p  class="subTitle">Interference from other Endogenous Systems</p>
+
<div class="project_image">
+
<img style="width:80%" src="https://static.igem.org/mediawiki/2015/4/40/HKUST_Rice15_Comparison_of_kdpFp_in_E_2.png" alt="image caption">
+
<p style="font-size:110%; padding-left:6%;"><strong>Figure 4. Comparison between the activities of <i>P<sub>kdpF</sub></i>[-15, T>G] in DH10B and TK2240 strain. </strong> Error bar present SEM from 3 biological replicates.</p>
+
 
</div>
 
</div>
<div class="des">
+
<p>The low-affinity K<sup>+</sup> transport systems Trk and Kup native to <i>E. coli</i> are constitutively expressed (Epstein & Kim, 1971). Laermann et al. (2013) discovered that knocking out the two systems in the strain TK2240 <i>(kdp+ Δtrk Δkup)</i> will result in a increase in expression of the <i>kdpFABC</i> system. We repeated that comparsion using DH10B with our <i>P<sub>kdpF</sub></i>[-15,T>G] promoter but obtained different results - below 0.0125 mM K<sup>+</sup>, the activity of the promoter in DH10B was significantly greater than that in TK2240. Only when [K<sup>+</sup>] > 0.05mM would we be able to observe stronger promoter activities in TK2240. We are uncertain about what causes the discrepancies in the comparisons.</p>
+
<div class="project_row">
 +
<hr class="para">
 +
<h1>Future Plan</h1>
 +
<p>In the interest of providing an efficient and accessible device that can identify the [K<sup>+</sup>] into real field, we plan to optimize our construct in a device using a paper-based cell-free transcription-translation (TX-TL) system.</p>
 
</div>
 
</div>
</div>
 
 
<div class="project_row">
 
<hr class="para">
 
<h1>Future Plan</h1>
 
<p>In the interest of providing an efficient and accessible device that can identify the [K<sup>+</sup>] into real field, we plan to optimize our construct in a device using a paper-based cell-free transcription-translation (TX-TL) system.</p>
 
</div>
 
 
<div class="project_row">
 
<hr class="para">
 
<h2>Materials and Methods</h2>
 
<p>Please refer to <a href ="https://2015.igem.org/Team:HKUST-Rice/Protocol">our protocol page for the materials and methods used in characterization.</a></p>
 
</div>
 
 
<div class="project_row">
 
<hr class="para">
 
<h2>References</h2>
 
<p style="font-size:125%">Kelly, J. R., Rubin, A. J., Davis, J. H., Ajo-Franklin, C. M., Cumbers, J., Czar, M. J., ... & Endy, D. (2009). Measuring the activity of BioBrick promoters using an in vivo reference standard. <i>Journal of biological engineering</i>, 3(1), 4.
 
<br><br>International Plant Nutrition Institute. (1998). Functions of Potassium in Plants. <i>Better Crops</i>, 82(3).
 
<br><br>Keseler et al. (2013), EcoCyc: fusing model organism databases with systems biology, <i>Nucleic Acids Research</i> 41: D605-12.</p>
 
<h2>References on potassium uptake and regulation systesm in <i>E. coli</i></h2>
 
<p style="font-size:125%">Epstein, W., & Kim, B. S. (1971). Potassium transport loci in <i>Escherichia coli</i> K-12. <i>Journal of Bacteriology, 108</i>(2), 639-644.
 
<br><br>Jung, K., Tjaden, B., & Altendorf, K. (1997). Purification, reconstitution, and characterization of KdpD, the turgor sensor of <i>Escherichia coli.</i> <i>Journal of Biological Chemistry, 272</i>(16), 10847-10852.
 
<br><br>Jung, K., Veen, M., & Altendorf, K. (2000). K<sup>+</sup> and ionic strength directly influence the autophosphorylation activity of the putative turgor sensor KdpD of <i>Escherichia coli</i>. <i>Journal of Biological Chemistry, 275 </i>(51), 40142-40147.
 
<br><br>Jung, K., Krabusch, M., & Altendorf, K. (2001). Cs+ Induces the kdp operon of <i>Escherichia coli</i> by Lowering the Intracellular K<sup>+</sup> Concentration. <i>Journal of bacteriology, 183</i>(12), 3800-3803.
 
<br><br>Laermann, V., Ćudić, E., Kipschull, K., Zimmann, P., & Altendorf, K. (2013). The sensor kinase KdpD of <i>Escherichia coli</i> senses external K<sup>+</sup>. <i>Molecular microbiology, 88</i>(6), 1194-1204.
 
<br><br>Laimins, L. A., Rhoads, D. B., & Epstein, W. (1981). Osmotic control of kdp operon expression in <i>Escherichia coli. Proceedings of the National Academy of Sciences, 78 </i>(1), 464-468.
 
