<a href="#Detailed Proof">Detailed Proof</a>

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<a href="#CNanomaterial" style="font-size:14px;margin-left:15px;">Nanomaterial </a>

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<a href="#CBiofilm" style="font-size:14px;margin-left:15px;">Biofilm</a>

<a href="#CHydrogenase" style="font-size:14px;margin-left:15px;">Hydrogenase </a>

<a href="#Main Achievements">Main points</a>

 

<div id="Abstract" class="content">

  Solar Hunter is an artificial hydrogen production system comprising biofilm-anchored semiconductor nanorods (NRs) which efficiently convert photons to electrons, and engineered strain expressing [FeFe] hydrogenase that can efficiently catalyze Hydrogen production upon receiving the electrons donated by NRs.   The success of this integrative hydrogen-producing system relies on robust construction and functional characterization of each part separately.   We have proved that we successfully constructed and characterized our components, as revealed below.     For the full demonstration of the system with all the components, please refer to <b><a href="https://2016.igem.org/wiki/index.php?title=Team:ShanghaitechChina/Demonstration">Demonstration of our Work</a></b>

 

<div id="Main Achievements" class="content">

   <h1 align="center">Major Achievements in Constructing Our Device</h1>

  1. Successful production and characterization of engineered Biofilms, demonstrating that engineered biofilms composed of CsgA-Histag  fused protein allowed firm binding of semiconductor nanomaterials. <b><a href="http://parts.igem.org/Part:BBa_K2132001">BioBrick BBa_K2132001</a></b> <p></p>

  2.Next question is how to ensure normal enzyme activity by making these four enzymes can express simultaneously under a moderate level. So the built the device based on Acembl system and we make successful integration of [FeFe]-hydrogenase gene clusters from Clostridium acetobutylicum into one single plasmid to allow reliable expression.  <p></p> Please refer to <b><a href="https://2016.igem.org/Team:ShanghaitechChina/Hydrogen">Hydrogenase Session</a></b> for more details. </p>

  3.Finally, we need our enzyme to be functional to make a precondition for our whole plan. By the way, we can test the advantage of Acembl system vs pETDuet-1+pCDFDuet-1 system.So we observed successful hydrogen production with freely-flowing CdS Nanorods and find a higher enzyme catalysis activity. <p></p>

 

<div id="Detailed Proof" class="content">

   <h1 align="center">Detailed Proof</h1>

  <h3>A. To allow easy recycling of precious semiconductor nanomaterials, we utilized engineered biofilms to anchor nanomaterials via metal coordination chemistry. Please refer to <a href="https://2016.igem.org/Team:ShanghaitechChina/Biofilm"><b>Engineered Biofilms</b></a> for details of the successful construction and characterization of engineered biofilms that allow firm binding of nanomaterials. Key data are reproduced below. </h3>  <p></p></div>  

 

<h4> First, the simplest design, CsgA-Histag.</h4>

<img src="https://static.igem.org/mediawiki/parts/9/95/Shanghaitechchina_CsgAhis_CR.png" style="width:40%;">

This assay indicates the success in expression of the self-assembly curli fibers. <p></p>

Further, we use crystal violet assay to obtain quantitative data about the relative density of cells and biofilm adhesion to multi-wells cluster dishes.  

This assay indicates the success in expression of the self-assembly curli fibers. <p></p>

This difference between induced strains secreted CsgA-Histag and ΔCsgA manifest a distinct extracellular biofilm production in the modified strain. <p></p>

 

<h4 ><b>3.Quantum dots fluorescence test: successful binding test of Histag   with nanomaterials (CdSeS/CdSe/ZnS core/shell quantum dots)</b></h4>

</center>

 

 

<h4> Second, The complex design with extra function of binding SpyTag-linked enzymes in addition to its nanomaterial-binding through Histag. This is realized with our Part BBa_K2132001 under the promoter of aTc. </h4>

<div class="col-lg-4">

<img src="https://static.igem.org/mediawiki/parts/0/05/Shanghaitechchina_HISCsgASpyCatcher_CR.png" style="width:80%;">

<h4><b>2. Quantum dots fluorescence test: successful binding test of Histag   with nanomaterials</b></h4>

  As figure illustrated, his-CsgA-SpyCatcher-his mutant incubated with mcherry-SpyTag show a clear biofilm-associated mcherry fluorescence signal, which indicating the accurate conformation and function of the SpyTag and SpyCatcher linkage system. The distinct localization highlight of red fluorescence on E.coli, which to a large extent prove the specificity of our desired linkage between SpyTag and SpyCatcher system.  

<div class="col-lg-12">

</div>

<h4><b>6.Inducer concentration optimization</b></h4>

We cultured all E.coli mutants in multi-wells with increasing inducer gradient. The result demonstrated in accordance that 0.25 μg ml-1 of aTc will induce the best expression performance of biofilm, which is exactly the inducer concentration we applied in the project.  

