Team:SoundBio/Background

Project Background
While cellulose is best known as a plant product, some bacteria, most notably of the genus Acetobacter (a synonym for Komagataeibacter), can produce it as well. Bacterial cellulose (BC) is purer than plant cellulose and possesses properties such as high porosity and moisture retention that make it desirable for many applications. After first learning about Imperial College’s 2014 iGEM groundwork on functionalizing BC,< we were inspired to build off their project and use their genetic toolkit for engineering K. rhaeticus to better utilize the existing and introduce new properties to BC.

As we explored BC’s many applications, including clothing, packaging, jet fuel, and more, we found that BC has great potential in the field of tissue engineering. In engineered tissues, tissue scaffolds are materials that mimic the properties of the extracellular matrix (ECM). Tissue engineers currently use numerous strategies for creating tissue scaffolds, from taking the ECM from donor tissues to using self-assembling hydrogels, but “seeding therapeutic cells in pre-made porous scaffolds made of degradable biomaterials has become the most commonly used and well-established scaffolding approach”. Bacterial cellulose is an attractive biomaterial for tissue engineering applications because of its physical properties, such as porosity, biocompatibility, and mechanical strength. However, bacterial cellulose isn’t a silver bullet; “there are no materials that fully capture the intricacies of the native tissue nor restore function to an ideal level,” and this includes BC.


Diagram adapted from: https://onlinelibrary.wiley.com/doi/full/10.1111/1751-7915.13392

But this problem is fixable, as bacterial cellulose has great potential for functional modification. Numerous researchers have already demonstrated this potential by attaching proteins to sheets of bacterial cellulose, improving their function for applications such as tissue scaffolding. Given the inherent complexity of mimicking the extracellular matrix, fine control of such functionalization is highly desirable; “in order to recreate fully functional tissue, the biochemical and biophysical properties at the [sic] must be designed from the nanoscale up”. Spatial control of such functionalization is therefore a natural next step for tissue engineers working with bacterial cellulose. We present an optogenetic toolkit that can be used to spatially control the functionalization of bacterial cellulose.

Specifically, our project consists of two parts: a set of optogenetic circuits and a bioreactor for optogenetic control. We designed two genetic circuits, the Red Light Circuit (RLC) and the Blue Light Circuit (BLC), which allow for control over an arbitrary insert protein’s expression through control of ambient light intensities at particular wavelengths. We also designed and built a bioreactor to produce and functionalize bacterial cellulose; after the bacterium K. rhaeticus produces the BC, E. coli containing either of our optogenetic circuits can be cultured in the finished sheet itself, and light emitted from LEDs on top of the bioreactor can control the intensity of light that bacteria at different points on the sheet are exposed to. Taken together, these comprise a novel platform for spatially controlling the functionalization of bacterial cellulose.


Image Source: https://en.wikipedia.org/wiki/Bacterial_cellulose

Benefits of BC

BC has a number of desirable properties
  • Tensile strength
  • Biocompatibility & Non-toxicity, it does not induce an immune reaction
  • Water uptake/retention
  • Malleability
  • Cell adhesion, this plays a role in pain levels as it prevents environmental factors like air currents from triggering free nerve endings
  • Biodegradability, this is key to tissue engineering as the human extracellular matrix exists in an equilibrium of being destroyed and built again

Areas for Improvement/Development