The iGEM HKUST 2018 team attempts to generate electricity from the degradation of the most widely used plastic, polyethylene (PE), using a synthetic biology approach. Making use of E. coli engineered with genes encoding for laccase to degrade polyethylene into smaller alkane chains, our team recognizes the opportunity to further advance this project by addressing another key issue – energy. Using Shewanella oneidensis MR-1 strain’s inbuilt extracellular electron transport mechanism in tandem with genes responsible for alkane metabolism derived from Desulfatibacillum alkenivorans, we will generate electricity from the metabolism of degraded polyethylene, hoping that it will one day help in solving the world’s growing energy needs. Thus, our project serves as an integrated effort to simultaneously solve two crucial problems.
Aside from plastic degradation and alkane metabolism, generation of electricity was another important focus of our iGEM project.
For the Microbial Fuel Cell design, we focused on generating a stable electrical current by utilizing Shewanella oneidensis MR-1 strain’s inbuilt extracellular electron transport mechanism. In order to better harness its electrogenicity, we housed a culture of the bacterium within a microbial fuel cell of our design, aiming at maximizing electrical output for a given amount of substrate.
Our final design of biosphere-MFC conjugation had integrated the different comments and suggestions from our potential users. This MFC design aimed to be used both in households or indoor public areas.
Modeling plays a huge role in the whole project, as we fill in the gap between the experimental results and the existing data.
We characterized PE degradation rate based on previous iGEM data and predict how much adding OmpA to the sequence is going to affect the result of the laccase secretion. Kinetic parameters of fumarate addition mechanism were attempted to observe the activity of ASS genes and monitor the rate of conversion from alkane to succinate. This is very crucial since we do not have any laboratory experiment result to compare with. At the same time, we adopt Flux Balance Analysis to characterize how different factors from culturing media can affect direct electron transfers. For the MFC module, we have successfully established data to find the optimum culturing medium concentration for Shewanella oneidensis MR-1 growth, which aids the design of MFC experiment. Voltage and power density that can be produced from alkane were also estimated.
The innovative part of our modeling is using the existing model to further explore the effect of fumarate on the integrated alkane metabolism system, which guided our experimental design and will hopefully inspire future work on similar systems.
Public education is presented in the form of exhibition during our university's information day (open day) with the following goals:
1. Promote synthetic biology as a tool to solve current problems and explain how the synthetic biology field tries to involve safety, ethics, policies, and the environment into our research and product designs.
2. Promote renewable energies as a part of our project theme of environmental sustainability.
3. Integrate stakeholders to our product design by demonstrating our project and conducting surveys from our potential users to discover public’s concerns and area of focus for product improvements.
The survey data from our public engagement exhibition, collaborations, and interviews with Prof. Davis Bookhart (department head of the HKUST sustainability office), had been integrated into the systematic design of our Microbial Fuel Cell.