Applications

There are numerous applications of the PixCell system which are split into two broad categories. The first of which are core uses, which rely on the use of electrogenetics and utilise our PixCell electrode array. Experimental proofs of concept were achieved for two of these applications. The latter category of applications are extended-use ones, which apply the PixCell part library outside of an electrogenetic system.

Core Applications

Biocontainment (Environment)

Preventing the escape of GMOs is a major public worry and obstacle to their implementation. This device prevents the escape of GMOs using an electrical “cage” where an oxidising potential causes expression of a toxin or growth inhibitor. This operates similar to how an electric fence restrains livestock. A proof-of-concept for this device was experimentally confirmed using the Gp2 growth inhibitor (Shadrin et al., 2012). Our transcriptional repressor pSoxS mutant (BBa_K2862010) could be used to create a more robust device where cells require an electrical stimulus to survive.

Hybrid Digital-Biological Computation (Information Processing)

Integrating electronic and biological computation with our device would improve the complexity of synthetic biology devices without increasing the metabolic burden imposed on the biological chassis. For example, a fluorescence camera could be connected to our electrogenetic system, with the information it records being processed via an in silico feedback loop which changes the electrode array’s output. An example of this would be to use the in silico feedback to model an activator-inhibitor system, with parameters of the feedback function being altered to search for Turing patterning behaviours.

Spatially structured cocultures (Foundational Advance)

Spatial separation in co-cultures can provide numerous advantages when compared with disordered consortia (Kim et al., 2008). PixCell could be used for spatial patterning of co-cultures to improve their function, for a segregated co-culture of cells resembling the α- and β-cells of the pancreas. It must be noted that the structural organisation of the co-cultures can allow us to open new possibilities with regards processing and metabolic control on the synthesis of high-value chemicals

Fabric Printing (Manufacturing & Environmental)

The fabric dying industry involves the use of various toxic and environmentally damaging chemicals. Patterned expression of dyes in bacteria using the PixCell electrogenetic system would provide an affordable and environmentally friendly fabric printer. We developed a proof-of-concept of this system with the production of melanin which can be used to dye wool-cloth (Amal et al., 2018), but recent publication show it could also be used for indigo dyeing of denim (Hsu et al., 2018).

Bioelectrical Patches (Therapeutics)

Transdermal are currently used to treat a variety of diseases, such as L-DOPA patches to treat Parkinson’s disease. Although existing patches function passively and are expended after a day. A microelectrode array could be used to generate an active transdermal L-DOPA patch with a longer lifetime utilising a previously reported L-DOPA synthesis pathway (Wei et al., 2016).

Efficient Mutant Selection (Foundational Advance)

The efficiency of directed evolution experiments is dependent on adequate selection and separation of successful mutants. Previous literature shows how evolving various activities in protein, DNA and RNA can be linked to the expression of a transgene (Esvelt et al., 2011). By linking successful mutations to SoxR expression and bringing the flagella control gene CheY expression under the control of pSoxS you can create a system in which successful mutants would tumble around electrodes (Scharf et al., 1998). This not only allows for easy isolation of mutants, but by scanning various electrode potentials you can test a series of selection pressures in one reaction to select for libraries of mutants with various activities. Moreover, it hasn’t escaped our attention that his system can be used as the basis of an antibiotic-free selection system.

Biomaterial Patterning (Manufacturing)

Biomaterials are normally produced in liquid-phase and then undergo classical industrial processing to form the fibres used in manufacturing. Our electrogenetic system provides a method of precise spatial patterning which could be used to allow printing of high-value, processing-free biomaterials such as bacterial cellulose into ready-to-use defined shapes (Buldum et al., 2018).

Gene Activity Dosing (Foundational Advance)

Selecting an optimal expression level of a gene in synthetic biology is difficult, inefficient and costly when dosing the gene using a standard chemical inducer system. Activating transcription of the gene of interest along with GFP in our electrogenetic circuit would allow for easier selection of gene dosing. Electrode potentials could be varied across an electrode array, with the GFP fluorescence from the position with optimal dosage being used to calibrate this expression level to a constitutive promoter from the anderson set.

Bioreactor Control (Therapeutics, Industry and Nutrition)

By controlling flagella control via electrical stimulation, it would be possible to spatiotemporally regulate bacterial motion in a 3D culture. you could either keep cells in constant motion, or induce clearance of the liquid volume at the flick of a switch. We propose the above application where one could potentially have a co-culture in which one strain undergoes constant swimming via electrical induction, and another undergoes tumbling and becomes trapped in a mesh close to the electrodes. At the flick of a switch, we can change the behaviour of our culture composition, allowing us to develop and realise more complex biosynthetic pathways for applications such as therapeutics, industry and nutrition.

Tissue Engineering (Therapeutics / Food & Nutrition)

Although porting this electrogenetic device into a mammalian system may prove difficult, a series of redox-responsive transcription factors are found in mammalian cells which could be used to build a cognate system. One such example is USF-1 which responds to DTT in its reduced form only (Kraj et al., 2013; Brigelius-Flohé & Flohé, 2011). By applying the spatial control achievable with electrogenetics, such a system could be used to control cell-fates in embryonic stem cells for organ transplants. Alternatively it could be used in the production of synthetic meat, which if an efficient method existed would allow for significant reductions in the humanity’s carbon output.

Extended-Use Applications

High-Throughput Drug & Antibiotic Screening (Therapeutic)

Some antibiotics utilise oxidative stress to target cells, whereas antioxidants are commonly used to treat various diseases. Our reporter system responds to oxidative stress, and as such could be used for the high-throughput screening of drug and antibiotic candidates.

Sulfite Biosensor (Food & Nutrition)

Sulfite is also a common ingredient in many preserved foods, such as wine or canned goods, by maintaining reducing environment that is unfavorable for pathogenic growth, unfortunately some people are allergic to sulfite and, especially in wine, can have an adverse effect on taste. However, as our construct is an effective way of detecting redox levels, it could be used to detect levels of sulfite present in food and drink. This may prove helpful for the food industry where a compromise between food preservation and taste needs to be determined.

Oxidative Stress Detector (Diagnostic)

Cancer cells often survive in environments of oxidative stress, and evolve mutations which amplify this stress. Out reporter system could therefore be used in a cheap diagnostic to detect cancer. The Leiden 2018 iGEM team proved how the SoxR/pSoxS system can sense oxidative stress exerted by hydrogen peroxide.

Improved Biophotovoltaics (Energy)

Ferrocyanide/ferricyanide serves as a common electron carrier in biophotovoltaic systems: devices that generate electrical power from the electrons released by photosynthetic cells during photosynthesis (Anderson et al., 2016). As the cell generates power electron carriers are converted from ferricyanide to ferrocyanide. This would modulate the response of our system, meaning that its integration into these devices could be used to provide simple feedback control.

Inflammatory Bowel Disease Treatment (Therapeutic)

The Oxford 2018 iGEM team explored how the SoxR/pSoxS system could be used to treat inflammatory bowel disease.

Team:Imperial College/Applied Design