Team:XMU-China/background

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  <p align="center"><strong class="tit" >Background  and Approach </strong></p>
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  <p><strong class="subtitle">Logic gates: </strong>A&nbsp;logic  gate&nbsp;is an idealized or physical  device implementing a&nbsp;<a href="http://en.wikipedia.org/wiki/Boolean_function" title="Boolean function">Boolean function</a>, that is, it performs a <a href="http://en.wikipedia.org/wiki/Logical_operation" title="Logical operation">logical operation</a>&nbsp;on one or more logic inputs  and produces a single logic output. The <strong>AIM </strong>of our project is to construct a fluorescent digital&nbsp;display device of  genetic circuits with synthetic logic gates. The finished device will display  and switch numbers. Similar to electronic circuits, logic regulation operation  in cells integrates the extracellular and intracellular signals. We assemble  several pairs of promoters and their activators or repressors into computing  building block of the circuit: <em>PBAD</em>-Arabinose, <em>PcI</em>-CI, and <em>PtetR</em>-TetR. These computation  units act as genetic logic gates perform AND, OR and NOT gates function.&nbsp;</p>
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  <p><strong class="subtitle">GFP: </strong>The green fluorescent  protein (GFP) is a protein composed of 238 amino acid residues (26.9kDa) that  exhibits bright green fluorescence when exposed to light in the blue to  ultraviolet range.  Considering that the common types of GFP usually tend to be very stable and  hard to &quot;quench&quot;, we choose unstable GFP to make our device reusable  and convert in a fast speed which is tagged with a C-terminal extension that  will be recognized and degraded by tail-specific proteases, leading to a short  half-life and fast degradation of the protein. Degradation rate should  be confined at a suitable range; otherwise the device would either have no  light or take a long time to change numbers.</p>
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  <p><strong class="subtitle">Cell immobilization: </strong>It is a definition about the methods that how  to establish numeric display device and how to immobilize the engineering  bacteria in tubes. In our project, we have selected two of them to immobilize  our engineering bacteria: <br>
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    1) Entrapping cells in calcium alginate beads; <br>
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    2) Embedding cells in PDMDAAC-NaCS microcapsules.</p>
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  <p><strong class="subtitle">Quorum Sensing: </strong>It is  a method of communication between bacteria that enables the coordination of  group-based behavior based on population density. It was first observed in  Vibrio fischeri, a bioluminiscent bacterium that lives in the ocean. Bacteria  that use quorum sensing constantly produce and secrete certain signaling molecules  (called autoinducers or pheromones). These bacteria also have a receptor that  can specifically detect the signaling molecule (inducer). When the inducer  binds the receptor, it activates transcription of certain genes, including  those for inducer synthesis. There is a low likelihood of a bacterium detecting  its own secreted inducer. Thus, in order for gene transcription to be  activated, the cell must encounter signaling molecules secreted by other cells  in its environment. When only a few other bacteria of the same kind are in the  vicinity, diffusion reduces the concentration of the inducer in the surrounding  medium to almost zero, so the bacteria produce little inducer. However, as the  population grows, the concentration of the inducer passes a threshold, causing  more inducer to be synthesized. This forms a positive feedback loop, and the  receptor becomes fully activated. Activation of the receptor induces the  up-regulation of other specific genes, causing all of the cells to begin  transcription at approximately the same time. This coordinated behavior of  bacterial cells can be useful in a variety of situations. For instance, the  bioluminescent luciferase produced by V. fischeri would not be visible if it  were produced by a single cell. By using quorum sensing to limit the production  of luciferase to situations when cell populations are large, V. fischeri cells  are able to avoid wasting energy on the production of useless product. <strong></strong></p>
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  <p><strong class="subtitle">Time delay:</strong> Constructing a unique display device which can let each unit light up one after another is  beneficial for our team to accomplish the aim of time delay, which means that it is  necessary to construct a series of cells those can express the characteristic  of different time delay. As a result, we take advantage of Quorum Sensing system to change the time delay of  GFP expression via different promoters and intensity of RBS.</p>
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  <p><strong class="subtitle">Origin: </strong>In reality, we selected this  project from the first brainstorm which was put forward by the members of Group  2 and its previous name was Bioscreen , as you see, which is turned to be  E.lumoli nowadays. To gain knowledge about more details of the original task,  please link to: <br>
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  <u>Brainstorm: Contents: Group 2: Bioscreen </u></p>
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  <p><strong class="subtitle">Overview: </strong>Under usual condition, traditional segment  displays acted as a number &ldquo;8&rdquo; need 7 tubes. Through different combinations of  the tubes, the device can display different numbers or characters. Actually most  modern displays are controlled by electric signals which are converted by  chemical or biological signals. But in several situations, especially in detect  of trace amounts or minute amounts of biological signals, we found that it is  difficult to transfer and display the results. Besides, the relevant parameters  which are controlled in real time in some fields of industrial application are  hard to be the same as the reality. The aim of project is to design a  shining&nbsp;synthetic device&nbsp;for&nbsp;digit&nbsp;or time-course display  which can replace the traditional methods. <br>
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    Fortunately, 2012 XMU iGEM team has constructed a fluorescent  digital&nbsp;display device with synthetic logic gates,&nbsp;which is able to respond  to signals by displaying and switching numbers. We put GFP equipped with  degradation tags in downstream to illuminate our numbers and change them  quickly as well. Considering our engineering background, we accordingly employ  cell immobilization to build our device. Engineering bacteria have been  embedded in intra-hallow calcium alginate microcapsules and in PDMDAAC-NaCS  microcapsules respectively. In addition, 3D CAD design is performed for a  perfect device.<br>
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  Our genetic circuits vary in length and RBS strength, leading to  different durations of time delay for GFP expression which inspired us to  extend our work of 2011 XMU iGEM team. By altering the strength of RBS at five  grades, another five circuits have been built. After the induction by  arabinose, the duration of response time for GFP expression increases as the  strength of RBS declines, bringing about a time-course display.</p>
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Revision as of 07:46, 12 September 2012