<br><br>Narayanan, A., Paul, L. N., Tomar, S., Patil, D. N., Kumar, P., & Yernool, D. A. (2012). Structure-function studies of DNA binding domain of response regulator KdpE reveals equal affinity interactions at DNA half-sites. <i>PloS one, 7</i>(1), e30102.
 
<br><br>Polarek, J. W., Williams, G., & Epstein, W. (1992). The products of the kdpDE operon are required for expression of the Kdp ATPase of <i>Escherichia coli. Journal of bacteriology, 174 </i>(7), 2145-2151.
 
<br><br>Roe, A. J., McLaggan, D., O’Byrne, C. P., & Booth, I. R. (2000). Rapid inactivation of the <i>Escherichia coli</i> Kdp K<sup>+</sup> uptake system by high potassium concentrations. <i>Molecular microbiology, 35</i>(5), 1235-1243.
 
<br><br>Sugiura, A., Nakashima, K., Tanaka, K., & Mizuno, T. (1992). Clarification of the structural and functional features of the osmoregulated kdp operon of <i>Escherichia coli. Molecular microbiology, 6</i>(13), 1769-1776.
 
<br><br>Voelkner, P., Puppe, W., & Altendorf, K. (1993). Characterization of the KdpD protein, the sensor kinase of the K<sup>+</sup>‐translocating Kdp system of <i>Escherichia coli. European Journal of Biochemistry, 217</i>(3), 1019-1026.
 
<br><br>Walderhaug, M. O., Polarek, J. W., Voelkner, P., Daniel, J. M., Hesse, J. E., Altendorf, K., & Epstein, W. (1992). KdpD and KdpE, proteins that control expression of the kdpABC operon, are members of the two-component sensor-effector class of regulators. <i>Journal of bacteriology, 174</i>(7), 2152-2159.
 
<br><br>Yan, H., Fukamachi, T., Saito, H., & Kobayashi, H. (2011). Expression and activity of Kdp under acidic conditions in <i>Escherichia coli. Biological and Pharmaceutical Bulletin, 34</i>(3), 426-429.
 
<br><br>Zhang, L., Jiang, W., Nan, J., Almqvist, J., & Huang, Y. (2014). The <i>Escherichia coli</i> CysZ is a pH dependent sulfate transporter that can be inhibited by sulfite. <i>Biochimica et Biophysica Acta (BBA)-Biomembranes, 1838</i>(7), 1809-1816. </p>
 
 
 
