Team:AshesiGhana/Description
Plastic Degradation and Biocementation
What problems do we hope to solve?
We seek to solve the problem of plastic pollution on the beach and in the sea as well as coastal erosion. The aim of our project is to create a bio-brick from the processes of plastic degradation and biocementation. To achieve this we hope to engineer a series of the bacterium Vibrio natriegens, to degrade plastic (PET) and to induce biocementation through the hydrolysis of urea respectively.
How & why did we choose these problems?
In our project selection process, we had several presentation sessions during which members of the team brought forth their project ideas and we voted on the best one. Each team member brought forth very interesting and intriguing ideas and we were torn because we didn't know which idea to choose. Thus, we decided to cast a vote.
After our vote, we settled on this idea because we wanted to tackle two pressing issues at the same time while developing a solution that is practical. Moreover, we wanted to apply for the Revive and Restore iGEM 2020 grant, and so this influenced the theme of our project (conservation) as well.
What were our project goals this season?
During this year, our main aim was to provide a solid foundation for the team that would have access to the lab so that they could build on what has been done. We also wanted to have a human practices roadmap that next year’s team could refer to and refine to make sure that the project remains relevant.
What chassis bacterium did we choose?
We chose to use V. natriegens mainly because it is a marine bacterium, is non-pathogenic, and is considered safe to work with in the lab. It also has a characteristic generation time of less than 10 minutes - less than E.coli which has a generation time of 12 minutes.
Which other bacteria did we choose to work with?
A bacterium that is known to metabolize PET is Ideonella sakaiensis. It is able to execute this through the secretion of the two enzymes known as polyethylene terephthalate hydrolase (PETase) and mono-2-hydroxyethyl terephthalate hydrolase (MHETase). These enzymes are secreted onto the surface of the plastic to hydrolyze it into MHET. MHET is further broken down into the simplest and environmentally benign forms of PET, which are ethylene glycol and terephthalic acid (TPA). Our new organism would be transformed with the coding sequences of PETase and MHETase to enable it to carry out this function.
We also intend to transform another group of our new bacterium with urease genes (UreA, UreB and UreC) from Sporosarcina pasteurii to carry out biocementation through the precipitation of calcium carbonate which is initiated by urea hydrolysis. S.pasteurii, a calcite forming bacterium, breaks down urea into carbonate and ammonium ions using the enzyme urease. The carbonate ions combine with calcium ions to form and precipitate calcium carbonate which is responsible for holding sand particles together. In order to increase the durability of our bio-concrete, an additional self-repair feature using calcium carbonate precipitation in biocementation is also included in our bio-concrete.
I. sakaiensis and S. pasteurii are incapable of survival in or near a marine environment, so we engineered the strain of Vibrio natriegens - a marine bacterium - to produce the two enzymes involved in plastic degradation and the enzyme that is involved in the hydrolysis of urea to initiate biocementation.
A natural, bioluminescent bacterium known as Photobacterium leiognathi would be added to give our bio-concrete an aesthetic glow to beautify and illuminate the coast
In order to have a pH level that favors all the processes (plastic degradation and biocementation) involved in our system, we hope to discover the parameters responsible for maintaining the equilibrium in the ecosystem near-constant pH. To achieve this, a number of V. natriegens engineered for plastic degradation would possess a high pH-inducible promoter (Plasticina) and others for biocementation would be equipped with a low pH-inducible promoter (Cementin). In a case where the environment may be too acidic due to excess TPA released from plastic degradation, Cementin would be activated to produce more carbonate ions to neutralize the effect from TPA. Likewise when the environment becomes too basic as a result of excess carbonate ions released from urea hydrolysis, Plasticina is activated to counter this effect by producing TPA to neutralize the effect from the carbonate ions.