XMU-CSS

XMU

safetyindex

Contents[hide][show]
  • Researcher, Public and Environmental Safety
  • Biosafety Standards and Institutions
  • Biosafety Training
  • Future Safety and Security Suggestions
  • References
  • XMU-BACKGROUND

    Background and Approach

    Logic gates: A logic gate is an idealized or physical device implementing a Boolean function, that is, it performs a logical operation on one or more logic inputs and produces a single logic output. The AIM of our project is to construct a fluorescent digital display device of genetic circuits with synthetic logic gates. The finished device will display and switch numbers. Similar to electronic circuits, logic regulation operation in cells integrates the extracellular and intracellular signals. We assemble several pairs of promoters and their activators or repressors into computing building block of the circuit: PBAD-Arabinose, PcI-CI, and PtetR-TetR. These computation units act as genetic logic gates perform AND, OR and NOT gates function. 

    GFP: The green fluorescent protein (GFP) is a protein composed of 238 amino acid residues (26.9kDa) that exhibits bright green fluorescence when exposed to light in the blue to ultraviolet range. Considering that the common types of GFP usually tend to be very stable and hard to "quench", we choose unstable GFP to make our device reusable and convert in a fast speed which is tagged with a C-terminal extension that will be recognized and degraded by tail-specific proteases, leading to a short half-life and fast degradation of the protein. Degradation rate should be confined at a suitable range; otherwise the device would either have no light or take a long time to change numbers.

    Cell immobilization: It is a definition about the methods that how to establish numeric display device and how to immobilize the engineering bacteria in tubes. In our project, we have selected two of them to immobilize our engineering bacteria:
    1) Entrapping cells in calcium alginate beads;
    2) Embedding cells in PDMDAAC-NaCS microcapsules.

    Quorum Sensing: It is a method of communication between bacteria that enables the coordination of group-based behavior based on population density. It was first observed in Vibrio fischeri, a bioluminiscent bacterium that lives in the ocean. Bacteria that use quorum sensing constantly produce and secrete certain signaling molecules (called autoinducers or pheromones). These bacteria also have a receptor that can specifically detect the signaling molecule (inducer). When the inducer binds the receptor, it activates transcription of certain genes, including those for inducer synthesis. There is a low likelihood of a bacterium detecting its own secreted inducer. Thus, in order for gene transcription to be activated, the cell must encounter signaling molecules secreted by other cells in its environment. When only a few other bacteria of the same kind are in the vicinity, diffusion reduces the concentration of the inducer in the surrounding medium to almost zero, so the bacteria produce little inducer. However, as the population grows, the concentration of the inducer passes a threshold, causing more inducer to be synthesized. This forms a positive feedback loop, and the receptor becomes fully activated. Activation of the receptor induces the up-regulation of other specific genes, causing all of the cells to begin transcription at approximately the same time. This coordinated behavior of bacterial cells can be useful in a variety of situations. For instance, the bioluminescent luciferase produced by V. fischeri would not be visible if it were produced by a single cell. By using quorum sensing to limit the production of luciferase to situations when cell populations are large, V. fischeri cells are able to avoid wasting energy on the production of useless product.

    Time delay: Constructing a unique display device which can let each unit light up one after another is beneficial for our team to accomplish the aim of time delay, which means that it is necessary to construct a series of cells those can express the characteristic of different time delay. As a result, we take advantage of Quorum Sensing system to change the time delay of GFP expression via different promoters and intensity of RBS.

    Origin: In reality, we selected this project from the first brainstorm which was put forward by the members of Group 2 and its previous name was Bioscreen , as you see, which is turned to be E.lumoli nowadays. To gain knowledge about more details of the original task, please link to:
    Brainstorm: Contents: Group 2: Bioscreen

    Overview: Under usual condition, traditional segment displays acted as a number “8” need 7 tubes. Through different combinations of the tubes, the device can display different numbers or characters. Actually most modern displays are controlled by electric signals which are converted by chemical or biological signals. But in several situations, especially in detect of trace amounts or minute amounts of biological signals, we found that it is difficult to transfer and display the results. Besides, the relevant parameters which are controlled in real time in some fields of industrial application are hard to be the same as the reality. The aim of project is to design a shining synthetic device for digit or time-course display which can replace the traditional methods.
    Fortunately, 2012 XMU iGEM team has constructed a fluorescent digital display device with synthetic logic gates, which is able to respond to signals by displaying and switching numbers. We put GFP equipped with degradation tags in downstream to illuminate our numbers and change them quickly as well. Considering our engineering background, we accordingly employ cell immobilization to build our device. Engineering bacteria have been embedded in intra-hallow calcium alginate microcapsules and in PDMDAAC-NaCS microcapsules respectively. In addition, 3D CAD design is performed for a perfect device.
    Our genetic circuits vary in length and RBS strength, leading to different durations of time delay for GFP expression which inspired us to extend our work of 2011 XMU iGEM team. By altering the strength of RBS at five grades, another five circuits have been built. After the induction by arabinose, the duration of response time for GFP expression increases as the strength of RBS declines, bringing about a time-course display.