 +
<div class="project_row">
 +
<hr class="para">
 +
<h2>Materials and Methods</h2>
 +
<p>Please refer to <a href ="https://2015.igem.org/Team:HKUST-Rice/Protocol">our protocol page for the materials and methods used in characterization.</a></p>
 +
</div>
 +
 +
<div class="project_row">
 +
<hr class="para">
 +
<h2>References</h2>
 +
<p style="font-size:125%">Kelly, J. R., Rubin, A. J., Davis, J. H., Ajo-Franklin, C. M., Cumbers, J., Czar, M. J., ... & Endy, D. (2009). Measuring the activity of BioBrick promoters using an in vivo reference standard. <i>Journal of biological engineering</i>, 3(1), 4.
 +
<br><br>International Plant Nutrition Institute. (1998). Functions of Potassium in Plants. <i>Better Crops</i>, 82(3).
 +
<br><br>Keseler et al. (2013), EcoCyc: fusing model organism databases with systems biology, <i>Nucleic Acids Research</i> 41: D605-12.</p>
 +
<h2>References on potassium uptake and regulation systesm in <i>E. coli</i></h2>
 +
<p style="font-size:125%">Epstein, W., & Kim, B. S. (1971). Potassium transport loci in <i>Escherichia coli</i> K-12. <i>Journal of Bacteriology, 108</i>(2), 639-644.
 +
<br><br>Jung, K., Tjaden, B., & Altendorf, K. (1997). Purification, reconstitution, and characterization of KdpD, the turgor sensor of <i>Escherichia coli.</i> <i>Journal of Biological Chemistry, 272</i>(16), 10847-10852.
 +
<br><br>Jung, K., Veen, M., & Altendorf, K. (2000). K<sup>+</sup> and ionic strength directly influence the autophosphorylation activity of the putative turgor sensor KdpD of <i>Escherichia coli</i>. <i>Journal of Biological Chemistry, 275 </i>(51), 40142-40147.
 +
<br><br>Jung, K., Krabusch, M., & Altendorf, K. (2001). Cs+ Induces the kdp operon of <i>Escherichia coli</i> by Lowering the Intracellular K<sup>+</sup> Concentration. <i>Journal of bacteriology, 183</i>(12), 3800-3803.
 +
<br><br>Laermann, V., Ćudić, E., Kipschull, K., Zimmann, P., & Altendorf, K. (2013). The sensor kinase KdpD of <i>Escherichia coli</i> senses external K<sup>+</sup>. <i>Molecular microbiology, 88</i>(6), 1194-1204.
 +
<br><br>Laimins, L. A., Rhoads, D. B., & Epstein, W. (1981). Osmotic control of kdp operon expression in <i>Escherichia coli. Proceedings of the National Academy of Sciences, 78 </i>(1), 464-468.
 +
<br><br>Narayanan, A., Paul, L. N., Tomar, S., Patil, D. N., Kumar, P., & Yernool, D. A. (2012). Structure-function studies of DNA binding domain of response regulator KdpE reveals equal affinity interactions at DNA half-sites. <i>PloS one, 7</i>(1), e30102.
 +
<br><br>Polarek, J. W., Williams, G., & Epstein, W. (1992). The products of the kdpDE operon are required for expression of the Kdp ATPase of <i>Escherichia coli. Journal of bacteriology, 174 </i>(7), 2145-2151.
 +
<br><br>Roe, A. J., McLaggan, D., O’Byrne, C. P., & Booth, I. R. (2000). Rapid inactivation of the <i>Escherichia coli</i> Kdp K<sup>+</sup> uptake system by high potassium concentrations. <i>Molecular microbiology, 35</i>(5), 1235-1243.
 +
<br><br>Sugiura, A., Nakashima, K., Tanaka, K., & Mizuno, T. (1992). Clarification of the structural and functional features of the osmoregulated kdp operon of <i>Escherichia coli. Molecular microbiology, 6</i>(13), 1769-1776.
 +
<br><br>Voelkner, P., Puppe, W., & Altendorf, K. (1993). Characterization of the KdpD protein, the sensor kinase of the K<sup>+</sup>‐translocating Kdp system of <i>Escherichia coli. European Journal of Biochemistry, 217</i>(3), 1019-1026.
 +
<br><br>Walderhaug, M. O., Polarek, J. W., Voelkner, P., Daniel, J. M., Hesse, J. E., Altendorf, K., & Epstein, W. (1992). KdpD and KdpE, proteins that control expression of the kdpABC operon, are members of the two-component sensor-effector class of regulators. <i>Journal of bacteriology, 174</i>(7), 2152-2159.
 +
<br><br>Yan, H., Fukamachi, T., Saito, H., & Kobayashi, H. (2011). Expression and activity of Kdp under acidic conditions in <i>Escherichia coli. Biological and Pharmaceutical Bulletin, 34</i>(3), 426-429.
 +
<br><br>Zhang, L., Jiang, W., Nan, J., Almqvist, J., & Huang, Y. (2014). The <i>Escherichia coli</i> CysZ is a pH dependent sulfate transporter that can be inhibited by sulfite. <i>Biochimica et Biophysica Acta (BBA)-Biomembranes, 1838</i>(7), 1809-1816. </p>
 +
 +
</div>
 
</div>
 
</div>
</div>
 
 
</div>
 
</div>
 
</body>
 
</body>

Revision as of 09:54, 18 September 2015



Potassium Sensor - PkdpF

E. coli that glows in paucity of K+ - at a glance

A. E. coli engineered with BBa_K1682005 functions as a potassium biosensor. High concentrations of K+ indirectly represses the promoter KkdpF and decreases the expression of GFP.

B. The potassium sensing promoter BBa_K1682004 can detect a gradient of K+ concentrations and its activities were reported in Relative Promoter Units (RPU).

  • K+ is an essential plant macronutrient and plays vital role for maintaining high crop yield.
  • Our biosensor BBa_K1682005 monitors K+ concentration.
  • Activity of K+ sensing promoter (BBa_K1682000) was measured in Relative Promoter Unit. It can be reliably reused.


PkdpF and our engineered K+ sensor BBa_K1682005 - the full story

Potassium is an essential plant macronutrient as it is required for photosynthesis, osmoregulation, stomatal control, sugar and protein synthesis. (IPNI, 1998) The deficiency of K+ ion will result in abnormalities in plant growth and metabolism.Our aim is to engineer a potassium sensor in Escherichia coli and detect lack of K+ in soil. To this end, we engineered PkdpF, a promoter activated under low [K+] condition, and fused it with gfp (gfpmut3b).


Endogenous K+ sensing system in E. coli

image caption

Figure 1. The kdp K+ uptake system in E.coli.

