Team:Tokyo-NoKoGen/trehalose production

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<img src="https://static.igem.org/mediawiki/2014/5/52/Noko14_Trepro2.png"><br><br>
 
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<h2><b>The trehalose biosynthetic operon – <i>otsA</i> and <i>otsB</i></b></h2>
 
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<p> Trehalose (α-D-glucopyranosyl-[1,1]-α-D-glucopyranoside) is a non-reducing disaccharide in which two glucose units are linked by an α,α-1,1 bond and is common in nature. In yeast and fungi, trehalose plays an important role in protection against environmental stresses such as desiccation, heat, frost, and high osmolarity(1, 2). The pathway for trehalose synthesis induced by osmotic stress in <i>E. coli </i> is the same as in other species(3, 4).</p><br>
 
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<p> The genes <i>otsA</i> and <i>otsB</i> are required for trehalose production in <i>E. coli</i>. The <i>otsA</i> gene encodes trehalose-6-phosphate synthase. This enzyme converts UDP-glucose and D-glucose-6-phosphate to trehalose-6-phosphate. The <i>otsB</i> gene encodes trehalose-6-phosphate phosphatase. This enzyme converts trehalose-6-phosphate to trehalose. </p><br>
 
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<p> The operon <i>otsBA</i> is induced by osmotic stress, extreme heat, extreme cold, desiccation, and entry into stationary phase. Therefore, we decided to culture <i>E. coli</i> under high salt level in order to overexpress the genes.</p><br><br>
 
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<br>
 
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<h2><b>Construction of Biobrick</b></h2>
 
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<p> <i>otsA</i> gene and <i>otsB</i> gene were cloned from <i>E.coli</i> K-12 strain. PCR products were digested with <i>EcoR</i>I and <i>Pst</i>I and digested products were inserted into pSB1A2.<br>
 
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 <i>otsB</i> gene and <i>otsA</i> gene were ligated with four promoters and double terminator (BBa_B0010 and BBa_B0012).</p><br>
 
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<img src="https://static.igem.org/mediawiki/2014/f/f4/Noko14_Otsveccon1.png" width="80%"><br>
 
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<p>Fig.1 Constructed vectors</p><br>
 
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<p> One of those promoters is arabinose inducible, and the others are constitutive promoter.</p>
 
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<p>Table.1 Promoter</p>
 
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<img src="https://static.igem.org/mediawiki/2014/e/e1/Noko14_Promoter.PNG" width="80%"><br><br>
 
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<h2><b>Evaluation of trehalose production</b></h2><br>
 
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<p><b>1. Optimization of culture condition </b></p>
 
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<p> It has been reported that trehalase derived from host <i>E. coli</i> was expressed higher when <i>E. coli</i> reach to stationary phase (1). At first, we monitored the growth of transformants and optimized the growth condition for further experiments.  </p>
 
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<p> We added 600 mM NaCl and 2% Glucose to LB medium because it is known that storage of trehalose is increased under osmotic stress and glucose is a precursor of trehalose (2).
 
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<i>Escherichia coli </i> strain TOP10/ pSB1A2-P<sub>low</sub>-RBS-<i>otsBA</i> (BBa_K1339018) was cultured in LB medium containing 600 mM NaCl and 2% glucose at 150 rpm, 30 ℃.</p>
 
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<p> Fig.2 shows the growth curve of transformants. From the result, we found that this transformants reached stationary state after 15 hours cultivation.
 
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So, we decided to culture the cell harboring <i>otsBA</i> for 12 hours (while growth state) for further evaluation. </p>
 
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<img src="https://static.igem.org/mediawiki/2014/e/ee/Noko14_Monit1.png" width="80%"><br>
 
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<p>Fig.2  OD<sub>660</sub> monitoring of empty vector and P<sub>low</sub>-RBS-<i>otsBA</i>-DT</p><br>
 
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<p> <b>2. Optimization of trehalose detection by thin-layer chromatography (TLC) method </b></p>
 
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<p> We used TLC plate coated with silica gel. As standard sample, 1 μL of 1, 5, 10, 50 and 100 mM glucose and trehalose were spotted onto TLC plates and dried at room temperature. The TLC plates were developed in acetonitrile –water (7:3), dried and dipped into H <SUB> 2 </SUB> SO<SUB>4</SUB>-ethanol (5:95). Fig. 3 showed the result of TLC of glucose and trehalose. The Rf value of glucose is approximately 0.47. And the Rf value of trehalose is approximately 0.35. The detection limit of glucose and trehalose were 5 mM and 10 mM respectively. </p>
 
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<p> Thus, in our experiments, we tried to confirm the production of trehalose by <i>E.coli </i> by this method. </p>
 
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<img src="https://static.igem.org/mediawiki/2014/c/ca/Noko14_Otstlc1.png" width="80%"><br>
 
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<p>Fig.3 The result of TLC of standard samples; glucose and trehalose</p><br><br>
 
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<p><b>3. Optimization of enzyme reaction time</b></p>
 
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<p>  To measure the concentration of trehalose, trehalose was converted to glucose with trehalase, which was then measured using a glucose dehydrogenase.
 