<img src="https://static.igem.org/mediawiki/parts/2/23/Shanghaitechchina_inducer_concentration.png" style="width:60%;">

<p style="text-align:center"><b>Fig 10.</b>Inducer concentration gradient test. </p>

<div id="CHydrogenase"class="col-lg-12">

<h3>Hydrogenese gene clusters</h3><p></p>

  <p>High-activity hydrogenase is necessary for our system. To achieve efficient enzymatic activities, we codon-optimized and constructed the whole hydrogenase gene clusters (from Clostridium Acetobutylicum) by leveraging the multi-expression Acembl System.  Please refer to <b><a href="https://2016.igem.org/Team:ShanghaitechChina/Hydrogen">Hydrogenase Session</a></b> for more details. </p>   

In this section,we start with a single device of one gene from hydrogenase. A single device including following feagment

<img src="https://static.igem.org/mediawiki/2016/6/65/Pict2.png" style="width:40%;">

<p style="text-align:center"><b>Figure 3A</b> Integration of four basic plasmid backbones into one.</p>

<p style="text-align:center"><b>Figure 4A</b> Fusion of plasmid 1 and plasmid 4.</p>

<p style="text-align:center"><b>Figure 4B</b> Fusion of plasmid 2 and plasmid 4.</p>

Figure 4A/B shows that plasmid1/2 and 4 are successfully fused.<p></p>

<p style="text-align:center"><b>Figure 4C</b> Fusion of the plasmid in step one(4A) and plasmid 3.</p>

<p style="text-align:center"><b>Figure 4D</b> Fusion of the plasmid in step one(4B) and plasmid 3.</p>

<p style="text-align:center"><b>Figure 4E</b> Fusion of the plasmid in step (4C) and plasmid 3.</p>

Given the inconvenience with testing by restriction, we turned to resistance screening. The result is that it is resistant to four antibodies (Ampicillin, Chloramphenicol, kanamycin and Spectinomycin). Figure 4E shows that plasmids obtained in step 2 and plasmid 4 are successfully fused. Thus, we obtained a plasmid with all four subunits, HydA, HydE, HydF, HydG, fused together. The next step is to induce the expression of the hydrogenase.<p></p>

<p id="AResults"></p>

   <h1 align="center">Results</h1>

<h4><b>a) Hydrogen production system with free-flowing CdS nanorod.</b></h4>

The first hydrogen production data using our system is the pink curve (curve 1) in Figure 1. It shows that lighting can induce hydrogen production in a closed system with nano rods (NR), mediator Methyl Viologen, and IPTG-induced bacteria transformed with fused plasmid. To prove that every element of the system is necessary and that it is our hydrogenase that produced the hydrogen rather than NR, we conducted a series of experiments.<p></p>

To see whether NR is necessary and whether the hydrogen is produced by the reaction between NR and water under lighting rather than our hydrogenase, we conducted the experiment where the system does not contain nano rods or contain only nano rods. The data is summarized in Figure 1A. The red curve (curve 2) represents the system with the transformed bacterial suspension but without nano rods (NR). The flat curve shows that the system without NR could not produce hydrogen with light; NR is necessary for the system. The black curve (curve 3) represents a system in which only NR and mediators are present, with no bacteria. The flat curve shows that it could not produce hydrogen, which proves that the elements of the bacteria is necessary in the synthesis of hydrogen.<p></p>

<p style="text-align:center"><b>Figure 2</b></p>

Hydrogen production evolution curve (Sensor Data/ Hydrogen amount vs Time) with different components. The pink curve (curve 1) in all pictures is the hydrogen production with all the components, nano rods (NR), IPTG induction, and the bacteria transformed with our hydrogenase plasmid. The rest are data with one or two components missing. In particular, data in the integrated picture are categorized into Figure 2A and 2B. Figure 2A shows the system with or without nano rods or with nano rods alone, and Figure 2B represents the system with or without induction. The curve 3 in each of the specific figure is the blank control with not transformed <em>E. coli</em> BL21. This series of experiments show that only when both nano rods (NR) and IPTG-induced transformed bacteria are present can the system produce hydrogen in a stable way.<p></p>

Another step in proving that it is that the hydrogenase is indeed responsible for hydrogen production is to contrast the production level between the induced and un-induced bacteria suspension. The experiment we conducted are summarized in Figure 6B In this set of experiment, the blue line (curve 4) acts as our blank control. In this group, we use the wild type BL21 cells without plasmid. Although we can see a positive oscillation during a short time in the curve, the production was not at high rate and is likely due to the native hydrogenase in <em>E. coli</em>. The green curve (curve 5) represents the transformed bacterial with no induction of IPTG after 12h cultivation. The flat curve shows that it could not produce hydrogen, which proves that the induction of the hydrogenase expression is necessary. To further confirm, we did another experiment using bacteria that have grown 36 hours with no induction. The purple curve (curve 6) clearly contrasts the induced BL21 and the non-induced one. With curve 4 to 6, we have demonstrated that, with the help of NR, it was our hydrogenase in the system that produced the hydrogen we detected.<p></p>

<h4><b>b) Bidirectional catalytic property of [FeFe] hydrogenase</b></h4>

As mentioned earlier, hydrogenase catalyzes the reversible oxidation of molecular hydrogen (H2). Thus, when we “turn off” the production mode, we should be able to see the consumption of hydrogen by hydrogenase. In testing this bidirectional catalytic property, conducted an experiment where we turned on and turned off the light alternately. The data is shown below in Figure 7. During lighting period, the hydrogen production increases, until we shut off the light at points that correspond to the tips. The curve then goes downward, showing that the hydrogen concentration is lowered, an evidence of the consumption of hydrogen. It is noteworthy that the hydrogenase shows the greatest production rate at the beginning of lighting: a transient sharp rise can be observed at the valleys. It is also obvious that each period of “light-on light-off” gives similar curves, which implies that our hydrogenase is stable.

         <p style="text-align:center"><b>Figure 2</b> Verifying the bidirectional catalytic property of [FeFe] hydrogenase.</p>