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<p>Figure 2.A compares the Cr(VI) reduction rate standardized for OD₆₀₀ of <i>E. coli</i> MG1655 versus <i>E. coli</i> MG1655 cotransformed with the sulfate transporter system (BBa_K2194004) and constitutively expressed chrR6 reductase enzyme (BBa_K2194000). The data indicates that below an initial [Cr(VI)] of 80 uM the cotransformed bacteria are more efficient at reducing Cr(VI) than wild type bacteria. Above 80 uM initial [Cr(VI)], the trend reverses and wild type bacteria are more efficient. This supports the hypothesis that increasing cell permeability to chromate (in this case via sulfate transporters) increases the reduction efficiency of chrR6, but that after a threshold concentration the increased permeability becomes toxic for the cell.

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<img src="https://static.igem.org/mediawiki/parts/d/d4/Corrected_c6%2C_cys.png" " style="width:60%">

In the experiment, which results shown below in Figure 3, we compared the Cr(VI) reduction efficiency of chrR6 versus nemA at different initial concentration of Cr(VI). The two reductases were expressed under constitutive promoters in <i>E. coli</i> MG1655. Final concentrations of Cr(VI) for each sample were measured at 12 hours after adding chromate. This data shows that at every initial concentration of Cr(VI), the enzyme chrR6 is a more efficient reductase than nemA.

<img src="https://static.igem.org/mediawiki/parts/9/9d/ChrR6_only.png

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<p class = "caption"><b>Figure 2A:</b> DPC Assay Reveals that MG1655 <i>E. coli</i> more efficient Cr(VI) reducers above threshold initial  [Cr(VI)]  

<p> Figure 2.B presents the same data as Figure 2.A but as an amount of total Cr(VI) reduced rather than the OD₆₀₀ standardized rate. (The x-axis and the light blue bars display the initial concentration of Cr(VI) and the y-axis displays the final concentration of Cr(VI). Comparison of the dark blue bars to the light blue bar at each different initial concentration of Cr(VI) reveals the total change in [Cr(VI)].

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<img src="https://static.igem.org/mediawiki/parts/d/d4/Corrected_c6%2C_cys.png" " style="width:60%">

<p class = "caption"><b>Figure 3:</b> Figure 3: chrR6 reductase enzyme is more efficient than nemA reductase in reducing Cr(VI) </p>

<p> n this experiment, we added varying concentrations of Cr(VI) to 0.05 OD₆₀₀ cultures of: <i>E. coli</i> MG1655, <i>E. coli</i> MG1655 transformed with a plasmid constitutively expressing reductase chrR6, and <i>E. coli</i> MG1655 cotransformed with a plasmid constitutively expressing reductase chrR6 and the sulfate transporter system cysPUWA-sbp. We grew the cultures for 12 hours shaking at 37C and took their final OD₆₀₀ measurements (presented here). The data indicates that the sulfate transporter system introduces toxicity to the cell (because it has the lowest OD₆₀₀ values for every initial concentration of Cr(VI) except [Cr(VI)]_i=0). Because the OD₆₀₀ values of the reductase and co-transformed reductase/transporter cultures are comparable at time 12 hours for no chromate, this indicates that the additional toxicity from the sulfate transporters is due to increase permeability of the cell to Cr(VI) rather than increased metabolic load of expressing a sythetically engineered plasmid. </p>

<img src="https://static.igem.org/mediawiki/parts/d/d4/Corrected_c6%2C_cys.png" " style="width:60%">

<p class = "caption"><b>Figure 3:</b> Figure XXX: chrR6 reductase enzyme is more efficient than nemA reductase in reducing Cr(VI) </p>

<p class = "caption"><b>Figure 1:</b> IPTG induces toxin expression leading to cell death <p/>

<img src="https://static.igem.org/mediawiki/parts/e/e1/Mcherry_fl.png" style="width:60%">

<p class = "caption"><b>Figure 4:</b> IPTG-induced mCherry fluorescence vs. time <p/>