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At first, we investigated the optimal enzyme reaction time. Trehalase was added to 50 mM trehalose solution and incubated for 30 min at 37 ℃.</p>
 
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<br>
 
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<p>  Fig.4 is the result of TLC. The Rf value of the trehalose+trehalase, trehalose, and glucose were 0.42, 0.37 and 0.45 respectively. 
 
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From this result, the time of trehalase reaction was not enough. Thus we decided to incubate for overnight. </p>
 
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<img src="https://static.igem.org/mediawiki/2014/a/a3/Noko14Otstlc2.png" width="50%"><br>
 
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<p>Fig.4 TLC after trehalase reaction</p><br>
 
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<p><b>4. Evaluation of trehalose production in <i>Escherichia coli </i> </b></p>
 
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<p> <i>Escherichia coli </i> strain TOP10 was transformed with the vectors that constitutively express <i>otsA</i> and <i>otsB</i> under different strength promoter (Table.) Transformants were cultured in Lysogeny Broth medium (LB medium) containing 600 mM NaCl and 2% Glucose) at 150 rpm and 37 ℃
 
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for 12 hours. The transformants were harvested and washed with phosphate buffered saline containing 600 mM NaCl and then, resuspended with ultra pure water. Trehalose was extracted by boiling cell pellets at 95 ℃ for 5 min and cells were removed by centrifugation at 8,000<i> g</i> for 15 min.
 
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The supernatant was concentrated by freeze-drying and used for TLC. 1 μL of each samples were spotted onto TLC plates and dried at room temperature. The TLC plates were developed in acetonitrile –water (7:3), dried and dipped into H <SUB> 2 </SUB> SO<SUB>4</SUB>-ethanol (5:95). The sugar spots were visualized by heating at 180 ℃. </p>
 
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<img src="https://static.igem.org/mediawiki/2014/f/f0/Noko14_Evots.png" width="80%"><br>
 
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<p>Fig.5 Flowchart of TLC</p><br><br>
 
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<img src="https://static.igem.org/mediawiki/2014/5/54/Noko14_Trehaloseproductiontlc.png" width="30%">
 
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<p>Fig.6 The result of TLC </p><br><br>
 
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<p><b>5. Improving a BioBrick part - OtsB </b></p>
 
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  <p>BBa_K200017<br></p>
 
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<p>  In iGEM 2009, Imperial College London team submitted OtsB part (BBa_K200017). However, evaluation data was not available in the parts registry, so we tried to evaluate the BBa_K200017 and compared with our BioBrick part encoding OtsB (BBa_K1339001).
 
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Promoter (medium constitutive promoter or low constitutive promoter) and double terminator was ligated to
 
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<i>otsB,</i> and inserted into pSB1A2 vector by 3A or standard assembly.</p>
 
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<p> <i>Escherichia coli</i> strain TOP10 transformed with the constructed vectors were cultured in LB medium containing 600 mM NaCl and 2% Glucose at 150 rpm and 37 ℃ for 20 hours. The transformants were harvested and washed with phosphate buffered saline containing 600 mM NaCl and then, resuspended with SPB buffer. Cells were fractured by sonication and then centrifugated at 8,000 <i>g</i> for 15 min. Trehalose 6-phosphate, which is a precursor of trehalose was added to the supernatant and incubated at 37 ℃ overnight. The supernatant was concentrated by freeze-drying and subjected to thin-layer chromatography (TLC) to detect trehalose (Fig. 7). Moreover, the expression of <i>otsB</i> was confirmed by SDS-PAGE using the cell pellet (Fig. 8).</p><br>
 
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<img src="https://static.igem.org/mediawiki/2014/6/65/Noko14_Compairots.png" width="30%">
 
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<p>Fig.7 The result of TLC</p><br><br>
 
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<img src="https://static.igem.org/mediawiki/2014/a/aa/Noko14_Impe.png"width="60%">
 
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<p>Fig.8 The result of SDS-PAGE</p><br><br>
 
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<p><b>Reference</b><br>
 
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(1) Crowe, J. H. <i>et al</i>., (1990) Are freezing and dehydration similar stress vectors? A comparison of modes of interaction of stabilizing solutes with biomolecules., <i>Cryobiology</i>. <b>27</b>, 219-231.<br>
 
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(2) Crowe, J. H. <i>et al</i>., (1992) Anhydrobiosis., <i>Annu Rev Physio</i>. <b>54</b>, 579–599.<br>
 
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(3) Kaasen, I. <i>et al</i>., (1992) Molecular cloning and physical mapping of the otsBA genes, which encode the osmoregulatory trehalose pathway of <i>Escherichia coli</i>: evidence that transcription is activated by katF (AppR)., <i>J Bacteriol.</i> <b>174</b>, 889–898.<br>
 
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(4) Giaever, H. M. <i>et al</i>., (1988) Biochemical and genetic characterization of osmoregulatory trehalose synthesis in <i>Escherichia coli</i>., <i>J Bacteriol.</i> <b>170</b>, 2841–2849.<br>
 
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Revision as of 23:56, 17 October 2014