E. coli has multiple native K+ sensing and uptake systems that we could put to use. Among them, we chose the KdpDE two-component system (TCS). It contains a membrane-bound kinase KdpD and a cytoplasmic response regulator KdpE. Stimulated by low K+ concentration, both extracelluarly and intracellularly, KdpD transphosphorylates KdpE using its own phosphate. The phosph-KdpE is then capable of activating expression of the kdpFABC operon, which codes for a transporter complex that is activated by low K+ concentration.

Apart from that, E. coli also has constitutively expressed Trk and Kup transporters for K+ uptake.

*The above text is our summarized understanding on K+-sensing system using information from EcoCyc. (Keseler et al., 2013). Please refer to our references section below for a full list of references cited.


Design and Testing of K+-sensing Device

image caption

Figure 2. Construction and Testing of PkdpF. A) Positions of base substitutions to standardize PkdpF into RFC10 format. B) Single time point transfer curve for PkdpF variants along a gradient of [K+] C) Relative GFP synthesis rate calculated from 3 measurement time points. Error bar present SEM from 3 biological replicates.

To construct a potassium-sensing device, we cloned the promoter upstream of kdpFABC operon, PkdpF, and fused it with a translation unit for GFP reporter BBa_E0240 in BioBrick RFC10 standard. The promoter activity can then be reported by the GFP level under different K+ concentrations.

However,PkdpF contains an illegal EcoRI site that prohibits standard assembly. We tackled this by constructing and testing 3 mutated versions with A (BBa_K1682002) , C (BBa_K1682003), or G (BBa_K1682004) substituting the orignal T.

Our results showed that all 3 variants are functional and sense [K+] from 0 to 0.1 mM. The C and G mutants had higher maximum promoter activities than the WT or A mutant. PkdpF[-15,T>G] performed well in both strength and reliablity and was therefore used in subsequent experiments.


Relative Promoter Unit Measurement of PkdpF[-15,T>G]

image caption

Figure 3. Relative promoter units (RPU) of PkdpF[-15,T>G] under different [K+]. Error bar present SEM from 3 independent experiments on different days.

We decided to report the promoter activites of PkdpF[-15,T>G] in Relative Promoter Units (RPU) because this will allow future users to compare its promoter strength with that from another promoter, and perhaps, further improve this part. The activities of PkdpF[-15,T>G] in different [K+] were measured and compared to that by BBa_I20260 following a modified protocol (see below) from Kelly et. al (2009), and was found to be ~0.5 RPU at 0mM K+ and ~0.13 RPU 0.025 mM K+. From 0 - 0.4 mM K+, there is a 3.8 fold change in RPU.


Interference from other Endogenous Systems

image caption

Figure 4. Comparison between the activities of PkdpF[-15, T>G] in DH10B and TK2240 strain. Error bar present SEM from 3 biological replicates.

The low-affinity K+ transport systems Trk and Kup native to E. coli are constitutively expressed (Epstein & Kim, 1971). Laermann et al. (2013) discovered that knocking out the two systems in the strain TK2240 (kdp+ Δtrk Δkup) will result in a increase in expression of the kdpFABC system. We repeated that comparsion using DH10B with our PkdpF[-15,T>G] promoter but obtained different results - below 0.0125 mM K+, the activity of the promoter in DH10B was significantly greater than that in TK2240. Only when [K+] > 0.05mM would we be able to observe stronger promoter activities in TK2240. We are uncertain about what causes the discrepancies in the comparisons.


Future Plan

In the interest of providing an efficient and accessible device that can identify the [K+] into real field, we plan to optimize our construct in a device using a paper-based cell-free transcription-translation (TX-TL) system.


References

Kelly, J. R., Rubin, A. J., Davis, J. H., Ajo-Franklin, C. M., Cumbers, J., Czar, M. J., ... & Endy, D. (2009). Measuring the activity of BioBrick promoters using an in vivo reference standard. Journal of biological engineering, 3(1), 4.

International Plant Nutrition Institute. (1998). Functions of Potassium in Plants. Better Crops, 82(3).

Keseler et al. (2013), EcoCyc: fusing model organism databases with systems biology, Nucleic Acids Research 41: D605-12.

References on potassium uptake and regulation systesm in E. coli

Epstein, W., & Kim, B. S. (1971). Potassium transport loci in Escherichia coli K-12. Journal of Bacteriology, 108(2), 639-644.

Jung, K., Tjaden, B., & Altendorf, K. (1997). Purification, reconstitution, and characterization of KdpD, the turgor sensor of Escherichia coli. Journal of Biological Chemistry, 272(16), 10847-10852.

Jung, K., Veen, M., & Altendorf, K. (2000). K+ and ionic strength directly influence the autophosphorylation activity of the putative turgor sensor KdpD of Escherichia coli. Journal of Biological Chemistry, 275 (51), 40142-40147.

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