Part:BBa_K3470015

SoxS promoter – RBS – GFP - Double Terminator

SoxS is a conditional promoter, regulated by the SoxR transcription factor (In Composite BioBrick 1). In the active state (when it is bound to NO; pro-inflammatory signal), SoxR activates the SoxS promoter and starts the transcription of the genes downstream to it. (Hidalgo et al., 1998). Escherichia coli Nissle 1917 transformed with SoxR and SoxS genes is tested to analyse the relationship between the amount of oxidative stress and transcription rates of the genes in response to methyl viologen dichloride hydrate which acts as an inducer by measuring GFP intensity. The intensity of GFP increases with time indicating that even if the concentration of the oxidative stress inducer is constant, the rate of activation of SoxR and thus the rate of transcription of SoxS promoter increases and then stabilizes to a constant rate with a higher transcription rate of SoxS promoter with a higher inducer concentration. The team checked for the basal level of transcription of SoxS promoter so that unwanted anti-inflammatory substances will not be released without the presence of oxidative stress. The team observed that the GFP intensity should increase with time for all the concentrations except the control and stabilize after a few hours. The culture fluorescence will be more for a higher concentration of paraquat, with the highest being for the 40μM.The intensity of GFP increases with time indicating that even if the concentration of the oxidative stress inducer is constant, the rate of activation of SoxR and thus the rate of transcription of SoxS promoter increases and then stabilizes to a constant rate. The more the concentration of the inducer, the more is the transcription rate of SoxS promoter. The most likely unexpected result would be that the GFP intensity for the 40μM concentration is not the highest which could be the result of a high amount of oxidative stress on the bacteria which reduces the growth rate. This is checked by the experiment (Measurement of growth rate of Escherichia coli Nissle 1917: Under oxidative stresses) and the dosage of the probiotic can be modified accordingly.

References:

Hidalgo, E., Leautaud, V., & Demple, B. (1998). The redox-regulated SoxR protein acts from a single DNA site as a repressor and an allosteric activator. EMBO Journal, 17(9), 2629–2636. https://doi.org/10.1093/emboj/17.9.2629 Remington, S. J. (2011). Green fluorescent protein: A perspective. Protein Science, 20(9), 1509–1519. https://doi.org/10.1002/pro.684