Photoacoustic imaging is a technique in which contrast agents absorb photon energy and emit signals that can be analyzed by ultrasound. Currently, photoacoustics is used to image blood vessels because heme is a natural contrast agent found in blood. Photoacoustic imaging also provides a non-invasive alternative to current diagnostic tools used to detect internal tissue inflammation. In previous literature, hypoxia and nitric oxide have both been discovered to molecularly indicate gut inflammation, and iRFP670, 713, anacy and cyan have been found to emit wavelengths that are different from heme and can penetrate tissue with near-infrared wavelengths. Therefore, our goal is to report inflammation and cancer in the gut through photoacoustic imaging of engineered E. coli that express bacterial pigment violacein, as well as near-infrared fluorescent proteins iRFP670 and iRFP713.
Arabinose Induced iRFP 670 and 713 Fluorescence
pBAD is a very well-characterized expression system in E. coli. pBAD normally works by arabinose induction: araC, a constitutively produced transcription regulator, changes form in the presence of arabinose sugar, allowing for the activation of promoter pBAD. Therefore, we formed genetic circuits consisting of the pBAD expression system and iRFP670 and 713 to test the inducibility of our iRFPs.
Nitric-oxide-Induced Fluorescence
The next step was to test the nitric oxide induction of iRFP fluorescence. We used a genetic circuit consisting of a constitutive promoter that always expresses Part:BBa_K554003, which encodes for the expression of a SoxR. In the presence of nitric oxide, SoxR changes form to activate the promoter SoxS, which in turn is supposed to activate the expression of the iRFPs. Thus, for the next assay we added DETA/NO, a nitric oxide adduct in the presence of water.
Hypoxia-Induced Flourescence
In addition to the sinduction of iRFP fluorescence by nitric oxide, we also tested the induction of iRFP fluorescence with a hypoxia promoter. We expected iRFP fluorescence to increase with increased hypoxic conditions (less oxygen) when using NarK promoter and fdhf promoters, both characterized as hypoxia-inducible.
Transcription of the fdhf promoter is regulated by an RNA polymerase with sigma factor 54 whose binding is dictated by presence of an additional activator complex consisting of FhlA and formate. Only when the FhlA-formate complex is present will the sigma-54 polymerase initiate transcription. This process is induced by formate, but is also heavily repressed by presence of oxygen, giving it characterization as a hypoxia sensor.
Hypoxia induced fluorescence
In addition to the sinduction of iRFP fluorescence by nitric oxide, we also tested the induction of iRFP fluorescence with a hypoxia promoter. We expected iRFP fluorescence to increase with increased hypoxic conditions (less oxygen) when using NarK promoter and fdhf promoters, both characterized as hypoxia-inducible.
Transcription of the fdhf promoter is regulated by an RNA polymerase with sigma factor 54 whose binding is dictated by presence of an additional activator complex consisting of FhlA and formate. Only when the FhlA-formate complex is present will the sigma-54 polymerase initiate transcription. This process is induced by formate, but is also heavily repressed by presence of oxygen, giving it characterization as a hypoxia sensor.
Hypoxia induced fluorescence
In addition to the sinduction of iRFP fluorescence by nitric oxide, we also tested the induction of iRFP fluorescence with a hypoxia promoter. We expected iRFP fluorescence to increase with increased hypoxic conditions (less oxygen) when using NarK promoter and fdhf promoters, both characterized as hypoxia-inducible.
Transcription of the fdhf promoter is regulated by an RNA polymerase with sigma factor 54 whose binding is dictated by presence of an additional activator complex consisting of FhlA and formate. Only when the FhlA-formate complex is present will the sigma-54 polymerase initiate transcription. This process is induced by formate, but is also heavily repressed by presence of oxygen, giving it characterization as a hypoxia sensor.
Hypoxia induced fluorescence
In addition to the sinduction of iRFP fluorescence by nitric oxide, we also tested the induction of iRFP fluorescence with a hypoxia promoter. We expected iRFP fluorescence to increase with increased hypoxic conditions (less oxygen) when using NarK promoter and fdhf promoters, both characterized as hypoxia-inducible.
Transcription of the fdhf promoter is regulated by an RNA polymerase with sigma factor 54 whose binding is dictated by presence of an additional activator complex consisting of FhlA and formate. Only when the FhlA-formate complex is present will the sigma-54 polymerase initiate transcription. This process is induced by formate, but is also heavily repressed by presence of oxygen, giving it characterization as a hypoxia sensor.
Hypoxia induced fluorescence
In addition to the sinduction of iRFP fluorescence by nitric oxide, we also tested the induction of iRFP fluorescence with a hypoxia promoter. We expected iRFP fluorescence to increase with increased hypoxic conditions (less oxygen) when using NarK promoter and fdhf promoters, both characterized as hypoxia-inducible.
Transcription of the fdhf promoter is regulated by an RNA polymerase with sigma factor 54 whose binding is dictated by presence of an additional activator complex consisting of FhlA and formate. Only when the FhlA-formate complex is present will the sigma-54 polymerase initiate transcription. This process is induced by formate, but is also heavily repressed by presence of oxygen, giving it characterization as a hypoxia sensor.
